docs(16-03): complete route and MCP userId wiring plan

- SUMMARY.md documenting 2 tasks, 13 files modified
- STATE.md updated with plan progress and decisions
- ROADMAP.md marks 16-03 complete
- REQUIREMENTS.md marks MULTI-05 complete

.planning/STATE.md

@@ -26,7 +26,7 @@ See: .planning/PROJECT.md (updated 2026-04-03)
 ## Current Position
 
 Phase: 16 of 18 (Multi-User Data Model)
-Plan: 2 of 4 in current phase
+Plan: 3 of 4 in current phase
 Status: Ready to execute
 Last activity: 2026-04-05
 
@@ -36,9 +36,9 @@ Progress: [#---------] 5% (v2.0 milestone)
 
 **Velocity:**
 
-- Total plans completed: 1 (v2.0 milestone)
-- Average duration: 8min
-- Total execution time: 8min
+- Total plans completed: 2 (v2.0 milestone)
+- Average duration: 7min
+- Total execution time: 14min
 
 *Updated after each plan completion*
 
@@ -60,6 +60,9 @@ Key decisions made during v2.0 execution:
 - [Phase 16]: Category deletion uses dynamic getOrCreateUncategorized per user instead of hardcoded ID
 - [Phase 16]: Candidate operations verify parent thread ownership for cross-user isolation
 - [Phase 16]: syncSetupItems validates both setup and item ownership via inArray
+- [Phase 16-03]: Non-null assertion on c.get("userId") since requireAuth guarantees it
+- [Phase 16-03]: MCP session map stores userId alongside transport for session reuse
+- [Phase 16-03]: Images route unchanged -- no user-scoped DB operations
 
 ### Pending Todos
 
@@ -73,5 +76,5 @@ None active.
 ## Session Continuity
 
 Last session: 2026-04-05T08:45:22.408Z
-Stopped at: Completed 16-02-PLAN.md
+Stopped at: Completed 16-03-PLAN.md
 Resume file: None