refactor(app): extract focused window lifetime

Move the exact retryable shutdown manifest, typed root snapshot, terminal reporting, and native-window-last release out of GameWindow. Keep session and GPU convergence as hard barriers while reporting persistent physical callback cleanup without stranding dependent owners.

Co-authored-by: Codex <codex@openai.com>

docs/ISSUES.md

@@ -38,9 +38,12 @@ What does NOT go here:
   publication, and lifecycle resource snapshot source. I.8c makes session
   start the terminal `OnLoad` operation. I.9 corrected the production root to
   invoke the exact tested pipeline and made every consumed platform/settings
-  result explicit. `GameWindow.OnUpdate` and `GameWindow.OnRender` are typed
-  orchestration handoffs and the class is 1,945 raw lines. Checkpoint I is
-  complete; the shutdown/lifetime cutover and closeout remain active in
+  result explicit. Checkpoint J moves the exact retryable shutdown graph into
+  `GameWindowLifetime`, including typed roots, hard session/GPU barriers,
+  reportable physical detach, structured terminal state, and native-window-last
+  release. `GameWindow.OnUpdate` and `GameWindow.OnRender` are typed
+  orchestration handoffs and the class is 1,625 raw lines. Checkpoints K–L—the
+  canonical soak snapshots and final closeout—remain active in
   [`docs/architecture/code-structure.md`](architecture/code-structure.md).
   This is the behavior-preserving prerequisite before new M4 feature bodies.
 - **Connected-gate fidelity:** `#232` adds canonical managed/GPU/cache-owner