diff --git a/.planning/STATE.md b/.planning/STATE.md
index 47f9a49..20ebc7c 100644
--- a/.planning/STATE.md
+++ b/.planning/STATE.md
@@ -9,19 +9,19 @@ See: .planning/PROJECT.md (updated 2026-02-04)
 
 ## Current Position
 
-Phase: 19 of 21 (Agent Inbox) - IN PROGRESS
-Plan: 3 of 4 in current phase
-Status: Plan 19-03 complete
-Last activity: 2026-02-04 - Completed 19-03-PLAN.md (QuestionForm & Input Components)
+Phase: 19 of 21 (Agent Inbox) - COMPLETE
+Plan: 4 of 4 in current phase
+Status: Phase 19 complete
+Last activity: 2026-02-04 - Completed 19-04-PLAN.md (Inbox Page Assembly)
 
 Progress: █████████░ 98%
 
 ## Performance Metrics
 
 **Velocity:**
-- Total plans completed: 69
+- Total plans completed: 70
 - Average duration: 3 min
-- Total execution time: 195 min
+- Total execution time: 197 min
 
 **By Phase (v1.0):**
 
@@ -222,6 +222,9 @@ Recent decisions affecting current work:
 - 19-03: OptionGroup value is always string (comma-joined for multi-select) for consistent interface
 - 19-03: QuestionForm owns answer state internally via useState (self-contained component)
 - 19-03: allowOther defaults to true per plan spec
+- 19-04: Detail panel inline in page file (not a separate component) — page-specific layout
+- 19-04: useUtils() for query invalidation on mutation success (same pattern as initiative detail)
+- 19-04: Serialize agent/message data to string dates for InboxList props (wire format consistency)
 
 ### Pending Todos
 
@@ -244,5 +247,5 @@ None.
 ## Session Continuity
 
 Last session: 2026-02-04
-Stopped at: Completed 19-03 (QuestionForm & Input Components)
+Stopped at: Completed 19-04 (Inbox Page Assembly) — Phase 19 complete
 Resume file: None
diff --git a/.planning/phases/19-agent-inbox/19-04-SUMMARY.md b/.planning/phases/19-agent-inbox/19-04-SUMMARY.md
new file mode 100644
index 0000000..6cfcd7a
--- /dev/null
+++ b/.planning/phases/19-agent-inbox/19-04-SUMMARY.md
@@ -0,0 +1,96 @@
+---
+phase: 19-agent-inbox
+plan: 04
+subsystem: ui
+tags: [react, trpc, tanstack-query, tailwind, inbox, agent-questions]
+
+# Dependency graph
+requires:
+  - phase: 19-agent-inbox
+    provides: InboxList, MessageCard, QuestionForm, OptionGroup, FreeTextInput components and tRPC procedures (getAgentQuestions, listWaitingAgents)
+  - phase: 18-initiative-detail
+    provides: Query management patterns, mutation/invalidation flow, loading/error state patterns
+provides:
+  - Fully functional Agent Inbox page at /inbox route
+  - Answer submission flow (QuestionForm → resumeAgent mutation → query invalidation)
+  - Notification dismissal flow (respondToMessage mutation)
+  - Two-column responsive layout with detail panel
+affects: [21-polish-integration]
+
+# Tech tracking
+tech-stack:
+  added: []
+  patterns: ["Two-column inbox layout with list + detail panel", "Conditional query enabling via selectedAgentId"]
+
+key-files:
+  created: []
+  modified:
+    - packages/web/src/routes/inbox.tsx
+
+key-decisions:
+  - "Detail panel is inline in page file (not a separate component) — page-specific layout"
+  - "useUtils() for query invalidation on mutation success (same pattern as initiative detail)"
+  - "Serialize agent/message data to string dates for InboxList props (wire format consistency)"
+
+patterns-established:
+  - "Conditional tRPC query: enabled: !!selectedId pattern for detail-on-select"
+  - "Mutation → invalidate → clear selection flow for submit/dismiss actions"
+
+# Metrics
+duration: 2min
+completed: 2026-02-04
+---
+
+# Phase 19 Plan 04: Inbox Page Assembly Summary
+
+**Agent Inbox page wired with tRPC data fetching, two-column layout (InboxList + detail panel), answer submission via resumeAgent, and notification dismissal via respondToMessage**
+
+## Performance
+
+- **Duration:** 2 min
+- **Started:** 2026-02-04
+- **Completed:** 2026-02-04
+- **Tasks:** 2
+- **Files modified:** 1
+
+## Accomplishments
+- Replaced stub inbox page with full implementation connecting all Phase 19 components
+- Wired InboxList with listWaitingAgents and listMessages tRPC queries
+- Detail panel shows agent header, structured QuestionForm, or notification content based on selection
+- Answer submission calls resumeAgent mutation and refreshes data on success
+- Notification messages can be dismissed via respondToMessage mutation
+- Loading and error states handled following initiative detail page patterns
+
+## Task Commits
+
+Each task was committed atomically:
+
+1. **Task 1: Wire inbox page with data fetching, detail panel, and answer submission** - `3cac453` (feat)
+2. **Task 2: Full build verification and integration check** - No code changes needed (all checks pass)
+
+## Files Created/Modified
+- `packages/web/src/routes/inbox.tsx` - Full inbox page with tRPC queries, mutations, InboxList, QuestionForm, detail panel, loading/error states
+
+## Decisions Made
+- Detail panel implemented inline in the page file (not a separate component) since it's page-specific layout
+- useUtils() for query invalidation on mutation success, following the same pattern used in initiative detail page
+- Agent/message data serialized to string dates before passing to InboxList (wire format consistency with other components)
+
+## Deviations from Plan
+
+None - plan executed exactly as written.
+
+## Issues Encountered
+None
+
+## User Setup Required
+None - no external service configuration required.
+
+## Next Phase Readiness
+- Phase 19 (Agent Inbox) is complete — all 4 plans executed
+- Inbox page fully functional with list view, detail panel, question answering, and notification dismissal
+- Ready for Phase 20+ (polish and integration)
+
+---
+*Phase: 19-agent-inbox*
+*Completed: 2026-02-04*