Clear TODO backlog: --debug/--profile, codex selection, MCP orientation, perf

- Add --debug[=DIR] / --profile[=DIR] flags that write run artefacts
  (patterm.log, events.jsonl, per-child raw PTY captures, CPU + heap
  + goroutine pprof) to a dir without polluting stdout/stderr.
- Strengthen vendor-TUI orientation in three places (MCP
  initialize.instructions, the spawn_agent tool description, and
  help('spawning')) to head off codex's habits of poking the Unix
  socket via perl and shelling out to launch peers — both bypass
  caller identity and produce orphaned top-level tabs.
- Fix click-and-drag text selection from alt-screen TUIs. Host SGR
  mouse reporting now follows the focused child's screen side
  instead of being permanently armed; alt-screen TUIs that need
  mouse re-enable it themselves and the toggle is forwarded.
- Move drawSidebar() off the per-PTY-chunk hot path. Long claude
  session resume was paying a full sidebar rebuild for every
  scrolled chunk; the chrome ticker now drains a dirty flag at 60 Hz.
- Gate the per-chunk Title() CGO poll on a containsOSC scan so
  codex/ratatui's many SGR-only chunks no longer pay a CGO call each.

internal/app/viewport_renderer_test.go

@@ -24,8 +24,36 @@ func TestViewportRendererShiftsCursor(t *testing.T) {
 func TestViewportRendererSwallowsAltScreenToggles(t *testing.T) {
 	vr := newViewportRenderer(newTerminalLayout(120, 40))
 	got := string(vr.Render([]byte("a\x1b[?1049hb\x1b[?1049lc")))
+	// The ?1049h/l toggles themselves must not reach the host (patterm
+	// owns its own alt screen). On the transition we re-sync host mouse
+	// reporting so codex (which doesn't request mouse) lets the user
+	// drag-select; leaving alt re-arms it for primary-screen wheel
+	// scrollback.
+	want := "a\x1b[?1000l\x1b[?1006lb\x1b[?1000h\x1b[?1006hc"
+	if got != want {
+		t.Fatalf("alt-screen toggles: got %q want %q", got, want)
+	}
+}
+
+func TestViewportRendererMouseTrackingFilteredOnPrimary(t *testing.T) {
+	vr := newViewportRenderer(newTerminalLayout(120, 40))
+	got := string(vr.Render([]byte("a\x1b[?1000lb\x1b[?1000hc")))
 	if got != "abc" {
-		t.Fatalf("alt-screen toggles: got %q", got)
+		t.Fatalf("mouse mode on primary should be filtered: got %q", got)
+	}
+}
+
+func TestViewportRendererMouseTrackingForwardedOnAlt(t *testing.T) {
+	vr := newViewportRenderer(newTerminalLayout(120, 40))
+	// Enter alt; subsequent mouse-mode toggles should reach the host so
+	// alt-screen TUIs (vim, less) can run with mouse on, and selection-
+	// using ones (codex) stay with mouse off.
+	got := string(vr.Render([]byte("\x1b[?1049h\x1b[?1000lx\x1b[?1000hy")))
+	if !strings.Contains(got, "\x1b[?1000l") {
+		t.Fatalf("alt-screen mouse disable should reach host: %q", got)
+	}
+	if !strings.Contains(got, "\x1b[?1000h") {
+		t.Fatalf("alt-screen mouse enable should reach host: %q", got)
 	}
 }