feat: add diagnostic interview loop

.planning/STATE.md

@@ -7,7 +7,7 @@ See: `.planning/PROJECT.md` (updated 2026-04-26)
 **Core value:** The user should feel and prove that they are becoming more
 interview-ready after each short practice loop.
 
-**Current focus:** Phase 2 planning: Diagnostic Interview Loop.
+**Current focus:** Phase 3 planning: Learner Memory.
 
 ## Current Decisions
 
@@ -22,14 +22,16 @@ interview-ready after each short practice loop.
 - First interview track is Backend Developer Interview.
 - Phase 1 has context, research, and plan artifacts.
 - Phase 1 Go backend scaffold is implemented and verified.
+- Phase 2 diagnostic interview loop is implemented and verified with in-memory
+  sessions.
 
 ## Next Actions
 
-1. Plan Phase 2 diagnostic interview loop with GSD.
+1. Plan Phase 3 learner memory with GSD.
 2. Keep `docs/planning/WORKFLOW_CONTRACTS.md` aligned with Go structs during
    future workflow implementation.
-3. Decide whether Phase 2 starts with in-memory diagnostic sessions or a small
-   persistence boundary.
+3. Decide whether Phase 3 learner memory remains in-memory for MVP proof or
+   introduces a small persistence boundary.
 
 ## Validation Log
 
@@ -40,6 +42,9 @@ interview-ready after each short practice loop.
 - 2026-04-26: Phase 1 implementation verified with `go test ./...`,
   `openspec validate bootstrap-job-tutor-platform --strict`, and Go source
   line-count check.
+- 2026-04-26: Phase 2 implementation verified with `go test ./...`, live
+  `/healthz` smoke, live diagnostic create/answer/get smoke, OpenSpec, and Go
+  source line-count check.
 
 ---
 *State initialized: 2026-04-26.*