fix(sidebar): keep retained agent identity under a bare Terminal title

Hoisting titleShowsNoAgent also broadened it to treat any "Terminal N" as
evidence of exit, which dropped a pane's retained Codex identity
(use-tab-agent-retained-identity). A bare default-shaped title is only
exit evidence when it matches the tab's own defaultTitle.

src/renderer/src/lib/tui-agent-startup.test.ts

@@ -426,7 +426,10 @@ describe('titleShowsNoAgent', () => {
   it('treats shell names and default Terminal titles as no agent', () => {
     expect(titleShowsNoAgent('zsh')).toBe(true)
     expect(titleShowsNoAgent('cmd.exe')).toBe(true)
-    expect(titleShowsNoAgent('Terminal 1')).toBe(true)
+    // A bare "Terminal N" is NOT evidence of exit on its own: a pane can carry a
+    // retained agent identity under that title (use-tab-agent-retained-identity).
+    // It only means "no agent" when it matches the tab's own default title.
+    expect(titleShowsNoAgent('Terminal 1')).toBe(false)
     expect(titleShowsNoAgent('Terminal 1', 'Terminal 1')).toBe(true)
   })
 

src/shared/shell-process-detection.ts

@@ -22,17 +22,10 @@ export function isShellProcess(processName: string): boolean {
   )
 }
 
-const DEFAULT_TERMINAL_TITLE_RE = /^terminal \d+$/i
-
-/** A shell name or the tab's default Terminal title; blank titles are no evidence. */
+/** A shell name or the tab's own neutral default title; blank titles are no evidence. */
 export function titleShowsNoAgent(title: string, defaultTitle?: string): boolean {
   const trimmed = title.trim()
-  return (
-    trimmed.length > 0 &&
-    (isShellProcess(trimmed) ||
-      trimmed === defaultTitle?.trim() ||
-      DEFAULT_TERMINAL_TITLE_RE.test(trimmed))
-  )
+  return trimmed.length > 0 && (isShellProcess(trimmed) || trimmed === defaultTitle?.trim())
 }
 
 // Why: a ConPTY-side buffer clear cannot reach PSReadLine's cached cursor