Merge pull request #217 from fiddlerwoaroof/collapse-fu/ciw8

improvise-ciw8: a wire write reaches only a cell the host projects as a Record

context/test-evidence/command.md

@@ -5793,6 +5793,69 @@ on `Food/Jan/Profit`, where there is nothing to clear, and
 `Clothing/Jan/Profit = 5` survives. Injected alone into a full workspace run,
 the rival fails this test and nothing else.
 
+### a_wire_write_to_a_collapsed_fold_is_rejected_and_stores_nothing
+
+improvise-ciw8, through a real `Host` frame. Q2 is collapsed, and a hand-rolled
+client sends `SetCell` (then, separately, `ClearCell`) for `{Month=Q2, _Measure=Cost}`
+with a caught-up basis. At `ea119bd9` both were answered `Accepted`, and the
+`SetCell` stored `Month=Q2, _Measure=Cost = 7`, the non-item coordinate
+improvise-gw18 exists to prevent. The test asserts `Rejected(MutationRefused)`
+and an unchanged document for both. Rival: the aggregate refusal disabled. This
+test and the None-axis test fail. The control is
+`a_wire_write_to_a_stored_cell_beside_a_fold_is_accepted`, so a host that refused
+every wire write cannot pass.
+
+### a_wire_write_under_a_formula_is_rejected_and_stores_nothing
+
+improvise-ciw8's `Derived` arm: `SetCell` on Feb × Profit, where
+`Profit = Revenue - Cost`. At `ea119bd9` it was accepted and stored a value under
+the formula. Rival: the formula refusal disabled. Only this test fails.
+
+### a_wire_write_to_a_none_axis_aggregate_is_rejected_and_stores_nothing
+
+improvise-ciw8's other `Aggregate`. With `Product` on `Axis::None`, the grid's
+key `{Region=South, _Measure=Revenue}` is a partial key that no stored record
+has, so it resolves only through the layout, where `cell_id` says `Aggregate`.
+At `ea119bd9` it was accepted and stored the partial key. It fails under the
+same rival as the fold test.
+
+### a_wire_write_to_a_record_that_never_existed_is_rejected
+
+The evidence for keeping `model_effects`' `vec![]` arm rather than turning it
+into a refusal (`context/code/command.md`, "A wire write reaches only a cell the
+host projects as a Record"). A lone write naming a record that never existed is
+answered `RecordGone` before anything runs, both when a caught-up basis claims
+it and when a hand-rolled basis omits it. The second half was expected to be
+`ChainBroken`, and the test said otherwise: the create exemption covers only
+commands after the first in a frame. That surprise is why it is asserted rather
+than argued.
+
+### an_empty_cell_beside_a_collapsed_measure_group_is_writable
+
+improvise-sjdb, a regression PR #217 introduced and its review found. `_Measure`
+is on Column with Revenue and Cost in a collapsed group `Money` and `Units`
+ungrouped, and the Feb row is empty. The host projects Feb × Units as a
+`Record`. A caught-up `SetCell` on it was answered `Rejected(MutationRefused)`
+at `bc060f67`. It was accepted before #217. `aggregate_refusal` found the
+unstored record by `RecordHash` alone, which drops `_Measure`, so it judged the
+record at the first column on Feb's row, the `Money` fold, which `cell_id` calls
+`Aggregate`. The setup asserts that the fold comes before `Units` on the row and
+that the target projects as `Record`, so a fixture where the first column is
+harmless cannot pass. The fix looks the cell up by its whole key. The rival is
+the old lookup by record, which is this test's red commit, `6e021699`.
+
+### a_stored_record_the_hosts_view_aggregates_is_writable
+
+improvise-sjdb, from the #217 review. South/Revenue is stored, then `Product` is
+added on `Axis::None` in the host's view, so the host projects South's position
+as `Aggregate`. A stored record is a record wherever it is drawn, because
+`RecordHash` is document-scoped (gotcha 44). A records-mode client, or one on
+another view, may write it. The setup asserts the host really does project
+`Aggregate` there, so the test cannot pass on a view that draws South plainly.
+Rival: stored records sent through `cell_id` like unstored ones. That rival
+fails this test and nothing else in `improvise-command`. Before this test,
+nothing in the suite saw it.
+
 ### a_fresh_sessions_slice_is_the_hosts_startup_slice
 
 improvise-v8ab. A fresh session's slice is built twice: `App::with_storage`