v0.8.4 — the multiplayer transport: server and browser

The second release from the audit. Every fault here was invisible in solitaire, and four of
the five server faults were in the one file no test had ever stood up; `http.ts` now has an
end-to-end suite on a real port. CHANGELOG has the reasoning.

SERVER. Leaving a lobby freed the chair and kept the token, so a leaver could stream and
move for whoever took the seat next — revoked now, in memory and on disk. The browser
numbered intents from 1 per page load while the server remembered the seat's last number,
so the first move after a reload was swallowed as a resend — the connect push carries the
count and the client continues from it. Nothing serialised moves within a game and every
write shared one `.tmp` name, so two moves at once tore `game.json` (measured: 6 of 200),
and the boot's bare `JSON.parse` then took every game down — per-path write queues, a
per-game move queue, and a boot that skips one bad file. An error after the SSE head was
sent crashed the process. Bodies were unbounded before any secret check.

BROWSER. A double-click did the thing twice: one submit in flight at a time. A failed
submit is `false`, not an unhandled rejection. The documentation renderer flattened nested
bullets into a literal "- " mid-sentence on the published home-deck page. The make-up panel
promised cars the engine refuses; it asks `acceptsCar` now.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FrCWubm9GAftYCm2hWdKwK

docs/architecture/lobby-and-sessions.md

@@ -107,7 +107,9 @@ clashing join is refused (`NAME_TAKEN`, compared trimmed and case-insensitively)
 suffixed: a player should play under the name they chose, or be asked for another.
 
 **Anybody may leave, and the host may clear a chair.** `Lobby.Leave` frees the seat, drops the token
-from `joinOrder`, and passes host rights on exactly as a dropped connection does. Naming somebody
+from `joinOrder`, **revokes it** — in memory and in `sessions.json`, since v0.8.4; until then the
+leaver's token still opened the seat the next arrival took — and passes host rights on exactly as a
+dropped connection does. Naming somebody
 else's `seat` is host-only. When the last human leaves, the lobby is deleted outright — code, file and
 index row — rather than left as a table of bots waiting for a host who no longer exists. Before this
 existed a mis-join or a player who wandered off wedged the whole table, since Start needs every chair