feat(terminal): tmux pane-buffer primitives and session/render reliability

Mode-agnostic terminal foundation extracted from the downstream branch:
- formatPaneSnapshot: SGR/grapheme-aware tmux pane capture + active-pane
  resolution, with OSC/CSI redraw suppression and the buffer-load owner-token
  race fix on the terminal fetch path
- socket-correct tmux lifecycle: dedicated -L socket and /tmp launch cwd in
  createSession (restores the FUSE/getcwd hardening from #110), and a
  socket-aware re-attach window-size query (avoids the 120x40 flicker)
- inline-rename: commit/cancel state handling clears _activeRename and skips
  the API call on cancel
- selectSession: restored detached-window raise short-circuit

The codex-specific xterm snapshot/replay, the vendored serialize addon, and
the synchronous live pane-capture on the request path are intentionally
excluded: they depend on a 'codex' SessionMode that doesn't exist on master
and are deferred to COD-34 (which introduces that mode). The capture
primitives remain exported for COD-34 to build on.

Co-Authored-By: Saqeb Akhter <saqeb.akhter@gmail.com>

src/web/routes/session-routes.ts

@@ -889,8 +889,9 @@ export function registerSessionRoutes(
     const query = req.query as { tail?: string };
     const session = findSessionOrFail(ctx, id);
 
+    const rawBuffer = session.terminalBuffer;
     const tailBytes = query.tail ? parseInt(query.tail, 10) : 0;
-    const fullSize = session.terminalBufferLength;
+    const fullSize = rawBuffer.length;
     let truncated = false;
     let cleanBuffer: string;
 
@@ -898,7 +899,7 @@ export function registerSessionRoutes(
     // During long thinking phases, Ink rewrites the same rows thousands of times
     // (500KB+). Without stripping, tail mode returns only spinner frames and
     // the terminal appears empty when switching tabs.
-    const strippedBuffer = stripInkRedrawBloat(session.terminalBuffer);
+    const strippedBuffer = stripInkRedrawBloat(rawBuffer);
 
     if (tailBytes > 0 && strippedBuffer.length > tailBytes) {
       // Fast path: tail from the end, skip expensive banner search on full 2MB buffer.