diff --git a/Cargo.toml b/Cargo.toml
index 86f54e65..bda00df3 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -40,7 +40,9 @@ improvise-command = { path = "crates/improvise-command" }
 ratatui = "0.30"
 crossterm = "0.29"
 serde = { version = "1", features = ["derive"] }
-serde_json = "1"
+# Parses JSON a user's numbers cross, so it must read back the f64 written: per crate,
+# because each build stands alone (improvise-6yvg, context/code/protocol.md).
+serde_json = { version = "1", features = ["float_roundtrip"] }
 anyhow = "1"
 thiserror = "2"
 indexmap = { version = "2", features = ["serde"] }
diff --git a/context/code/command.md b/context/code/command.md
index a943e8bf..d6d2756f 100644
--- a/context/code/command.md
+++ b/context/code/command.md
@@ -935,6 +935,52 @@ There is deliberately **no `dirty = true`** in it: it declares
 of `MarkDirty` — harmless, and a second home for the one thing that commit set
 out to give exactly one.
 
+### `RecordRewrite` — a row's edits composed, not replayed (improvise-uo2p)
+
+A staged drill edit is a statement about the record **as the snapshot showed
+it**. It is not a statement about the model as the previous edit left it. The
+edits in one row do not commute when they are replayed one at a time. A rename
+moves every cell in the row (gotcha 1). A measure edit replayed after it writes
+the old key, which leaves a ghost record there and a stale value in the moved
+record. A second rename replayed after the first finds nothing at the old keys,
+so it is dropped. `ApplyAndClearDrill` replayed them in `HashMap` order, so the
+outcome was different from one App to the next. That is gotcha 18's class of
+bug, found in an effect rather than an index.
+
+**Sorting is not the fix.** "Measures before renames" repairs the ticket's own
+case and still drops a second rename every time (rival 1 in the evidence). Any
+fixed order makes the corruption reproducible instead of removing it. So the
+rule is **build each row's final record once, then write it**:
+
+- `RecordRewrite::of(model, row, edits)` collects the row's renames and measure
+  edits into maps keyed by column, and reads each unedited value off the model
+  **before anything is written**. It then states the rewrite: clear every old
+  key, and write every cell at the key with *all* renames applied. A measure
+  edit that is staged replaces the carried value. The result does not depend on
+  the order of the edits. A drill stages at most one edit per `(row, column)`,
+  so no two edits in a row name the same column. A blank rename is refused, and
+  the row's other edits still land at the unrenamed coordinates, as before.
+- `RecordRewrite::merged` concatenates the rows' rewrites **by phase**: every
+  refusal, then every item added, then every clear, then every write. The clears
+  come first so that a swap is a swap. Rows are taken in snapshot row order
+  (`BTreeMap`), so where two final records land on one cell, **the later row
+  wins**. That is the answer plain records mode gives for the same renames made
+  top to bottom.
+
+The collision rule is a **choice**, and it still loses the earlier row's values
+silently. Plain records mode loses them the same way when a rename lands on an
+existing record. Refusing the colliding rows instead would be a change to both
+paths.
+
+**One copy.** The plain records path (`commit.rs::commit_plain_records_edit`)
+calls the same `RecordRewrite::of` with its one edit, so `rename_record_coordinate`
+and the drill's `apply_coordinate_rename`/`apply_measure_edit` are gone. This is
+the consolidation improvise-fdk1 asked for, "regardless" of its wire half. For a
+single edit the output is the effects the plain path used to emit, reordered from
+`clear, set` per cell to all clears then all sets, which touches distinct keys.
+One behaviour moved on the drill side: it used to discard `add_item`'s error, and
+now goes through `effect::AddItem`, which refuses when the category has gone.
+
 ### `Save` / `SaveAs` abort the batch (improvise-8tk / improvise-lae)
 
 A failed save aborts the rest of the batch, so the `Quit` that `wq`/`ZZ` chains
@@ -2629,8 +2675,10 @@ At bottom-right `EnterAdvance` has no place to go, so it emits a single `AbortCh
 stages in drill pending edits while in drill mode, or applies directly in plain
 records mode; for real keys it writes to the model.
 
-`rename_record_coordinate` renames one coordinate of a records row. In wide format a
-row is a group of cells — one per measure — so the rename has to move **every** one
+`commit_plain_records_edit` hands a coordinate or measure edit to
+`effect::RecordRewrite::of`, the one home it shares with the drill (improvise-uo2p;
+see `RecordRewrite` above). It replaced `rename_record_coordinate`. In wide format a
+row is a group of cells — one per measure — so a rename has to move **every** one
 of them, not just the cell under the cursor (improvise-c5v, gotcha 1). Every cell in
 the row moves, and a row seeded by `add-record-row` has no measure cells yet: its
 coordinates live on a lone measure-less cell, which must move too or the row loses
@@ -3187,8 +3235,8 @@ the cursor**. The result was silent corruption of an unrelated record: appending
 a row changes `view_frame`'s hash, the frame observation inside `apply_effects`
 invalidates the cursor to the origin *mid-batch* (gotcha 24), and
 `EnterEditAtCursor` then pre-fills the editor with row 0's category coordinate.
-Enter commits through `rename_record_coordinate`, which by gotcha 1 moves every
-measure cell of that row.
+Enter commits through `rename_record_coordinate` (since improvise-uo2p,
+`RecordRewrite::of`), which by gotcha 1 moves every measure cell of that row.
 
 Two things are worth carrying past this fix.
 
@@ -3262,3 +3310,84 @@ key the two questions agree, because a cursor key never carries a None-axis
 category. The **collapsed-group fold** half of improvise-l4mp is not covered:
 its key carries the group's name as an ordinary coordinate, so no question about
 the key alone can see it — it needs `GridLayout::folds_a_group`.
+
+## A command is a function of its context — the determinism law (improvise-hzjo)
+
+`cmd/determinism.rs` holds the law the old `law_toggle_group_involution` claimed
+and could not state. For **every** registered command and every argument list
+that builds it, the effects `execute` returns must be equal, by `Debug` text,
+across contexts built **independently from equal data**: four `App`s, each
+parsed from `web/demo.improv` and given the same buffers, expanded categories,
+yank, panels and cursor.
+
+**Why the instances must be distinct.** The old test called `execute` twice
+against one `CmdContext`. Every `HashMap` it reached was the same instance with
+the same `RandomState`, so it iterated the same way both times: `f(x) == f(x)`,
+which nothing can fail. Separately built `App`s give every map its own seed. So a
+command whose effects follow hash iteration order disagrees with itself. Hash
+order is the one kind of nondeterminism this repo has actually shipped (gotcha
+18). This law can see it where a command's `execute` builds it, as the drill
+snapshot's record order was. It cannot see the other shipped instance, the
+analyzer's `HashSet`: `analyze_records` is reached only from inside
+`Effect::apply`, which is outside this law (see below). The companion test
+`only_distinct_instances_can_see_a_command_that_follows_hash_order` keeps that
+property checked: a test-only command that emits `ctx.buffers` in iteration
+order must agree with itself on one context and disagree across two.
+
+**Four instances, not two.** A rival that takes *the first* entry of a map, not
+all of them, agrees across two seeds whenever both happen to put the same entry
+first. With 21 buffers that is roughly one chance in 21, and three comparisons
+make it negligible. The fixture's values are also chosen to stay distinct under
+the edits commands make. A first version used `v0`…`v15`, which `pop()` collapses
+to `v`, and so it let `command-mode-backspace` reading an arbitrary buffer pass.
+
+**The store needs several records to order, so the drills come from the
+document (improvise-e1sm).** The registry's `candidate_args` are extended with
+names the demo really has, because coordinates that match nothing never reach
+the records a drill or a fit would order. A hand-picked name is not enough. The
+first version's only real drill was `Product/Latte, Quarter/Q2`: one record, two
+cells. With the store's sort removed, two contexts put those two cells in the
+same order about half the time, and with three comparisons the law passed about
+one run in eight (measured: 46 of 400). So the arguments now include **every
+item of every regular category as a one-coordinate drill**, read off the parsed
+document. A one-coordinate drill spans every other category whole, so it matches
+the whole slice of records under that item, not one record picked by name. In
+the demo that is four records and eight cells for each of the eight drills. The
+test
+also asserts that the widest candidate it actually passes matches at least four
+records. That guard catches a demo with too little data, and it catches the
+derived drills being dropped from the argument list. It does **not** catch the
+comparison losing its wide drills some other way, because it measures what the
+argument lists match, not what the built commands ordered (improvise-b9f2). The
+review showed this with a rival: a `drill-into-cell` parser that refuses fewer
+than two arguments sends every one-coordinate drill to the one-record cursor
+fallback. The guard still reports four records, and with the store's sort
+removed the law passed 38 of 300 runs. With the store's sort removed and the
+parser intact, the law fails 400 of 400 runs.
+
+**What it cannot see.** Only commands and arguments the fixture reaches. A
+command whose nondeterminism needs some other state, such as records mode, a
+wizard or a drill in progress, is outside this fixture. And `Debug` equality is
+text equality: two effects that differ only in something their `Debug` omits are
+equal here.
+
+**Its scope is what `execute` returns, not what `Effect::apply` does.** The law
+compares the effects a command hands back. Many effects are unit structs that
+decide all their work inside `apply`: `ApplyAndClearDrill`,
+`SortData`, `CleanEmptyRecords`, `Save`, `RebuildLayout`, `AcceptWizardModel`.
+Hash-order iteration inside an `apply` is therefore invisible here, however
+often the law runs. improvise-uo2p is the worked example.
+`ApplyAndClearDrill::apply` walks `drill.pending_edits`, a `HashMap`, in hash
+order. A measure edit and a category rename staged on one row can then write a
+ghost record. The command that emits it passes this law, because the effect's
+`Debug` is just its name. So "the one kind of nondeterminism this repo has
+shipped" is guarded here only on the `execute` side. The `apply` side needs its
+own test per effect, or a law over `App` state after `apply_effects`.
+
+**The exemption list.** `OUTSIDE_THE_CONTEXT` names commands that legitimately
+depend on something outside the context, such as a clock or an entropy source,
+each with its reason. It is empty: `fit-measure`'s seed is an argument with a
+fixed default, not a clock read. The list is checked in both directions. An
+unlisted command that diverges fails the test, and so does a listed one that
+does not diverge. A stale entry therefore cannot linger, and a new registration
+is covered the day it lands.
diff --git a/context/code/protocol.md b/context/code/protocol.md
index c79f0e56..032feab5 100644
--- a/context/code/protocol.md
+++ b/context/code/protocol.md
@@ -756,28 +756,54 @@ coming back one ULP off, both in `CellDisplay::value` (host to client, so `yy`
 copied a neighbour) and in a `SetCell` (client to host, so a typed or pasted
 number landed as a neighbour).
 
-The feature is on for **every crate that parses a frame**: `improvise-ws-server`
-(`transport.rs`), `improvise-worker-server` (`worker.rs`) and
-`improvise-wasm-client` (`socket.rs`). Each crate's own manifest names it,
-because each browser bundle is built from one crate alone. The `wasm` CI job
-and `wasm-pack` both invoke per crate, and feature unification cannot reach
-across separate invocations (`context/repo-map.md`, `## Wasm`). Enabling it in
-one crate and relying on the others to inherit it works in `cargo test` and
-nowhere else.
+The feature is on for **every workspace crate with a normal dependency on
+serde_json** (improvise-dz8c). Each crate's own manifest names it, because each
+build is made from one crate alone: the `wasm` CI job and `wasm-pack` invoke
+per crate, and feature unification cannot reach across separate invocations
+(`context/repo-map.md`, `## Wasm`). Enabling it in one crate and relying on the
+others to inherit it works in `cargo test` and nowhere else.
 
-That is also why the end-to-end tests cannot guard this alone. They run in one
-unified build with `improvise-ws-server` as a dev-dependency, so they stay
-green with the feature removed from the browser bundle.
-`every_build_that_parses_a_frame_enables_float_roundtrip` asks `cargo tree`
-per crate over normal edges instead. A new crate that parses frames belongs in
-its list.
+**Why "can parse" and not "parses a frame".** The first version of the rule
+covered only the three crates that parse frames and listed them by hand.
+Frames are not the only place a user's number crosses a JSON parser.
+`improvise-io`'s legacy-JSON `.improv` load, `improvise-command`'s JSON import
+(`StartImportWizard`, `ImportJsonHeadless`) and the root binary's
+`improvise import` all parsed with the lossy default, and in the TUI binary
+nothing enabled the feature (improvise-6yvg, reproduced: `0.24815714285714285`
+stored as `…283`). The worker bundle happened to be exact through unification,
+so one import gave different numbers in the two front ends. "Parses JSON input"
+cannot be read off a manifest, but "has a normal serde_json dependency" can, and
+it over-approximates in the cheap direction: the feature changes only parsing,
+so a crate that only serializes pays nothing for it. Dev-dependencies are out,
+because a test build ships nowhere. That also leaves out `gp-tree`, whose only
+serde_json is a dev-dependency (its example CLI reads a saved model). Every
+number it persists is an `f32`, and 3M random `f32`s all read back exactly
+through the lossy parser, against about 30% of random `f64`s.
 
-Not covered, and filed separately rather than widened into this change
-(improvise-6yvg): `improvise-io`'s JSON import and `improvise-command`'s JSON
-reads also parse numbers with the default parser. They are file formats, not
-frames. In the TUI binary nothing enables the feature. In the worker bundle
-unification happens to reach them, so one import can give different numbers
-in the two front ends.
+**Why a declaration and not the build graph.** The first check asked
+`cargo tree` whether each listed crate's *build* had the feature. That answer
+can be yes by accident. `improvise-command` depends on `improvise-io`, so with
+the feature removed from command's manifest, command's own test build still
+has it, and its import test stays green. The rule requires the crate's own
+manifest to say it, so a later change to a dependency cannot take it away.
+
+**Why not enable it once, in `improvise-protocol`.** That removes the list, but
+it would give the protocol a normal serde_json dependency it has no use for
+(its repo-map entry says core and serde only). It would also reach only builds
+that include the protocol, and `improvise-io` does not depend on it. Under this
+rule the protocol's one serde_json dependency, the optional `test-support` one,
+carries the feature too. That is off in every shipped build, so it costs
+nothing.
+
+`every_crate_that_can_parse_json_enables_float_roundtrip` (`tests/json_numbers.rs`)
+reads `cargo metadata --no-deps` and names every package, and every
+target-specific entry, whose normal serde_json dependency lacks the feature. A
+new crate is covered the day it declares the dependency. It does not reach
+`harness/opfs-contract`, which is its own workspace and only serializes.
+
+The end-to-end tests cannot guard this alone. They run in one unified build
+with `improvise-ws-server` as a dev-dependency, so they stay green with the
+feature removed from the browser bundle.
 
 ### `AxisFrame` — the grid's frame, and why it is *one* type
 
diff --git a/context/test-evidence/clients.md b/context/test-evidence/clients.md
index 57eb87f6..15ff6714 100644
--- a/context/test-evidence/clients.md
+++ b/context/test-evidence/clients.md
@@ -4626,24 +4626,12 @@ before #178 too, as the review noted.
 **Fault injected:** the same pre-fix tree. Fails: the host stored
 `4598108823619341467` in South/Cost.
 
-### `every_build_that_parses_a_frame_enables_float_roundtrip`
-
-The two tests above run in **one** feature-unified test build, which includes
-`improvise-ws-server` and `improvise-command` as dev-dependencies. So they pass
-whenever **any** crate in that build enables the feature. The shipped browser
-bundle is built from one crate alone, so it would still be lossy. That was
-demonstrated: with the feature removed from `improvise-wasm-client` only, both
-tests stayed green while `cargo tree` showed no `float_roundtrip` in the wasm
-bundle. This test asks cargo instead, once per crate that parses a frame:
-`cargo tree --locked --edges normal,features --invert serde_json --package
-<crate>`, with `--target wasm32-unknown-unknown` for the two bundles. It uses
-normal edges only, because a dev edge would unify the feature back in
-(`context/repo-map.md`, `## Wasm`).
-
-**Faults injected:** the feature removed from `improvise-wasm-client` alone,
-which fails naming that crate while the two tests above pass. Then removed from
-`improvise-ws-server` alone, which fails naming it. The native path runs
-without `--target`, so the two arms are different invocations.
+**Retired: `every_build_that_parses_a_frame_enables_float_roundtrip`.** It asked
+`cargo tree` about three crates listed by hand. improvise-dz8c replaced it with
+`every_crate_that_can_parse_json_enables_float_roundtrip`, whose entry is in
+`tooling.md`. The injections recorded for it still hold: with the feature
+removed from `improvise-wasm-client` alone, the two tests above stay green, so
+they cannot guard the bundle alone.
 
 ### resolve::tests::every_grid_move_lands_where_its_binding_says
 
@@ -4677,6 +4665,43 @@ laundering invisible (the edge) is also the one that makes a wrong-direction
 jump visible, so moving off the edge fixed one blind spot and opened the other,
 and each needs its own question.
 
+**improvise-w7qd, and the floor was the hole.** As first written the test
+covered `move-selection` and a four-entry jump table, behind `pressed >= 14`.
+Two things passed the whole workspace, both found in re-review of #180 at
+544744c: negating the `scroll-rows` and `page-scroll` arms, so `Ctrl-d`/`Ctrl-u`
+and `PgDn`/`PgUp` all scroll the wrong way (advertised, and still "acting" from
+the centre); and dropping the jump table *with* `$` sent to the first column,
+because the sixteen `move-selection` sequences met the floor on their own. The
+test now walks **every** command Normal binds. `scroll-rows` and `page-scroll`
+state their landing from their own argument exactly as `move-selection` does —
+from the centre of a 3x3 grid any step of at least one lands at `1 + d`
+clamped, so a sign is visible whatever the page size — and a command that moves
+the cursor (in the same view) without a stated landing **fails** rather than
+being skipped. So a dropped table entry is caught by derivation, not by a count:
+under the second rival it fails naming every jump as moving with nothing stating
+where. The first rival fails on `PgUp` (`page-scroll ["-1"]`) and, alone, on
+`Ctrl-u` (`scroll-rows ["-5"]`). A last assertion that each kind was pressed at
+least once guards the other direction — a binding vanishing — and is a named
+list on purpose, since that is the one thing no walk over bindings can see.
+
+**improvise-5kdr: the 3x3 fixture saw only a sign.** From the centre of a 3x3
+grid every step of one or more clamps to an edge, so the w7qd version stated
+`page-scroll` as `1 + d` — one row, which is not what it does — and passed
+because the true landing clamped to the same edge. Measured on #198 at 8772db2:
+`page-scroll` ignoring the page size together with `scroll-rows` moving one row,
+or `move-selection` moving `2d`, left the test green. The walk now stands at
+(10,10) of a 21x21 grid with an 8x8 window, far from every edge, so a landing
+shows magnitude: `10+d` for `move-selection` and `scroll-rows`, `10 + page·d`
+for `page-scroll`, 0/20 for the jumps. The page size is not written into the
+test: `grid_move`'s page rule moved into `page_rows(window_rows)` and the test
+asks it, so the rule has one home. Rivals, each run: `move-selection` doubled
+fails on `Up` (`move-selection ["-1","0"]`); the page-size-and-one-row pair
+fails on `PgUp` (`page-scroll ["-1"]`); the one-row `scroll-rows` alone fails on
+`Ctrl-u` (`scroll-rows ["-5"]`); the jump-table rival still fails naming every
+jump. The residual, stated: because the test reads `page_rows`, a change to the
+page rule itself moves the test with it — whether that rule is the TUI's is
+`tests/lockstep.rs`'s question, not this one's.
+
 ### an_edit_is_refused_when_the_cell_was_written_while_the_editor_was_open
 
 improvise-0j0f, found by the review of PR #188 at 48f52e7 and confirmed
diff --git a/context/test-evidence/command.md b/context/test-evidence/command.md
index f085ebb4..eb785201 100644
--- a/context/test-evidence/command.md
+++ b/context/test-evidence/command.md
@@ -5314,6 +5314,63 @@ before `refuse_and_stop` was applied to its arms. For `load`, the injected fault
 is removing its abort (`refuse_and_stop` back to `app.refuse`), and the test
 then fails with "`load absent.improv . q` quit having loaded nothing".
 
+### ui::effect::tests::a_drill_rows_measure_edits_follow_its_rename
+
+improvise-uo2p. `ApplyAndClearDrill` walked `pending_edits`, a `HashMap`, and
+applied each edit alone against the model as the previous one left it. A rename
+moves the row's cells. A measure edit then wrote `row.cell_key(measure)`, the
+snapshot's old key. So when the rename came first, a ghost record appeared at the
+old coordinates carrying the new value, and the moved record kept the stale one.
+The reviewer saw this in 16 of 40 fresh Apps. The fixture stages two measure edits
+and a rename on drill row 1, so a wrong answer needs only one of the three orders
+that put the rename last. Each assertion runs over 32 fresh Apps and compares the
+**whole** store, so the ghost and the stale value are both visible. Before the
+fix it failed on five of five runs. Rival 3 (the rewrite addresses measure edits
+at the unrenamed key) fails it.
+
+### ui::effect::tests::a_drill_row_renamed_twice_and_edited_lands_as_one_record
+
+improvise-uo2p. This is the case that fails **every** time, not with some
+probability. Each rename read the snapshot's old keys. The second rename found
+nothing there, because the first had moved it, so one rename was always dropped
+and the row split into a `Clothing/Feb` record and a `Drink/Jan` record. Rival 1
+is the ticket's proposed fix direction: measures before renames, each edit
+applied alone. It passes the ticket's own case and fails here. So "a fixed
+order" is not a fix; the renames have to be composed.
+
+### ui::effect::tests::a_drill_that_swaps_two_records_coordinates_swaps_them
+
+improvise-uo2p. Row 0 is renamed onto row 1's coordinates and row 1 onto row 0's.
+If the rows are applied in sequence, the first move overwrites the other record
+and the second move carries the overwritten values back, so one record's data
+is lost in either order. Rival 2 composes each row correctly but writes it
+before reading the next row, and it fails here and nowhere else. That is why
+`RecordRewrite::merged` reads every row off the model first, then clears every
+old key, then writes.
+
+### ui::effect::tests::a_drill_edit_addresses_its_own_record_not_the_one_renamed_onto_its_coordinates
+
+improvise-uo2p. Row 1's staged `Cost` belongs to row 1's record, even though row
+0 is being renamed away from coordinates and row 1 onto them. Before the fix,
+some hash orders left `Clothing/Jan/Cost = 999` as a ghost. Rival 3 fails it.
+
+### ui::effect::tests::two_drill_rows_renamed_onto_one_record_resolve_to_the_later_row
+
+improvise-uo2p. Two rows renamed onto the same coordinates collide per cell. The
+rule chosen is that the later snapshot row wins, which is what plain records
+mode gives when the same renames are made top to bottom. Before the fix the
+winner was the hash order's choice. Rival 4 reverses the row order in `merged`
+and fails here. The rule is a choice, and it still loses data silently. See
+`context/code/command.md`, `RecordRewrite`.
+
+### ui::effect::tests::a_record_rewrite_is_the_same_under_every_order_of_its_edits
+
+improvise-uo2p. The composition is order-independent **by construction**, so it
+is asserted over all 24 orders of four edits on one row: two renames, a measure
+write and a measure clear. The test pins one value as well as the equality, so
+a rewrite that is the same wrong answer in every order still fails. Rival 3
+fails it.
+
 ## `command/cmd/tile.rs` — the tile bar's offered set, by name (improvise-jgzw)
 
 ### the_tile_bar_offers_every_category_by_name_measure_and_records_axes_included
@@ -5337,3 +5394,83 @@ Rivals, injected, full workspace run:
   *else* fails: `renders_each_tile_with_its_axis_label` (TUI) and
   `the_tile_bar_route_into_records_mode_does_not_strand_the_user`. The second one
   is improvise-bd9o's own test of the route this decision keeps.
+
+## `command/cmd/determinism.rs` — the determinism law over every command (improvise-hzjo)
+
+The reasoning is in `context/code/command.md`, "A command is a function of its
+context". This entry records what each test can see.
+
+### every_command_gives_equal_effects_in_independently_built_equal_contexts
+
+It runs all 89 registrations, 1500+ (command, args) pairs, in four contexts built
+from four separately parsed copies of `web/demo.improv`, and requires equal
+effect `Debug` text. It passed at `ae96b8c` with no exemptions. It is not a
+regression test for a live bug. It restores a law, and the evidence is which
+rivals it catches:
+
+- **`command-mode-backspace` reading `ctx.buffers.values().next()`** instead of
+  the `command` buffer: a real command following hash order. Injected, full
+  workspace run: this test is the **only** failure, because every
+  `text_buffer.rs` test builds a one-entry buffer map. With the comparison
+  switched to one reused context (`compare(&a, from_ref(&a))`) the same rival
+  **passes**. That is the half the ticket required: the distinct construction
+  is what does the work.
+- **`DataStore::matching_positions` without its sort**: gotcha 18 re-shipped.
+  This entry first said the test catches it through `drill-into-cell` and
+  `fit-measure`'s record order. That was wrong (improvise-e1sm). `fit-measure`
+  never diverged, in 60 failing runs in review and in 354 here. And the catch
+  was a matter of luck. The only real drill was `Product/Latte, Quarter/Q2`,
+  which is one record with two cells, so each other context agrees with
+  probability 1/2. With the sort removed and the test binary run in a loop, the
+  law **passed 46 of 400 runs** at `fc0b13c`, and `drill-into-cell
+  ["Product/Latte", "Quarter/Q2"]` was the only pair that ever diverged. The
+  arguments now include every item of every regular category as a
+  one-coordinate drill, read off the parsed document (four records, eight cells
+  each in the demo). With the same injection the law **passed 0 of 400**, and
+  all eight new drills diverged in about 1195 of 1200 pairwise comparisons each.
+  Without the injection it passed 400 of 400. The three `cell.rs` order tests
+  still pin the store directly.
+- **The derived drills dropped from the argument list** (the
+  `all.extend(one_coordinate_drills(model))` line commented out): the test
+  fails before comparing anything, with "the widest drill orders 1 records".
+  That is the only way of losing the wide drills the guard can see. It measures
+  what the argument lists match, not what the built commands ordered, so it can
+  pass while the comparison has lost its wide drills (improvise-b9f2). Review
+  rival: `drill-into-cell`'s parser changed to refuse fewer than two arguments,
+  which sends every one-coordinate drill to the one-record cursor fallback. The
+  guard stays silent and, with gotcha 18 re-injected, the law passed 38 of 300
+  runs.
+- **A stale exemption**: `("quit", "stale")` listed in `OUTSIDE_THE_CONTEXT`.
+  It fails as "listed … but did not".
+
+**A vacuity this test itself had on its first version.** The fixture's filler
+buffers held `v0`…`v15`. The `command-mode-backspace` rival pops a character,
+so every value collapsed to `v` (or `v1`), and the rival passed across two
+distinct contexts. This is the "two derivations the fixture makes agree" shape.
+The values are now `value {i} of 16`. The comparison was also widened from one
+other instance to three, because a take-the-first rival agrees across two seeds
+about one time in 21.
+
+### only_distinct_instances_can_see_a_command_that_follows_hash_order
+
+The check-the-checker behind the law. A test-only `EmitsInHashOrder` emits one
+`SetBuffer` per `ctx.buffers` entry in iteration order. It must equal itself on
+one context, which is why the old single-context law was vacuous, and differ
+across two independently built ones. If a future refactor made the fixture
+share one map, or share one `RandomState`, the second assertion fails. Without
+this test the law would then pass everything and look healthy.
+
+## JSON import numbers (improvise-6yvg)
+
+### `a_json_import_stores_its_numbers_bit_for_bit`
+
+`ImportJsonHeadless` imports `[{"Region":"East","Revenue":0.24815714285714285}]`
+and the test reads Region=East, _Measure=Revenue back by `f64::to_bits`.
+`StartImportWizard` parses through the same `serde_json::from_slice` call, so
+one test covers the crate's feature.
+
+**Red at `1158c23`** in `cargo test -p improvise-command`: stored
+`0.24815714285714283`. That reproduces improvise-6yvg. **Limitation:** this test
+cannot see the feature removed from `improvise-command` alone, because
+`improvise-io`, a normal dependency, enables it in the same build. That case is
+held by `every_crate_that_can_parse_json_enables_float_roundtrip` (`tooling.md`).
diff --git a/context/test-evidence/core.md b/context/test-evidence/core.md
index d27feb93..f51186c9 100644
--- a/context/test-evidence/core.md
+++ b/context/test-evidence/core.md
@@ -1361,3 +1361,26 @@ fold is the row `z` names the group from. Note the narrowing this implies: an
 **empty** collapsed group now has an empty fold row, which `prune_empty` drops, and
 its header goes with it. lhi4 kept that header because it was the only way back to
 the rows; the fold is now that way back.
+
+### records_steps_are_the_spine_then_every_non_index_dim_category_on_none
+
+improvise-t0ma. Before this, `records_steps` was guarded by one incidental test: the
+`is_index_or_dim() → is_measure()` rival failed only
+`save_with_unfinished_record_is_readable`, a persistence test that happens to enter
+records mode. This asserts the **steps**, not the effects `cmd/grid.rs` translates
+them into, because the steps are the model-side answer a browser will also consume.
+The expected list filters `_Index`/`_Dim` by **name**, not by `CategoryKind`, so it
+is not a second copy of the predicate under test, and the setup asserts `_Measure`
+and a regular category are both present, since a model with neither could not tell
+the two predicates apart. Rival: `is_measure()` in place of `is_index_or_dim()`.
+This test fails, because `_Measure` is dropped and `_Index`/`_Dim` are put on `None`
+after the spine that just placed them.
+
+### drill_steps_filter_each_coordinate_and_free_the_rest
+
+improvise-t0ma's companion for `drill_steps`. The fixture includes a `none_cat` that
+the key also fixes (`Region`) and one that is virtual (`_Index`), so both exclusions
+are exercised. It also lists the key's coordinates out of sorted order, which checks
+that the steps follow `CellKey`'s canonical order. Rival: `Axis::Page` in place of
+`Axis::Filter` for a fixed coordinate, which reopens improvise-dz8 (a drilled
+coordinate the user could page away from). This test fails.
diff --git a/context/test-evidence/formula-and-io.md b/context/test-evidence/formula-and-io.md
index daf7a527..48e8bd5a 100644
--- a/context/test-evidence/formula-and-io.md
+++ b/context/test-evidence/formula-and-io.md
@@ -1434,3 +1434,17 @@ rather than defaulted: the alternative — expanding the group in the export —
 reintroduce the iot6 divergence between what the user sees and what they export.
 On the pre-6qet tree the body is empty (the group had no row, and pruning left
 nothing), so the test fails there.
+
+## Legacy JSON numbers (improvise-6yvg)
+
+### `a_legacy_json_workbook_loads_its_numbers_bit_for_bit`
+
+A workbook with Food/Jan holding `0.24815714285714285` is serialized with
+`serde_json` and loaded through `load_from`. A leading `{` sends it down the
+legacy JSON path. The test first asserts that the text holds the exact decimal,
+so what it measures is the parse. It compares `f64::to_bits`. Found by the
+review of PR #190, not by the ticket.
+
+**Red at `1158c23`** in `cargo test -p improvise-io`: loaded
+`0.24815714285714283`. Green once `improvise-io`'s own manifest enables
+`float_roundtrip`, and red again with only that line reverted.
diff --git a/context/test-evidence/protocol.md b/context/test-evidence/protocol.md
index 9fea26b7..aa7d04d9 100644
--- a/context/test-evidence/protocol.md
+++ b/context/test-evidence/protocol.md
@@ -1159,3 +1159,35 @@ failed: ex_usage_is_placeholders("q  or press Q")`. The rule cost one row:
 `:add-items <cat> a b c ...` had three bare words and is now
 `:add-items <cat> <item> ...`. This test pins the rule the macro asks, in both
 directions, including that shipped usage and the rival.
+
+### help::tests::every_keys_row_drawn_is_one_the_builders_asked_for
+
+improvise-ssoe, found in re-review of #180 at 544744c. `KeyRow` closed
+hand-typed keys, but `KeyRow::looked_up` was `pub(super)`, so a page builder
+could call it directly instead of through its `keys` parameter — and
+`help_bindings()` records only what goes through the parameter. Injected into
+`editing()`: `KeyRow::looked_up(n, "clear-cell", None, "Edit the current
+cell")`, which captions `x` as editing the cell — the exact lie `jhdf`'s test
+exists for — and the whole workspace stayed green, because both guards that
+would object read `help_bindings()`.
+
+Two changes. `looked_up` is now private to the `key_row` module, whose one
+caller is the module's own `keys` — the lookup `pages()` hands every builder —
+so the reviewer's injection is `E0624: associated function looked_up is
+private`. That narrows the door without closing it: a builder can still reach
+the module-level `keys` by path (`self::keys(..)`) rather than through its
+shadowing parameter. So this test states the premise directly — the number of
+keys rows drawn equals the number of rows the builders asked for (every asked
+row finds its keys, by `every_keys_row_the_pages_ask_for_finds_its_keys`) —
+and the `self::keys` bypass fails it `51 != 50`.
+
+**improvise-aszt: a count is not the premise.** The test above compared
+*counts*, so a bypass that also drops one real row keeps them equal. Injected in
+`editing()`: call the parameter `keys(e, "clear-buffer", …)` and discard it with
+`let _ =`, then return `self::keys(n, "clear-cell", None, "Edit the current
+cell")` in its place. The asked row is recorded and never drawn, the drawn row
+is never recorded, 50 = 50, and the whole workspace stayed green. The test now
+compares **content in order**: the drawn keys rows must equal
+`help_bindings()` looked up through the same `keys`, row for row. The same
+injection now fails. What still passes is a bypass that draws exactly what the
+builders asked for, in the order they asked — which is harmless by definition.
diff --git a/context/test-evidence/tooling.md b/context/test-evidence/tooling.md
index 0bdaca76..cd8ff234 100644
--- a/context/test-evidence/tooling.md
+++ b/context/test-evidence/tooling.md
@@ -681,3 +681,41 @@ reproduction.
 alone fails, exiting 0. All 44 others pass. That is the review's point: the
 older `a head that moves mid-wait is not a pass` starts from MERGEABLE, so it
 cannot see this rival.
+
+## Every JSON parser reads numbers exactly (improvise-dz8c)
+
+### `every_crate_that_can_parse_json_enables_float_roundtrip`
+
+It replaces a check over three crates listed by hand. It reads
+`cargo metadata --no-deps` and fails naming every workspace package, and
+every target-specific entry, whose **normal** serde_json dependency lacks
+`float_roundtrip`. The rule and why it was chosen over the alternatives are in
+`context/code/protocol.md`. It is red at `1158c23`, naming `improvise`,
+`improvise-command`, `improvise-io` and `improvise-protocol`.
+
+**Faults injected, each run:**
+
+- **The feature removed from `improvise-io` alone.** The check fails naming
+  `improvise-io (all targets)`, and so does
+  `a_legacy_json_workbook_loads_its_numbers_bit_for_bit`.
+  `a_json_import_stores_its_numbers_bit_for_bit` stays green, because
+  `improvise-command` enables the feature and unification reaches io in its
+  build.
+- **The feature removed from `improvise-command` alone.** The check fails naming
+  `improvise-command (all targets)`. The command crate's own import test
+  **stays green**: `cargo tree -p improvise-command` shows io's declaration
+  switching the feature on. So the manifest check is the only guard that
+  sees this case. It is also the case the retired build-graph check would
+  have passed.
+- **A throwaway workspace member**, `zz-throwaway`, with normal dependencies on
+  `improvise-protocol` and `serde_json` and no feature (the lockfile updated,
+  as a real new crate would be). The check fails naming
+  `zz-throwaway (all targets)`. With the unconditional dependency carrying the
+  feature and a `cfg(target_arch = "wasm32")` one lacking it, the check fails
+  naming `zz-throwaway (cfg(target_arch = "wasm32"))`. That is stricter than
+  the build needs, since a wasm build unifies the two entries, and cheap to
+  satisfy. The crate was then removed.
+
+The `checked.len() >= 2` assertion is the positive signal. If a cargo change
+renamed the metadata fields, the check would find no serde_json dependency and
+pass vacuously without it.
diff --git a/crates/improvise-command/Cargo.toml b/crates/improvise-command/Cargo.toml
index 5f1bd1d9..acc61a1f 100644
--- a/crates/improvise-command/Cargo.toml
+++ b/crates/improvise-command/Cargo.toml
@@ -14,7 +14,9 @@ improvise-io = { path = "../improvise-io" }
 improvise-gp = { path = "../improvise-gp" }
 anyhow = "1"
 serde = { version = "1", features = ["derive"] }
-serde_json = "1"
+# Parses JSON a user's numbers cross, so it must read back the f64 written: per crate,
+# because each build stands alone (improvise-6yvg, context/code/protocol.md).
+serde_json = { version = "1", features = ["float_roundtrip"] }
 unicode-width = "^0.2"
 # Instant::now() panics on wasm32-unknown-unknown; web_time re-exports
 # std::time off-wasm and uses performance.now() on it (improvise-ywd).
diff --git a/crates/improvise-command/src/command/cmd/commit.rs b/crates/improvise-command/src/command/cmd/commit.rs
index 6846f198..86e4e55d 100644
--- a/crates/improvise-command/src/command/cmd/commit.rs
+++ b/crates/improvise-command/src/command/cmd/commit.rs
@@ -1,8 +1,8 @@
 use crate::model::category::MEASURE_CATEGORY;
-use crate::model::cell::{CellKey, CellValue};
+use crate::model::cell::CellKey;
 use crate::ui::app::AppMode;
 use crate::ui::effect::{self, Effect};
-use crate::view::{RecordCol, RecordRow};
+use crate::view::RecordCol;
 
 use super::core::{Cmd, CmdContext, read_buffer};
 use super::grid::AddRecordRow;
@@ -14,6 +14,7 @@ mod tests {
 
     use super::*;
     use crate::command::cmd::test_helpers::*;
+    use crate::model::cell::CellValue;
     use crate::workbook::Workbook;
 
     fn commit(kind: CommitKind) -> CommitBuffer {
@@ -622,47 +623,8 @@ fn stage_drill_edit(record_idx: usize, col: RecordCol, value: &str) -> Box<dyn E
     })
 }
 
-/// Rename one coordinate of a records row. In wide format a row is a group of cells,
-/// so the rename moves **every** one of them (improvise-c5v, gotcha 1).
-fn rename_record_coordinate(
-    model: &crate::model::Model,
-    row: &RecordRow,
-    category: &str,
-    value: &str,
-    effects: &mut Vec<Box<dyn Effect>>,
-) {
-    if value.is_empty() {
-        effects.push(effect::refuse(effect::RECORD_COORDS_CANNOT_BE_EMPTY));
-        return;
-    }
-    effects.push(Box::new(effect::AddItem {
-        category: category.to_string(),
-        item: value.to_string(),
-    }));
-
-    // Every cell in the row moves. A row seeded by `add-record-row` carries its
-    // coordinates on a lone measure-less cell, which must move too.
-    let cells: Vec<(CellKey, CellValue)> = if row.values.is_empty() {
-        model
-            .get_cell(&row.coords)
-            .map(|v| vec![(row.coords.clone(), v.clone())])
-            .unwrap_or_default()
-    } else {
-        row.values
-            .iter()
-            .map(|(measure, v)| (row.cell_key(measure), v.clone()))
-            .collect()
-    };
-    for (old_key, cell_value) in cells {
-        effects.push(Box::new(effect::ClearCell(old_key.clone())));
-        effects.push(Box::new(effect::SetCell(
-            old_key.with(category, value),
-            cell_value,
-        )));
-    }
-}
-
-/// Apply a records-mode edit directly to the model (no drill state).
+/// Apply a records-mode edit directly to the model (no drill state). A drill's staged
+/// edits go through the same `RecordRewrite`, all of a row's at once (gotcha 19).
 fn commit_plain_records_edit(
     ctx: &CmdContext,
     record_idx: usize,
@@ -674,11 +636,8 @@ fn commit_plain_records_edit(
         return;
     };
     match col {
-        RecordCol::Category(category) => {
-            rename_record_coordinate(ctx.model, row, category, value, effects);
-        }
-        RecordCol::Measure(measure) => {
-            commit_regular_cell_value(&row.cell_key(measure), value, effects);
+        RecordCol::Category(_) | RecordCol::Measure(_) => {
+            effects.extend(effect::RecordRewrite::of(ctx.model, row, [(col, value)]).effects());
         }
         RecordCol::NewMeasure => add_measure(value, effects),
         RecordCol::NewCategory => add_category(value, effects),
diff --git a/crates/improvise-command/src/command/cmd/determinism.rs b/crates/improvise-command/src/command/cmd/determinism.rs
new file mode 100644
index 00000000..8f0a71e5
--- /dev/null
+++ b/crates/improvise-command/src/command/cmd/determinism.rs
@@ -0,0 +1,233 @@
+//! A command is a function of its context: two contexts built independently from
+//! equal data give equal effects — `context/code/command.md`, improvise-hzjo.
+
+use std::collections::{BTreeSet, HashSet};
+
+use super::core::{Cmd, CmdContext};
+use super::registry::tests::candidate_args;
+use crate::command::key::{KeyCode, KeyModifiers};
+use crate::model::Model;
+use crate::model::cell::{CellKey, CellValue};
+use crate::model::record::record_of;
+use crate::ui::app::App;
+use crate::ui::effect::{self, Effect};
+
+/// Commands whose effects depend on something outside the context, with why.
+const OUTSIDE_THE_CONTEXT: &[(&str, &str)] = &[];
+
+const DOCUMENT: &str = include_str!("../../../../../web/demo.improv");
+
+/// One `App` over the shipped demo. Every context map holds several entries that
+/// stay distinct under an edit like `pop()` — see the evidence.
+fn fixture() -> App {
+    let workbook = crate::persistence::parse_md(DOCUMENT).expect("the demo parses");
+    let mut app = App::new(workbook, None);
+    let vs = &mut app.view_state;
+    for i in 0..16 {
+        vs.buffers
+            .insert(format!("b{i}"), format!("value {i} of 16"));
+    }
+    for (name, text) in [
+        ("edit", "42"),
+        ("formula", "Margin = Profit / Revenue"),
+        ("category", "Region"),
+        ("command", "add-item Product Mocha"),
+        ("export", "/tmp/improvise-hzjo.csv"),
+    ] {
+        vs.buffers.insert(name.into(), text.into());
+    }
+    for cat in ["Product", "Quarter", "_Measure", "_Index", "_Dim"] {
+        vs.expanded_cats.insert(cat.into());
+    }
+    vs.yanked = Some(CellValue::Number(7.0));
+    vs.formula_panel_open = true;
+    vs.category_panel_open = true;
+    vs.view_panel_open = true;
+    vs.cat_panel_cursor = 2;
+    vs.view_panel_cursor = 1;
+    app.cursor_mut().selected = (1, 1);
+    app
+}
+
+/// Every item as a one-coordinate drill: each spans the other categories whole,
+/// so the store has several records to order — see the evidence.
+fn one_coordinate_drills(model: &Model) -> Vec<Vec<String>> {
+    let mut drills = Vec::new();
+    for cat in model.regular_category_names() {
+        for item in model.category(cat).expect("listed").ordered_item_names() {
+            drills.push(vec![format!("{cat}/{item}")]);
+        }
+    }
+    drills
+}
+
+/// How many distinct records the widest all-`Cat/Item` candidate matches.
+fn widest_drill(model: &Model, candidates: &[Vec<String>]) -> usize {
+    let coordinates = |args: &Vec<String>| -> Option<Vec<(String, String)>> {
+        args.iter()
+            .map(|a| {
+                a.split_once('/')
+                    .map(|(c, i)| (c.to_string(), i.to_string()))
+            })
+            .collect()
+    };
+    candidates
+        .iter()
+        .filter(|args| !args.is_empty())
+        .filter_map(coordinates)
+        .map(|partial| {
+            let cells = model.data.matching_cells(&partial);
+            let records: HashSet<CellKey> = cells.iter().map(|(k, _)| record_of(k)).collect();
+            records.len()
+        })
+        .max()
+        .unwrap_or(0)
+}
+
+/// The registry's candidates, plus names the demo really has: a drill or a fit
+/// over coordinates that match nothing never reaches the records it would order.
+fn args_the_document_names(model: &Model) -> Vec<Vec<String>> {
+    let mut all = candidate_args();
+    all.extend(one_coordinate_drills(model));
+    all.extend(
+        [
+            vec!["Revenue"],
+            vec!["Product/Latte", "Quarter/Q2"],
+            vec!["Product/Latte", "Quarter/Q2", "_Measure/Cost"],
+            vec![
+                "editing",
+                "5",
+                "Product/Latte",
+                "Quarter/Q2",
+                "_Measure/Cost",
+            ],
+        ]
+        .into_iter()
+        .map(|v| v.into_iter().map(String::from).collect()),
+    );
+    all
+}
+
+fn effects_of(name: &str, args: &[String], ctx: &CmdContext) -> Option<String> {
+    let cmd = ctx.registry.interactive(name, args, ctx).ok()?;
+    Some(format!("{:?}", cmd.execute(ctx)))
+}
+
+/// What running every registered command under `a` and under each of `others` found.
+#[derive(Default)]
+struct Comparison {
+    diverged: BTreeSet<&'static str>,
+    shown: Vec<String>,
+    never_built: Vec<&'static str>,
+    compared: usize,
+}
+
+fn compare(a: &CmdContext, others: &[CmdContext]) -> Comparison {
+    let mut found = Comparison::default();
+    let candidates = args_the_document_names(a.model);
+    for name in a.registry.names().collect::<Vec<_>>() {
+        let before = found.compared;
+        for args in &candidates {
+            let Some(left) = effects_of(name, args, a) else {
+                continue;
+            };
+            found.compared += 1;
+            for b in others {
+                let right = effects_of(name, args, b).unwrap_or_default();
+                if left != right {
+                    found.diverged.insert(name);
+                    found
+                        .shown
+                        .push(format!("{name} {args:?}:\n  {left}\n  {right}"));
+                }
+            }
+        }
+        if found.compared == before {
+            found.never_built.push(name);
+        }
+    }
+    found
+}
+
+/// Evidence: `context/test-evidence/command.md`.
+#[test]
+fn every_command_gives_equal_effects_in_independently_built_equal_contexts() {
+    let apps: Vec<App> = (0..4).map(|_| fixture()).collect();
+    let contexts: Vec<CmdContext> = apps
+        .iter()
+        .map(|app| app.cmd_context(KeyCode::Null, KeyModifiers::NONE))
+        .collect();
+    let model = contexts[0].model;
+    let widest = widest_drill(model, &args_the_document_names(model));
+    assert!(
+        widest >= 4,
+        "the widest drill orders {widest} records, so the store's order is nearly a coin toss"
+    );
+    let found = compare(&contexts[0], &contexts[1..]);
+    assert!(
+        found.never_built.is_empty(),
+        "no candidate args build these in the fixture, so the law never ran them: {:?}",
+        found.never_built
+    );
+    let listed: BTreeSet<&str> = OUTSIDE_THE_CONTEXT.iter().map(|(n, _)| *n).collect();
+    let unlisted: Vec<&str> = found
+        .shown
+        .iter()
+        .filter(|s| !listed.iter().any(|n| s.starts_with(&format!("{n} "))))
+        .map(String::as_str)
+        .collect();
+    assert!(
+        unlisted.is_empty(),
+        "effects depend on more than the context ({} pairs compared):\n{}",
+        found.compared,
+        unlisted.join("\n")
+    );
+    let stale: Vec<&&str> = listed
+        .iter()
+        .filter(|n| !found.diverged.contains(**n))
+        .collect();
+    assert!(
+        stale.is_empty(),
+        "listed as depending on something outside the context, but did not: {stale:?}"
+    );
+}
+
+/// Iterates a context `HashMap` and emits in that order: the one nondeterminism
+/// this repo has shipped (gotcha 18). The law must see it; a reused context cannot.
+#[derive(Debug)]
+struct EmitsInHashOrder;
+impl Cmd for EmitsInHashOrder {
+    fn name(&self) -> &'static str {
+        "emits-in-hash-order"
+    }
+    fn execute(&self, ctx: &CmdContext) -> Vec<Box<dyn Effect>> {
+        ctx.buffers
+            .iter()
+            .map(|(name, value)| {
+                Box::new(effect::SetBuffer {
+                    name: name.clone(),
+                    value: value.clone(),
+                }) as Box<dyn Effect>
+            })
+            .collect()
+    }
+}
+
+/// Evidence: `context/test-evidence/command.md`.
+#[test]
+fn only_distinct_instances_can_see_a_command_that_follows_hash_order() {
+    let (first, second) = (fixture(), fixture());
+    let a = first.cmd_context(KeyCode::Null, KeyModifiers::NONE);
+    let b = second.cmd_context(KeyCode::Null, KeyModifiers::NONE);
+    let run = |ctx: &CmdContext| format!("{:?}", EmitsInHashOrder.execute(ctx));
+    assert_eq!(
+        run(&a),
+        run(&a),
+        "one reused context iterates its maps the same way twice"
+    );
+    assert_ne!(
+        run(&a),
+        run(&b),
+        "two independently built contexts must iterate differently, or the law is vacuous"
+    );
+}
diff --git a/crates/improvise-command/src/command/cmd/mod.rs b/crates/improvise-command/src/command/cmd/mod.rs
index c7f86714..07edab36 100644
--- a/crates/improvise-command/src/command/cmd/mod.rs
+++ b/crates/improvise-command/src/command/cmd/mod.rs
@@ -13,6 +13,9 @@ pub mod text_buffer;
 pub mod tile;
 pub mod wizard;
 
+#[cfg(test)]
+mod determinism;
+
 // Re-export items used by external code
 pub use self::core::{Cmd, CmdContext, CmdRegistry};
 pub use registry::default_registry;
diff --git a/crates/improvise-command/src/command/cmd/registry.rs b/crates/improvise-command/src/command/cmd/registry.rs
index 0534709e..dbd86d68 100644
--- a/crates/improvise-command/src/command/cmd/registry.rs
+++ b/crates/improvise-command/src/command/cmd/registry.rs
@@ -498,13 +498,13 @@ pub fn default_registry() -> CmdRegistry {
 }
 
 #[cfg(test)]
-mod tests {
+pub(super) mod tests {
     use super::*;
     use crate::command::cmd::test_helpers::*;
 
     /// Argument vectors to try when constructing a command, most specific
     /// first. A command is exercised by the first one its parser accepts.
-    fn candidate_args() -> Vec<Vec<String>> {
+    pub(in crate::command::cmd) fn candidate_args() -> Vec<Vec<String>> {
         [
             vec![],
             vec!["1"],
diff --git a/crates/improvise-command/src/ui/effect.rs b/crates/improvise-command/src/ui/effect.rs
index 18528e69..f07adea5 100644
--- a/crates/improvise-command/src/ui/effect.rs
+++ b/crates/improvise-command/src/ui/effect.rs
@@ -1,3 +1,4 @@
+use std::collections::BTreeMap;
 use std::fmt::Debug;
 use std::path::PathBuf;
 
@@ -663,24 +664,19 @@ impl Effect for ApplyAndClearDrill {
         let Some(drill) = app.drill_state.take() else {
             return;
         };
-        if drill.pending_edits.is_empty() {
-            return;
-        }
+        let mut rows: BTreeMap<usize, Vec<(&RecordCol, &str)>> = BTreeMap::new();
         for ((record_idx, col), new_value) in &drill.pending_edits {
-            let Some(row) = drill.records.get(*record_idx) else {
-                continue;
-            };
-            match col {
-                RecordCol::Measure(measure) => {
-                    apply_measure_edit(app, &row.cell_key(measure), new_value);
-                }
-                RecordCol::Category(category) => {
-                    apply_coordinate_rename(app, row, category, new_value);
-                }
-                // Never staged: `commit_cell_value` applies a new measure or
-                // category immediately — a schema change is not a cell edit.
-                RecordCol::NewMeasure | RecordCol::NewCategory => {}
-            }
+            rows.entry(*record_idx)
+                .or_default()
+                .push((col, new_value.as_str()));
+        }
+        let model = &app.model_state.workbook.model;
+        let rewrite = RecordRewrite::merged(rows.iter().filter_map(|(record_idx, edits)| {
+            let row = drill.records.get(*record_idx)?;
+            Some(RecordRewrite::of(model, row, edits.iter().copied()))
+        }));
+        for effect in rewrite.effects() {
+            effect.apply(app);
         }
         // No `dirty = true` here: this declares `Model(CellData)` and
         // `App::apply_effects` raises the flag off that (improvise-gv9r).
@@ -690,51 +686,114 @@ impl Effect for ApplyAndClearDrill {
     }
 }
 
-/// Write one measure cell, or clear it when the edit is blank.
-fn apply_measure_edit(app: &mut App, key: &CellKey, new_value: &str) {
-    let model = &mut app.model_state.workbook.model;
-    match new_value {
-        "" => {
-            model.clear_cell(key);
-        }
-        v => {
-            let value = v
-                .parse::<f64>()
-                .map(CellValue::Number)
-                .unwrap_or_else(|_| CellValue::Text(v.to_string()));
-            model.set_cell(key.clone(), value);
-        }
-    }
+/// A records row's edits composed into the one record they mean, read off the model
+/// before anything is written. Why composed: `context/code/command.md`, `RecordRewrite`.
+#[derive(Debug, Default, PartialEq)]
+pub(crate) struct RecordRewrite {
+    refused: bool,
+    items: Vec<(String, String)>,
+    clears: Vec<CellKey>,
+    sets: Vec<(CellKey, CellValue)>,
 }
 
-/// Rename one coordinate of a records row. The row is a group of cells —
-/// one per measure — so every one of them moves (improvise-c5v).
-fn apply_coordinate_rename(app: &mut App, row: &RecordRow, category: &str, new_value: &str) {
-    if new_value.is_empty() {
-        app.refuse(RECORD_COORDS_CANNOT_BE_EMPTY);
-        return;
-    }
-    let keys: Vec<CellKey> = if row.values.is_empty() {
-        vec![row.coords.clone()]
-    } else {
-        row.values
-            .iter()
-            .map(|(measure, _)| row.cell_key(measure))
-            .collect()
-    };
-    let _ = app
-        .model_state
-        .workbook
-        .add_item(category, new_value.to_string());
-    for old_key in keys {
-        let Some(value) = app.model_state.workbook.model.get_cell(&old_key).cloned() else {
-            continue;
+impl RecordRewrite {
+    /// `row`'s edits, each naming a distinct column. The result does not depend on
+    /// their order: every coordinate is renamed before any cell is placed.
+    pub(crate) fn of<'a>(
+        model: &crate::model::Model,
+        row: &RecordRow,
+        edits: impl IntoIterator<Item = (&'a RecordCol, &'a str)>,
+    ) -> Self {
+        let mut refused = false;
+        let mut renames: BTreeMap<&str, &str> = BTreeMap::new();
+        let mut measures: BTreeMap<&str, Option<CellValue>> = BTreeMap::new();
+        for (col, value) in edits {
+            match col {
+                RecordCol::Category(_) if value.is_empty() => refused = true,
+                RecordCol::Category(category) => {
+                    renames.insert(category.as_str(), value);
+                }
+                RecordCol::Measure(measure) => {
+                    measures.insert(measure.as_str(), improvise_protocol::typed(value));
+                }
+                // Never staged: a new measure or category is a schema change,
+                // applied at once by `commit_cell_value`.
+                RecordCol::NewMeasure | RecordCol::NewCategory => {}
+            }
+        }
+        let renamed = |key: &CellKey| {
+            renames.iter().fold(key.clone(), |key, (category, item)| {
+                key.with(*category, *item)
+            })
         };
-        app.model_state.workbook.model.clear_cell(&old_key);
-        app.model_state
-            .workbook
-            .model
-            .set_cell(old_key.with(category, new_value), value);
+        let moved: Vec<(Option<&str>, CellKey)> = match (renames.is_empty(), row.values.is_empty())
+        {
+            (true, _) => Vec::new(),
+            (false, true) => vec![(None, row.coords.clone())],
+            (false, false) => row
+                .values
+                .iter()
+                .map(|(measure, _)| (Some(measure.as_str()), row.cell_key(measure)))
+                .collect(),
+        };
+        let mut rewrite = RecordRewrite {
+            refused,
+            items: renames
+                .iter()
+                .map(|(category, item)| (category.to_string(), item.to_string()))
+                .collect(),
+            ..Self::default()
+        };
+        for (measure, old) in &moved {
+            let value = match measure.and_then(|m| measures.remove(m)) {
+                Some(edit) => edit,
+                None => model.get_cell(old).cloned(),
+            };
+            rewrite.clears.push(old.clone());
+            rewrite.sets.extend(value.map(|v| (renamed(old), v)));
+        }
+        for (measure, edit) in measures {
+            let key = renamed(&row.cell_key(measure));
+            match edit {
+                Some(value) => rewrite.sets.push((key, value)),
+                None => rewrite.clears.push(key),
+            }
+        }
+        rewrite
+    }
+
+    /// Several rows' rewrites as one: every clear lands before any write, so a
+    /// swap is a swap, and where two rows land on one cell the later row wins.
+    pub(crate) fn merged(rewrites: impl IntoIterator<Item = Self>) -> Self {
+        rewrites.into_iter().fold(Self::default(), |mut all, one| {
+            all.refused |= one.refused;
+            all.items.extend(one.items);
+            all.clears.extend(one.clears);
+            all.sets.extend(one.sets);
+            all
+        })
+    }
+
+    pub(crate) fn effects(self) -> Vec<Box<dyn Effect>> {
+        let refusal = self.refused.then(|| refuse(RECORD_COORDS_CANNOT_BE_EMPTY));
+        let items = self
+            .items
+            .into_iter()
+            .map(|(category, item)| Box::new(AddItem { category, item }) as Box<dyn Effect>);
+        let clears = self
+            .clears
+            .into_iter()
+            .map(|key| Box::new(ClearCell(key)) as Box<dyn Effect>);
+        let sets = self
+            .sets
+            .into_iter()
+            .map(|(key, value)| Box::new(SetCell(key, value)) as Box<dyn Effect>);
+        refusal
+            .into_iter()
+            .chain(items)
+            .chain(clears)
+            .chain(sets)
+            .collect()
     }
 }
 
@@ -3071,6 +3130,209 @@ mod tests {
         assert_eq!(app.model_state.workbook.model.get_cell(&key), None);
     }
 
+    // ── Composing a drill's staged edits (improvise-uo2p) ───────────────
+
+    fn drill_cell(ty: &str, month: &str, measure: &str) -> CellKey {
+        CellKey::new(vec![
+            ("Type".into(), ty.into()),
+            ("Month".into(), month.into()),
+            ("_Measure".into(), measure.into()),
+        ])
+    }
+
+    /// Two records, each carrying Revenue and Cost: row 0 is Food/Jan (1, 2),
+    /// row 1 is Clothing/Jan (42, 17). Every edit below is staged on row 1 at least.
+    fn two_record_drill() -> App {
+        let mut app = test_app();
+        let cells = [
+            (drill_cell("Food", "Jan", "Revenue"), CellValue::Number(1.0)),
+            (drill_cell("Food", "Jan", "Cost"), CellValue::Number(2.0)),
+            (
+                drill_cell("Clothing", "Jan", "Revenue"),
+                CellValue::Number(42.0),
+            ),
+            (
+                drill_cell("Clothing", "Jan", "Cost"),
+                CellValue::Number(17.0),
+            ),
+        ];
+        for (key, value) in cells.clone() {
+            app.model_state.workbook.model.set_cell(key, value);
+        }
+        let records = RecordRow::group(cells);
+        assert_eq!(records.len(), 2, "one row per coordinate tuple");
+        assert_eq!(records[1].coords.get("Type"), Some("Clothing"));
+        StartDrill(records).apply(&mut app);
+        app
+    }
+
+    fn stage(app: &mut App, record_idx: usize, col: RecordCol, value: &str) {
+        SetDrillPendingEdit {
+            record_idx,
+            col,
+            new_value: value.to_string(),
+        }
+        .apply(app);
+    }
+
+    /// The whole store, as `(Type, Month, measure) = n`, so a ghost cannot hide.
+    fn drill_store(app: &App) -> std::collections::BTreeSet<String> {
+        app.model_state
+            .workbook
+            .model
+            .data
+            .iter_cells()
+            .map(|(key, value)| {
+                let coord = |c: &str| key.get(c).unwrap_or("-").to_string();
+                let n = value.as_f64().expect("every drill cell here is a number");
+                format!(
+                    "{}/{}/{} = {n}",
+                    coord("Type"),
+                    coord("Month"),
+                    coord("_Measure")
+                )
+            })
+            .collect()
+    }
+
+    fn category(name: &str) -> RecordCol {
+        RecordCol::Category(name.into())
+    }
+
+    fn measure(name: &str) -> RecordCol {
+        RecordCol::Measure(name.into())
+    }
+
+    /// Stage `edits` and leave the drill, in 32 fresh Apps: each `HashMap` gets its
+    /// own `RandomState`, and one map iterates the same way twice.
+    fn assert_drill_commits_to(edits: &[(usize, RecordCol, &str)], expected: &[&str]) {
+        let expected: std::collections::BTreeSet<String> =
+            expected.iter().map(|s| s.to_string()).collect();
+        for attempt in 0..32 {
+            let mut app = two_record_drill();
+            for (row, col, value) in edits {
+                stage(&mut app, *row, col.clone(), value);
+            }
+            app.apply_effects(vec![Box::new(ApplyAndClearDrill)]);
+            assert_eq!(drill_store(&app), expected, "fresh App #{attempt}");
+        }
+    }
+
+    #[test]
+    fn a_drill_row_renamed_twice_and_edited_lands_as_one_record() {
+        assert_drill_commits_to(
+            &[
+                (1, measure("Cost"), "999"),
+                (1, category("Type"), "Drink"),
+                (1, category("Month"), "Feb"),
+            ],
+            &[
+                "Food/Jan/Revenue = 1",
+                "Food/Jan/Cost = 2",
+                "Drink/Feb/Revenue = 42",
+                "Drink/Feb/Cost = 999",
+            ],
+        );
+    }
+
+    #[test]
+    fn a_drill_rows_measure_edits_follow_its_rename() {
+        assert_drill_commits_to(
+            &[
+                (1, measure("Revenue"), "100"),
+                (1, measure("Cost"), "999"),
+                (1, category("Type"), "Drink"),
+            ],
+            &[
+                "Food/Jan/Revenue = 1",
+                "Food/Jan/Cost = 2",
+                "Drink/Jan/Revenue = 100",
+                "Drink/Jan/Cost = 999",
+            ],
+        );
+    }
+
+    #[test]
+    fn a_drill_that_swaps_two_records_coordinates_swaps_them() {
+        assert_drill_commits_to(
+            &[
+                (0, category("Type"), "Clothing"),
+                (1, category("Type"), "Food"),
+            ],
+            &[
+                "Clothing/Jan/Revenue = 1",
+                "Clothing/Jan/Cost = 2",
+                "Food/Jan/Revenue = 42",
+                "Food/Jan/Cost = 17",
+            ],
+        );
+    }
+
+    #[test]
+    fn a_drill_edit_addresses_its_own_record_not_the_one_renamed_onto_its_coordinates() {
+        assert_drill_commits_to(
+            &[
+                (0, category("Type"), "Drink"),
+                (1, category("Type"), "Food"),
+                (1, measure("Cost"), "999"),
+            ],
+            &[
+                "Drink/Jan/Revenue = 1",
+                "Drink/Jan/Cost = 2",
+                "Food/Jan/Revenue = 42",
+                "Food/Jan/Cost = 999",
+            ],
+        );
+    }
+
+    #[test]
+    fn a_record_rewrite_is_the_same_under_every_order_of_its_edits() {
+        let app = two_record_drill();
+        let row = app.drill_state.as_ref().unwrap().records[1].clone();
+        let edits = [
+            (measure("Cost"), "999"),
+            (category("Type"), "Drink"),
+            (measure("Revenue"), ""),
+            (category("Month"), "Feb"),
+        ];
+        let model = &app.model_state.workbook.model;
+        let mut seen = Vec::new();
+        for a in 0..4 {
+            for b in (0..4).filter(|&b| b != a) {
+                for c in (0..4).filter(|&c| c != a && c != b) {
+                    let d = 6 - a - b - c;
+                    let order = [a, b, c, d].map(|i| (&edits[i].0, edits[i].1));
+                    seen.push(RecordRewrite::of(model, &row, order));
+                }
+            }
+        }
+        assert_eq!(seen.len(), 24);
+        let first = &seen[0];
+        assert_eq!(
+            first.clears,
+            vec![
+                drill_cell("Clothing", "Jan", "Revenue"),
+                drill_cell("Clothing", "Jan", "Cost")
+            ]
+        );
+        assert_eq!(
+            first.sets,
+            vec![(drill_cell("Drink", "Feb", "Cost"), CellValue::Number(999.0))]
+        );
+        assert!(seen.iter().all(|rewrite| rewrite == first));
+    }
+
+    #[test]
+    fn two_drill_rows_renamed_onto_one_record_resolve_to_the_later_row() {
+        assert_drill_commits_to(
+            &[
+                (0, category("Type"), "Drink"),
+                (1, category("Type"), "Drink"),
+            ],
+            &["Drink/Jan/Revenue = 42", "Drink/Jan/Cost = 17"],
+        );
+    }
+
     // ── Toggle effects ──────────────────────────────────────────────────
 
     #[test]
@@ -3283,6 +3545,38 @@ mod tests {
         assert_eq!(app.view_state.status_msg, "Imported successfully");
     }
 
+    #[test]
+    fn a_json_import_stores_its_numbers_bit_for_bit() {
+        const LOSSY: f64 = 0.248_157_142_857_142_85;
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("data.json");
+        std::fs::write(
+            &path,
+            r#"[{"Region":"East","Revenue":0.24815714285714285}]"#,
+        )
+        .unwrap();
+
+        let mut app = test_app();
+        ImportJsonHeadless {
+            path,
+            model_name: None,
+            array_path: None,
+        }
+        .apply(&mut app);
+
+        let key = CellKey::new(vec![
+            ("Region".to_string(), "East".to_string()),
+            ("_Measure".to_string(), "Revenue".to_string()),
+        ]);
+        let Some(CellValue::Number(n)) = app.model_state.workbook.model.get_cell(&key) else {
+            panic!(
+                "the import must store the number; status {:?}",
+                app.view_state.status_msg
+            );
+        };
+        assert_eq!(n.to_bits(), LOSSY.to_bits(), "stored {n:?}, not {LOSSY:?}");
+    }
+
     // ── json_import_records (improvise-oaq helper) ──────────────────────
 
     #[test]
diff --git a/crates/improvise-core/src/view/layout.rs b/crates/improvise-core/src/view/layout.rs
index 1105655f..fbb3e312 100644
--- a/crates/improvise-core/src/view/layout.rs
+++ b/crates/improvise-core/src/view/layout.rs
@@ -1741,4 +1741,66 @@ mod tests {
             "Sep is in no group — Q2's GroupEnd closed Q1's re-opened run"
         );
     }
+
+    /// improvise-t0ma: the steps themselves, not their translation into effects —
+    /// see context/test-evidence/core.md.
+    #[test]
+    fn records_steps_are_the_spine_then_every_non_index_dim_category_on_none() {
+        use super::{ViewStep, records_spine, records_steps};
+        let mut m = crate::model::Model::new("T");
+        m.add_category("Region").unwrap();
+        m.add_category("Product").unwrap();
+        let none = |c: &str| ViewStep::Axis {
+            category: c.to_string(),
+            axis: Axis::None,
+        };
+        let mut expected = records_spine();
+        expected.extend(
+            m.categories
+                .keys()
+                .filter(|c| !matches!(c.as_str(), "_Index" | "_Dim"))
+                .map(|c| none(c)),
+        );
+        assert!(
+            expected.contains(&none("_Measure")) && expected.contains(&none("Region")),
+            "setup: the model carries _Measure and a regular category"
+        );
+        assert_eq!(records_steps(&m), expected);
+    }
+
+    /// improvise-t0ma: a drill FIXES its coordinates on Filter and frees only the
+    /// unfixed, non-virtual aggregated categories.
+    #[test]
+    fn drill_steps_filter_each_coordinate_and_free_the_rest() {
+        use super::{ViewStep, drill_steps, records_spine};
+        let key = CellKey::new(vec![
+            ("Region".into(), "North".into()),
+            ("Month".into(), "Feb".into()),
+            ("_Measure".into(), "Revenue".into()),
+        ]);
+        let none_cats: Vec<String> = ["Product", "Region", "_Index", "Customer"]
+            .map(String::from)
+            .to_vec();
+        let fixed = |c: &str, i: &str| {
+            [
+                ViewStep::Axis {
+                    category: c.into(),
+                    axis: Axis::Filter,
+                },
+                ViewStep::PageSelection {
+                    category: c.into(),
+                    item: i.into(),
+                },
+            ]
+        };
+        let mut expected = records_spine();
+        expected.extend(fixed("Month", "Feb"));
+        expected.extend(fixed("Region", "North"));
+        expected.extend(fixed("_Measure", "Revenue"));
+        expected.extend(["Product", "Customer"].map(|c| ViewStep::Axis {
+            category: c.into(),
+            axis: Axis::None,
+        }));
+        assert_eq!(drill_steps(&key, &none_cats), expected);
+    }
 }
diff --git a/crates/improvise-io/Cargo.toml b/crates/improvise-io/Cargo.toml
index 1fdfcaf1..1ec96762 100644
--- a/crates/improvise-io/Cargo.toml
+++ b/crates/improvise-io/Cargo.toml
@@ -17,7 +17,9 @@ indexmap = { version = "2", features = ["serde"] }
 pest = "2.9.2"
 pest_derive = "2.9.2"
 serde = { version = "1", features = ["derive"] }
-serde_json = "1"
+# Parses JSON a user's numbers cross, so it must read back the f64 written: per crate,
+# because each build stands alone (improvise-6yvg, context/code/protocol.md).
+serde_json = { version = "1", features = ["float_roundtrip"] }
 
 # The browser backend. Only the wasm build pulls these in; the native
 # binary never sees them (improvise-i34).
diff --git a/crates/improvise-io/src/persistence/mod.rs b/crates/improvise-io/src/persistence/mod.rs
index ab355b1e..505dfa2c 100644
--- a/crates/improvise-io/src/persistence/mod.rs
+++ b/crates/improvise-io/src/persistence/mod.rs
@@ -205,6 +205,28 @@ mod tests {
         assert_eq!(m2.model.name, "Budget");
     }
 
+    #[test]
+    fn a_legacy_json_workbook_loads_its_numbers_bit_for_bit() {
+        use crate::storage::{MemoryFs, Storage};
+        const LOSSY: f64 = 0.248_157_142_857_142_85;
+        let key = coord(&[("Type", "Food"), ("Month", "Jan")]);
+        let mut wb = two_cat_model();
+        wb.model.set_cell(key.clone(), CellValue::Number(LOSSY));
+        let json = serde_json::to_string(&wb).unwrap();
+        assert!(
+            json.contains("0.24815714285714285"),
+            "the file holds the exact text"
+        );
+        let fs = MemoryFs::new();
+        let path = std::path::Path::new("legacy.improv");
+        fs.write(path, json.as_bytes()).unwrap();
+        let loaded = super::load_from(&fs, path).unwrap();
+        let Some(CellValue::Number(n)) = loaded.model.get_cell(&key) else {
+            panic!("the cell must load as a number");
+        };
+        assert_eq!(n.to_bits(), LOSSY.to_bits(), "loaded {n:?}, not {LOSSY:?}");
+    }
+
     // ── save/load roundtrip via file ────────────────────────────────────
 
     #[test]
diff --git a/crates/improvise-protocol/Cargo.toml b/crates/improvise-protocol/Cargo.toml
index c114f10c..62c4a498 100644
--- a/crates/improvise-protocol/Cargo.toml
+++ b/crates/improvise-protocol/Cargo.toml
@@ -14,7 +14,8 @@ serde = { version = "1", features = ["derive"] }
 # `char`, and the TUI has always measured it this way.
 unicode-width = "^0.2"
 # Only for `variants`, which is off unless a test build asks for it.
-serde_json = { version = "1", optional = true }
+# float_roundtrip because every normal serde_json dep carries it (improvise-dz8c).
+serde_json = { version = "1", optional = true, features = ["float_roundtrip"] }
 
 [features]
 # `variants` reaches OUT of this crate: improvise-command bounds its own
diff --git a/crates/improvise-protocol/src/help.rs b/crates/improvise-protocol/src/help.rs
index 017bff2a..117f4fde 100644
--- a/crates/improvise-protocol/src/help.rs
+++ b/crates/improvise-protocol/src/help.rs
@@ -324,11 +324,12 @@ pub struct HelpPage {
 }
 
 pub use key_row::KeyRow;
+use key_row::keys;
 
 /// The one door to a keys row: its fields are private to this module, and its
 /// only constructor looks the keys up.
 mod key_row {
-    use super::{ModeKey, key_label, keys_for, prefixed_labels};
+    use super::{HelpLine, ModeKey, key_label, keys_for, prefixed_labels};
 
     #[derive(Debug, Clone, PartialEq, Eq)]
     pub struct KeyRow {
@@ -347,7 +348,7 @@ mod key_row {
 
         /// An unbound command yields no keys and no row, so the page never
         /// advertises a key that does not exist.
-        pub(super) fn looked_up(
+        fn looked_up(
             mode: &ModeKey,
             command: &str,
             args: Option<&[String]>,
@@ -361,17 +362,18 @@ mod key_row {
             (!keys.is_empty()).then_some(Self { keys, description })
         }
     }
-}
 
-/// A keys row, looked up in `mode`.
-fn keys(
-    mode: &ModeKey,
-    command: &'static str,
-    args: Option<&[&str]>,
-    description: &'static str,
-) -> Option<HelpLine> {
-    let args: Option<Vec<String>> = args.map(|a| a.iter().map(|s| (*s).to_string()).collect());
-    KeyRow::looked_up(mode, command, args.as_deref(), description).map(HelpLine::Keys)
+    /// A keys row, looked up in `mode`: the one caller of [`KeyRow::looked_up`],
+    /// and the lookup `pages` hands every builder (improvise-ssoe).
+    pub(super) fn keys(
+        mode: &ModeKey,
+        command: &'static str,
+        args: Option<&[&str]>,
+        description: &'static str,
+    ) -> Option<HelpLine> {
+        let args: Option<Vec<String>> = args.map(|a| a.iter().map(|s| (*s).to_string()).collect());
+        KeyRow::looked_up(mode, command, args.as_deref(), description).map(HelpLine::Keys)
+    }
 }
 
 /// `gg`, `yy`, `ZZ`: a prefix key and the key after it, both off the keymap.
@@ -1021,6 +1023,29 @@ mod tests {
         }
     }
 
+    /// improvise-ssoe: a keys row drawn but never asked for through the builders'
+    /// parameter is invisible to every guard. See `context/test-evidence/protocol.md`.
+    #[test]
+    fn every_keys_row_drawn_is_one_the_builders_asked_for() {
+        let drawn: Vec<HelpLine> = pages()
+            .into_iter()
+            .flat_map(|page| page.lines)
+            .filter(|line| matches!(line, HelpLine::Keys(_)))
+            .collect();
+        // Content, in order, not a count: a bypass that also drops a real row
+        // keeps the count and changes this (improvise-aszt).
+        let asked: Vec<HelpLine> = help_bindings()
+            .iter()
+            .filter_map(|(mode, command, args, description)| {
+                let args: Option<Vec<&str>> = args
+                    .as_ref()
+                    .map(|a| a.iter().map(String::as_str).collect());
+                keys(mode, command, args.as_deref(), description)
+            })
+            .collect();
+        assert_eq!(drawn, asked);
+    }
+
     /// A row whose lookup finds no key is dropped silently, so a broken lookup
     /// looks like a shorter page. See `context/test-evidence/protocol.md`.
     #[test]
diff --git a/crates/improvise-protocol/src/resolve.rs b/crates/improvise-protocol/src/resolve.rs
index b44921aa..d88b4e23 100644
--- a/crates/improvise-protocol/src/resolve.rs
+++ b/crates/improvise-protocol/src/resolve.rs
@@ -619,6 +619,11 @@ enum GridMove {
     Page(i32),
 }
 
+/// Rows one `page-scroll` step moves: three quarters of the window, at least one.
+fn page_rows(window_rows: usize) -> i32 {
+    (window_rows as i32 * 3 / 4).max(1)
+}
+
 fn grid_move(state: &ClientState, kind: GridMove) -> Option<Vec<Command>> {
     let GridExtent { rows, cols } = state.grid.extent;
     let (window_rows, window_cols) = state.window;
@@ -641,7 +646,7 @@ fn grid_move(state: &ClientState, kind: GridMove) -> Option<Vec<Command>> {
         GridMove::ToEnd(true) => (row_max as usize, cursor.selected.1),
         GridMove::ToEnd(false) => (cursor.selected.0, col_max as usize),
         GridMove::Page(dir) => {
-            let delta = (window_rows as i32 * 3 / 4).max(1) * dir;
+            let delta = page_rows(window_rows) * dir;
             ((row + delta).clamp(0, row_max) as usize, cursor.selected.1)
         }
     };
@@ -2362,47 +2367,90 @@ mod tests {
     #[test]
     fn every_grid_move_lands_where_its_binding_says() {
         let keymap = Keymaps::shared().get(&ModeKey::Normal).expect("Normal");
-        let mut moves = Vec::new();
-        bound_commands(keymap, &mut moves);
-        // A move's destination is its own args; a jump's is its name.
-        let mut expected: Vec<(String, Vec<String>, (usize, usize))> = moves
-            .into_iter()
-            .filter(|(name, _)| name == "move-selection")
-            .map(|(name, args)| {
-                let d = |i: usize| args[i].parse::<isize>().expect("a delta");
-                let to = ((1 + d(0)) as usize, (1 + d(1)) as usize);
-                (name, args, to)
-            })
-            .collect();
-        for (name, to) in [
-            ("jump-first-row", (0, 1)),
-            ("jump-last-row", (2, 1)),
-            ("jump-first-col", (1, 0)),
-            ("jump-last-col", (1, 2)),
-        ] {
-            expected.push((name.to_string(), Vec::new(), to));
-        }
-        let mut pressed = 0;
-        for (name, args, to) in expected {
-            let wanted = (!args.is_empty()).then_some(args.as_slice());
-            for sequence in sequences_running(keymap, &name, wanted) {
+        let mut bound = Vec::new();
+        bound_commands(keymap, &mut bound);
+        bound.sort();
+        bound.dedup();
+        // Far from every edge of a grid far larger than any step, so a landing
+        // shows magnitude as well as sign (improvise-5kdr); a jump's is its name.
+        const START: (usize, usize) = (10, 10);
+        const WINDOW: (usize, usize) = (8, 8);
+        let d = |a: &String| a.parse::<isize>().expect("a delta");
+        let at = |base: usize, by: isize| base.checked_add_signed(by).expect("inside the grid");
+        let page = page_rows(WINDOW.0) as isize;
+        let destination = |name: &str, args: &[String]| match name {
+            "move-selection" => Some((at(START.0, d(&args[0])), at(START.1, d(&args[1])))),
+            "scroll-rows" => Some((at(START.0, d(&args[0])), START.1)),
+            "page-scroll" => Some((at(START.0, page * d(&args[0])), START.1)),
+            "jump-first-row" => Some((0, START.1)),
+            "jump-last-row" => Some((20, START.1)),
+            "jump-first-col" => Some((START.0, 0)),
+            "jump-last-col" => Some((START.0, 20)),
+            _ => None,
+        };
+        let mut unstated = Vec::new();
+        let mut unpressed = Vec::new();
+        let mut pressed = std::collections::BTreeSet::new();
+        for (name, args) in &bound {
+            let to = destination(name, args);
+            let sequences = sequences_running(keymap, name, Some(args.as_slice()));
+            if to.is_some() && sequences.is_empty() {
+                unpressed.push(format!("{name} {args:?}"));
+            }
+            for sequence in sequences {
                 let mut state = furnished(AppMode::Normal);
+                state.grid.extent = GridExtent { rows: 21, cols: 21 };
+                state.window = WINDOW;
+                *state.view.cursor_mut() = crate::ViewCursor {
+                    selected: START,
+                    row_offset: 5,
+                    col_offset: 5,
+                };
+                let view = state.view.active_view.clone();
                 for key in &sequence {
                     if let KeyOutcome::Local(commands) = resolve(&state, *key) {
                         commands.iter().for_each(|c| state.fold(c));
                     }
                 }
-                assert_eq!(
-                    state.view.cursor().selected,
-                    to,
-                    "{sequence:?} runs `{name} {args:?}` from (1,1)"
-                );
-                pressed += 1;
+                let landed = state.view.cursor().selected;
+                if to.is_some() {
+                    pressed.insert(name.as_str());
+                }
+                match to {
+                    Some(to) => {
+                        assert_eq!(
+                            landed, to,
+                            "{sequence:?} runs `{name} {args:?}` from {START:?}"
+                        )
+                    }
+                    None if state.view.active_view == view && landed != START => {
+                        unstated.push(format!("{name} {args:?} -> {landed:?}"))
+                    }
+                    None => {}
+                }
             }
         }
         assert!(
-            pressed >= 14,
-            "only {pressed} keys pressed; the walk went blind"
+            unpressed.is_empty(),
+            "stated and never pressed: {unpressed:?}"
+        );
+        assert!(
+            unstated.is_empty(),
+            "these move the cursor and nothing states where to: {unstated:?}"
+        );
+        let every = [
+            "jump-first-col",
+            "jump-first-row",
+            "jump-last-col",
+            "jump-last-row",
+            "move-selection",
+            "page-scroll",
+            "scroll-rows",
+        ];
+        assert_eq!(
+            pressed.into_iter().collect::<Vec<_>>(),
+            every,
+            "each kind is pressed"
         );
     }
 
diff --git a/crates/improvise-wasm-client/tests/browser_round_trip.rs b/crates/improvise-wasm-client/tests/browser_round_trip.rs
index 83af13a8..f92e9deb 100644
--- a/crates/improvise-wasm-client/tests/browser_round_trip.rs
+++ b/crates/improvise-wasm-client/tests/browser_round_trip.rs
@@ -889,44 +889,6 @@ fn a_yanked_number_crosses_the_serialized_wire_exactly() {
     );
 }
 
-/// The two tests around this one share a feature-unified build, so neither can
-/// see ONE frame-parsing crate lacking `float_roundtrip`. Evidence file.
-#[test]
-fn every_build_that_parses_a_frame_enables_float_roundtrip() {
-    for (krate, target) in [
-        ("improvise-wasm-client", Some("wasm32-unknown-unknown")),
-        ("improvise-worker-server", Some("wasm32-unknown-unknown")),
-        ("improvise-ws-server", None),
-    ] {
-        let mut cargo = std::process::Command::new(env!("CARGO"));
-        cargo.current_dir(env!("CARGO_MANIFEST_DIR")).args([
-            "tree",
-            "--locked",
-            "--edges",
-            "normal,features",
-            "--invert",
-            "serde_json",
-            "--package",
-            krate,
-        ]);
-        if let Some(target) = target {
-            cargo.args(["--target", target]);
-        }
-        let out = cargo.output().expect("cargo tree must run");
-        assert!(
-            out.status.success(),
-            "{krate}: cargo tree failed: {}",
-            String::from_utf8_lossy(&out.stderr)
-        );
-        let tree = String::from_utf8(out.stdout).expect("cargo tree prints UTF-8");
-        assert!(
-            tree.contains(r#"serde_json feature "float_roundtrip""#),
-            "{krate} parses frames without float_roundtrip, so its numbers land \
-             one ULP off:\n{tree}"
-        );
-    }
-}
-
 /// A typed number is parsed exactly in the client and re-parsed from JSON by
 /// the host. Evidence file.
 #[test]
diff --git a/tests/json_numbers.rs b/tests/json_numbers.rs
new file mode 100644
index 00000000..506a59ec
--- /dev/null
+++ b/tests/json_numbers.rs
@@ -0,0 +1,61 @@
+//! A number read through serde_json must be the number written (improvise-6yvg,
+//! improvise-dz8c). The rule and its derivation: `context/code/protocol.md`.
+
+use serde_json::Value;
+
+/// Every NORMAL serde_json dependency in the workspace, and those lacking
+/// `float_roundtrip`, each spelled `package (target)`.
+fn lossy_json_dependencies(metadata: &Value) -> (Vec<String>, Vec<String>) {
+    let mut checked = vec![];
+    let mut lossy = vec![];
+    let packages = metadata["packages"]
+        .as_array()
+        .expect("metadata lists packages");
+    for package in packages {
+        let name = package["name"].as_str().expect("a package has a name");
+        let deps = package["dependencies"]
+            .as_array()
+            .expect("a package lists deps");
+        for dep in deps {
+            if dep["name"] != "serde_json" || !dep["kind"].is_null() {
+                continue;
+            }
+            let target = dep["target"].as_str().unwrap_or("all targets");
+            let spelled = format!("{name} ({target})");
+            let features = dep["features"].as_array().expect("a dep lists features");
+            if !features.iter().any(|f| f == "float_roundtrip") {
+                lossy.push(spelled.clone());
+            }
+            checked.push(spelled);
+        }
+    }
+    (checked, lossy)
+}
+
+/// Derived from `cargo metadata`, not listed: a new crate that can parse JSON
+/// is covered the day it declares the dependency. Evidence file.
+#[test]
+fn every_crate_that_can_parse_json_enables_float_roundtrip() {
+    let out = std::process::Command::new(env!("CARGO"))
+        .current_dir(env!("CARGO_MANIFEST_DIR"))
+        .args(["metadata", "--no-deps", "--format-version", "1"])
+        .output()
+        .expect("cargo metadata must run");
+    assert!(
+        out.status.success(),
+        "cargo metadata failed: {}",
+        String::from_utf8_lossy(&out.stderr)
+    );
+    let metadata: Value = serde_json::from_slice(&out.stdout).expect("metadata is JSON");
+    let (checked, lossy) = lossy_json_dependencies(&metadata);
+    assert!(
+        checked.len() >= 2,
+        "the derivation found {checked:?}: too few to be reading the metadata right"
+    );
+    assert!(
+        lossy.is_empty(),
+        "these parse JSON numbers with serde_json's lossy default, one ULP off \
+         for roughly one decimal in seven; add features = [\"float_roundtrip\"] \
+         to each crate's own manifest: {lossy:?}"
+    );
+}