record the defect the useDashboardState tests found

section 9 now carries a concrete instance of its own argument: a test found a bug that
two careful readings of the file had not, in code written three days earlier to prevent
exactly that failure. also records the two bun/testing-library harness facts that cost
more than the fix did, since both present as an unrelated file breaking for no reason.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/workspace-panel-todo.md

@@ -988,6 +988,28 @@ they are marked below, because a dead-code list that is itself wrong is the wors
       as an *updater*, never as a computed tree, which is the structural fix; a test there would be
       guarding the fix rather than finding the bug. Checked, not assumed — `bun test src/workspaces/officerdev/src/components/Workspace/`.
 
+- [x] **`useDashboardState`, and the strongest argument this section has for itself.** _(`4f8046d`,
+      branch `agent-coordination-mvp`)_ — 14 tests over the store every layout and every
+      `config.agentName` is persisted through. They found a live Tier-A-class defect on the first run,
+      in code written three days earlier to *stop* silent write loss: `revert` decided whether to roll
+      back by asking "does the cache still hold exactly what I wrote?" **by reference**, and
+      `setQueryData` runs React Query's structural sharing, which rebuilds the object it stores rather
+      than keeping the one it was handed. Measured against @tanstack/react-query 5.101.4 — an object
+      value comes back `!==`, a string comes back `===`. So the guard was false for every *container*
+      the store exists to hold, and a refused write kept its optimistic value in the cache while the
+      toast said it had been rolled back; the change then vanished at the next reload. Only primitives
+      ever reverted, which is exactly why nobody saw it. Replaced with a per-key write sequence, which
+      asks the question the identity check meant to ask and does not depend on identity at all. The
+      regression pin is the test named "a refused OBJECT write is rolled back too".
+      Two things worth carrying forward. **A test found a bug that review had not**, in a file that had
+      been read carefully twice — which is the case for §9 stated better than any argument. And
+      `mock.module` is **process-wide and permanent** in Bun: a stub that does not spread the real
+      module deletes exports out from under files that never heard of it. Likewise
+      `@testing-library/react` auto-registers `afterEach(cleanup)` at *import* time, so it lands in
+      whichever test file imports the library first and every later file silently gets none — that is
+      now registered in `test-setup.ts`, where preload's lack of a file scope makes it global. Adding
+      one test file broke fourteen assertions in `DataTable.test.tsx` before both were understood.
+
 - [x] **A panel is told where it is, instead of being handed a key to reverse-engineer.** _(`dbe585f` +
       `717580f` + `585f234`, branch `agent-coordination-mvp`)_ — the first three items of §5.9. The
       context field `dashboardId: string` — which was never an id, always the whole `workspace.key` —