fix(e24): review round 4 — a test that pinned nothing, and prose still ahead of the code

Round 4 reviewed round 3's commit. Nothing in production behaviour was wrong; what was wrong
was the round's own test and its comments, which is the failure class this loop keeps
finding.

- The new NavigationProvider case named after the `&& !channelViewRef.current` clause never
  reached it. With storage cleared and a bare URL the provider lands on "home" (E24's own
  default), not "feed", so asking for "feed" was an ordinary page change and the guard's
  first conjunct short-circuited. Deleting the clause left all 828 tests green — a dead nav
  control (the rail's own module stops closing an open channel page) with no red anywhere.
  The test now asserts the precondition and calls `setPage` with the page that IS current.
- Both new Home cases rejected a promise and then asserted after one fixed macrotask.
  React-query notifies through `notifyManager`'s own `setTimeout(0)`, registered after any
  timer the test schedules, so the assertion raced it; two reviewers measured intermittent
  reds. They poll for a signal that the rejection LANDED instead — the reroll button
  releasing, which is also the honest one for the empty-answer case, where the empty state is
  already on screen while the press is in flight and asserting it early would pass either way.
- `buryUnder`'s comment still opened with "one rule for both entry points" ten lines above the
  paragraph saying the rule is complete only for one of them, listed the non-reporting palette
  rows without `openChannel` — which has its own `replaceState` no-push branch and is reached
  from PlayerModal too — and pointed at a ROADMAP.md this repository does not contain.
- `history.dom.test.ts`'s header claimed its layers close by genuine Backs only, which two of
  its own tests contradict; and `CommandPalette.ordering.dom.test.tsx` still claimed to be
  "the only assertion in the suite" doing what the file corrected in round 3 also does. Round
  3's message said that pair was handled and only one side had been.

The provider test was re-mutation-checked (dropping the clause now goes red), and both
hardened Home tests still go red against their own reverts. Seven consecutive full runs green.
Gate: ruff, ruff format, 3x tsc, eslint (0 errors), prettier, knip, vitest 828, pytest 1005.

frontend/src/lib/history.dom.test.ts

@@ -7,8 +7,12 @@
 // A GENUINE user Back is simulated by dispatching `popstate` directly: the real-Back branch in
 // history.ts does NOT call history.back() (it only decrements its own historyDepth to match the
 // entry the browser already dropped), so a raw popstate reproduces it deterministically without
-// depending on jsdom's async back() semantics. Each test closes its layers via genuine Backs, so
-// no reconcile-driven history.back() runs and the shared module state stays clean between tests.
+// depending on jsdom's async back() semantics. The invariant that keeps the module-global
+// bookkeeping clean between tests here is NOT "only genuine Backs" — two closeThenNavigate cases
+// deliberately drive a reconcile into history.back() — it is that no REAL back() is ever left in
+// flight: a layer is closed by a genuine Back, by a STUBBED back() that lands its own popstate, or
+// by an unmount whose burial mark is consumed. A test that needs an unstubbed one belongs in its own
+// file (see history.burial.dom.test.ts).
 import { describe, it, expect, vi, afterEach } from "vitest";
 import { renderHook, act } from "@testing-library/react";
 import { closeThenNavigate, navigateOverOverlays, useBackToClose, useBackToExit } from "./history";