docs(01-04): complete scan engine plan

- SUMMARY.md with pipeline implementation details
- STATE.md updated with progress and decisions
- ROADMAP.md and REQUIREMENTS.md updated

.planning/STATE.md

@@ -3,14 +3,14 @@ gsd_state_version: 1.0
 milestone: v1.0
 milestone_name: milestone
 status: planning
-stopped_at: Completed 01-foundation 01-02-PLAN.md
-last_updated: "2026-04-04T21:12:49.099Z"
+stopped_at: Completed 01-foundation 01-04-PLAN.md
+last_updated: "2026-04-05T09:22:35.186Z"
 last_activity: 2026-04-04 — Roadmap created, 18 phases defined covering 146 v1 requirements
 progress:
   total_phases: 18
   completed_phases: 0
   total_plans: 5
-  completed_plans: 1
+  completed_plans: 4
   percent: 20
 ---
 
@@ -53,6 +53,7 @@ Progress: [██░░░░░░░░] 20%
 
 *Updated after each plan completion*
 | Phase 01-foundation P02 | 9 | 2 tasks | 11 files |
+| Phase 01-foundation P04 | 5min | 2 tasks | 12 files |
 
 ## Accumulated Context
 
@@ -67,6 +68,7 @@ Recent decisions affecting current work:
 - Roadmap: Verification (Phase 5) requires consent prompt + LEGAL.md — not optional polish
 - [Phase 01-foundation]: Provider YAML in dual locations: providers/ (user-visible) and pkg/providers/definitions/ (embed) — Go embed cannot use '..' paths
 - [Phase 01-foundation]: Aho-Corasick built with DFA=true at NewRegistry() for O(n) keyword pre-filtering across all providers
+- [Phase 01-foundation]: pkg/types/chunk.go breaks engine<->sources circular import; ants pool with WaitGroup+Mutex for detector coordination
 
 ### Pending Todos
 
@@ -81,6 +83,6 @@ None yet.
 
 ## Session Continuity
 
-Last session: 2026-04-04T21:12:49.095Z
-Stopped at: Completed 01-foundation 01-02-PLAN.md
+Last session: 2026-04-05T09:22:35.183Z
+Stopped at: Completed 01-foundation 01-04-PLAN.md
 Resume file: None