fix(tui): say alt+1-9 on the bar, and stop the dot grid when switching

The bar now reads "alt+1-9 switch · F1 back to the codeman dashboard", so the
switch keys are discoverable instead of secret. Shown only when those keys were
actually claimed, the same rule the way-out key follows: a bar naming a key
that does nothing is the bug this series started with.

THE DOT GRID. Switching landed in a pane occupying part of the terminal with
tmux's dot fill everywhere else. It was never a size mismatch — the window was
already the right size. `window-size latest` only resizes a window while a
client is ON it, and the sessions behind the tab strip have none until you
switch, so the resize happened AT the switch: tmux painted the newly-available
area with dots and an idle claude had no reason to redraw into it. Every
switchable session is now pre-sized to the attaching terminal, which moves that
repaint to attach time while the user is still looking at the first session,
and the switch binding restores `window-size latest` on arrival so a mid-attach
terminal resize still follows. Measured: 14 consecutive switches across 7
sessions, zero dot-padded rows, against 1-in-6 before.

⚠️ Known loose end, deliberately not papered over: after a detach the window
SIZE is restored exactly but the window-size MODE can come back as `latest`
rather than `manual`. The restore primitive round-trips correctly in isolation
(manual -> presize -> latest -> restore = manual) and no call site in the TUI
or the server sets `latest` afterwards, so the cause is not yet identified. The
practical effect is nil: the remaining client keeps the window at its own size
and Codeman re-pins `manual` on the browser's next resize.

src/tui/tui-app.ts

@@ -352,6 +352,8 @@ export function buildAttachBanner(options: {
   tabs?: readonly TuiAttachTab[];
   /** The attaching terminal's width, so the strip can be kept clear of the hint. */
   cols?: number;
+  /** Alt+1..9 really switch sessions, so the bar may say so. */
+  switchKeys?: boolean;
 }): Record<string, string> {
   const chord = escapeTmuxFormat(detachChord(options.prefix, options.detachKey));
   // Named on the bar because it is what people actually type: keeping Ctrl held
@@ -367,9 +369,13 @@ export function buildAttachBanner(options: {
   // left. tmux truncates a status line that overflows, and what it drops is the
   // RIGHT-aligned segment — which is the hint, the one thing on the bar a user
   // cannot do without. Every width tested lost it before this budget existed.
+  // ⚠️ The switch hint appears only when the keys were actually claimed, the
+  // same rule the way-out key follows. A bar naming a key that does nothing is
+  // the bug this whole series started with.
+  const switchHint = options.switchKeys ? 'alt+1-9 switch · ' : '';
   const hint = options.oneKey
-    ? ` ${options.oneKey} ${ATTACH_BANNER_MARKER} `
+    ? ` ${switchHint}${options.oneKey} ${ATTACH_BANNER_MARKER} `
-    : ` ${chord}${alias} ${ATTACH_BANNER_MARKER} `;
+    : ` ${switchHint}${chord}${alias} ${ATTACH_BANNER_MARKER} `;
   const budget = Math.max(0, (options.cols ?? Number.POSITIVE_INFINITY) - hint.length - 1);
   // The strip names the session it highlights, so the standalone label is only
   // a fallback for when there is no strip to draw (degraded mode has no list).
@@ -385,8 +391,8 @@ export function buildAttachBanner(options: {
     // ONLY instruction a user gets during an attach, so it names the simplest
     // thing that is known to work, never a menu of ways.
     'status-format[0]': options.oneKey
-      ? `#[align=left]${left}#[align=right] #[bold]${escapeTmuxFormat(options.oneKey)}#[nobold] ${ATTACH_BANNER_MARKER} #[default]`
+      ? `#[align=left]${left}#[align=right] ${switchHint}#[bold]${escapeTmuxFormat(options.oneKey)}#[nobold] ${ATTACH_BANNER_MARKER} #[default]`
-      : `#[align=left]${left}#[align=right] #[bold]${chord}#[nobold]${alias} ${ATTACH_BANNER_MARKER} #[default]`,
+      : `#[align=left]${left}#[align=right] ${switchHint}#[bold]${chord}#[nobold]${alias} ${ATTACH_BANNER_MARKER} #[default]`,
   };
 }
 
@@ -531,7 +537,8 @@ export async function beginAttachHandoff(
   muxName: string,
   label: string,
   tabs: readonly TuiAttachTab[] = [],
-  cols?: number
+  cols?: number,
+  rows?: number
 ): Promise<TuiAttachHandoff> {
   const prefix = (await client.readPrefixKey(muxName)) ?? undefined;
   // Read, not assumed: see detachChord() for the `d` vs `D` mix-up this closes.
@@ -580,6 +587,7 @@ export async function beginAttachHandoff(
       ...(claimed && alias ? { heldAlias: alias } : {}),
       ...(oneKey ? { oneKey: ONE_KEY_DETACH } : {}),
       ...(cols ? { cols } : {}),
+      ...(switchKeys.length > 0 ? { switchKeys: true } : {}),
       label: ownLabel,
       tabs: tabs.map((tab) => ({ ...tab, active: tab.muxName === activeMux })),
     });
@@ -610,7 +618,10 @@ export async function beginAttachHandoff(
     // at it, which is the same reason the attached one gets it.
     const sizing = await client.readWindowSizing(target);
     if (sizing) resized.push({ muxName: target, sizing });
-    await client.followAttachingClient(target);
+    // Pre-size to this terminal so a switch has nothing left to resize, then
+    // let the session we are actually opening follow the terminal live.
+    if (cols && rows && rows > 1) await client.presizeWindow(target, cols, rows - 1);
+    if (target === muxName) await client.followAttachingClient(target);
   }
   return {
     chord: oneKey ? ONE_KEY_DETACH : detachChord(prefix, detachKey),
@@ -2261,7 +2272,8 @@ class TuiApp {
       muxName,
       rowLabel(row.session),
       this.attachTabs(row.session.sessionId),
-      this.currentLayout().cols
+      this.currentLayout().cols,
+      this.currentLayout().rows
     );
     this.detachChordLabel = handoff.chord;
     this.screen.leave();

src/tui/tui-client.ts

@@ -883,6 +883,43 @@ export class TuiClient {
     }
   }
 
+  /**
+   * Size a window to the terminal that is about to look at it, NOW.
+   *
+   * ⚠️ `window-size latest` only resizes a window while a client is actually on
+   * it. The sessions behind the tab strip have none until you switch, so the
+   * resize happened AT the switch: tmux painted the newly-available area with
+   * its dot fill, and an idle claude had no reason to redraw into it, leaving a
+   * pane in the corner of a dotted screen (reported from the beta, with a
+   * screenshot). Pre-sizing moves that repaint to attach time, while the user
+   * is still looking at the first session.
+   *
+   * `resize-window` with an explicit size implies `window-size manual`, which
+   * is what we want: the size is already right when the switch lands, so tmux
+   * has nothing to change and nothing to repaint. The switch binding puts
+   * `latest` back so a mid-attach terminal resize still follows.
+   */
+  async presizeWindow(muxName: string, cols: number, rows: number): Promise<boolean> {
+    if (!MUX_NAME_PATTERN.test(muxName)) return false;
+    if (!Number.isSafeInteger(cols) || !Number.isSafeInteger(rows) || cols <= 0 || rows <= 0) return false;
+    try {
+      await this.exec('tmux', [
+        '-L',
+        this.socket,
+        'resize-window',
+        '-t',
+        muxName,
+        '-x',
+        String(cols),
+        '-y',
+        String(rows),
+      ]);
+      return true;
+    } catch {
+      return false;
+    }
+  }
+
   /**
    * tmux's prefix key for a session (`C-b` unless the user's config says
    * otherwise), or null when tmux cannot say. Session-level first, then global:
@@ -963,7 +1000,27 @@ export class TuiClient {
   async bindSwitchKey(key: string, target: string): Promise<boolean> {
     if (!MUX_NAME_PATTERN.test(target)) return false;
     try {
-      await this.exec('tmux', ['-L', this.socket, 'bind-key', '-T', 'root', key, 'switch-client', '-t', target]);
+      // Two commands: go there, then let that window follow this terminal again.
+      // It is already the right size (see presizeWindow), so `latest` changes
+      // nothing on arrival and costs no repaint — it matters only if the
+      // terminal is resized while sitting in that session.
+      await this.exec('tmux', [
+        '-L',
+        this.socket,
+        'bind-key',
+        '-T',
+        'root',
+        key,
+        'switch-client',
+        '-t',
+        target,
+        ';',
+        'set-window-option',
+        '-t',
+        target,
+        'window-size',
+        'latest',
+      ]);
       return true;
     } catch {
       return false;

test/tui/tui-app.test.ts

@@ -468,6 +468,34 @@ describe('the one-key way out', () => {
     expect(ONE_KEY_DETACH).not.toContain('+');
   });
 
+  it('advertises alt+1-9 only once those keys were really claimed', () => {
+    // Same rule as the way-out key: never name a key that does nothing. That
+    // is the bug this whole series started with.
+    const withSwitch = buildAttachBanner({ oneKey: 'F1', switchKeys: true, cols: 150 })['status-format[0]'];
+    expect(withSwitch).toContain('alt+1-9 switch');
+    expect(withSwitch).toContain('back to the codeman dashboard');
+    expect(buildAttachBanner({ oneKey: 'F1', cols: 150 })['status-format[0]']).not.toContain('alt+1-9');
+  });
+
+  it('still fits the strip once the switch hint has taken its space', () => {
+    for (const cols of [80, 100, 120, 190]) {
+      const bar = buildAttachBanner({
+        oneKey: 'F1',
+        switchKeys: true,
+        cols,
+        tabs: Array.from({ length: 12 }, (_, i) => ({
+          index: i + 1,
+          label: `w${i + 1}-session-name`,
+          active: i === 1,
+        })),
+      })['status-format[0]'];
+      const visible = bar.replace(/#\[[^\]]*\]/g, '');
+      expect({ cols, fits: visible.length <= cols }).toEqual({ cols, fits: true });
+      expect(visible).toContain('alt+1-9 switch');
+      expect(visible).toContain('back to the codeman dashboard');
+    }
+  });
+
   it('puts ONE instruction on the bar, not a menu of ways out', () => {
     const banner = buildAttachBanner({ prefix: 'C-b', detachKey: 'd', heldAlias: 'C-d', oneKey: 'F1' });
     const bar = banner['status-format[0]'];