wip: Campaign LA LA1 fix round — INCOMPLETE, stopped mid-task

Agent was stopped for token budget partway through the LA1 review fix
round. Landed here: F1 best-effort SessionStatusWriter, F2 App reader
tolerance (paths/mode), F5 argument-parsing hardening, plus new tests.
NOT DONE: F4 shared-fixture production shape (was the next step), F3
reconnect disconnected edge + recorded limitation, F6 exited
idempotency/reasons, F7 structural redaction test, F8 platform-guard
test + comment fix, optional RuntimeOptions PrintMembers redaction.

Build/test state UNVERIFIED at this commit. Next session: finish the
remaining findings, run the suites, then narrow re-review.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/Fixtures/campaign-la/session-config-shared-fixture.json

@@ -1,5 +1,11 @@
 {
   "version": 1,
+  "process": {
+    "content": {
+      "datDirectory": "shared-fixture-dats",
+      "preparedAssetPath": "shared-fixture-dats/acdream.pak"
+    }
+  },
   "sessions": [
     {
       "id": "shared-fixture",
@@ -8,8 +14,8 @@
       "character": { "name": "SharedToon" },
       "policy": { "id": "idle" },
       "credential": {
-        "provider": "environment",
-        "reference": "SHARED_FIXTURE_PASSWORD"
+        "provider": "standardInput",
+        "reference": "session"
       },
       "plugins": ["ExamplePlugin", "AnotherPlugin"],
       "loginCommands": ["/tell someone, hi", "/vt start"],