docs: CellDisplay::value and the dsxq evidence

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VdfEGXA7aJ6ftMsCc9PJze

context/code/protocol.md

@@ -552,8 +552,39 @@ client over the same grid, and they disagreed by a comma.
 
 `numeric` and `error` are decided by the server for the same reason: it is
 the side that knows which it was, and re-deriving client-side is how the two
-ends drift apart. `CellDisplay` is deliberately not a `CellValue` — by the
-time a cell reaches a client the number formatting has already happened.
+ends drift apart. `CellDisplay` is deliberately not *drawn from* a `CellValue`
+— by the time a cell reaches a client the number formatting has already
+happened, and `text` is what a renderer paints.
+
+### `CellDisplay::value` — what `yank` copies (improvise-dsxq)
+
+The value the host evaluated at this position, the same `Option<CellValue>`
+that `text` was formatted from: `evaluate_aggregated` over the view's
+`none_cats` in a pivot grid, `records_value` in a records grid. It exists
+because the browser's `yy` has to copy what the TUI's `YankCell` copies, and
+neither string on the cell can be turned back into it:
+
+- `edit_text` is `CellValue::to_string()`, which writes a non-whole number
+  `{:.4}` — `1.23456789` becomes `1.2346`.
+- Re-parsing any text with `typed()` turns number-like text into a number —
+  `Text("007")` becomes `Number(7.0)`.
+- In a pivot grid `edit_text` is the *stored* cell (`get_cell`), so an
+  aggregate or a formula cell has none and yanked nothing at all.
+
+So the value is **projected**, not re-derived (gotcha 47): a client that
+wants the value asks for the value. It is kept separate from `edit_text`
+rather than replacing it, because the two answer different questions — what
+an editor starts with is a *string*, deliberately the one the TUI's buffer
+holds, and changing it would change what the TUI's own editor shows.
+
+It cost `Eq`: `CellValue` holds an `f64`, so `CellDisplay`, `GridCache` and
+`GridUpdate` are `PartialEq` only. Nothing hashed or `Eq`-bounded them.
+
+In a records grid the TUI does **not** yank this value: `YankCell` and
+`PasteCell` resolve the synthetic `(_Index, _Dim)` key, so the TUI yanks
+`None` and pastes a junk cell into the document (improvise-6p8q). The browser
+is right there and the TUI is wrong, which is why the lockstep yank test stays
+on a pivot grid.
 
 ### `AxisFrame` — the grid's frame, and why it is *one* type
 

context/test-evidence/clients.md

@@ -4101,6 +4101,12 @@ so the paste is evidence about the yank rather than about a hand-seeded field.
 
 **Fault injected:** the `"yank"` arm of `composed` renamed. Fails on the yank.
 
+**Superseded in part by improvise-dsxq** (entry at the end of this file). The
+fixture's `1200` is the one kind of value on which the edit text and the value
+agree, so this test could not see that the arm yanked the edit text re-parsed.
+The arm now yanks `CellDisplay::value`, and the test sets that field on its
+hand-built cell. The parity claim lives in the lockstep tests, not here.
+
 ### `a_second_key_that_matches_nothing_still_spends_the_prefix`
 
 `App::dispatch_key` `take()`s the prefix before looking the second key up, so
@@ -4177,3 +4183,62 @@ and converged.
 
 **Fault injected:** the same `Binding::Prefix` → `Upstream` reversion. Fails on
 the second press.
+
+## improvise-dsxq — the browser's `yy` copies the value, not a string
+
+PR #161 (improvise-lut7) made the browser's `yank` arm compose
+`SetYanked(typed(edit_text))`. The TUI's `YankCell` yanks
+`evaluate_aggregated(key)`, the value itself. Those differ in three ways, and
+#161's only fixture, `1200`, hits none of them:
+
+- `edit_text` is `CellValue::to_string()`, which rounds a non-whole number to
+  four places.
+- `typed()` turns number-like text into a number.
+- In a pivot grid `edit_text` is the stored cell only, so an aggregate or a
+  formula cell has none and the browser yanked `None`.
+
+The fix projects the evaluated value as `CellDisplay::value`, and the arm yanks
+that (`context/code/protocol.md` §3). Reproduced at `40b8913` by both tests
+below before the fix: the browser yanked `Number(1.2346)` for `1.23456789`, and
+`None` for the aggregate.
+
+### `yy_then_p_copies_the_value_the_host_copies`
+
+Three cases, one per disagreement, each on a real `App` and a `ClientState`
+seeded by `grid_of`. The host presses `y y p` through `reduce_key`; a twin
+host applies exactly what the client composed. Each case asserts the host
+yanked the expected value (so a fixture that yanks nothing cannot pass), that
+the client yanked the same, that the host's paste landed, and that the two
+documents match. Sources sit at row 2 or 3 and targets at row 1, never row 0,
+and the first column is an unused `Units` measure, so no cursor is at index 0.
+
+- `1.23456789`, a non-whole number.
+- `Text("007")`, number-like text.
+- `Profit = Revenue - Cost` over `10.123456` and `0.5`, a formula's value,
+  pasted into a stored `Revenue` cell.
+
+**Faults injected, each run:**
+- The pre-fix arm, `typed(edit_text)`. Fails on the first case with
+  `Number(1.2346)`.
+- The arm yanking `typed(&value.to_string())`, the projected value re-rendered.
+  Fails on the first case with `Number(1.2346)`.
+- The producer coercing number-like `Text` through `typed()`. The first case
+  passes, and the second fails with `Number(7.0)`.
+- The producer projecting the raw `get_cell` instead of the evaluated value.
+  The first two cases pass, and the third fails with `None`.
+
+### `yy_over_an_aggregate_copies_the_sum_the_host_copies`
+
+`Product` on the None axis with two stored records, `1.23456789` and `1.0`, so
+the cell at row 1 is an `Aggregate` with no stored value. Yank only, since an
+all-aggregate grid has no record cell to paste into. The host must yank
+`Number(2.23456789)`, which rules out a fixture that is not an aggregate.
+
+**Faults injected, each run:** the pre-fix arm (fails with `None`), the
+re-rendered value (fails with `Number(2.2346)`), and the raw `get_cell`
+producer (fails with `None`).
+
+Records mode is deliberately not covered. There the TUI yanks `None` and its
+`p` writes a junk `_Dim`/`_Index` cell, because it resolves the synthetic key
+(improvise-6p8q). The browser is right and the TUI is wrong, so a lockstep
+case there would assert the bug.