improvise/context/test-evidence/clients.md

# Test evidence: browser client, hosts, harness

What each of these tests proves, what fault was injected to prove it can fail,
and — where it applies — the bug it was written against. Keyed by exact test
name; a renamed test orphans its entry, which
`scripts/check-comment-runs.py --check-evidence` reports.

The design argument each of these belongs to is in `context/code/clients.md`.

---

## `improvise-worker-server/src/worker.rs`

### an_edit_is_persisted_without_the_client_asking_to_save

The persistence half of improvise-9x6's acceptance criterion 2, and the reason
the worker saves on its own behalf: there is no `ModelCommand::Save` for a
client to send, because `effect::Save` is `ViewOnly` and the wire vocabulary is
derived from the *model* effects. So an edit must reach storage with the client
having asked for nothing but the edit. The test writes one cell over the wire
and reopens the document through the same VFS.

### a_partly_refused_batch_does_not_leave_disk_and_memory_disagreeing

improvise-955n's **second-order effect**, which nobody had written down until it
was found while declining the ticket: `on_frame` skipped `persist()` when any
frame in the answer was `Rejected`, so a batch that *did* apply its earlier
command before being refused left the document moved in memory and not written
back — disk and worker disagreeing, silently.

Two changes close it independently, which is why this is worth a test of its own
rather than trusting either: the batch no longer applies partially at all
(improvise-955n), and the persist trigger is now the document's own dirtiness
rather than "was anything rejected" (improvise-gv9r), so a batch that *did*
change something would be written whatever else the answer contained.

The fixture is a refused frame with a command behind the refusal, and the
assertion is that the axes on disk and the axes in memory agree. Under the
settled contract the refusal comes from the **frame's** basis — answered once,
on the first command that carries one — so that is where the staleness is
injected; a later command carries no answer of its own.

### an_explicit_save_is_not_retried_by_the_automatic_write

Found by Copilot on PR #26. A failed write leaves `model_state.dirty` set —
deliberately, so the next frame retries — and the automatic trigger runs after
*every* frame. A save frame therefore attempted the same write twice: extra I/O
on a permanent failure, and on a transient one something worse, because the
answer is composed from the *first* attempt, so the client is told `SaveFailed`
about a document that is now on disk.

The fix is a per-frame question rather than a per-document one, and that is the
right shape precisely because the automatic write exists for edits **nobody
asked** to save; one that was asked for has already been answered.

The fixture is a `Storage` backend whose writes always fail and that counts
them. **Counting is the point**: "it was refused" is true whether the write was
attempted once or twice, so a test asserting only the refusal would pass against
the bug. **Failing is the point too**: a successful save clears `dirty`, so the
redundant second attempt never happens and the bug is invisible from the happy
path.

### a_key_resolved_on_the_host_moves_state_no_client_can_hear

*Why* the `Key` arm answers nothing, demonstrated rather than asserted in prose.

A worker can call `reduce_key` — it holds the authoritative `App`, which is the
thing a socket server lacks. What neither has is a way to tell a client that the
**host's own `ViewState`** moved: a client's slice advances only by folding
`Command`s, and resolving a keypress produces none. So the two slices diverge,
and `ClientSession::viewport` goes on reading the mirror's cursor, which means
the grid does not even follow. That is improvise-bpq2's real cost, and it is a
ticket rather than plumbing. The test asserts all three: the authoritative
cursor moved, the mirror did not, and nothing `reduce_key` emits would let a
client catch up.

---

## `improvise-worker-server/src/vfs.rs`

### an_entry_that_holds_no_document_is_seeded_over

The first browser run of the deployed page failed here, and no host test could
see it: `attach(create: true)` leaves a **zero-byte** entry behind, `documents`
listed it, and `open` therefore took the seed as already applied and read an
empty file. The precondition is asserted before the act, because a test that
only opens cannot tell "the seed landed" from "there was nothing in the way".
The rule it pins is the one gotcha 45 states for the index: what is indexed is
a document, and an entry nobody has written bytes to is not one.

This entry exists because the test cites this file and `--check-evidence` now
requires that (improvise-lyyc); it was written from the test, so read the test
first if the two ever disagree.

---

## `improvise-ws-server`

### distinct_stems_both_open

`doctrine(check_the_checker)` for `colliding_stems_are_fatal`: inject the fault
that test rules out — distinct stems — and both documents must open. Otherwise
an `open_all` that failed on every second file would pass the collision test.

### a_bystander_on_the_same_document_is_projected_the_edit

`doctrine(check_the_checker)` for
`an_edit_is_projected_only_to_the_edited_documents_clients`: put the bystander
on the *same* document and the assertion must flip. Without it, an isolation
test that passed because nobody is ever projected anything looks identical.

### the_other_document_would_also_have_a_cursor_to_invalidate

`doctrine(check_the_checker)` for `a_broadcast_does_not_cross_a_document_boundary`.
The fault to rule out is the other document being *incapable* of producing the
broadcast at all — then a server-wide relay would be silent over there for the
wrong reason and the isolation test would pass without proving isolation. So the
checker drives the same `TransposeAxes` against `beta` and asserts it does produce
a `ResetCursor` there; `beta`'s silence in the isolation test is the routing and
nothing else.

Both tests moved from `Command::SwitchView` to `ModelCommand::TransposeAxes` with
improvise-jytm: a view switch is now addressed to one session and relays nothing,
so it can no longer carry an isolation test. `ResetCursor` is the surviving
`Broadcast::ToAll`.

### a_load_that_fails_rebases_nobody

`doctrine(check_the_checker)` for `a_rebase_stops_at_the_document_boundary`:
inject a load that cannot happen. The generation does not move, so nobody is
rebased — which is also what a routing bug that sent `Snapshot` to nobody would
look like, so the rebase test needs this one beside it to mean anything.

### a_reopened_document_would_have_lost_the_edit_and_the_basis

`doctrine(check_the_checker)` for
`the_last_session_leaving_does_not_close_the_document`: inject the eviction — a
document freshly opened from the same fixture, which is exactly what closing on
last-disconnect would hand the next client. Both assertions in the lifecycle
test fail against it, so neither passes for a reason other than the document
having stayed put.

### a_rebase_stops_at_the_document_boundary

Fixture note, and it is gotcha 39's warning: the swapped-in document keeps the
**same active view name** and changes only its shape. A rename would make
`apply_model` broadcast a `SwitchView`, the client would fold it, and the stale
cursor would then be read under a key nothing has written — right by accident,
with the bug invisible.

### a_client_on_a_socket_is_seeded_and_gets_its_edit_back

(`crates/improvise-ws-server/tests/socket.rs`, and its neighbours in that file.)
Everything the socket test asserts is already asserted in `host.rs` without a
socket, and deliberately so: its subject is the **shell**, not the decisions. It
earns its place by covering what the unit tests structurally cannot — the
handshake rule, JSON framing in both directions, the routing from a `SessionId`
back to the connection it came from, and the one fact that lives only in a URL:
which document the connection asked for. If it ever starts being the place a
behaviour is pinned, that behaviour belongs in `host.rs` or `registry.rs`.

Two disciplines inside it are load-bearing rather than stylistic. The write is
composed from the surrogate the server projected (ADR 002) — a `CellKey` there
would be the test knowing something a browser does not — and the basis is
composed from what the server published, because a basis the test built itself
would be a client claiming to have seen something it was never sent.

---

## `improvise-wasm-client/src/keys.rs`

#### text_entry_modes (a fixture, not a test)

Not a test — a fixture, and its limitation is the evidence. The comment here
used to claim a new mode "shows up as a missing line rather than as untested
behaviour". It does not: this is a hand-written list and nothing checks it
against `AppMode`, so a new text-entry mode is simply absent and silently
uncovered — which is what happened to `save_prompt` (improvise-lae) until it was
added by hand. There is a second hand-written copy in the command crate's
`keymap::tests::text_entry_modes_with_exits`. Deriving both from one place is
filed, not done.

### a_modified_character_now_types_because_the_fallback_is_the_shared_one

The old classifier sent a modified character upstream in a text-entry mode,
because the host's `AnyChar` fallback matches under **any** modifier and a
hand-written rule could only safely be a subset of it. Reading the same table
removes the question: `Ctrl-x` falls through to `AnyChar` here exactly as it
does on the host.

### search_typing_writes_the_query_and_not_a_buffer

Search typing resolves on the client for the first time, and only because the
keymap is shared: `SearchMode` binds `append-char ["search"]`, and the name
`"search"` is `ViewState::search_query` rather than an entry in `buffers`
(improvise-gdl). The old classifier sent every search key upstream into an empty
vec. The negative half of the test matters too: `Esc` stays upstream, because
`exit-search-mode` owns the query and is the host's.

### the_command_names_that_still_need_the_host_are_these

The command **names** this client cannot execute, one by one, so that closing
one of these gaps has to come here and say so. This replaced a list of *keys*,
and that is the whole gain of sharing the keymap: a rebinding no longer
invalidates the list, and a new binding for an already-executable command works
in a browser with no change to this crate. Each entry is driven through the key
that reaches it, because a name that is not bound anywhere would otherwise sit
in the list forever looking like a gap.

### a_prompt_this_client_cannot_commit_is_never_entered

The refusal list above is only half the property. `Upstream` says the key
produced no `Command`; it does not say the client stayed put, and the bug being
guarded is precisely *entering a room with no exit*.

Found by Copilot on PR #27. Without `strands_the_user`, `Ctrl-W` resolved
`enter-mode save-prompt` locally — `ChangeMode(SavePrompt)`, a perfectly good
`Command` — and the user then typed a path into a prompt whose Enter goes
nowhere. `Ctrl-E` did the same into `ExportPrompt` and had done since before
that branch.

**The negative arm has two halves, and both are needed.** Half one: a mode that
is *not* refused is still entered — the half that goes through
`strands_the_user`, so the only thing that can fail when the predicate
degenerates to "refuse everything". `?` is honest here where `:` was not: Help
has no commit at all, so nothing a user types into it can be swallowed, and Esc
closes it locally. (Its page keys *are* upstream, which makes page navigation
inert — but inert navigation loses no work, which is the line the predicate
draws.) Half two: the property is about *finishing*, not entering, so something
has to press Enter and observe. The first version of this test asserted only
that `:` entered its mode, and `:` is itself a dead room — so that arm was
certifying the very behaviour it existed to rule out.

### the_command_line_cannot_be_committed_by_this_client

The evidence behind listing `CommandMode` in `strands_the_user`, rather than the
assertion that it is listed. `:` opens locally and typing appends locally, but
Enter is `[execute-command, clear-buffer]` and `step` has no `execute-command`
arm — so the whole sequence fails to resolve, `Host::handle` drops the frame,
and every ex-command behind `:` is inert. That is what makes refusing the mode
cost no working surface. **When improvise-e24v gives this client
`execute-command`, this is the test that should start failing**, and the
`CommandMode` arm of `strands_the_user` is what it points at.

### a_commit_in_the_last_cell_exits_editing_instead_of_advancing

At the bottom-right corner `EnterAdvance` returns `AbortChain`, so the re-entry
is skipped and the commit leaves the user in normal mode. That abort is a fact
about the host's effect chain and it has to be mirrored, or the browser would
sit in an editor on a cell the terminal has left. The fixture is a one-by-one
grid, so the only cell *is* the corner.

### a_move_that_goes_nowhere_follows_the_command_it_mirrors

Which widgets say nothing about a move that goes nowhere is **not a rule of
`keys.rs`** — it is whatever the `Cmd` being mirrored does, and the three
differ: `Move` emits even when it clamps, `MovePanelCursor` returns nothing when
the cursor does not move, `MoveTileCursor` emits regardless. The grid arm
carries its own check-the-checker inline (a `j` that does move), so "emits when
clamped" cannot pass against a fixture that is simply inert.

### i_on_an_aggregate_declines_out_loud

`i` on an aggregate must not go upstream: `Host::handle` answers a `Key` frame
with an empty vec, so that would be a keypress the user sees do nothing at all
(`doctrine(an_upstream_key_is_a_black_hole)`).

### enter_commits_the_cell_advances_and_re_enters_editing

Enter in `Editing` is `[commit-cell-edit editing, clear-buffer edit]`, and every
part of that sequence shows up in what the client composes — **including the
trailing clear that empties the buffer `EnterEditAtCursor` has just seeded**.
That ordering looks wrong and is exactly what the TUI does; mirroring it line
for line is the contract.

---

## `improvise-wasm-client` — lib, socket, state, render

### a_client_with_no_basis_composes_nothing

The fourth `None`, and the one ADR 001 adds: a client that has not been told the
document's basis has nothing truthful to say about what it composed against, so
it composes nothing. That is the property that makes the basis check unforgeable
from a browser — `BasisCache::claim` is the only constructor, and it withholds.

The other three `None` shapes — an aggregate, `id: None`, and a position outside
the grid — are pinned against the same composition in `socket.rs`'s
`typing_into_a_cell_that_is_not_a_record_composes_nothing`. They were asserted
twice, once against each of two compositions, until improvise-r4lo left only one.

### a_refused_batch_is_kept_as_a_rejection_and_not_only_as_a_sentence

A refused batch must reach the person who composed it, and it must reach them as
more than a sentence. ADR 001 makes rejection a *normal outcome*, and the
obligation that comes with it is that the client keeps the typing and can
re-compose. Force needs the `Rejection` itself — `RecordGone` cannot be forced at
all where `RecordMoved` can — so collapsing it into `status_msg` would throw away
the input to the very feature rejection exists to enable. **Both halves are
asserted, because setting the string alone is the plausible half-fix**, and the
revision bump is asserted too: a renderer polls the revision, and a rejection it
cannot see is a rejection it cannot draw.

### every_rejection_message_says_the_edit_did_not_land

Found by the PR #12 Copilot review: `DocumentReplaced` read "the document was
replaced — reloading", and nothing in `fold_frame` reloads anything. **A message
that names an action the code does not take is worse than a vague one, because
the user waits for it.** The per-variant wording still differs — the classes are
different things to be told — but the one fact they share is the one the ADR
guarantees, so it is asserted over all of them rather than one at a time.

### a_typed_string_is_classified_as_the_host_classifies_it

The three-way split, matching `commit_regular_cell_value`: a number is a number,
anything else is text, and *empty clears* rather than writing an empty string.
**This test states an obligation it does not discharge**: it asserts the three
outcomes by hand rather than comparing with the host's function, so the two
copies could drift and stay green. See `context/code/clients.md` for why the
duplication exists and what the real fix is.

### a_cell_projection_that_overtakes_its_labels_is_lost

Gotcha 33, carried across *this crate's* dispatch. The protocol crate pins the
drop inside `GridCache::apply`; what is this crate's is that nothing between the
socket and that cache buffers, sorts or retries — so the same early `Cells` is
still lost after routing. The second half of the test feeds the same three
updates in frame-first order and requires them to land, so "everything is
dropped" cannot pass it.

### bootstrapping_from_a_compaction_lands_where_the_stream_lands

`doctrine(fold_tests_must_test_order_not_the_axiom)`: a client that bootstraps
from a compaction of the host's state must end up where a client that folded the
whole stream is. The seed is the host's *current* state expressed as projections,
not the head of the history.

### the_selection_is_placed_by_subtracting_the_scroll_offset

(`render.rs`.) The conversion that looks right until the first scroll: the grid
is viewport-indexed, the cursor is not. The offsets in the fixture are **nonzero
and unequal**, which is what separates "reconciles" from "ignores the offset"
*and* from "swaps the two offsets".

### column_groups_coalesce_by_name_as_the_tui_does

(`render.rs`.) The run boundary must be the **name alone**, because that is what
`src/ui/grid.rs` uses (`group_name != prev_group`) and the two ends must not
disagree about where a span begins. Collapse is category-scoped, so two adjacent
groups from different categories may legally share a name and differ in it.
Keying the run on the pair would start a second run — a second indicator the TUI
suppresses — which is a front-end divergence of exactly the kind improvise-anr9
exists to remove (raised by Copilot on PR #23).

### a_keyboard_edit_in_progress_is_part_of_the_render_model

(`render.rs`.) A keyboard edit has to be *visible*, and what is visible is
decided in Rust rather than in the page. The failure this rules out is quiet: a
client that resolved `i` locally would change its mode label, put the typing into
`buffers["edit"]`, and draw the cell's old value the whole time — so the user
sees a keystroke do nothing, types over it, and commits something they never
read. `None` outside an editing mode is the other half: a stale buffer must not
draw an editor that is not open.

---

## `improvise-wasm-client/tests/browser_round_trip.rs`

The file's scope is improvise-1ey's, quoted: *"open an existing document
server-side, view it in the browser, type a number into a cell, see the server
value update and the projection arrive with the new value."* Everything in that
sentence except the DOM is Rust on both sides, so the test drives the whole of
it: a real `Host` over an authoritative `App`, and a real `Client` reached only
through the string calls the page makes. The socket is the one thing left out,
and it is covered by `improvise-ws-server`'s own `tests/socket.rs`; what this
adds is the half that crate cannot reach — that the **browser client** seeds,
renders, composes and folds correctly against it.

**The discipline that makes it evidence rather than decoration**: the client is
touched **only** through `Client::viewport`, `Client::on_frame`,
`Client::render_model` and `Client::typed_cell` — strings in and out — and it
learns the cell to write from its own render model, never from the fixture. A
`CellKey` anywhere in it would be the test knowing something a browser does not
(ADR 002).

### a_grouped_row_axis_does_not_shift_the_write

A group header is a **row of the render model and not a row of the grid**, and a
write composed against the wrong one lands on a different record — silently,
because both are `usize`. `FirstEditable` therefore returns two numbers.

A fixture with no groups makes them coincide, which is exactly how an earlier
version of the `first_editable` helper handed a *visual* index to `typed_cell`
and passed (Copilot, PR #23). This test is the fixture the main round trip cannot
be: a `Coastal` header sits *between* the two rows, so for the second row
`visual_row` and `data_row` differ. Injecting the confusion — passing
`at.visual_row` to `typed_cell` — leaves `East` unwritten. Note the ordering of
the fixture is load-bearing: `West` comes first and ungrouped, because a header
*before* the first row is dropped by `AxisFrame::body_from` and the two
coordinates would coincide again.

### a_commit_keypress_is_one_mutation_among_view_commands_and_is_accepted

improvise-955n: **the one real producer of a multi-command frame must still be
accepted.** `CheckedBatch::against` answers a frame's basis before applying any
of it, and every mutation answers for its own records. Getting that check right
is the easy half; the expensive half is not tightening it until the browser stops
working. A commit keypress is exactly the shape at risk — one `SetCell` plus the
mode change, the scroll offsets and the re-seeded buffer around it — and it is
produced by `keys.rs::commit`, which no test in the command crate can reach.

So it drives a **real keypress** through a **real `Host`** and asserts the frame
is accepted *and* lands: `ServerFrame::Rejected` anywhere in the answer, or an
unchanged cell, is the regression. Asserting only "no rejection" would pass
against a host that dropped the frame on the floor. The "exactly one mutation"
assertion is a **characterization of what `keys::commit` emits, not a protocol
constraint** — a frame may carry more than one — so that if `commit` ever
started batching two, the test would be exercising something else and should be
re-read rather than silently re-scoped. And the fixture types `888` *after* `i`
has seeded the buffer, so the assertion is on the appended value: `888` alone
would also be produced by a client that ignored the seed.

---

## `improvise-wasm-client/tests/lockstep.rs`

`src/keys.rs` decides a small set of keypresses without the document. The claim
that makes that safe is not "the rule looks the same" but **the two ends land in
the same `ViewState`**, and that is checkable: the host's `reduce_key` runs the
real keymap, registry and effect pipeline against an authoritative `App`, and
`ViewState` is the protocol's own type on both sides. So every local outcome is
driven through both and compared.

This is why the command crate is a dev-dependency. Dev-dependencies are not
built for `--target wasm32-unknown-unknown`, so nothing the host owns reaches the
browser bundle.

### a_locally_typed_character_lands_where_the_host_would_put_it

Driving one mode would say nothing about the others
(`doctrine(one_arm_of_a_symmetric_rule_is_evidence_about_that_arm_only)`), so
every text-entry mode is driven, and each with a **non-empty** buffer so an
append that silently *replaced* the buffer would be visible.

### a_forwarded_key_reaches_the_host_unchanged

An unresolvable key must reach the host as a keypress, and what the host then
does to *its* copy of this client's view slice is what the client will be told.
Pinned as the shape the transport owes: the message carries the code and
modifiers, and they survive the round trip. `Enter` rather than an arrow key,
because since improvise-bpq2 the arrows resolve locally and `enter-advance` is
one of the movements deliberately left upstream — it aborts the rest of its batch
at the bottom-right corner, which is a fact about the host's effect chain and not
a cursor position.

### a_locally_resolved_cursor_move_lands_where_the_host_would_put_it

The headline claim for improvise-bpq2's first gap: a cursor key resolved on the
client lands where the host would have put it — **including the scroll that
follows it**, and including the clamp at the end of the grid.

The fixture is six rows in a three-row window, and the keys walk past the bottom
of the window (so `row_offset` must move) and then past the bottom of the *grid*
(so the clamp must hold). A client reading its bound off the row frame's length
would stop at row 2 and never scroll; one that clamped against nothing would run
off the end. Both are visible. Eight presses for six rows: the last three are the
clamp.

**The fixture's one column is deliberate.** The two ends measure their windows
differently: the host's `visible_rows` is `term_height - 8` and its
`visible_cols` is computed from column widths, while a browser announces both
outright. `term_height` can be chosen to match the rows; nothing can be chosen to
match the columns, so the fixture removes the question rather than guessing at an
answer.

### a_locally_resolved_panel_cursor_agrees_with_the_host

improvise-bpq2's second named gap, which turned out not to be one: the category
panel's flattening depends on `expanded_cats`, but the derivation already lives
in `improvise_protocol::viewmodel` and *both* ends call it (improvise-edp). So
this is not two derivations agreeing by luck — it is one derivation, and the test
says so by **expanding** a category, which changes the flattened length the
cursor clamps against. A client that counted categories would stop several rows
early.

### the_buffer_i_seeds_is_the_value_the_host_would_seed

`i` seeds the edit buffer from the cell's **display value**, and the two ends
must agree on what that is: the host reads `App::display_value_at_cursor`, the
client reads the text the server projected into its `GridCache`. Those are two
paths to one string, and this is the assertion that they are the same string.

### entering_typing_and_cancelling_an_edit_agrees_with_the_host

`Esc` rather than `Enter` for the cancel arm, because it is a
`Binding::Sequence` and so exercises the all-or-nothing rule: half of it — a
cleared buffer in a mode the user has not left — is worse than none.

### a_locally_committed_edit_leaves_both_ends_in_the_same_place

What is *not* compared is the document, and deliberately: the client answers with
a `Command::Model`, which `reduce_view` drops, while `reduce_key` writes through
the effect pipeline. The write's composition is asserted in `keys.rs` against
`typed_cell`'s own — the shared one — so what is left to prove here is the half a
unit test cannot see, which is that the advance and the re-entry land in the same
place.

#### client_ready_to_edit (a fixture, not a test)

The published basis a real client folds before it is allowed to compose a write
(ADR 001). The tiers are the ones lockstep never checks — the host applies the
keypress directly rather than the client's `Command::Model` — but
`BasisCache::claim` withholds until it has *something*, so a client without one
resolves no commit at all.

---

## `harness/` — the browser specs

These are Playwright tests, so the checker's `--check-evidence` pass (which
scans Rust `fn` names) cannot see their names. They are recorded here under
their exact `test("…")` titles anyway, because they are where the JavaScript
evidence lives.

#### harness/tests/shell.spec.js — the file's own scope

The three assertions improvise-hwpi could not write. That ticket fixed four
things and said of itself that the fixes were "as unverified as the bugs",
because three of them are one-assertion tests that needed a browser. These are
those three, plus the watchdog — which was found by reading, and only because
someone went looking. Until this file, `web/app.js` and `web/worker.js` had
never been rendered or run.

Two fixtures are load-bearing. `NO_WEBSOCKET_HERE` is a peer that accepts the
TCP connection and then refuses the WebSocket upgrade — the harness's own static
file server — **deterministic where a closed port is not**: a refused port's
`close` timing is a property of the host's network stack, and on the GitHub
runner it did not arrive inside the window. The page cannot tell the two apart
and neither can `web/app.js`: in both cases the socket never opened.
`HANDSHAKE_TIMEOUT_MS` restates `web/app.js`'s own constant, because two tests
have to outlast it and a number that silently disagreed with the page would make
them pass for the wrong reason. `logStatus` records **every distinct `#status`**,
not just the last one, because several of these tests are about a message being
*replaced*, which the final value cannot see.

#### "a frame the client cannot fold says so on screen"

improvise-hwpi: `on_frame` returns a `Result`, which wasm-bindgen throws. Thrown
in a bare listener it reached the devtools console and nothing else — the grid
simply stopped updating with nothing on screen saying why. **The fault is
injected at the *peer*, not in the page** — a mocked socket that answers the
handshake with a frame the client cannot fold — so this exercises the real
`on_frame` and the real catch.

#### "a peer that cannot be reached is named, and not called a disconnect"

improvise-hwpi: without an `error` listener, a connection that never opened left
`#status` blank, and "the server is not running" read exactly like "still
connecting". **This test no longer says anything about the watchdog, and the
paragraph below is why it never could.** `shell.arm` runs only after
`await transport.ready`, which resolves on `open` — so on a socket that never
opens the watchdog is **never armed at all**, and denying its message here
denies an unreachable event.

**That sentence was already in this file, five lines above an assertion that
contradicted it.** PR #65 added the watchdog clause *and edited this very
paragraph*, inserting "`runFor(10s)` advances the watchdog" immediately before
the sentence saying it is never armed. Reverting PR #21's routing, or stripping
`fail()` of its `sawFrame()`, both left that clause **passing**. So a PR whose
subject was "a deleted guard went unnoticed" planted the same shape one level
up: three injections, three distinct test names, and two of them proving
nothing. What the test guards now is the **naming** — `close` on a socket that
never opened must not read as "disconnected" (improvise-taxx) — which is the
half injection 3 really does exercise.

**The mechanism, so it cannot come back.** `outlastTheWatchdog` now asks the
page `timesArmed() > 0` before jumping, and a watchdog denial re-added to this
path **fails by name**. It asks *ever armed* rather than *armed now*: by the
time the disconnect test jumps, a correct page has already disarmed — that is
the property — so `armed()` would have denied the passing case. Building that
guard is what surfaced the distinction, which no amount of reading had.

#### "a socket that opened and then dropped reads as disconnected, and stays that way"

The other arm, which must keep working when the first is fixed: a socket that
really did open and then dropped IS a disconnect, and saying so is the whole
reason `close` cannot simply be suppressed.

**It runs past `HANDSHAKE_TIMEOUT_MS` on purpose** — through `page.clock`, not
through a real wait. On this arm the watchdog IS
armed — `armWatchdog` runs after `transport.ready` resolves, i.e. on `open` — so
"disconnected" is written while a timer is pending, and the only reason it
survives is that `close` goes through `setShellFailure`, which clears it. That
was argued in a comment and asserted nowhere, and **the argument was got wrong
from the outside**: a bug report (improvise-xps8) claimed the timer fired 8s
later and overwrote "disconnected" with "sent no document". It had been measured,
honestly, but against a tree predating PR #21 — and the "confirmation" that it
survived PR #21 simulated only that PR's `opened` flag and **not its other half**,
routing BOTH close arms through `setShellFailure`. *A simulated fix that is not
the fix you named reproduces a bug the real code does not have, and reads exactly
like a confirmation.* The ticket was filed and closed **invalid**. Hence this
assertion rather than another paragraph — proved discriminating by making
`setShellFailure` skip its `clearTimeout`, which makes it fail. Same rule as
`doctrine(an_injected_fault_must_be_the_fault_you_named)`, one level up.

**And it was lost a third time, by the PR that was arguing about exactly this.**
PR #61 split the browser tests into boundary contracts (Playwright) and unit
tests (`node --test`), and merged these two tests into one that kept only the
last-value assertions. `shell.test.js`'s "a loud failure DISARMS the watchdog"
covers `createShell` in isolation and **cannot see whether `app.js` routes the
close event through `fail()` rather than `setShell()`** — which is the half
PR #21 fixed and the half that keeps getting lost. Reverting both socket arms
to `setShell` left the node suite 26/26 and Playwright 13/13 green. Restored
under their original names, and re-proved with that exact revert: the two-arm
revert and the close-arm-only revert each fail "…and stays that way", and
dropping the `opened` flag fails "…the watchdog stays out of it". **Three
injections, three different tests, none of them the unit test.**

**And the helper guards its own premise.** `page.clock.runFor` on a page where
`clock.install()` was never called does **nothing and throws nothing**, so a test
that forgot the install would assert "the watchdog never spoke" against a
watchdog never given the chance — vacuous, and green. `outlastTheWatchdog` reads
`Date.now()` inside the page either side of the jump and requires it to have
moved. Demonstrated both ways: with the install removed the suite passed 6/6,
and with the guard in place the same omission fails by name.

**The window is single-homed, and that is the second half of the same
finding.** `HANDSHAKE_TIMEOUT_MS` lived twice — once in `web/app.js`, once in
the spec — with a comment saying a silent disagreement "would pass for the
wrong reason" and nothing checking it. Setting the spec's copy to 1000 against
the page's 8000 made the whole suite green **against the reverted routing**:
the jump landed inside the window, the watchdog had not yet fired, and the
denial held vacuously. It is now exported from `web/shell.js` and imported by
both, so the two cannot disagree; shrinking it in its one home still catches
the routing revert, which is the demonstration that the guard did not go quiet.

**The faked clock is what makes the restoration cheap without weakening it**,
and the injections are the proof of that too: if `page.clock.runFor` did not
really advance the page's timers, a broken routing could not surface the
watchdog's message and those injections would have passed. They failed. The
test keeps the real page, the real socket, the real listeners and the real
`setTimeout` call — only the *passage of time* is simulated, and 9 seconds of
wall clock became 75 milliseconds.

**The measurement that could not become a CI guard.** Both of the above were once
asserted as `test.fail` expected-failures and **had to be removed**: neither
reproduced on the GitHub runner, where `close` does not follow `error` within the
window. An expected-failure is green when the bug is present and red when it is
absent, so one whose trigger is platform-dependent does not merely flake — **it
inverts CI's meaning**, and it failed the build twice saying "expected to fail,
but passed". The lesson stands even though the second bug did not: **assert the
PROPERTY THAT MUST HOLD, which is portable, rather than the fault, whose trigger
is the host's network stack.**

The first of the two, for the record, was real: the socket's `close` listener was
unconditional, so on a connection that never opened it overwrote "cannot reach …"
with "disconnected". FIXED by PR #21. An `opened` flag is the only discriminator
— `readyState` at close time cannot tell the two apart, and neither can the
`CloseEvent`: both cases are code 1006, `wasClean: false`.

#### "a peer that accepts and then says nothing trips the watchdog"

The first-frame watchdog, found by reading. The condition is one **no
per-transport check would catch**: the peer accepted the connection and then said
nothing. The mock accepts and never answers.

#### "the page draws the demo document out of the worker"

No `?ws=`, so `web/app.js` spawns the in-page worker over OPFS: the whole
application, with no server process. If this draws a grid, then `worker.js`,
`bindings.rs`, `OpfsFs`, `vfs::open` and the seed fetch all ran.

#### "committing an edit sends one frame and shows the host's value"

A commit round-trips through the host, and what lands on screen is the **host's**
value rather than the string that was typed. `20000` is typed and `20,000`
asserted: the number format is applied by the host and relayed back, so a page
that echoed the input would fail.

**This is deliberately NOT named for improvise-hwpi's third fix** (the `closed`
re-entry guard in `edit`), which Copilot asked for on PR #24. That guard is **not
observable from the DOM**, measured rather than assumed: with it removed, `close`
still runs exactly twice, the frame is still sent exactly once, `#grid` still
takes exactly two `childList` mutations, and the final text is identical. The only
difference is one extra *entry* into `repaint()` that produces no output — because
the second close is `close(false)`, so it does not re-send, and everything else it
does is idempotent. That is precisely why hwpi called it "harmless before, but
only by accident". Counting `repaint()` entries would need a test hook inside
`web/app.js`, which would be a page that knows it is being tested. So the test
name says what is checked and this entry says what is not. What *is* observable is
asserted: the editor is gone and did not come back, so no stray `<input>` is left
behind and the host's value is not overwritten by the `original` text the second
close writes before repainting.

#### "the harness can see a failure"

Check the checker, and it runs **first**: a green run against a worker that never
started is the failure this repo has a doctrine about. `run_canary` drives the
*same* reporting path every real check uses, and the spec asserts it is reported
as a failure with its message intact.

#### "every check in the battery runs and passes"

The battery is asserted **complete before any of it is believed**: the report's
names must equal `EXPECTED` exactly, so a build that dropped a check fails rather
than passing with fewer.

#### "what OPFS held survives a reload, and a committed delete does not"

The one thing no in-page check can establish. A delete is visible immediately and
lands in OPFS at the end of the batch — so "`commit_deletes` actually removed it"
is only answered by a fresh page. This is also the storage half of improvise-bck's
persistence criterion.

#### The opfs-contract checks (`harness/opfs-contract/src/lib.rs`)

- **`an_attached_but_unwritten_entry_is_not_a_document`** — `attach` must create
  the file to obtain a sync access handle for a document that does not exist yet,
  and that created file is zero bytes, which is NOT a document. `Storage::list`
  promises document names, so an attached-but-unwritten name must not be listed.
  Indexing it is exactly the improvise-9x6 browser failure: the seed was skipped
  as "already there" and `load_from` got an empty buffer. The check also opens a
  **second instance**, which shares no index, because the filter has to be in
  `refresh` and not only in the omission from `attach` — and then writes through
  the handle to show it is real and the name IS then a document.
- **`a_directory_entry_is_not_a_document`** — `keys()` yields DIRECTORIES as well
  as files, and `getFileHandle` on a directory rejects with `TypeMismatchError`.
  Treating that as "could not measure, so assume a document" would list an entry
  that can never be attached or read — the same picker bug the zero-byte filter
  removes (Copilot, PR #24). `OpfsFs` never creates a directory, so the harness
  makes one itself, and asserts a real file beside it IS listed — the
  precondition, so the check cannot pass by the directory never having been
  created, and evidence that `keys()` walked the root at all.
- **`refresh_walks_every_key_and_sorts_them`** — the hand-rolled `keys()`
  async-iterator walk in `refresh` is the least certain code in `opfs.rs`
  (improvise-xf1 named it). One entry could pass by accident; several, out of
  order, cannot. It wipes first, like every other check: a battery whose steps
  depend on the leftovers of the step before breaks when one is inserted, which
  is exactly what inserting the directory check did.
- **`read_and_write_are_absolute_at_offset_zero`** — `FileSystemReadWriteOptions`'
  `at` handling, the other thing xf1 called out. A `write` that appended instead
  of overwriting, or a `read` that started anywhere but 0, is invisible on a
  single short write and obvious across a long one followed by a short one.
- **`storage_contract_at_…`** — the point of the whole exercise. `attach` is
  hoisted out because acquiring a handle is the async half and `Storage::write`
  cannot await; **the contract itself is the shared function, not a transcription
  of it**.
- **`a_delete_is_visible_at_once_and_lands_on_commit`** — both halves, because
  either one alone would pass against a backend that got the timing exactly
  backwards.

### a_locally_cycled_panel_focus_agrees_with_the_host

`cycle-panel-focus` is bound to Tab in Normal only: `PanelKeymap`'s spine binds
Tab to `enter-mode normal` inside every panel (gotcha 12), so the *wrap* arms of
`CyclePanelFocus` — the ones that start from the focused panel — are
unreachable by keypress. The test therefore asserts the one reachable path and
says so, rather than looping three times and passing on a mode that never moved.
The first draft did loop, and failed on step 1 with the mode back at `Normal`;
that failure is the evidence for this paragraph.

### a_locally_resolved_tile_axis_change_agrees_with_the_host

Both of `TileAxisOp`'s names in one walk, because the command names itself off
its `axis` field: `r` takes the `Some` arm (`SetAxis`) and `Enter` the `None`
arm (`CycleAxis`), and a test that drove only one would leave a whole `Cmd`
unmirrored. Injecting `parse_axis("row") => Axis::Column` fails it.

### the_category_panel_bindings_agree_with_the_host

The fixture sits on a **header** row for `Space`/`a` and on an **item** row for
`Enter`/`d`, and then on a header again for a second `d`. Both of
`FilterToItem`'s arms and both of `DeleteCategoryAtCursor`'s arms are therefore
reached. That is not decoration: the first version sat only on the item row,
and injecting a wrong sentence into the *category* arm of
`delete_at_cat_cursor` did **not** fail it. One fixture position, one arm —
and a check that passes against an arm it never enters is the defect this repo
keeps finding.

### the_view_panel_bindings_agree_with_the_host

Two views in the fixture, and the cursor moved to 1 before `Enter`, because
`view_at_cursor` reading `.get(0)` is the natural wrong implementation and a
single-view fixture cannot tell it from the right one. Injecting `.get(0)`
fails it.

It presses `d` as well, and that was added after the fact: the first version
said "create, switch and delete" in its doc comment and pressed only `n` and
`Enter`, so `delete_view_at_cursor` — whose *only* decision is the cursor
step-back it makes away from the top of the list — was never run. The
adversarial review of PR #50 deleted that step-back and the workspace stayed at
1322 passing. `d` is pressed at index 1 so the decision is reached, and
`both_ends` now compares every cursor (see below), without which the deletion
would still be invisible.

### a_locally_committed_minibuffer_agrees_with_the_host

`commit-buffer` for **all three** kinds, driven as keystrokes so the
`TextEntry` spine's `clear-buffer` weld is part of what is compared.
`CommitKind::Item` carries its category, resolved from `AppMode::ItemAdd` —
so the mode the test starts in is load-bearing, not scene-setting. Injecting
`AddCategory` in place of `AddItem` fails it on the document comparison.

Formula was missing from the first version, and it is the kind that matters
most: it is the **only** one whose `on_commit()` is `Some`, so a test of the
other two cannot see the mode a commit returns to. The review of PR #50 broke
both `CommitKind::status`'s and `on_commit`'s Formula arms and nothing failed.
Its text is **seeded rather than typed**, and valid, for the reason the next
entry gives.

### a_formula_the_client_cannot_parse_diverges_on_the_status_line

The one thing a client cannot mirror about `commit-buffer formula`, found by
widening the test above and kept as a **pinned divergence** rather than a fix
(improvise-cl7y).

`CommitBuffer` emits its optimistic status first and the add effect last, so
on the host a parse failure overwrites "Formula added" with "Formula error: …"
(improvise-6t3). The client reproduces the command line for line — which is
right — but it cannot parse, so it folds "Formula added" and stops. The user
sees a browser confidently report a formula it did not add.

This asserts **both** sides, so a fix has to come here and change it. That is
the difference between a pinned divergence and a comment: `a_locally_committed
_minibuffer_agrees_with_the_host` would otherwise have to use a valid formula
forever with no record of why.

### panel_focus_cycles_from_the_focused_panel_not_the_first

`CyclePanelFocus`'s wrap arms, driven directly rather than through a key.
`PanelKeymap`'s spine binds Tab to `enter-mode normal` inside every panel
(gotcha 12), so **no keypress reaches them** — which is why the lockstep test
asserts only the reachable path and why breaking the `start` index survived
the review's injection pass. Mirroring a `Cmd` faithfully includes the arms
the keymap cannot reach today; testing them takes a direct call.

The fixture leaves the **category** panel closed, so "the next open one" and
"the next one" give different answers and a mirror that walked the array
blindly would fail.

### a_locally_resolved_clear_and_paste_agree_with_the_host

The two writes ADR 002 lets a thin client name. Note the fixture's cell key has
**three** coordinates: `Workbook::add_category` puts a new category on
`Axis::Column`, so `Product` is part of the cell's address and a two-coordinate
key names a cell the grid never shows. The first version asserted on the
two-coordinate key, and passed the per-key comparisons while asserting against
a cell nothing had touched.

### walking_off_the_end_of_the_help_pages_agrees_with_the_host

The bug this was written to demonstrate: `effect::HelpPageNext` clamps and
`HelpPagePrev` saturates, while `reduce_view`'s `Command::HelpPage` arm
*wrapped*. Two derivations of one fact, in disagreement, invisible because
`h`/`l` in the help overlay were upstream keys and no client had ever sent the
command. It failed on the first press past the end — client 0, host 4 — and the
wire was changed to match the effect. Whether both should wrap instead is
improvise-trd3.

#### "? opens help, and its rows carry the keys and the words, not empty frames"

This entry was demoted to prose as Retired when PR #61 deleted the spec. PR #72
restored the coverage under a new name, so the claim is live again and the
heading now names the test that exists. What follows is the original evidence;
improvise-igxp's stronger assertions are recorded separately below.

improvise-ktv1's acceptance in one place: **a browser shows help.** `?` had
entered `AppMode::Help` since the keymap was shared, and nothing appeared —
the mode changed and the page had no overlay, which is worse than a key that
does nothing because the user thinks they missed it.

It asserts the shape, not merely that something is visible: the active tab is
the shared module's page title (`Welcome`, then `Navigation` after `l`, which
also exercises `Command::HelpPage` folding on the client), and the body has a
key row. Two faults were injected and each failed it. Dropping the
`paintHelp(model)` call fails `toBeVisible`; removing the `mode != Help` guard
in `help_rows` — so the overlay is never empty and therefore never hidden —
fails `toBeHidden`. The second is the one worth having: an overlay that is
always open passes any check that only ever opens it.

It runs against the **assembled** site like every other test here, so it
covers `render.rs`, the serialized model, `web/app.js` and the CSS together.

**It was gone for a release, and that is why the entry reads oddly.** `36ade35`
deleted it with the rest of `harness/tests/widgets.spec.js` and nothing replaced
it, so the heading promised coverage that did not exist -- exactly the cost
improvise-5ray names, and invisible because the evidence checker then read only
`###` headings and only Rust names. PR #69 taught it to see both; PR #72
restored the coverage under the current name, with the stronger content
assertions improvise-igxp asked for.

The injections above are the original two and still describe the property. The
present test is `harness/tests/help.spec.js`, and its own entry below records
what igxp added: the rows are read as `dt`/`dd` pairs and asserted as text, so
blanking `keys.textContent` fails it where `toBeVisible` passed.

### the_shipped_demo_seeds_a_worker_whose_raw_cells_are_settable

improvise-ir7l renamed this from `..._whose_every_cell_is_settable` and
narrowed what it claims. The old loop called `MainThread::cell` — which panics
on anything but a stored cell — over *every* column including `Profit`, which
`web/demo.improv` defines as `Revenue - Cost`. It passed only because a formula
target projected `CellId::Record`, which is the bug the ticket names: a test
whose name was false for a third of the grid it walked.

It now walks the two raw columns and asserts separately that the `Profit`
column is `CellId::Derived`, so it fails if either half moves. That second
assertion is what makes the narrowing honest rather than a retreat — dropping
the column would have left the page free to offer it again with nothing
noticing.

### the_page_keys_turn_the_odometer_as_the_command_does

improvise-p1ym. `GridCache::page_coords` carried `(category, selected item)`
and nothing else, so `[`/`]` resolved to a command name the client held but
could not compose an argument for. They reached `Host::handle`, which answers
an empty vec — `doctrine(an_upstream_key_is_a_black_hole)` — so an independent
smoke test found them inert against the live page, where `Quarter` sits on the
page axis precisely because paging is a thing a visitor tries.

The test asserts the *shape* composed, not that something resolved: two page
axes, the least significant at Q4, so one press must both wrap `Quarter` and
carry into `Year`. A resolver that moved only the first axis, or carried the
wrong way, fails it.

### a_filter_axis_is_projected_but_not_cycled

The gotcha-27 arm. Page and Filter both constrain which records are visible,
and `GridLayout::page_coords` is deliberately `filtering_cats()` (Page ∪
Filter) because the *layout* does not care which the user can navigate. The
projection copied that verbatim, so a client handed the list would have tried
to cycle a drill's fixed coordinate.

`PageAxis::items` is `Some` only for `Axis::Page`, so the difference is in the
type rather than in a rule each client remembers. The test adds a Filter entry
to a client that is otherwise paging normally and asserts the two Page axes
still move while the Filter one does not — an assertion that only the Filter
axis is skipped, not that paging stopped.

### a_locally_resolved_page_turn_lands_where_the_host_would_put_it

The lockstep claim, and **the first version of it was vacuous**, which is worth
recording because it looked exactly right. It rebuilt the client's cache from
the host after every press and then compared the client's cache against that
same host's document — two readings of one value. Reversing the odometer's
significance in `page_cycle` left it green.

It now drives two independent documents: one `Host` fed the commands the client
composed, one `App` fed the same keypress through `reduce_key`, compared on
`View::page_selection` — the document, never a projection. Proved discriminating
by that same injection (`for i in (0..axes.len()).rev()` → `for i in
0..axes.len()`), which now reports Q2 against Q3. The `assert_ne!` against a
fresh fixture is the second half: without it, a resolver that emitted nothing
at all would pass by moving neither.


#### harness/tests/widgets.spec.js — the file's own scope

**Both files were deleted by PR #61**, which moved the pointer's and the
widgets' browser halves into `harness/tests/contract.spec.js` and the rest into
`node --test web/tests`. What follows is the history of how these assertions
were arrived at; the assertions themselves now live there.

**The file is gone; its subject is not.** All four widgets it named were one
failure at one boundary — a `RenderModel` field with no element painting it —
and that is now asserted once, from both sides, by
`web/tests/render_surface.test.js` and `harness/tests/contract.spec.js`. What
is *not* carried over is each key's meaning, which `improvise_protocol::resolve`
decides and tests. Everything below is the history of the bug, and still true.

A user reported three things as broken: "I can't expand categories, and the
Tile + View UIs don't work." None of the three was a regression. Driving the
assembled site under Chromium separated them, and the separation is the point:
two of the three had *every* layer but the last one, and the layer they were
missing was not the same in each case.

**Category expand already worked, by keyboard.** `Shift-C`, `j`, `Enter` folds
`Command::ToggleCatExpand` client-side and the items appear. What does not work
is the *mouse*: `categoryList` builds plain `<li>`s with no listener, so a
click on the triangle does nothing at all. That half is improvise-7ybz, and it
is a product decision about the whole page's pointer model rather than a defect
in an implemented feature — `#grid` offers a click only on an editable cell, so
there is no click-to-select either.

**The tile bar and the view panel had the cache, the keymap, the resolver and
the host round trip, and no DOM.** Before the fix, `render_state()` in the
browser carried five `TileBarCache` entries and both `ViewListCache` views;
`Shift-T` entered `TileSelect` and `ArrowRight` moved `tile_cat_idx`; `r`/`c`/`p`
reached the host and really did move a category between axes. `RenderModel`
simply had no field for either, and `web/index.html` had no element. So the
keys worked and the user was aiming them at nothing — which reads exactly like
"the Tile UI doesn't work". The formula panel was the third of `Panel::ALL` in
the same state and is fixed by the same mechanism.

**The fault injection was the unfixed bundle itself.** Run against the tree at
`a3bef6e`, the category test passes and the other four fail — `#tiles`,
`#views` and `#formulas` resolve to zero elements. That is the evidence the
four tests are discriminating, and it is why the category test stays: it is the
control that says the harness really is driving the keyboard.

Two assertions in the first draft were wrong, and both corrections are worth
keeping. `Axis::short_label()` is **three columns**, so a `Page` tile reads
`Quarter Pag`, not `Quarter Page` — a test asserting the long spelling would
have forced the page to invent a label instead of echoing `Axis`'s own. And
switching views leaves the panel **open**: `switch-view-at-cursor` returns to
Normal and never closes the panel, exactly as `src/draw.rs` keeps drawing it
off `view_panel_open` alone. Asserting it hidden would have pinned the browser
to behaviour the TUI does not have.

The gating rule itself — an empty list is what says a panel is closed, the same
rule `help` follows — is asserted in Rust as well, by
`a_closed_panel_projects_no_rows_and_an_open_one_does` and
`the_tile_bar_is_always_present_and_only_its_cursor_is_modal`, because a browser
test cannot distinguish "closed" from "the cache is empty" and those two tests
fill the caches first.

What these tests do **not** cover: the pointer (improvise-7ybz), and the
inconsistency that `#views`/`#formulas` honour their open flags while
`#categories` is drawn unconditionally because `app.js` has never read
`category_panel_open` (improvise-wsaw).

One assertion was added after the first green run and is worth naming: the tile
test originally asserted only that the *tile label* changed to `Product Col`.
That is the bar reporting itself, which is exactly the shape of test this repo
keeps catching — it would pass against a tile bar that displayed an axis the
document had not taken. It now also asserts the grid reshaped: `Espresso` moves
from a `tbody` row header to a `thead` column header. `.first()` is needed there
because Product then shares the column axis with `_Measure`, so the label
appears once per header level — which is itself a small confirmation that
gotcha 44's multi-level frame reaches the browser.

**Three review findings, applied.** The second is the one worth carrying.

**The page had two spellings of the same triangle, inside the file that
declares it has one.** `indicator()` carries the comment *"only this spelling is
the page's (gotcha 26)"* — singular — and `categoryList` did not call it: it
inlined U+25B8/U+25BE (the SMALL triangles) where `indicator()`, the page's own
grid group headers and `src/ui/category_panel.rs` all draw U+25B6/U+25BC. So the
browser's category panel disagreed with the TUI's *and* with its own grid.
`categoryList` now calls `indicator(!row.expanded)`.

**And the first version of this spec pinned the wrong spelling.** It asserted
`/▸ Product/` and `▾` — the divergent pair — so the obvious cure, which the
file's own comment implies should already be in place, would have *failed a test
this work added*. That is this repo's characteristic defect exactly: not a wrong
line, a test that cements a state the doctrine says is wrong, and it makes the
cure more expensive the longer it sits. The spec now asserts `▶`/`▼`, and the
change was proved discriminating by running it against the pre-fix bundle, where
it fails with `Received string: "▸ Product (4) R"`.

Note what this does **not** settle: whether glyphs should move to the protocol
the way `short_label()` did. That is **improvise-h04z**, not answered here —
what is fixed is the page contradicting itself. `viewRow` still spells `"▶ "`
as a literal duplicating `src/ui/view_panel.rs:62`; the two agree today, which
is precisely the state `categoryList` was in before it drifted.

**And the drift was already spreading, which is the evidence that ticket needs.**
`harness/tests/pointer.spec.js`, written on a different branch, had
*independently* grown the same `▸`/`▾` assertions — so the corrected
`indicator()` broke it too. Three files converging on a spelling nothing
compares is the failure design-principles §5 predicts, observed rather than
argued, and it is what answers "is one duplicated literal worth a protocol
change" with data instead of doctrine.

**`el.tiles.hidden` was a no-op**, removed with its comment. `#tiles` declares
`display: flex`, an author-origin rule that beats the UA sheet's
`[hidden] { display: none }` at any specificity, so the guard never hid
anything and "an empty tile list draws nothing at all" was false. `#views`,
`#formulas` and `#help` declare no `display` and so are genuinely hidden by the
attribute. Worth knowing before anyone "fixes" it: because `#tiles` is always
laid out, its height never changes, so it feeds nothing back into the
`ResizeObserver` — restoring the guard would introduce exactly the first-paint
height change the observer argument assumes away.

**The `ResizeObserver` loop is no longer "argued, not tested", and the proof is
worth more than the measurement.** It was measured: 820 combinations — four
panel states (none / views / formulas / tile-select) × heights 360-440 in 2px
steps × five widths straddling the `COL_PX = 110` boundary, each counting
`#grid` child replacements in a 500ms quiet window. Every size settled; nothing
repainted twice. But the reason is structural, so the measurement is a check on
it rather than the evidence itself: **the `frameCost` dependency graph is
acyclic.** `frameCost.cols` is `row_levels`, the number of row-axis header
*levels*, which does not depend on how many rows are projected.
`frameCost.rows` derives from `col_levels.length` and `col_groups`, which depend
on the projected *column* window, which depends on width and `frameCost.cols`.
So `cols → rows`, and nothing depends on `rows`. There is no cycle to oscillate.
A change that made either term depend on the projected row count would create
one, and that — not the pixel arithmetic — is the thing to check.

**A harness port collision can make a run test somebody else's tree, silently.**
`playwright.config.js` hard-coded 8099 with `reuseExistingServer: true`, so a
`python3 -m http.server` left by another worktree is *adopted*, and the run then
exercises that checkout with no warning. The port is now
`IMPROVISE_HARNESS_PORT`, defaulting to 8099 so CI is unchanged. The tell is a
result that disagrees with the file you just read: check
`lsof -a -p <pid> -d cwd` on the listener before believing it.

**It fires in both directions, and the dangerous one is the false PASS.** Two
agents hit it in one session. One got a false *negative* — a glyph fix reported
absent, because the adopted tree did not have it — which is merely confusing,
since a failure sends you looking. The other got `widgets.spec.js` reporting
**5 passed against a tree it had content-verified as having no `#tiles` and no
`paintTiles` at all**, which is impossible and was caught only because that
agent knew what the tree contained and refused to believe the number. **A false
pass prompts nobody.** That is what makes a hard-coded port with
`reuseExistingServer` a correctness bug rather than an inconvenience, and it is
the same rule as the rest of this file: a green result is evidence only once you
know what it measured.

### a_click_focuses_the_panel_moves_its_cursor_and_activates_the_row

improvise-7ybz's whole difficulty in one assertion, and the reason the click
resolvers take an **index** rather than reading the cursor.

A click means three things at once — focus the panel, move its cursor to the row
under the pointer, activate that row — and the third is resolved in the *same
pure call* as the first two, before any of them has been folded. So
`filter_to_item_at(state, index)` must be asked about `index`; asking
`filter_to_item(state)` reads `view.cat_panel_cursor`, which is still wherever
the keyboard last left it. That is why `cat_tree_entry`, `toggle_cat_expand`,
`filter_to_item` and `tile_axis` each gained an `_at` twin and the cursor-reading
form became a one-line call of it: one definition, two entry points.

**Injected fault**, run: `commands.extend(filter_to_item_at(state, index)…)` →
`filter_to_item(state)`. The test fails with
`ToggleCatExpand("Region")` against `ToggleCatExpand("Product")` — the panel
cursor lands on the row clicked while the *expansion* happens to the row that
was selected before, which is the silent half. The fixture therefore has two
categories and clicks the **second**: with one category, or with a click on the
row already under the cursor, the bug is invisible.

The sibling `a_click_in_an_already_focused_panel_only_moves_and_activates` pins
the other half: `focus` emits only what is not already true, so a click inside
the focused panel is not a mode change on every click. Without it, "always emit
`SetPanelOpen` + `ChangeMode`" passes the first test.

### a_cell_click_is_absolute_even_though_the_page_paints_a_window

The pointer's version of `the_selection_is_placed_by_subtracting_the_scroll_offset`,
and it fails the same way: `GridCache` is viewport-indexed, `ViewState::selected`
is absolute, so a click at painted `(2,1)` under offsets `(12,3)` is `(14,4)`.
Offsets are **nonzero and unequal** for the same reason as its sibling — equal
offsets cannot separate "reconciles" from "swaps the two". The second half
asserts a click past the grid's extent resolves to nothing, which is what stops
a click on the padding below the last row selecting a cell that does not exist.

### a_click_past_the_last_row_resolves_to_nothing

`doctrine(check_the_checker)` for the two above: the empty-answer path. Without
it, a `click` that returned `Vec::new()` unconditionally would pass every
"resolves to nothing" expectation while failing silently everywhere else — so
this one is only meaningful *because* its neighbours assert non-empty answers.

#### harness/tests/pointer.spec.js — the file's own scope

**Both files were deleted by PR #61**, which moved the pointer's and the
widgets' browser halves into `harness/tests/contract.spec.js` and the rest into
`node --test web/tests`. What follows is the history of how these assertions
were arrived at; the assertions themselves now live there.

**The file is gone; one test carries it.** `contract.spec.js`'s "each clickable
surface is wired to its own index" keeps what only a browser can say — the
handler is on the element, it passes *that* element's index, and the answer is
painted — against three surfaces. What each click *means* is
`improvise_protocol::resolve`'s, and its tests are named below. The six tests'
injection stands as recorded.

The user's ruling on improvise-7ybz ("build it — one entry point per widget")
and improvise-wsaw ("honour the flag"), executed in a real browser.

Six tests, and **all six fail against the bundle built immediately before them**
— the tree that already had the three widgets drawn (PR #55) but no click
handlers and no `category_panel_open` read. That is the injection: the sidebar
is visible when it should be hidden, and every `click()` resolves to a `<li>`
that has no listener, so nothing moves. The category test is the sharpest,
because the element it clicks *exists and looks interactive* in the unfixed
tree — which is exactly what the user hit.

Two properties here that the Rust tests structurally cannot reach. **The
pointer and the keyboard are one cursor**: `the keyboard continues from where
the pointer left the cursor` clicks a cell, closes the editor, presses
ArrowLeft, and requires the move to start from the clicked cell — if the click
had only opened an editor (the pre-fix behaviour) the arrow would move from the
origin instead. And **the tile click is asserted against the grid**, not only
against its own label: `Espresso` must appear as a `thead` header, because a
tile bar reporting an axis the document did not take is the failure shape this
repo keeps finding.

One fixture note worth keeping: `openPanelThenLeave` opens the panel with
`Shift-C` and then presses `Escape`, which returns to Normal **without closing
the panel** (`PanelKeymap`'s Esc is `enter-mode normal`, nothing more). That is
the only state in which the "focus" third of the click is observable — from a
freshly opened panel the mode is already `CategoryPanel` and the assertion
would pass without the focus commands existing at all.

#### harness/tests/drill.spec.js — the file's own scope

The fourth widget the user reported, and the one with a **different answer from
the other three**. The tile bar, view panel and formula panel were each one
`RenderModel` field short — cheap. Drill is not: **there is no wire vocabulary
for it**, which is improvise-gd28, and these tests document the refusal rather
than pretending the gap is a bug to be fixed here.

**Where it stops, by layer.** Everything below the command exists and was
verified in the browser, not read: `project::grid_of` emits `CellId::Aggregate`,
the client receives it (`{"Aggregate":"750ab1f5ffa96d5e…"}` in `render_state`),
`render.rs::editable` correctly answers false for it, and `resolve.rs` reaches
the aggregate arm. What is missing is one link: `reduce.rs` contains **no
`Drill` variant at all** — not `Command`, not `ModelCommand`. The seam is ready
and the sentence is not sayable.

**Why it was left out is a decision, not an oversight** (gotcha 38): drilling
creates the `_Drill` view and writes `drill_state`, which gotchas 30 and 1 rule
**session-local** — `pending_edits` are keyed by `(row, RecordCol)` and belong
to whoever staged them. A `Command::Model` is routed with **no `SessionId`**,
which is right exactly when a change is addressed to *no one* session; drill is
addressed to precisely one. That is the same argument that removed
`ApplyAndClearDrill` from the wire in improvise-3x3u, so adding
`ModelCommand::Drill` would reintroduce the bug that removal fixed. It needs the
**addressed** form — ADR 001 layer 2.

**The two entry points used to fail differently, and that asymmetry was the
finding.** `i`/`a` on an aggregate declines **out loud**: `edit_or_drill`
answers the `CellId::Aggregate` arm with a status the user can read. But `>`
(`drill-into-cell`) was a name `resolve::step` did not handle, so it became
`KeyOutcome::Upstream` → `ClientFrame::Key` → `Host::handle`, whose `Key` arm is
an explicit empty vec — **a black hole, not a slow path** (gotcha 47). Pressing
`>` in the browser did nothing whatsoever: no status, no mode change, nothing.
That is why this read as "never confirmed working" rather than as a refusal.

**That silence is now closed, and the closing is what this file ships.** `step`
answers `"drill-into-cell"` with a `SetStatus` saying drill is not available in
the browser yet — an interim the wording of which is load-bearing, since it must
be true both today and on the day improvise-gd28 lands. The wire vocabulary is
still absent; only the *silence* was fixed. Note for gd28: when the real drill
arrives, a leftover `"drill-into-cell"` arm in `step` would **shadow** it with
nothing failing, because a name that resolves never reaches the host.

**The TUI is the control and it works**: 12 drill tests pass across
`cmd/grid.rs`, `cmd/mode.rs`, `ui/effect.rs` and `ui/app.rs`. So this is
isolated to the client/wire, not a general regression.

**A fixture fact that is itself part of the answer.** `web/demo.improv` has **no
aggregate cell at all** — gotcha 46 puts exactly one category on each visible
axis precisely so every cell is a `Record`, and `tests/web_demo_model.rs`
asserts it. So on the shipped demo a user cannot even reach the refusal without
first changing an axis. `anAggregateGrid` therefore *makes* one, through the
tile bar, the way a user would: `Quarter` cycles Page → None and every cell
becomes an aggregate. The precondition is then **asserted** (`td.editable`
count 0) rather than assumed, so neither test can pass against a grid of
Records.

**Both injections, run** — against the tree *before* the interim, which is what
made them two faults rather than one. Replacing the aggregate arm with `None` —
silencing the honest refusal — failed **both** tests, and the second failed on
its *`check_the_checker` control*, which is the point: with nothing answering,
the control can no longer tell "`>` is silent" from "the page is dead", and the
test correctly refuses to pass. Adding `"drill-into-cell" => Some(vec![SetStatus(…)])`
to `step` — making `>` resolve — failed **only** the second test and left the
first green. Two faults, two different failure signatures, neither test passing
for the other's reason. That second injection is now the shipped code, which is
why the test it broke was rewritten rather than kept.

That control is load-bearing and not decoration: a test asserting *nothing
happened* passes against a page that has stopped listening, so it presses `i`
afterwards and requires `#status` to change. Without that, this file would be
folklore with a green tick.

### the_drill_key_and_an_aggregate_edit_refuse_for_different_reasons

The Rust half of the interim, and the assertion that carries the whole weight.
Two keys on the same aggregate cell must both refuse and must **not** refuse
with the same sentence: `>` says drill is unavailable, `i` says drilling into an
aggregate needs the host. Collapsing them into one message would be the
tempting tidy-up and would lose the distinction between "this key does nothing
here yet" and "this cell is not one you may write".

**The injection, and why it is not the obvious one.** Replacing `>`'s sentence
with the *aggregate* sentence looks like it should fail on the first assertion —
and does not: that sentence contains both "drill" and "browser", so it clears
the substring check. What fires is the anti-aggregate assertion lower down. The
claim that the second assertion is the load-bearing one was doubted on review,
tested, and confirmed; record it here because the first assertion reads like the
discriminating one and is not.

The harness sibling (`drill.spec.js`) asserts the same distinction in a browser,
but its `not.toContainText("aggregate")` is **decoration under the only
injection that exists** — Playwright throws at the positive assertion above it
first, so that line is never reached. The Rust assertion is the guard; the
harness one is end-to-end confirmation that the string survives the wire.

### a_view_row_click_focuses_moves_and_switches_to_the_row_clicked

improvise-iioi, and it is the **same trap** as the category click one level
over: the activation must be resolved against the row **clicked**, never
`view_panel_cursor`, because the `SetPanelCursor` ahead of it has not been
folded when the resolver runs. Injecting exactly that — reading the name at the
cursor instead of at `index` — yields
`SwitchView("Default")` beside `SetPanelCursor { cursor: 1 }`, i.e. the cursor
lands on `Plan` and the document switches to `Default`. Silent, and wrong in the
half a user does not watch.

The fixture therefore holds **two** views and clicks the **second**. With one
view, or with a click on the row already under the cursor, the bug is invisible
— the same reason `a_click_focuses_the_panel_moves_its_cursor_and_activates_the_row`
clicks Product rather than `_Index`.

### a_formula_row_click_navigates_and_activates_nothing

The negative arm, and it is a statement about the *rule* rather than about the
formula panel. The rule is "go there, then do what `Enter` does there";
`ModeKey::FormulaPanel`'s keymap binds `a`/`n`/`o` to `enter-mode formula-edit`
and `d`/`Delete` to delete, and **no `Enter` at all**. So the rule yields
navigation and nothing else, and that is the rule applying rather than the fix
stopping half way.

This test asserts the *exact* command vector, which is the whole of what it can
say. It once carried a second, explanatory `assert!` that no `FormulaEdit` mode
change appears — **which could never have been the failing assertion**, because
the `assert_eq!` above it pins the same three commands and aborts first. A
reviewer demonstrated it by injecting a `ChangeMode(FormulaEdit)` and watching
the panic land on the `assert_eq!` with the explanatory message never printed.
It was a comment wearing an `assert!`, and the argument now lives in
`context/code/clients.md` where a comment run cannot hold it.

### the_formula_panel_has_no_enter_to_mirror_and_the_view_panel_does

The guard that the removed assertion was pretending to be. The asymmetry — a
view-row click activates, a formula-row click does not — is a fact about the
**keymap**, and nothing tied the click to it. The reviewer proved the gap by
adding `Enter -> enter-mode formula-edit` to `ModeKey::FormulaPanel` and running
the whole workspace: **1381 passing, nothing failed**, while `click_formula_row`
still activated nothing. The click and the keyboard then disagree about what a
formula row does, silently.

Injecting that same binding now fails this test and only this test. The failure
message names `click_formula_row` as what must change, because the person who
adds an `Enter` binding is not the person reading `resolve.rs`'s click arms. The
positive half (`ViewPanel` *does* bind `Enter`) is there so the test cannot pass
by asserting that no panel binds anything.

#### The view and formula row clicks in the browser (improvise-iioi)

These began as two tests in `harness/tests/pointer.spec.js`. **That file no
longer exists**: PR #61 deleted it and moved the pointer's browser half into
`harness/tests/contract.spec.js`, whose stated scope is the wiring — the handler
is on the element and passes *that* element's index — while what a click MEANS
is `improvise_protocol::resolve`'s and tested there. The assertions were merged
into that file's own click test rather than restored, because resurrecting a
file a merge deleted is how a deliberate removal gets undone by reflex.

They leave the panel **open but unfocused** — the only state in which the
*focus* third of the click is observable.

**History, not current evidence:** the original pair was proved against the
bundle built immediately before the fix, both failing there while the
pre-existing pointer assertions passed. That run was against
`harness/tests/pointer.spec.js`, which no longer exists. What holds the
relocated assertions honest is the injection below, run in their new home.

The view test asserts three things — `#view-name`, the `active` marker and the
`selected` cursor — because switching ends in `NORMAL` and a test that only
checked the mode would pass against a click that did nothing but leave the
panel. **The relocation initially dropped two of the three**, and a reviewer
caught it; they are restored.

**And the fixture was vacuous in a way the prose had already warned about.**
`Default` is index 0 and holds `view_panel_cursor` by default, so clicking it —
which both the old `pointer.spec.js` and the first relocated version did — makes
`index` and the cursor the same number, and reading either gives the same name.
A reviewer injected `switch_view_at(state, state.view.view_panel_cursor)` into
`click_view_row` and **the whole contract suite passed 3/3**: the exact fault
this test, the ticket and the Rust test all exist for was invisible to the
browser half. The fixture now switches to `Default` by **keyboard**, leaving the
cursor there, then **clicks `Plan`** — so the two readings name different rows
and the outcomes differ. Re-running that injection now fails it.

The blindness was inherited rather than introduced: the deleted file clicked
`Default` too. It became worth fixing because the relocated test is now the
*only* browser assertion on that surface.

**One fact the reviewer's report supplied and this fix leans on**: shipping the
cure for one panel and not its two siblings *reproduces the original report*. A
user who has just learned category rows are clickable clicks a view row and
reads the silence as broken — which is literally what "I can't expand
categories" meant.

#### The harness port: reuse is now opt-in

`reuseExistingServer: !process.env.CI` became `=== "1"` on
`IMPROVISE_HARNESS_REUSE`. A default-on reuse adopts a server another checkout
left on the port and then tests **that tree**, which fired in both directions in
one session — a false negative and, worse, a false *positive*. A path-hash
default was considered and rejected: it still silently reuses when two agents
share a worktree path, where an explicit opt-in cannot. CI is unaffected (it
never reused) and a developer wanting the old speed sets the variable.

### a_click_that_cannot_compose_its_activation_composes_nothing

improvise-hkr8. `click_category_row` ended with
`filter_to_item_at(state, index).unwrap_or_default()`, and that `None` arm is
not "nothing to do" — it is `BasisCache::claim` answering that the server has
published no basis yet (gotcha 43), so the document change cannot be composed.
The click therefore kept its **navigation prefix** (focus the panel, move the
cursor), dropped its activation, and reported success. The keyboard handles the
identical `None` correctly, by mapping `step(..) == None` to
`KeyOutcome::Upstream`.

The fixture has to do two things a careless one would not. It **expands
`Region`** so that row 1 is an `Item` row — a header row activates via
`ToggleCatExpand`, which needs no basis and so cannot show the bug — and it
asserts both preconditions (`cat_tree_entry_at` is an `Item`, `claim` is `None`)
rather than assuming them, because an empty `ClientState` makes every
state-dependent refusal look like the one under test.

Injecting the old `unwrap_or_default()` fails this test and only this test.

### the_same_click_composes_everything_once_a_basis_is_published

The positive arm of the one above, and it is what stops the fix from being
"return nothing more often". With a basis published, the same click composes all
six commands: open, focus, move the cursor, two `Command::Model`s and the
status. Without this, deleting the activation entirely would pass hkr8's test.

### a_first_tile_click_selects_without_touching_the_document

The user's ruling: a click selects, a second click cycles. The fixture publishes
a basis **deliberately**, so the absence of a `Command::Model` is a decision
rather than a client that could not compose one — pointed at an unpublished
basis this test would pass for hkr8's reason instead of its own.

Both halves are asserted, because "the axis did not change" passes against a
page where nothing happened at all: the positive half requires `SetTileCatIdx`
plus `ChangeMode(TileSelect)`, the negative half requires no `Command::Model`.

**Four injections, four distinct signatures.** "First click also cycles" fails
this test, `the_first_click_on_tile_zero_selects_it_like_any_other` and
`clicking_a_different_tile_selects_it_rather_than_cycling_it` — and **not**
`a_second_click_on_the_selected_tile_cycles_its_axis`. "Second click does not
cycle" fails only that last one. "`already_selected` reads the index alone"
fails only the tile-zero test. Reverting hkr8 fails only the hkr8 test. No
injection passes for another's reason.

### t_then_a_click_on_the_leftmost_tile_cycles_it_immediately

Found on review, and it is a defect in the *wording* rather than the code. `T`
enters `TileSelect` leaving `tile_cat_idx` at **0**, so a click on the leftmost
tile is a click on the already-selected one and cycles on the **first** gesture.
Both loose summaries of the ruling — "a click never mutates on its own" and "a
**second** click cycles" — are false against that probe.

The behaviour is right: a click does what `Enter` does there, and `Enter` in
`TileSelect` cycles the tile under the cursor. The resolver cannot see how the
state arose and must not try to. So the test exists to **name** the case rather
than to change it, and it asserts the neighbouring tile answers the identical
gesture by selecting — because the surprising half is that two adjacent tiles
differ, and a reader who meets that in the wild should find it written down.

Note what this means for its sibling `a_second_click_on_the_selected_tile_cycles_its_axis`:
that test sets the state directly rather than by clicking, so it **already was**
the keyboard-entry case. Nothing was untested; the name and the argument were
missing.

### enter_in_an_empty_view_panel_resolves_locally_rather_than_upstream

`switch_view_at` returns `Option`, and its two callers answer the `None`
differently on purpose. **From a `click_*`, `None` means "this gesture composed
nothing"** — a dynamic fact, and hkr8's rule. **From `step`, `None` means "this
client cannot execute this command *name*"** — a *static* fact about the
vocabulary, which `the_command_names_that_still_need_the_host_are_these` exists
to keep static. Two questions sharing one type, which is why the asymmetry reads
wrong at first. (`delete_view_at_cursor` already answered `Some(Vec::new())` the
same way, so this follows the file rather than inventing.)

Nothing held the keyboard side to it until this test. A reviewer removed the
`unwrap_or_default()` so out-of-range propagates `None` — making `Enter` in an
empty view panel `KeyOutcome::Upstream`, gotcha 47's black hole — and **the whole
workspace passed under `--no-fail-fast`**. That would make membership of the
host-needed list state-dependent, the one property that list denies. Injecting
it now fails this test and only this test.

The assertion is `Ignored`, not `Local(vec![])`: `KeyOutcome::of` maps an empty
vec to `Ignored` by construction, so `Local` is never empty. What matters is
that it is not `Upstream`.

### the_first_click_on_tile_zero_selects_it_like_any_other

The trap in the ruling's own wording. "A second click on the already-selected
tile" reads as an index comparison, and `tile_cat_idx` is **0 before anything
has selected anything** — so an index-only test would read tile 0 as already
selected and cycle it on its very first click, making the non-mutation
guarantee true of every tile but one. The condition is `mode == TileSelect`
**and** `tile_cat_idx == index`.

### clicking_a_different_tile_selects_it_rather_than_cycling_it

The other half of the same trap, from the opposite side: without it, "a click
does not mutate" would hold only for the first click of a session, since every
click after the first is a "second click" in the loose reading. Clicking A then
B must select B.

#### How to know a launch default has stopped disarming things

The question this left open was **how to know you have exhausted the class**.
Grep does not answer it: grep finds sites that *name* the flag, and the hazard
is a test that merely **starts from a default-built state** and asserts
something downstream, mentioning nothing. Three disarmed tests were found by
grepping `category_panel_open`; that was luck, not method.

**Mutation answers it, because it does not care what a test mentions.** The
recipe, which a reviewer ran across five sites in about twenty minutes:

> For every production site that **writes, propagates or reads** the value,
> replace it with the constant the default supplies, and run
> `--no-fail-fast`. Sites where nothing fails are suspects. Then **re-run each
> suspect with the default inverted.** If it now fails something, the test was
> **vacuous** — the default disarmed it, and the fix is the fixture. If it
> still fails nothing, it was simply **unguarded** — a different problem,
> pre-existing, and a bead rather than a fixture.

**The second step is the one that matters**, and without it the two classes are
indistinguishable: both look like "nothing failed". It is what established that
the class is closed at **two** (`set_panel_open_and_cursor`,
`panel_commands_address_the_named_panel_only`) and that two further silent sites
are older problems this ruling did not cause:

- `ui/app.rs`'s `App::cmd_context` propagator — hardcode it `true` and the whole
  workspace passes. `registry.rs` reads it for `toggle-panel-and-focus`'s
  open-vs-close decision, so `C` on a closed panel would decide to *close* and
  nothing would fail. Invisible because `cmd/mod.rs`'s test helper sets the
  field explicitly, so no command test reaches the propagator. Filed.
- `improvise-wasm-client/src/render.rs`'s `RenderModel` field — hardcode it
  `true` and **Rust sees nothing at all**; only the Chromium harness catches it,
  at `contract.spec.js`'s `toBeHidden`. That is literally improvise-wsaw
  reintroduced one layer up, and **a Rust-only CI run cannot see it** — which is
  the sharpest argument on file for why the browser job must be able to fail the
  build.

**And a repair needs its own probe, because a repair can be shaped like a fix.**
The two-step recipe above finds a *disarmed* test; it does not tell you whether
the repair you then write is real. That gap is not hypothetical — the first
repair of `panel_commands_address_the_named_panel_only` folded
`[open:false, open:true]`, read as a fix in review, and was still vacuous.

The probe that settles it is a **one-directional** fault: make the writer
`if open { set true }`, so the flag can be raised but never lowered. **A vacuous
repair cannot see this**, because a test that only ever asserts the `true`
direction is satisfied by a writer that only ever writes `true`. Injected into
both copies at once, it fails `set_panel_open_and_cursor` **and**
`panel_commands_address_the_named_panel_only`, each in its own copy — which is
what establishes both repairs are genuine rather than merely differently
spelled. Prefer it to re-reading the diff: the diff contained `open: false` in
the version that was vacuous.

Note `resolve.rs`'s `panel_open` reader is **well** guarded by contrast:
hardcoding it `true` fails two click tests. So the picture is not "everything
touching this flag is untested"; it is specifically the propagators.

### the_terminal_constructor_inherits_the_shared_default_rather_than_setting_it

**Prospective rather than present-tense, and the doc comment says so.** With
three panels, `the_terminal_app_launches_with_the_category_panel_open` and
`the_other_two_panels_are_shut_at_launch` already cover every `Panel::ALL`
member, so this test cannot currently fail without one of them failing too. A
reviewer confirmed that by control.

It earns its place the way gotcha 12 describes `Panel::ALL`: a **fourth** panel
reaches it from one `ALL` entry, and at that moment it becomes the only test
asserting that `App::new` did not quietly give the TUI its own launch state —
the divergence improvise-wsaw closed. Recorded here so nobody later reads a
green tick as evidence of something it is not yet checking.

### the_terminal_app_launches_with_the_category_panel_open

The user ruled (2026-09-20) that the category sidebar is visible at launch in
the **TUI as well as** the browser, so `improvise model.improv` opening with it
showing is intended. This is the guard on the front end the ruling newly
changes: `a_fresh_session_opens_with_the_category_panel` asserts
`ViewState::default()` in the *protocol* crate, and nothing downstream of it.

Why not a rendered-frame test: design-principles §7 says not to test ratatui
`Widget::render`, and there is no `TestBackend` anywhere in this repo. The
honest target is the TUI's own constructor. `src/draw.rs`'s one-line read of the
flag stays argued-not-tested, as gotcha 48 has it.

Three injections. Putting the shared default back to `false` fails this test and
`a_fresh_session_opens_with_the_category_panel`. Making `App::new` override the
default (`app.view_state.category_panel_open = false`) fails this test **and**
`the_terminal_constructor_inherits_the_shared_default_rather_than_setting_it` —
which is the one that would catch a TUI-only launch state being reintroduced, the
divergence improvise-wsaw closed. `the_other_two_panels_are_shut_at_launch`
stops "open everything at launch" passing the first.

### set_panel_open_and_cursor

**The launch default silently disarmed this test, and that is the finding.** It
did `SetPanelOpen { Category, open: true }` then asserted the flag was true — but
`test_app()` builds from `ViewState::default()`, where it is *already* true. Its
Formula and View siblings still default to `false`, so only the category arm
went vacuous.

What that cost, demonstrated: replacing `Panel::Category =>
app.view_state.category_panel_open = self.open` with a **no-op** — so no effect
could open or close the TUI's category sidebar at all — left the entire
workspace green. `C` could be made to do nothing in the terminal with 1391 tests
passing.

The fix is the fixture stating its own precondition: close the panel first and
assert it closed, so the effect has to move the flag before the `true` direction
is asserted. Injecting the no-op now fails this test.

Note the harness cannot see this one, and that is correct rather than a gap: the
browser folds `Command::SetPanelOpen` through `reduce_view`, a *different*
three-way match in a different crate from `effect::SetPanelOpen`'s. Two
derivations of one mapping — which is why the `reduce_view` guard needed the same
repair independently. **Since improvise-56ek there is one derivation**, so that is
history rather than a standing hazard; see below.

### a_panel_command_writes_that_panel_and_no_other

The `reduce_view` half of the one above, and **the first repair of it was still
vacuous** — worth recording because the mistake is subtle. Folding
`[open: false, open: true]` and asserting the final state is *true* passes
against a reducer that folds nothing at all: the default is already true, so
neither command needs to land. Only asserting the **`false`** direction
discriminates, because that is the one the default cannot supply. Caught by
injection rather than by reading — the no-op fold reported NONE failing after the
first fix.

improvise-56ek then removed the second derivation entirely: `ViewState::panel_open_mut`
and `panel_cursor_mut` (plus their read halves) are the one place a `Panel` becomes
a field, and both `effect::SetPanelOpen::apply` and `reduce_view` call them. The
cure is one home, not a test holding two copies in step
(`doctrine(a_consolidation_that_keeps_its_compatibility_test_is_unfinished)`), so
there is deliberately no "the two agree" test — a wrong field in the one home is a
failure in every caller.

This test replaces `panel_commands_address_the_named_panel_only`, which drove
`Panel::Category` only and so could not tell one panel from another. It keeps that
test's lesson by zeroing every panel before opening one.

Injected fault: point `Panel::Category`'s arm at `formula_panel_open`. Fails by
name for every panel in `Panel::ALL`.

**That injection alone was not enough, and the gap is gotcha 3's shape.** The first
version asserted only through `panel_open`/`panel_cursor` — the read halves of the
mapping it was testing. A *consistent* permutation of all four accessors is a
self-consistent bijection: injecting Formula↔Category into `panel_open_mut`,
`panel_open`, `panel_cursor_mut` and `panel_cursor` together left the test passing,
while two unrelated tests that read raw fields failed. It caught only a
**non-injective** mapping, which is exactly the injection first recorded here. The
test now reads the three field pairs by name once per panel, and the consistent
permutation fails it: "Formula is not the field Formula names".

Also corrected here: the claim that consolidation left "no second copy to agree
with" was false when written. `resolve.rs` carried a fourth copy of the same
`Panel` → `ViewState` three-way match, **in the same crate on the same type**; it
is deleted and its three call sites go through `ViewState::panel_open`. What
remains is *not* the same mapping: `registry.rs` maps `Panel` to `CmdContext`
fields, a different type whose values are copied from `view_state`, and
`resolve.rs`/`registry.rs` each map `Panel` to a (cursor, collection length) pair,
which is a second derivation of something else and is `lockstep.rs`'s subject.

### a_fresh_session_opens_with_the_category_panel

The user's ruling that the category panel is visible at launch, implemented as
the **shared** `ViewState::default()` rather than a browser special case — a
browser-only default is "the page overrides the flag", which is the same defect
as the "the page ignores the flag" bug improvise-wsaw fixed. The consequence,
accepted deliberately, is that the TUI opens with the panel too.

The test also asserts the *other two* panels stay shut, so it cannot pass
against a default that simply opens everything.

Two existing tests had to change, and both were pinning the old decision by
**inheriting** it rather than stating it.
`panel_focus_cycles_from_the_focused_panel_not_the_first` is about skipping a
*closed* panel and took "the category panel is closed" from the default; it now
spells that precondition. `with_categories()` is used by tests about a click
*opening* the panel, so it now shuts it explicitly. Neither is the decision
being re-made — the decision is re-made only in the harness, deliberately.

#### The launch state and the tile ruling in the browser

Also merged into `harness/tests/contract.spec.js` rather than left in the
deleted `pointer.spec.js` — see the note above.

Two states, one mechanism: the sidebar is visible with no keypress, **and** `C`
still hides it. Proved by injection in a real browser: setting
`el.categories.hidden = false` (the page ignoring the flag) fails on
`toBeHidden`; setting the shared default back to `false` fails on `toBeVisible`.
Different signatures, different halves.

**Only the second is a guard, and an earlier wording here got that wrong.** It
claimed "either alone passes against the bug wsaw fixed" — but under the new
default, visible-at-launch passes for correct code *and* for a sidebar drawn
unconditionally. The launch assertion states the **ruling**; the `toBeHidden`
after the toggle is the only thing that still catches wsaw.

Note the first `C` now **focuses** rather than opens, since the panel is already
open — `toggle-panel-and-focus` closes only when the panel is both open and
focused — so the test presses it twice and the hide is the second press.

The tile tests were rewritten rather than adjusted, because the previous one
asserted the behaviour the ruling reverses; its failure against the new code was
itself the injection. The first-click test waits out a timeout before asserting
the axis did not move, since a cycle would arrive asynchronously and an
instantaneous assertion would pass against a slow one.
---

## `web/tests/` — the Node suite, and what was injected into it

No `###` headings here on purpose: `--check-evidence` resolves a heading to a
Rust `fn`, and a JavaScript test name under one would read as an orphan. These
are keyed by file.

Every test below was proved able to fail by patching the code it names,
checking the patch was on disk, running the suite and reading the failure —
never by the absence of an error. Thirteen injections, thirteen failures:

**What `shell.test.js` cannot reach, and the PR found out the hard way:** it
tests `createShell` in isolation, so it sees the watchdog RULE and never the
`app.js` wiring that calls it. That distinction is now written into
`context/code/clients.md` and guarded in `shell.spec.js`.

**`shell.test.js`** — `socketUrl` stops upgrading `ws://` on an https page;
`composeStatus` returns the model fact alone (which fails five tests, because
the watchdog's messages are shell facts and vanish with it); `fail()` stops
clearing the timer, so the watchdog *pre-empts* rather than being disarmed —
the bug PR #13 fixed and PR #21 half-lost; `extentOf` stops subtracting the
frame; `frameCostOf` stops counting the column-group line.

**`grid_plan.test.js`** — the data-row index is taken from the row's position
in `rows`, so a group header consumes one (the click coordinate bug gotcha 1
is about); the group label is tested for truthiness, so a group legitimately
named `""` draws as "in no group"; `typing` is `Boolean(model.editing)`, so an
empty edit buffer reads as no editor open.

**`serial.test.js`** — the chain is replaced by `Promise.resolve().then(...)`,
which is what an `async` listener does: the slow first frame is overtaken. The
suite also keeps that fault as a *passing* test in its own right, asserting the
unchained pair really does come back swapped, so the ordering test cannot be
green for want of a race.

**`render_surface.test.js`** — a `pub sparkline: String` added to `RenderModel`
is reported unpainted; deleting `paintTiles` reports `tiles` unpainted; a
`getElementById` that names an id `index.html` has not got is reported. The
first is the shape of the bug the four widgets shared, and the list it checks
against currently names `doc_name`/`doc_dirty`/`doc_stored_as` — improvise-5jna,
which this test found rather than remembered.

**`bundle/wasm_surface.test.js`** — `client.render_model()` renamed to
`client.render_modal()` fails both its tests. It reads the generated `.d.ts`, so
a missing bundle is an assertion failure and never a skip.

**`web/assemble.sh`** — dropping `web/shell.js` from the copy list, with the
page's own imports as the check. The first version of that guard anchored its
`sed` at `^import`, so it could not see the **multi-line** import that is the
only one it exists for, and the injection passed: the guard was written, landed,
and blind. That is what the injection was for.

## `harness/tests/contract.spec.js` — eight injections into the served page

Patched in `harness/serve/app/app.js`, which is what the browser loads, so no
rebuild stands between the fault and the run. The sidebar ignoring
`category_panel_open`; the tile bar, view panel, formula panel and help overlay
each never drawn; `click_cell` sending a constant row; `click_category` sending
a constant index; and the typed buffer drawn without its caret. All eight fail.

The last one did **not** fail at first: the test asserted the `typing` class and
not the text, so a cell drawn blank passed. The assertion was strengthened until
the injection failed, which is the only reason it is worth having — and it is
the same lesson as the eleven tests above: a class is a flag, and a flag is not
a pixel.

### every_advertised_command_answers_in_its_own_mode

improvise-rmvx. Gotcha 47 says an upstream key is a black hole, and
`the_command_names_that_still_need_the_host_are_these` is the guard that was
supposed to keep the list of them honest. It was built with
`in_mode(AppMode::Normal)`, so it only ever asked about Normal-mode bindings:
`add-record-row` (RecordsNormal) and `delete-formula-at-cursor` (FormulaPanel)
were outside its reach entirely and could never have failed it. **A named list
that silently scopes itself to one mode is a guard that looks broader than it
is.**

This asks it of every mode, and it asks it the only way that is not
over-reporting. The naive version resolves every advertised name against an
EMPTY `ClientState` and flags `edit-or-drill`, `commit-cell-edit`,
`create-and-switch-view` and `page-prev`/`page-next` — but those are *handled*
names refused by STATE, which is correct behaviour and not this bug. So the
fixture is `furnished`: every widget has something in it, a basis is published,
and a window is announced, so an `Upstream` can only mean the name is
unhandled.

Two things it does NOT do, each because the first attempt did and was wrong.
It does not call `step` with the advertised args: `advertised` carries `None`
for "any binding of this command", and `step`'s numeric and mode arguments are
mandatory, so that reports `move-selection`, `move-panel-cursor` and
`move-tile-cursor` as gaps in every mode. And it does not tokenise the rendered
hint string: `help::advertised` is a table of command NAMES, so the
cross-reference is exact and anything reading the rendered text is solving a
harder problem than exists. The keys come off `Keymap::keys_running`, which
`labels_for` now shares so "which keys" and "how are they spelled" cannot give
two answers.

**It watches BOTH silent variants, and the first version did not.** `KeyOutcome`
has two ways of saying nothing: `Upstream`, and `Ignored` — which
`KeyOutcome::of(vec![])` produces whenever a resolver composes an empty vector.
To a user they are the same black hole. The first version asserted
`resolve(..) == Upstream(event)`, so **three of the six commands this whole
change exists to make audible could go completely silent with the entire
evidence base green**: degrading only `add-record-row`, `delete-formula-at-cursor`
and `view-back` to `Step::Declined(Vec::new())` left 1397 Rust tests, 19 harness
tests and 26 node tests passing, because no browser spec presses those three
keys. Found on review of PR #71. The check is now `!matches!(.., Upstream(_) |
Ignored)`.

**The generalisation is worth more than the fix.** `KeyOutcome::of` turning an
empty `Local` into an honest `Ignored` is good design and it is also a
**laundering** step: every wrong answer that composes nothing arrives wearing
the variant that is usually innocent. So a guard's discriminator has to be
*state* — did anything the user can see change — and never the shape of the
return value. That is exactly why the `+cat` injection in
`a_locally_committed_creating_column_agrees_with_the_host` failed (it compares
documents and cursors) and the decline injection passed everywhere (nothing
compared a screen).

Widening the check costs ten more entries, all one legitimate boundary case:
`move-panel-cursor` mirrors `MovePanelCursor`, which returns nothing when the
cursor does not move, so a one-row panel or a cursor on an edge answers
`Ignored` for a reason that is not this test's subject. `furnished` therefore
carries **three** of everything with all three panel cursors seated at index 1.
Note what that rules out: seating them at 0 and calling the `Up` results
expected would have hidden the real defect in the same list as the boundary
case.

**The injection**: delete the `"toggle-prune-empty"` arm from `declined`. The
test fails naming `NORMAL: Char('P')` and `RECORDS: Char('P')` — both modes,
which is the widening the ticket was about, and a build that ran rather than a
compile error. The review's own injection is also kept as a check: degrading the
three unpressed declines to empty now fails naming `FORMULAS: Char('d')`,
`FORMULAS: Delete`, `RECORDS: Char('<')` and `RECORDS: Char('o')`.

What it found that the ticket did not predict: `view-back` is advertised in
RecordsNormal (`<`, captioned "back"), so it was a seventh instance of the same
class. The ticket had it filed under the Normal-mode host list instead, where
being upstream is not a defect.

The five that remain are listed by name with a reason each. Three of them —
`commit-export`, `commit-save`, `execute-command` — are reachable only from a
mode `declined` refuses at the door, so a browser never stands in front of the
hint; the other two are improvise-gcvb's records-cell commit, which needs
`record_col`.

### a_locally_committed_creating_column_agrees_with_the_host

improvise-gcvb. `resolve`'s commit returned `None` for the whole of records
mode, and the reason given was sound for the coordinate and measure columns —
a category column renames every measure cell in the row, which needs
`record_col` (gotcha 1). The guard was broader than its reason: a cell at the
cursor now projects `CellId::Create`, and committing one is a single existing
`ModelCommand` over the typed NAME that reads no `record_col` and writes no
cell.

Both halves are proved by injection, and the second is the one that matters.
Putting the broad `is_records()` early return back makes the test fail at "the
client must answer this key locally". Deleting the `CreateKind::Category` early
return — so `+cat` advances like any other column — fails with the client in
`RecordsEditing` where the host is in `RecordsNormal`: the TUI returns straight
after a `+cat` commit with a `RebuildLayout` and no cursor move, because an
inserted column renumbers every index to its right and the advance was computed
from the pre-commit layout (gotcha 23). A client that advanced anyway would land
one column off, silently.

`both_ends` compares the document as `.improv` text, the mode, the status and
every cursor, so neither half can pass by agreeing on the wrong thing. The
fixture drives *both* hosts into records mode with the `R` key rather than
hand-building a `_Records` view, because `twin_of` copies only the session
slice and a twin without the view would refuse the commit for the wrong reason.

### every_minibuffer_mode_paints_what_is_being_typed

improvise-fdt6. `commit-buffer formula` already resolved on the client — that
half of the ticket was closed by an earlier wave — so the browser could enter
FormulaEdit, type a formula and commit it. What did not exist was any way to
SEE it: `RenderModel::editing` is populated only when `mode.is_editing()`, which
is the two *cell*-editing modes, and it reads the `"edit"` buffer by name. Every
character typed into FormulaEdit, CategoryAdd, ItemAdd, SavePrompt,
ExportPrompt or CommandMode went into a buffer nothing painted. The mode opened,
the user typed, and the screen did not move — which is exactly the dead-room
shape the ticket names, arrived at from the rendering side rather than the
resolution side.

The value is read with `improvise_protocol::read_buffer` rather than
`buffers.get`, so the `"search"` special case (gotcha 11) keeps its one home.

**The injection**: `.filter(|_| state.view.mode.is_editing())` on the new
field, which is the pre-fix behaviour exactly. It fails naming `"formula"`.

**And the static check was not enough, which is the part worth keeping.**
`web/tests/render_surface.test.js` asserts that every `pub` field of
`RenderModel` appears as `model.<field>` somewhere in `app.js`. It passed while
the page was still broken: the string `model.minibuffer` was inside
`paintMinibuffer`, and `paintMinibuffer` was never called and `el.minibuffer`
was never looked up. A field can be *mentioned* by a function nothing invokes.
`harness/tests/keys.spec.js` caught it on the first run, in the browser, which
is the whole argument for that directory existing (gotcha 48).

### nothing_declined_is_also_composed

`step` is `declined` then `composed`, and until this test the claim that the two
lists cannot overlap was a **doc comment**. The dangerous direction is not a
typo: it is a future ticket implementing `view-back` (or `toggle-prune-empty`,
which is one projection field away) in `composed` and not thinking to delete its
`declined` arm. The browser then goes on saying "not available in the browser
yet" while the working code sits unreachable, and nothing notices — the classic
shape of a check passing while the thing it names is broken. Raised on review of
PR #71.

It is **derived from `declined` itself**, not from a list beside it: it walks
every `(name, args)` bound in every mode's keymap — parents and prefix
sub-keymaps included, sequence steps included — and for each one `declined`
answers, asserts `composed` does not. A seventh decline is covered without
coming here, which is the property a hand-written list could not have.

**The injection**: add `"view-back" => Some(vec![Command::SwitchView(..)])` to
`composed`. It fails naming `NORMAL: view-back []` and `RECORDS: view-back []`.

It also found a real overlap on its first run. `enter-mode` is answered by
`declined` for the three stranding modes *and* by `composed` for every mode, so
`composed`'s arm would have opened `SavePrompt`, `ExportPrompt` or `CommandMode`
if `declined` were ever bypassed. Rather than moving the check, **both halves now
hold the rule** — `composed` returns `None` for a stranded mode — so the failure
direction if one is removed is the pre-PR `Upstream`, not a dead room.
---

## `harness/tests/help.spec.js` — the overlay, asserted as words

PR #61 deleted `"? opens help, and its rows are the shared ones"` and nothing
replaced it, so `paintHelp`, `help`, `help_page` and `help_titles` reached no
assertion at all (improvise-78v6). What `contract.spec.js` carried in its place
said only that a `dt` was VISIBLE — and an empty `dt` is a visible `dt`
(improvise-igxp), which is the same shape as the caret bug above: a row is a
frame, and a frame is not a word.

**The injection both tickets name**: blank `keys.textContent` in `paintHelp`,
patched in `harness/serve/app/app.js`. Before this work it left all three
contract tests passing. It now fails both tests in this file (the Welcome
banner reads empty; the advertised key reads empty) **and** `contract.spec.js`,
whose two help lines were strengthened from `toBeVisible` to the banner's text
and the first `dt.help-keys`'s text.

**What the pairs helper is for.** The overlay is a `<dl>`, and the association
between a key row and its description is document order — `dt` then `dd`. Read
as two lists they zip wrong, because a prose row emits **no** `dd` at all
(deliberately: an empty one would leave a blank grid cell). Welcome is prose end
to end, so `dd` count zero there is an assertion about that rule and not a
coincidence.

#### "a key the overlay advertises does what the overlay says it does"

The assertions above are still about a string on a screen; this one asks whether
the string is **true**. The key for `Jump to last row` is read OUT OF THE DOM,
the overlay closed, the key pressed, and the selection asserted onto the last
row. A page drawing a plausible key it does not have — what a hand-spelled table
decays into — fails here, and the spec holds no second copy of the keymap.

It presses the FIRST key the row names because a row is a compaction of every
binding that reaches the command (`h  j  k  l  ←  ↑  →  ↓` is eight).

## `harness/tests/grouped.spec.js` — the first browser run of improvise-anr9

`web/demo.improv` has no groups and one category per visible axis, deliberately
(gotcha 46), so the multi-level header, the group span, the collapse indicator
and the inline group row — exactly the code improvise-anr9 added — had never
been rendered anywhere a test could see (improvise-plcx). The fixture is
`harness/fixtures/grouped.improv`, served beside the shipped demo by
`harness/build.sh`, and the shipped document is unchanged.

**A missing seed is not an error**: `web/worker.js` answers a fetch that 404s
with an empty model. So a typo in the filename yields a page that draws a grid,
and "a grid is drawn" would pass on it. Every assertion here is about labels the
fixture really carries.

**`openGrouped` waits with retrying assertions and the tests then read once.**
The head and the row labels are read in a single `evaluate` each, because what
these tests assert is the RELATION between the lines — and a one-shot read
cannot wait. The grid is painted from the first projection and reframed by the
viewport the page then announces, so the helper gates on the head's shape, its
first group and the first row's innermost label before anything is read.

**Five injections, five distinct failures**, patched in `harness/serve/` so no
rebuild stands between the fault and the run:

- `gridPlan` slash-joins the level tuples into one line (the exact defect anr9
  fixed) — fails all three, because `openGrouped` waits on the head's shape
  before any test reads it;
- `th.colSpan = 1` on every column group header — fails the span test alone;
- a stray `tr.insertCell()` on the inline group row — fails the group-row test
  alone, which is the DOM half of `RenderRow::Group` carrying no cells;
- `indicator(false)` hard-coded — fails on `▶ Upland` while `▼ Inland` still
  passes, which is why the fixture has one collapsed group and one open one;
- `collapsed: Region/Upland` removed from the served document — fails on the
  rows that reappear, so the assertions see the collapse and not just the glyph.

**A bug this fixture surfaced rather than predicted.** `Coastal` is the row
frame's FIRST entry and its header is never drawn: the spec asserts **two**
group rows where the document has three, with improvise-0o6x named on the line.
That count is a record of an open bug, not an endorsement — when 0o6x lands it
becomes 3 and this line is where the change must be argued.

## `harness/tests/landing.spec.js` — the front door

`docs/index.html` is copied to the site root by `web/assemble.sh`, so the
harness has been serving it all along with nothing asserted about it
(improvise-bgtf).

**Counting the four `.ap-player` elements proves nothing**, and that is the
whole reason this is a spec rather than a one-liner: `autoPlay` is false, so
asciinema-player fetches no cast until play is pressed. A page whose every cast
path 404s constructs four players, throws no page error, and looks identical to
a working one. Injected while the page was being written (`./casts/` ->
`./cats/`) the construction-only check passed on the broken page.

Re-injected into `harness/serve/index.html` now, the spec fails at the first
player: `.ap-line` elements exist only once there is a cast to lay out. The spec
also asserts, BEFORE pressing anything, that no `.cast` has been requested —
without which the network evidence below could be satisfied by a page that
fetched them eagerly, which is not the page we ship.

Two assertions where one looks sufficient: the rendering says a cast played, and
the recorded responses say **four distinct** casts answered 200. Three players
showing the same recording satisfies the first and fails the second.

`"the front door reaches the app it advertises"` follows the footer link rather
than asserting its text, because whether `./app/` resolves is a fact about the
assembled tree. Injecting `href="./aplication/"` fails it.

## `harness/tests/contract.spec.js` — the ninth injection, and a lost guard

**The lost guard.** improvise-78v6 asks for the test-name diff over PR #61's
range, and it finds a fourth loss beyond the help test: `"a click on an item row
filters, as Enter does"`. `contract.spec.js` asserts the CATEGORY arm of
`click_category_row` (the row expands) and nothing asserts the ITEM arm, whose
rule is "do what Enter does here" — filter. Only `#status` distinguishes them,
so a click wired to the wrong arm passed the whole file. Restored inside the
click test, and proved by injecting `click_category(row.is_category ? index :
0)`, which fails that line alone.

The diff that finds this is two commands, and is worth running on any PR whose
subject is a lost guard:

```sh
M=$(gh pr view 61 --json mergeCommit -q .mergeCommit.oid)
for r in "$M^1" "$M"; do
  git ls-tree -r --name-only "$r" -- harness/tests web/tests |
    while read -r f; do git show "$r:$f" | grep -oE 'test\("[^"]*"'; done
done
```

The other two losses are deliberate: `pointer.spec.js`'s sidebar test was
superseded by the open-at-launch ruling, and the widgets file was merged into
this one.

#### "a click moves the selection from an editing state too"

improvise-0x9u, and the fault was injected by running this assertion against the
bundle as it stood: `cells.nth(4).locator("input")` came back **0**, with the
selection still on cell 0, exactly as the bug report measured in Chromium.

Two things about it are worth more than the assertion. First, **what it does not
do**: it never presses Escape between the two clicks. The sibling test does, and
that single line is why the property it names ("a click moves the selection") was
asserted for a whole wave while the neighbouring state was broken — the click
path from an *editing* page was never exercised.

Second, **the fix's own first attempt failed this same test**, which is the part
to remember. Moving the handler to `mousedown` is necessary and not sufficient:
`close` still repainted, and removing a focused `<input>` fires `blur`
**synchronously**, so `close` rebuilt the table from inside itself and detached
the `<td>` the handler was about to open an editor on. The assertion could not
tell that apart from the original bug — same symptom, different cause — so it is
the debug run rather than the test that separated them. `close` therefore no
longer repaints, and the `blur` arm checks `closed` before dismissing.

Third — and this is the edit the repair nearly shipped unguarded — **the fix is
three edits, not two**, and the third is the one with the most careful comment:
`close` restores `td.textContent` (the *drawn* value) instead of `seed` (the
*stored* one), because `close` no longer repaints and `repaint()` early-returns
for as long as `editing` is set. Reverting that one line to
`td.replaceChildren(original)` left the whole suite green, and the defect was on
the front page: `web/demo.improv` carries `format: ,.0` over `18400`, and this
test's own two clicks — no Escape between them — leave cell 0 reading `18400`
where the page had drawn `18,400`, for as long as the second editor stays open.
The assertion added for it is `toHaveText("18,400")` after the second click, and
the injection is exactly that revert: it fails with `unexpected value "18400"`,
naming this test and no other.

The pattern is worth carrying past this entry. A repair of N edits whose N−1
guarded ones pass is not a guarded repair, and the unguarded edit is reliably
the one the author understood best — which is why it carries the clearest
comment and why it felt covered. For each distinct edit, name the test that
fails when only that edit is reverted; a line with a comment and no answer to
that question is the line to inject.

#### "the widgets the demo document fills are drawn, in the state that fills them"

The `#doc-name` row is improvise-5jna, and the reason it belongs in a **browser**
test rather than in `render_surface.test.js` is that the latter is a substring
search over the page's source: `doc_name` mentioned by a function nothing calls
reads as painted. That is how `model.minibuffer` once shipped dead, and how
z754's three title-bar fields sat projected and unpainted for a wave while the
static check was green. Proved by adding the assertion first: `element(s) not
found` for `#doc-name`.

The `[+]` marker is deliberately **not** asserted here. The standalone deployment
persists on every accepted batch and `effect::Save` clears the flag in the same
round trip (gotcha 45), so the marker is transient in a browser and any timing
assertion over it would be flaky rather than discriminating. Its spelling — the
order `name (stored_as) [+]`, the `null` `stored_as` writing no empty parens — is
`web/tests/shell.test.js`, over `documentTitle` directly.

#### "a selection driven below the fold scrolls itself into view"

improvise-jq8l, and the expensive half was the **fixture**, not the assertion.
Neither shipped document can reach the state: `web/demo.improv` is four rows and
`harness/fixtures/grouped.improv` is eight, and a probe measured both at
`scrollHeight === clientHeight` in a 484px box — nothing to scroll, so the
assertion would have passed against a page that never scrolls. That is the
vacuity this entry exists to record, and it is why the spec asserts
`scrollHeight - clientHeight > 0` **before** it presses a key.

`harness/fixtures/tall.improv` is thirty rows in three groups, which overflows for
a reason worth stating: `ROW_PX` is 26 and a real row measures 28.6px, and inline
group rows are not charged for at all, so the page renders more rows than its own
box can show. Measured against the unfixed page: 105px of overflow, the selected
cell 96px below the visible bottom, `scrollTop` still 0 after twenty-five
`ArrowDown`s.

Both directions are asserted, and neither alone is enough: the cell being inside
`#grid`'s rect would also hold if the selection had never moved, and `scrollTop >
0` would also hold if the page scrolled to the wrong place.

#### "the casts are legible on a phone, and the page still does not scroll sideways"

improvise-o31u, and **the instrument is the finding**. `getBoundingClientRect`
reports a height for a `content-visibility`-hidden child, and heading text
overflows its box without widening it, so neither "the element is present" nor a
box measurement can see this defect at all. What a reader sees is the **computed
font size**, and that is what is asserted.

Measured against the unfixed page, and it reproduces the ticket's figure to five
digits: `pivot.cast` renders its terminal at **4.83258px** on a 390px viewport.
The arithmetic is not subtle — the player is told `cols: 120`, the container is
~356px inside the page's 16px gutters, and the player DERIVES its font size from
the width it is given. After the fix: **11.9457px**.

Two assertions guard the trade this fix must not make. The page's own
`scrollWidth - clientWidth` must stay **0** — a document that scrolls sideways
on a phone is a worse bug than one unreadable section — and `#cast-pivot` must
be the thing that scrolls, which is what separates "contained the overflow" from
"removed the overflow by shrinking something else".

#### "a desktop viewport is unchanged by the phone fix"

The negative arm, and **it is forward-looking: no fault available today makes it
fail.** The entry previously named two mechanisms and both were measured, at a
1280px viewport, against the shipped page:

- `@media (max-width: 900px)` → `@media all`: this test **passes** (13.1131px,
  `scrollWidth === clientWidth`).
- `min-width: 880px` moved from `.player > *` onto `.player`: this test
  **passes**; the *phone* arm fails instead, on `scrolls.page === 0`.

The arithmetic is why, and it is worth stating rather than re-deriving: at
1280px `#cast-pivot` measures `clientWidth === scrollWidth === 966`, so an 880px
floor is inert at desktop wherever it is placed. The floor would have to exceed
the ~966px the player actually gets — or the content column would have to
narrow — before either assertion here could move. That is a real future fault
and the reason to keep the test: it pins 13.11px and "nothing to scroll" against
a floor raised past the player's own width. It is not a reason to claim the arm
currently discriminates between the two placements, because it does not.

Note also that the **phone** arm is stronger than this entry used to credit it
with: the misplaced-`min-width` fault, attributed here to the desktop arm, is
caught there. `scrolls.page === 0` is the assertion that separates "contained
the overflow" from "moved it onto the document".

#### "no cast carries the recording machine's shell, clock or geometry"

improvise-2oxt, and **both clauses were injected separately**, which matters
because the first would otherwise mask the second. Serving the pre-2oxt
`pivot.cast` fails on `env` — `Received: {"SHELL": "/bin/zsh", "TERM":
"screen-256color"}` — and stops there. Stripping `env` and `timestamp` from that
same header and serving the body unchanged then fails on `pivot.cast sets a
window title`, which is the clause that actually watches for the leak: an OSC
window-title sequence, emitted by a shell once per prompt and carrying the cwd,
and emitted by `improvise` never.

Asserted over the cast **file** rather than over the rendering, and that is the
finding. A player draws a shell prompt as ordinary terminal text, so a
screenshot or a `toContainText` assertion would have to know what the hostname
and home directory had been — a check that can only be written by someone who
has already seen the leak. The file-level signature can be written by anyone.

What no assertion here reaches, and how it was checked instead: whether each
cast SHOWS what its section claims. That is not a property of the bytes. It was
verified by replaying each recording through a small ANSI reconstruction and
reading the frames as text, which found two scenarios that recorded cleanly and
demonstrated nothing — a drill into a cell with no records behind it, and a `c`
pressed on a category already on the column axis. Both are true frames about the
wrong thing, which is the failure mode this repo keeps meeting, and neither was
visible from the keystroke list.

---

## `improvise-ws-server` — the `Origin` check (improvise-kc7n)

The bug: `grep -rni origin crates/improvise-ws-server/src/` returned nothing.
The server inspected no `Origin` header and accepted every handshake, and a
websocket handshake is exempt from the same-origin policy — no CORS preflight —
so any page a user visited could open a socket from that user's own allowed
address and read and edit every document served. An address check cannot see
it; the argument is `context/code/clients.md` §Origin.

Five edits, five guards. Each was reverted alone and the named test failed;
nothing here is covered only by a comment. Review added a sixth — see
`two_origins_state_none_this_policy_can_answer_for`.

### a_handshake_from_a_foreign_origin_is_refused

The reproduction, written first and watched fail on `2afbf37`: a handshake
carrying `Origin: https://evil.example` connected, and the test's
`connect_async(...).err()` was `None`. After the fix the upgrade is refused with
a 403 and the assertion is on the status, not merely on "an error happened" —
a refused upgrade and a dropped connection are different outcomes and only one
of them is the fix.

**Injection:** replacing the handshake callback's `admitted(&origins, req)` with
`Ok(())` — the transport collecting a policy it never asks — fails this and
`a_named_origin_reaches_the_document`, and nothing else in the workspace.

### a_handshake_with_no_origin_is_accepted

The case most likely to be wrong later, so it is named rather than left to a
match arm. Non-browser clients send no `Origin`: curl, a native client, this
file's own other tests. **Injection:** flipping `OriginPolicy::permits`'s `None`
arm to `false` fails this, `an_absent_origin_is_allowed`,
`the_handshake_refuses_what_the_policy_refuses`, and *both pre-existing socket
tests* — which is the point: the repo's own instrument is the non-browser client
this arm is about.

### a_handshake_from_a_loopback_page_is_accepted

The shipped local recipe — the page served by `python3 -m http.server 8080`,
the socket on another loopback port — must keep working with no flag, or the
default is a different bug from the one being fixed. **Injection:** making
`is_loopback` return `false` fails this and
`a_loopback_page_is_allowed_by_default` and leaves the refusal tests green,
which separates "allows loopback" from "allows everything".

### a_named_origin_reaches_the_document

`--allow-origin` end to end over a real socket, plus the negative arm in the
same test: widening for one page does not widen for its neighbours. Without
that second assertion the test passes against a policy that permits everything,
which is the fault E1a injects.

### allow_origin_widens_the_policy_and_nothing_else_does

The wiring, which no socket test can reach: the other tests build an
`OriginPolicy` directly, so a flag collected by clap and dropped on the floor is
invisible to every one of them. This drives `Args::parse_from` and asserts both
directions — bare refuses the deployed https origin and still allows loopback;
widened allows the named origin and not its neighbours. **Injection:** making
`Args::origin_policy` return `OriginPolicy::default()` fails this test alone.

### two_origins_state_none_this_policy_can_answer_for

Found by review rather than by the ticket. `HeaderMap::get` is **first-wins**,
and the deployment this README recommends puts a reverse proxy in front of the
socket — a proxy that *appends* `Origin` rather than setting it leaves two, and
reading the first lets the second be anything at all. No browser sends two, so
two is not a state any policy can answer for and the handshake is refused.
**Injection:** restoring the first-wins read (`(Some(value), Some(_))` answering
from `value`) fails this test alone, across the whole workspace. The test also
asserts the allowed origin *by itself* is still allowed, so the refusal is
demonstrably the second header rather than the first.

### a_refusal_is_a_forbidden_response

The refusal has to be a refused *upgrade*, and the socket test asserts the
`Error::Http` **kind** and the status rather than matching "403" in a
`Display` string: a dropped connection and a refused handshake are different
outcomes and only one of them is this fix. **Injection:** changing `forbidden()`
to `UNAUTHORIZED` fails this and `a_handshake_from_a_foreign_origin_is_refused`,
which is what shows the socket test reads the status rather than merely
observing that connecting failed.

What the signature covers instead of a test: `transport::serve` **takes** the
policy, so a host cannot forget to pass one — `doctrine(an_invariant_is_made_
unrepresentable_not_validated)`. What remains uncovered and is stated rather
than guarded: a proxy that strips `Origin` turns the check off, which is why the
proxy's own Origin allow-list stays in `README.md` as defence in depth.