fix(terminal): yield only the resize send, and take sizing back on redock

Review of the previous commit found four defects in it.

The guard sat above the local fit, so it suppressed a reflow as well as the
server write. tab-rail-resize performs its single settle-time refit through
sendResize and has no fallback for a truthy activeSessionId, so dragging the
rail stopped reflowing a detached session's terminal in the dashboard. The
mobile-keyboard guard fourteen lines below already draws the line correctly —
withhold the send, never the reflow — and the guard now sits after the fit.

_lastResizeDims is one value for the whole window, and both guards skip
updating it, so while a popup owns a session that value no longer describes
the PTY. _redock repaired it only for the active session. Pop out A, switch to
B, close the popup: selecting A later found unchanged dimensions, returned
"unchanged", and selectSession skipped its 400ms redraw wait — while the
server, comparing against the real pane, did resize and did raise SIGWINCH, so
the fetch painted the pre-redraw frame. _redock now clears the record on every
path, active or not.

_redock could also fire a resize for a session already gone: _onSessionDeleted
redocks before cleanup, so the id can be dead and the request is a guaranteed
404. It now checks the session still exists.

restoreTerminalSize — the header's redraw button and Ctrl+Shift+R — silently
did nothing for a detached session while still reporting success with
dimensions nothing was set to. It now says the session is sized by its own
window, where the same button works.

The `force` comment claimed a client-side dedupe that does not exist; the
deduplication is server-side against the real pane. Corrected to say what the
flag actually buys. The _redock doc comment now records that the function
writes to the server and is not idempotent.

Tests: _redock was the untested half and is the half three of these defects
sit in. It now has coverage for clearing the stale record on both the active
and inactive paths, re-asserting only for the session being shown, and staying
silent for a deleted session. The existing sendResize test now asserts the
local fit still runs.

src/web/public/app.js

@@ -1332,7 +1332,11 @@ class CodemanApp {
     this._redock(id);
   }
 
-  /** Clear all dashboard-side detached state/timers for a session. */
+  /** Clear all dashboard-side detached state/timers for a session, and take its
+   *  sizing back: the popup owned the pane while it was open, so the dashboard's
+   *  record of it is stale and the session it is showing needs re-measuring.
+   *  ⚠️ Not idempotent — each call re-asserts, so a path that redocks twice for
+   *  one close sends two SIGWINCHs. */
   _redock(id) {
     const t = this._detachWatchTimers.get(id);
     if (t) { clearInterval(t); this._detachWatchTimers.delete(id); }
@@ -1340,12 +1344,19 @@ class CodemanApp {
     this._detachOrphanStrikes.delete(id);
     this.detachedWindows.delete(id);
     this._markDetached(id, false);
-    // Sizing comes back with the session. While the popup owned it the dashboard
-    // sent no resizes, so the PTY still holds the popup's geometry; the session
-    // this window is actually showing has to be re-sized to this window, and
-    // `force` is required because the dimensions the dashboard last sent are
-    // the ones it is about to send again.
-    if (id === this.activeSessionId) {
+    // While the popup owned this session the dashboard sent no resizes, so
+    // `_lastResizeDims` — one value for the whole window — no longer describes
+    // the PTY, which the popup has been sizing. Clearing it makes the next
+    // sendResize report truthfully, on every redock path rather than only the
+    // active one: `selectSession` reads that answer to decide whether to wait
+    // for the TUI's redraw, and a false "unchanged" makes it fetch the frame
+    // before the redraw lands.
+    this._lastResizeDims = null;
+    // Sizing comes back with the session. `force` buys a guaranteed repaint for
+    // the case where popup and dashboard happened to agree on a size; the server
+    // already resizes on its own comparison against the real pane whenever the
+    // two differ.
+    if (this.sessions.has(id) && id === this.activeSessionId) {
       this.sendResize(id, { force: true })?.catch?.(() => {});
     }
   }

src/web/public/terminal-ui.js

@@ -3846,6 +3846,14 @@ Object.assign(CodemanApp.prototype, {
       return;
     }
 
+    // The pane belongs to the popup showing it, so this window has nothing to
+    // restore. Say so rather than reporting a size that was never sent — the
+    // same button in that window does the job.
+    if (!this.isSoloWindow && this.detachedSessions?.has(this.activeSessionId)) {
+      this.showToast('This session is sized by its own window', 'warning');
+      return;
+    }
+
     const dims = this.getTerminalDimensions();
     if (!dims) {
       this.showToast('Could not determine terminal size', 'error');
@@ -4827,16 +4835,20 @@ Object.assign(CodemanApp.prototype, {
    * @returns {Promise<boolean>} Whether dimensions changed from the last send
    */
   async sendResize(sessionId, options = {}) {
+    // Fit terminal to container before reading dimensions — ensures local
+    // terminal size matches what we report to the server PTY.
+    if (this.fitAddon) this.fitAddon.fit();
     // One PTY cannot hold two sizes. A detached session is owned by its own
     // window, and the dashboard's terminal is narrower than that window because
     // the session rail takes width the popup does not have — so both sizing it
     // makes the CLI draw frames that fit neither, which garbles the popup. The
     // dashboard yields; the solo window sizes what it alone displays.
     // (_maybeRefetchFullHistory already stands aside for the same reason.)
+    // ⚠️ AFTER the fit, never before: the local reflow keeps the dashboard's own
+    // xterm right, and only the SERVER write is the dashboard's to withhold —
+    // the mobile-keyboard guard below draws exactly this line. tab-rail-resize
+    // performs its one settle-time refit through this call and has no fallback.
     if (!this.isSoloWindow && this.detachedSessions?.has(sessionId)) return false;
-    // Fit terminal to container before reading dimensions — ensures local
-    // terminal size matches what we report to the server PTY.
-    if (this.fitAddon) this.fitAddon.fit();
     const dims = this.getTerminalDimensions();
     if (!dims) return false;
     // Did the dimensions actually change since the last resize we sent? Callers