fix(mobile): address review blockers on the touch-device change set

Review follow-ups on PR #111 (rebased onto master post-#112/#113):

Resize arbitration redesigned (review blocker 2): the previous
'cols < _ptyCols' guard froze a mobile-only session's PTY at the spawn
default — narrow phones rendered clipped and could never re-fit. The
guard now uses connection-scoped desktop sizing claims instead:
ws-routes registers a claim on a desktop-typed resize and releases it
on socket close (or when the same connection later reports a small
viewport), and Session.resize() ignores mobile/tablet resizes only
while at least one desktop connection holds a claim. A phone alone
fully controls its size (shrink, rows-only shrink, re-grow); a phone
glancing at a desktop-driven session can no longer reflow it.
mobile-handlers' keyboard open/close resize now declares its viewport
type so it participates in arbitration. Tests rewritten to cover
mobile-only shrink/rows-only/re-grow, claim/release lifecycle, multi-
claim behavior, and untyped legacy resizes; ws-routes test covers the
claim lifecycle over a real socket.

Solo/detached header restored (review blocker 3): index.html had
removed #soloSessionTitle and #soloRedockBtn, which _applySoloMode
still references — every detached window hit a null deref. Both are
back alongside the new mobile utility toggle.

Desktop leak fixed (review should-fix): .mobile-header-utility-toggle
had no rule outside the <=768px media queries, so the raw button
rendered on desktop. styles.css now hides it by default; the mobile/
tablet queries re-enable it.

Visual-regression baselines reverted to master (review should-fix):
the 18 contributor-machine PNGs are environment-specific (8 of the
behavioral tests already report environment-sensitive failures across
machines); re-baseline deliberately on the canonical machine instead.
The 24 behavioral keyboard/layout/tabs tests are kept as-is.

AGENTS.md trimmed to a pointer at CLAUDE.md (review should-fix) to
avoid drift between duplicated guidance.

Also dropped a dead getAttachmentHistoryForPersist stub (codex-branch
residue — no such method exists in src/).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/session.ts

@@ -2052,17 +2052,43 @@ export class Session extends EventEmitter {
   private _ptyCols = 120;
   private _ptyRows = 40;
 
+  /**
+   * Live WebSocket connections that have announced a desktop viewport for this
+   * session. While at least one is registered, small-viewport (mobile/tablet)
+   * resizes are ignored so a phone glancing at the session can't reflow the
+   * PTY under an active desktop view. Claims are connection-scoped: ws-routes
+   * registers them on a desktop-typed resize and releases them on socket
+   * close, so a mobile-only session (no desktop connected) keeps full control
+   * of its own size — including narrowing below the spawn default.
+   */
+  private _desktopSizeClaims = new Set<symbol>();
+
+  /** Register a live desktop sizing claim (see _desktopSizeClaims). */
+  claimDesktopSizing(token: symbol): void {
+    this._desktopSizeClaims.add(token);
+  }
+
+  /** Release a desktop sizing claim when its connection goes away. */
+  releaseDesktopSizing(token: symbol): void {
+    this._desktopSizeClaims.delete(token);
+  }
+
   /**
    * Resizes the PTY terminal dimensions.
    * Skips the resize if dimensions haven't changed to avoid triggering
    * unnecessary Ink full-screen redraws (visible flicker on tab switch).
    *
+   * Arbitration: while a desktop connection holds a sizing claim, resizes from
+   * small viewports (mobile/tablet) are ignored entirely — shrink AND grow
+   * would both reflow the desktop view. Without a desktop connected, small
+   * viewports control the PTY size freely.
+   *
    * @param cols - Number of columns (width in characters)
    * @param rows - Number of rows (height in lines)
    */
   resize(cols: number, rows: number, options: { viewportType?: ResizeViewportType } = {}): void {
     const isSmallViewport = options.viewportType === 'mobile' || options.viewportType === 'tablet';
-    if (isSmallViewport && cols < this._ptyCols) {
+    if (isSmallViewport && this._desktopSizeClaims.size > 0) {
       return;
     }
     if (this.ptyProcess && (cols !== this._ptyCols || rows !== this._ptyRows)) {