docs(02-01): complete core overlay merge plan

- SUMMARY.md with 2 task commits, 10 new tests, 3 min duration
- STATE.md updated: Phase 2 in_progress, 02-01 done
- ROADMAP.md updated: 02-01 checked off

.planning/STATE.md

@@ -8,17 +8,17 @@
 
 ## Current Position
 
-**Phase:** 1 — Daemon Decomposition
-**Plan:** 3 of 3 complete (01-01, 01-02, 01-03 done)
-**Status:** phase_complete
-**Progress:** ███░░░░░░░ 1/3 phases complete
+**Phase:** 2 — Config Overlays
+**Plan:** 1 of 2 complete (02-01 done)
+**Status:** in_progress
+**Progress:** █████░░░░░ 1/3 phases complete (02-01 of Phase 2 done)
 
 ## Phase Status
 
 | Phase | Status | Plans |
 |-------|--------|-------|
 | 1 — Daemon Decomposition | **complete** | 3/3 plans complete |
-| 2 — Config Overlays | not_started | — |
+| 2 — Config Overlays | **in_progress** | 1/2 plans complete |
 | 3 — Live Ops Dashboard | not_started | — |
 
 ## Performance Metrics
@@ -34,6 +34,8 @@
 | Plan 01-02 tasks | 3/3 |
 | Plan 01-03 duration | ~8 min |
 | Plan 01-03 tasks | 2/2 |
+| Plan 02-01 duration | 3 min |
+| Plan 02-01 tasks | 2/2 |
 
 ## Accumulated Context
 
@@ -51,6 +53,9 @@
 - Grouped skills/MCP/pairing/gateway/startup into services.ts rather than multiple tiny modules
 - getChannelAgents callback for late-binding channel agents into gateway token usage reporting
 - Type-only imports in index.ts for values only referenced in DaemonContext type definition
+- Overlay merge before env expansion and Zod validation — overlays don't need required fields
+- Arrays in overlays replace (not concat) — explicit override semantics
+- resolveOverlayPath returns path without checking existence — callers decide error handling
 
 ### Technical Notes
 - daemon/index.ts now 140 lines — thin composition root: imports → init calls → wire → return DaemonContext
@@ -59,6 +64,8 @@
 - Tier 1 agent tools (session, agent list, message send, cron) remain in index.ts — they need deps from multiple init functions
 - Web dashboard is vanilla JS SPA at src/gateway/ui/
 - Config loader at src/config/loader.ts, schema at src/config/schema.ts (409 lines)
+- deepMerge + overlay-aware loadConfig in loader.ts; resolveOverlayPath + overlay-aware loadConfigSafe in cli/shared.ts
+- FLYNN_ENV maps to {configDir}/{env}.yaml sibling file; no env = no overlay (backward compatible)
 
 ### TODOs
 _(none)_
@@ -68,9 +75,9 @@ _(none)_
 
 ## Session Continuity
 
-**Last session:** Plan 01-03 (composition root finalization) completed — Phase 1 done
-**Stopped at:** Completed 01-03-PLAN.md (final plan in Phase 1)
-**Next action:** Plan Phase 2 (Config Overlays) — run `/gsd-plan-phase` for Phase 2
+**Last session:** Plan 02-01 (core overlay merge) completed
+**Stopped at:** Completed 02-01-PLAN.md
+**Next action:** Execute Plan 02-02 (doctor overlay validation check)
 
 ---
 *State initialized: 2026-02-09*