test: cover hostname title (#82) and tmux size-query (#80)

Backfill the two regression gaps flagged on master after the recent
hostname-title and tmux-flicker fixes shipped without server-side
assertions.

* test/server-index-title.test.ts (8 tests) — exercises WebServer's
  index.html templating path: default os.hostname(), --title-hostname
  override, HTML-escape against `<script>`-style breakout, ampersand
  non-double-encoding, exact-once substitution, and byte-identical
  template-tail invariance.

* test/tmux-window-size-query.test.ts (15 tests) — mocks
  child_process.execFileSync and walks the helper through the
  browser-resize-between-attaches happy path, query-then-die race,
  zero/negative/empty/non-numeric output, plus argv-form/timeout
  assertions to lock down the no-shell-interpolation guarantee.

* src/session.ts — extracts the inline 14-line tmux size query into
  a named `queryTmuxWindowSize()` export so the test surface is a
  pure function. Behavior unchanged.

* src/web/public/notification-manager.js — Browser Notification API
  (layer 3) now uses `${this.originalTitle}: ${title}` so OS-level
  desktop pop-ups carry the same `codeman:<host>` prefix that the
  tab title and Web Push payloads already do, finishing the
  hostname plumb-through started in #82.

* CLAUDE.md, README.md — document the dual-CLI env-prefix discipline
  (CLAUDE_CODE_* vs OPENCODE_*), expand the xterm-zerolag-input
  duplication gotcha to mention the published-package side-effect,
  and note that the hostname prefix now applies uniformly to tab
  title, tab-flash, and OS notifications.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/session.ts

@@ -121,6 +121,37 @@ const NEWLINE_SPLIT_PATTERN = /\r?\n/;
 
 // Note: Claude CLI PATH resolution moved to session-cli-builder.ts (buildClaudeEnv)
 
+/** PTY fallback geometry when tmux can't be queried (matches pre-#80 hardcoded values). */
+const DEFAULT_PTY_COLS = 120;
+const DEFAULT_PTY_ROWS = 40;
+const TMUX_DISPLAY_TIMEOUT_MS = 2000;
+
+/**
+ * Ask tmux for the current window geometry of `muxName` so a re-attaching PTY
+ * client can spawn at the same size and avoid the resize-flicker / scrollback
+ * loss documented in #80. Returns `{ cols: 120, rows: 40 }` on any failure
+ * (tmux dead, muxName unknown, malformed output) — caller never has to
+ * differentiate "tmux unreachable" from "size 120x40".
+ *
+ * Argv form (execFileSync, not execSync) keeps `muxName` out of any shell so
+ * a hostile session name can't inject options.
+ */
+export function queryTmuxWindowSize(muxName: string): { cols: number; rows: number } {
+  try {
+    const sizeStr = execFileSync('tmux', ['display', '-t', muxName, '-p', '#{window_width} #{window_height}'], {
+      timeout: TMUX_DISPLAY_TIMEOUT_MS,
+      encoding: 'utf8',
+    }).trim();
+    const [w, h] = sizeStr.split(' ').map(Number);
+    if (w > 0 && h > 0) {
+      return { cols: w, rows: h };
+    }
+  } catch {
+    /* fall back below */
+  }
+  return { cols: DEFAULT_PTY_COLS, rows: DEFAULT_PTY_ROWS };
+}
+
 /**
  * Represents a JSON message from Claude CLI's stream-json output format.
  * Messages are newline-delimited JSON objects parsed from PTY output.
@@ -947,22 +978,7 @@ export class Session extends EventEmitter {
 
     // Attach to the mux session via PTY
     // Query existing tmux window size so re-attach matches (avoids flicker from 120x40 default)
-    let ptyCols = 120;
-    let ptyRows = 40;
-    try {
-      const sizeStr = execFileSync(
-        'tmux',
-        ['display', '-t', this._muxSession!.muxName, '-p', '#{window_width} #{window_height}'],
-        { timeout: 2000, encoding: 'utf8' }
-      ).trim();
-      const [w, h] = sizeStr.split(' ').map(Number);
-      if (w > 0 && h > 0) {
-        ptyCols = w;
-        ptyRows = h;
-      }
-    } catch {
-      /* fall back to 120x40 */
-    }
+    const { cols: ptyCols, rows: ptyRows } = queryTmuxWindowSize(this._muxSession!.muxName);
     try {
       this.ptyProcess = pty.spawn(mux.getAttachCommand(), mux.getAttachArgs(this._muxSession!.muxName), {
         name: 'xterm-256color',

src/web/public/notification-manager.js

@@ -3,7 +3,7 @@
  *
  * The NotificationManager class implements five notification layers:
  *   1. In-app notification drawer (slide-out panel with grouped notifications)
- *   2. Tab title flash (alternating "(*) Codeman" when tab is hidden)
+ *   2. Tab title flash (alternating "⚠️ (N) codeman:<host>" / "codeman:<host>" when tab is hidden; uses this.originalTitle so it tracks any per-host title)
  *   3. Browser Notification API (desktop push with auto-close after 8s)
  *   4. Web Push via service worker (OS-level notifications when tab is closed)
  *   5. Audio alerts (Web Audio API beep, user-opt-in)
@@ -330,7 +330,7 @@ class NotificationManager {
     if (now - this.lastBrowserNotifTime < BROWSER_NOTIF_RATE_LIMIT_MS) return;
     this.lastBrowserNotifTime = now;
 
-    const notif = new Notification(`Codeman: ${title}`, {
+    const notif = new Notification(`${this.originalTitle}: ${title}`, {
       body,
       tag, // Groups same-tag notifications
       icon: '/favicon.ico',