routes: phone-context auto-creates session instead of 404

Real-world phone failure observed 2026-05-27:
  POST /troubleshoot/phone-context HTTP/1.1" 404 Not Found
  → App shows "[http-not-found] Session not found"

Root causes the old 404 didn't handle gracefully:
  1. User taps "Share my phone's context" BEFORE the first
     /troubleshoot call — the app has generated a UUID for the
     upcoming session and tries to prime it with phone state. The
     server didn't know about the UUID yet.
  2. Container restarted between sessions — the app's cached
     session_id was valid before restart but the in-memory session
     map is now empty. App shows scary "Session not found" instead
     of just resuming.

Fix: when phone-context receives an unknown session_id, create the
session with that id instead of 404'ing. Idempotent prime-then-
troubleshoot — the next /troubleshoot with the same session_id
finds the session already there with phone_context attached.

The SessionManager.create(session_id=...) path already exists for
caller-supplied IDs in /troubleshoot; this just hooks it into
phone-context too.

Test updated: test_phone_context_unknown_session_returns_404 →
test_phone_context_unknown_session_auto_creates. Asserts the
session is created with the supplied id AND the phone_context is
attached. 244/244 tests still pass.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: ehsan6sha

src/routes/troubleshoot.py

@@ -167,15 +167,35 @@ async def user_reply(req: UserReplyRequest, request: Request) -> Response:
 async def phone_context(req: PhoneContextRequest, request: Request) -> Response:
     """Phase 11 contract: in-memory only. Validates body against
     phone_context.schema.json (the inner shape). On validation error,
-    sanitize SSID/BSSID/IP before any log line."""
+    sanitize SSID/BSSID/IP before any log line.
+
+    Auto-creates the session if the supplied session_id doesn't exist
+    (idempotent prime-then-troubleshoot pattern). This handles two
+    real-world cases observed in production:
+      1. User taps "Share my phone's context" BEFORE starting a
+         /troubleshoot session — the app has generated a UUID and
+         wants to attach the phone snapshot to it; the next
+         /troubleshoot with that same session_id will find the
+         pre-primed session with phone_context already loaded.
+      2. Container restarted between sessions — the app's cached
+         session_id was valid before the restart but the in-memory
+         session map is now empty. Auto-create avoids a confusing
+         "Session not found" error in the UI; the user gets the same
+         outcome as starting fresh, just labelled with the existing
+         session_id.
+    """
     schemas = request.app.state.schemas
     session_mgr = request.app.state.session_manager
     session = session_mgr.get(req.session_id)
     if session is None:
-        return JSONResponse(
-            status_code=404,
-            content=_error_body("session_not_found"),
+        # Don't 404 — create the session with the supplied id. Slide
+        # TTL via touch() at the end so the auto-created session has
+        # a full 30 min before pruning.
+        logger.info(
+            "session_auto_created_via_phone_context session=%s",
+            req.session_id,
         )
+        session = session_mgr.create(session_id=req.session_id)
     pc_validator = schemas.validator_for("phone_context.schema.json")
     errors = list(pc_validator.iter_errors(req.phone_context))
     if errors:

tests/test_troubleshoot_conversational.py

@@ -77,12 +77,34 @@ def _good_phone_context() -> dict:
     }
 
 
-def test_phone_context_unknown_session_returns_404(client):
+def test_phone_context_unknown_session_auto_creates(client):
+    """Behavior change 2026-05-27: phone-context with an unknown
+    session_id now AUTO-CREATES the session (matches the prime-then-
+    troubleshoot pattern + survives container restart). Previously
+    returned 404 with `session_not_found` and the phone app showed
+    "[http-not-found] Session not found" to the user.
+
+    Real-world cases this unblocks:
+      - User taps "Share my phone's context" before starting
+        /troubleshoot — the app's pre-generated session_id should
+        prime the session; the next /troubleshoot with that same
+        session_id finds the session with phone_context already
+        attached.
+      - Container restarted between sessions; the app's cached
+        session_id is no longer in the in-memory map. Auto-create
+        avoids a confusing "Session not found" error in the UI.
+    """
+    mgr = client.app.state.session_manager
+    assert mgr.get("nope") is None
     r = client.post("/troubleshoot/phone-context", json={
         "session_id": "nope",
         "phone_context": _good_phone_context(),
     })
-    assert r.status_code == 404
+    assert r.status_code == 200
+    # Session was created with the supplied id + phone_context attached
+    s = mgr.get("nope")
+    assert s is not None
+    assert s.phone_context == _good_phone_context()
 
 
 def test_phone_context_validates_body_envelope(client):