audit 4: sign-in timing and sessions, server timeouts, polling that recovers

Steps 1-3 of stage 4, tested together (their docs share files).

Step 1 (M8, L15, L16): an unknown name pays a bcrypt comparison at the
panel's work factor too (noSuchUserHash, made once) -
TestLoginTakesAsLongForAnUnknownName holds the medians within a factor of
two; the Account form's current-password check has its own limiter, per
user (AllowPasswordChange); a sign-in destroys every session the request
presents before it issues its own.

Step 2 (L14): newHTTPServer - ReadTimeout 30 s, WriteTimeout 60 s,
IdleTimeout 2 min beside ReadHeaderTimeout; the full backup moves its write
deadline to two hours through http.ResponseController (e2e: the log shows
no failure to move it).

Step 3 (M11), read in htmx 2.0.4's source (dev/upstream/htmx-2.0.4, the npm
build byte-equal to the shipped htmx.min.js): the poll passes source: box,
and the next refresh is scheduled from htmx:afterRequest, which htmx fires
on load, error, abort and timeout, and after a swap on the nearest parent
left (the box found by detail.target's id); failures in a row double the
wait to 60 s. RequireAuth answers htmx with 401 + HX-Redirect: /login,
which htmx follows before it looks at the status. testdata/poll_test.js
runs panel.js in node against a stand-in DOM and clock (TestPanelJS; skipped
without node, which the test server lacks - run here, and it fails on the
old panel.js).

Also measured: the stage-3 e2e regression for H1 fails as it should on HEAD
with the old entrypoint ("check data/postfix/e2e_extra_map: permission
denied", the panel restarting).

Tested on the test server: go vet + go test of 25 packages, make e2e (all
pass, 639 s) on this tree.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/audit-2026-10-12.md

@@ -1185,15 +1185,40 @@ command whose leftover is the owner's alone.
 
 ### Stage 4 — panel behaviour (M8, M11, L10–L19) → `2.5.4`
 
-- [ ] Login: dummy bcrypt on unknown user; a test that measures both paths within
+- [x] Login: dummy bcrypt on unknown user; a test that measures both paths within
    a tolerance. Account password change gets its own limiter bucket. Login
    destroys the presented session. — **Opus**
-- [ ] `http.Server`: `ReadTimeout`, `WriteTimeout`, `IdleTimeout`. — **Opus**
-- [ ] **Polling recovery**: schedule from `htmx:afterRequest` on the box (or pass
+   *Done 2026-10-15:* `noSuchUserHash` (BcryptCost, made once) compared
+   against for an unknown name or a failed lookup;
+   `TestLoginTakesAsLongForAnUnknownName` holds the medians of five tries
+   each within a factor of two at the real work factor. The bucket is per
+   user (`AllowPasswordChange(userID)`, 10 in 15 min): the guesser is
+   whoever holds that user's session. Sign-in destroys every session cookie
+   the request carries before it creates its own.
+- [x] `http.Server`: `ReadTimeout`, `WriteTimeout`, `IdleTimeout`. — **Opus**
+   *Done 2026-10-15:* 30 s, 60 s, 2 min (`newHTTPServer`); the full backup
+   would have been cut at 60 s, so `HandleBackup` moves its write deadline
+   to two hours through `http.ResponseController` (no wrapper of the
+   ResponseWriter in the chain; e2e checks the log has no failure to move
+   it). A test pins the four values.
+- [x] **Polling recovery**: schedule from `htmx:afterRequest` on the box (or pass
    `source`), handle `sendError`/`timeout` with back-off; `RequireAuth`
    answers an `HX-Request` with `HX-Redirect: /login` instead of a 303. A
    minimal JS test (node + jsdom) or at least an e2e that restarts the panel
    with Overview open. — **Sonnet**
+   *Done 2026-10-15,* read in htmx 2.0.4's source (the npm build, byte-equal
+   to the shipped `htmx.min.js`, in `dev/upstream/htmx-2.0.4`): both -
+   `source: el`, and the schedule from `htmx:afterRequest`, which
+   `issueAjaxRequest()` fires on load, error, abort and timeout, and after a
+   swap that removed the box fires again on the nearest parent still in the
+   page (so the box is found by `detail.target`'s id);
+   `detail.successful` tells failure. Back-off doubles per failure in a row
+   to 60 s. `toLogin`: 401 + `HX-Redirect` for htmx, which
+   `handleAjaxResponse()` follows before it looks at the status. No jsdom
+   (no node tooling in the repo): `testdata/poll_test.js` runs panel.js in
+   node against a stand-in for the DOM and htmx with a moved clock, from
+   `TestPanelJSPolling` (skipped where node is absent - the test server's
+   Go has none; it fails on the old panel.js with ten findings).
 - [ ] `parsePage` clamp; `NaN` refused; `rate-limited` tag red (add the status to
    `components.go`, flip the test); the recalc button posts only what it
    needs or warns; `HandleReload` either covers DMARC maps and filter lists or