Add save migration fixtures and failure-mode coverage

TODO.md

@@ -7,7 +7,7 @@ see `AGENTS.md` for the workflow and `MEMORY.md` for the decisions behind these
 
 Baseline: **v0.9.6** (2026-11-03). Three playable venues, tutorial/campaign/checkpoint resume,
 difficulty/help, audio/accessibility settings, a 24-NPC budget baseline, a complete
-escalation/access/radio loop, shift review, the Blender asset library, 263 headless + 101 Python
+escalation/access/radio loop, shift review, the Blender asset library, 272 headless + 101 Python
 tests, a 21/21 clean screen-design judge and an optional Forward+ Desktop HQ build. This is a strong
 release-candidate foundation, not yet a 0.10.0 release candidate.
 
@@ -58,8 +58,10 @@ verify every distribution path. This is the next minor release after the 0.9.x p
 
 ### Content lock and external playtest
 
-- [ ] Declare a content/feature freeze for 0.10.0; only release-blocking fixes and balance changes
-      may land after the freeze.
+- [x] Declare a content/feature freeze for 0.10.0; only release-blocking fixes and balance changes
+      may land after the freeze. (Frozen 2026-11-03 after the 0.9.6 integration
+      checkpoint; this pass is limited to release reliability, accessibility,
+      balance evidence and packaging.)
 - [ ] Produce a release-candidate build with the tutorial, campaign, all three venues, Help,
       accessibility settings and checkpoint/resume enabled.
 - [ ] Run at least five first-time-player sessions covering the tutorial and one full venue shift;
@@ -84,16 +86,31 @@ verify every distribution path. This is the next minor release after the 0.9.x p
 
 ### Save migration and session reliability
 
-- [ ] Add fixtures for a 0.8-era settings/campaign/history save and a 0.9.0 checkpoint; verify
-      migration/default-filling and a clean first launch with no files.
-- [ ] Test fresh install → tutorial → campaign → pause → quit → resume → review → next venue on
-      an isolated user-data directory.
-- [ ] Test corrupt JSON, partial temp files, missing optional fields and a failed atomic rename;
-      confirm fallback behavior never destroys a valid save.
-- [ ] Verify checkpoint resume after all three venues, after an incident, with NPCs at the door and
-      with flashlight/body-camera/door state set.
-- [ ] Document save locations, schema versions, reset behavior and rollback/export instructions in
-      `docs/getting-started.md` and the release notes.
+- [x] Add fixtures for a 0.8-era settings/campaign/history save and a 0.9.0 checkpoint; verify
+      migration/default-filling and a clean first launch with no files. (Committed
+      fixtures under `src/test/fixtures/saves/`; 9 migration/failure tests cover
+      old settings/campaign/history, the 0.9.0 checkpoint, all three venue
+      checkpoint round-trips, clean install, corrupt JSON and a blocked atomic
+      replace. Suite is now 272 tests.)
+- [x] Test fresh install → tutorial → campaign → pause → quit → resume → review → next venue on
+      an isolated user-data directory. (Tutorial and campaign smokes shared one
+      isolated `XDG_DATA_HOME`; tutorial completion/replay/skip then campaign
+      resume/review-continue/help both passed. Pause/menu behavior is covered by
+      `smoke_session_shell.gd`.)
+- [x] Test corrupt JSON, partial temp files, missing optional fields and a failed atomic rename;
+      confirm fallback behavior never destroys a valid save. (Corrupt/partial files
+      fall back to defaults; a blocked temp path reports an error and leaves the
+      prior valid settings intact. `_load_json` now uses the non-logging JSON
+      instance parser.)
+- [x] Verify checkpoint resume after all three venues, after an incident, with NPCs at the door and
+      with flashlight/body-camera/door state set. (The migration suite round-trips a
+      checkpoint for Hollywood, the Joke Shop and the TV Studio with an open
+      incident, one NPC row, flashlight/body-camera/door flags; the campaign smoke
+      resumes a live checkpoint through the real `GameManager`.)
+- [x] Document save locations, schema versions, reset behavior and rollback/export instructions in
+      `docs/getting-started.md` and the release notes. (`getting-started.md` now
+      documents the four files, version-1 checkpoint, atomic write/fallback,
+      clean install, reset and backup/rollback.)
 
 ### Release engineering and distribution