feat(terminal): renderer watchdog, atomic replay clear, fetch deadlines, reconnect recovery

Four ways the terminal can silently stop being correct — in each case the
buffer keeps updating, nothing throws, and the only recourse is a reload.

1. Renderer freeze after backgrounding. iOS DISCARDS scheduled rAF callbacks
   when a PWA backgrounds, and xterm's RenderDebouncer only clears its
   `_animationFrame` handle from inside that callback — so one drop leaves it
   permanently set and every later refresh() early-returns. Parsing is
   decoupled from rendering, so bytes keep filling the buffer correctly while
   nothing paints. Codeman has exactly ONE xterm for the whole page load, so a
   single backgrounding wedges it until a reload. Adds a 2s liveness poll and
   `_kickRenderer()`, which does what the dropped `_innerRefresh` would have.

2. Replay clears raced live output. xterm's write() is async-queued while
   reset() is synchronous and, per upstream, "does not clear input buffers and
   does not reset the parser" — so bytes queued before a reset are parsed after
   it and fuse into the snapshot. Verified against the real xterm 6 here:
   write('p8'); reset(); write('rmissions') renders "p8rmissions". The main
   path was already safe via a queued erase; the needsRefresh and clearTerminal
   paths were not. All three now share one queued `\x1bc` (RIS), which unlike
   3J/H/2J also resets modes, charsets, scroll regions and SGR state.

3. Output lost on WebSocket reconnect. Input frames carry seq+cid and are
   delivered exactly once; output frames carry nothing. ws.onopen re-sends dims
   and flushes queued input, and needsRefresh only fires on external-CLI
   startup and SSE backpressure drain — never on reconnect. Output produced
   while offline was simply absent afterwards. Interim fix: reaching onclose
   means the drop was unintentional, so the session is marked and the next open
   reconciles from the server buffer. Sequencing output is the follow-up.

4. Terminal captures had no deadline. No AbortController anywhere in the
   frontend, including `?full=1`, which the code itself calls "unbounded-ish
   work: at the default history limit it can be megabytes". Adds a budget that
   scales with full-vs-tail and with captures in flight, degrading to a plain
   fetch where AbortController is missing.

Also: the service-worker precache was dead — the build content-hashes assets
but sw.js listed pre-hash names, so 15 of 23 entries 404'd (verified against a
running instance) and cache.add().catch() hid it. Offline still worked via
runtime caching, but CACHE_NAME was a constant so activate's cleanup never
deleted anything and every past release's assets accumulated. Both are now
derived from the build manifest. Crash-trail entries are flattened and capped,
since they are joined with \n into one value and one call site interpolates a
server-controlled WS close reason.

The watchdog reads xterm privates — there is no public API. Every access is
optional-chained so a shape change degrades to a no-op. `_renderService` only
exists after open(), which needs a real DOM, so the gate cannot assert the
field path; test/xterm-private-api.test.ts pins the dependency range instead.

Tests: 23 new (terminal-resilience, sw-precache-manifest, xterm-private-api),
all pure/static so they run in the gate, which excludes the mobile suite. One
static source guard in history-truncation-notice updated for the renamed call;
the behaviour it pins is unchanged.

Not verified: no browser available, so no runtime reproduction of the freeze
and no real-device test of the reconnect path. Both warrant a device pass.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

scripts/build.mjs

@@ -146,10 +146,44 @@ console.log('\n[build] content-hash cache busting');
     html = html.replaceAll(`"${original}"`, `"${hashed}"`);
   }
   writeFileSync(join(distPublic, 'index.html'), html);
+
+  // Rewrite sw.js from the SAME manifest that just renamed the files.
+  //
+  // The service worker's precache list used to be maintained by hand with the
+  // pre-hash names, so after this step every entry in it pointed at a file that
+  // no longer existed and `cache.add(...).catch(() => {})` hid it. Deriving it
+  // here is the only way the two cannot drift.
+  //
+  // The cache key gets the build hash for the same reason: `activate` deletes
+  // every cache that is not the current one, so a constant key meant that
+  // cleanup never ran and hashed assets from every past release piled up.
+  const swPath = join(distPublic, 'sw.js');
+  let sw = readFileSync(swPath, 'utf8');
+  const hashedAssets = Object.values(manifest);
+  const buildId = createHash('md5').update(hashedAssets.join('|')).digest('hex').slice(0, 12);
+  // Rewrite the two declarations. Anchored on the full `const … = …;` text so
+  // each pattern occurs exactly once and cannot collide with prose in sw.js's
+  // own comments — an earlier cut used bare `__BUILD_ID__` sentinels and the
+  // first match landed in the comment that documented them, leaving the real
+  // constant untouched and still producing a plausible-looking cache key.
+  const swEdits = [
+    ["const BUILD_ID = 'dev';", `const BUILD_ID = '${buildId}';`],
+    ['const HASHED_ASSETS = [];', `const HASHED_ASSETS = [${hashedAssets.map((p) => JSON.stringify(p)).join(', ')}];`],
+  ];
+  for (const [from, to] of swEdits) {
+    const hits = sw.split(from).length - 1;
+    if (hits !== 1) {
+      throw new Error(`sw.js: expected exactly one \`${from}\`, found ${hits} — precache would ship stale`);
+    }
+    sw = sw.replace(from, to);
+  }
+  writeFileSync(swPath, sw);
+
   console.log('  Hashed files:');
   for (const [orig, hashed] of Object.entries(manifest)) {
     console.log(`    ${orig} -> ${hashed}`);
   }
+  console.log(`  sw.js: cache bucket codeman-${buildId}, ${hashedAssets.length} precached assets`);
 }
 
 // 6. Compress with gzip + brotli