feat(FN-1690): add RoadmapStore with SQLite persistence

- Implement RoadmapStore with CRUD operations for roadmaps, milestones, and features
- Add roadmap schema migration v32 with roadmaps, roadmap_milestones, and roadmap_features tables
- Add covering indexes for deterministic ordering within roadmaps and milestones
- Wire RoadmapStore access via TaskStore.getRoadmapStore()
- Update architecture.md documentation with RoadmapStore persistence
- Add comprehensive tests for RoadmapStore CRUD and ordering
- Update db.test.ts with schema v32 assertions
- Add UpdateInput type imports to task-documents.test.ts
- Export RoadmapStore from core index.ts

packages/core/src/db.ts

@@ -59,7 +59,7 @@ export function fromJson<T>(json: string | null | undefined): T | undefined {
 
 // ── Schema Definition ────────────────────────────────────────────────
 
-const SCHEMA_VERSION = 31;
+const SCHEMA_VERSION = 32;
 
 function normalizeTaskComments(
   steeringComments: SteeringComment[] | undefined,
@@ -1176,6 +1176,66 @@ export class Database {
         this.db.exec(`CREATE INDEX IF NOT EXISTS idxFixLineageRunId ON mission_fix_feature_lineage(runId)`);
       });
     }
+
+    // Roadmap persistence tables (FN-1690)
+    // Standalone roadmap: Roadmap → RoadmapMilestone → RoadmapFeature
+    // with deterministic ordering indexes and FK cascade integrity
+    if (version < 32) {
+      this.applyMigration(32, () => {
+        // Roadmaps table
+        this.db.exec(`
+          CREATE TABLE IF NOT EXISTS roadmaps (
+            id TEXT PRIMARY KEY,
+            title TEXT NOT NULL,
+            description TEXT,
+            createdAt TEXT NOT NULL,
+            updatedAt TEXT NOT NULL
+          )
+        `);
+
+        // Roadmap milestones table
+        this.db.exec(`
+          CREATE TABLE IF NOT EXISTS roadmap_milestones (
+            id TEXT PRIMARY KEY,
+            roadmapId TEXT NOT NULL,
+            title TEXT NOT NULL,
+            description TEXT,
+            orderIndex INTEGER NOT NULL,
+            createdAt TEXT NOT NULL,
+            updatedAt TEXT NOT NULL,
+            FOREIGN KEY (roadmapId) REFERENCES roadmaps(id) ON DELETE CASCADE
+          )
+        `);
+
+        // Roadmap features table
+        this.db.exec(`
+          CREATE TABLE IF NOT EXISTS roadmap_features (
+            id TEXT PRIMARY KEY,
+            milestoneId TEXT NOT NULL,
+            title TEXT NOT NULL,
+            description TEXT,
+            orderIndex INTEGER NOT NULL,
+            createdAt TEXT NOT NULL,
+            updatedAt TEXT NOT NULL,
+            FOREIGN KEY (milestoneId) REFERENCES roadmap_milestones(id) ON DELETE CASCADE
+          )
+        `);
+
+        // Covering index for deterministic milestone ordering within a roadmap
+        // Covers: WHERE roadmapId = ? ORDER BY orderIndex ASC, createdAt ASC, id ASC
+        this.db.exec(`
+          CREATE INDEX IF NOT EXISTS idxRoadmapMilestonesRoadmapOrder
+            ON roadmap_milestones(roadmapId, orderIndex, createdAt, id)
+        `);
+
+        // Covering index for deterministic feature ordering within a milestone
+        // Covers: WHERE milestoneId = ? ORDER BY orderIndex ASC, createdAt ASC, id ASC
+        this.db.exec(`
+          CREATE INDEX IF NOT EXISTS idxRoadmapFeaturesMilestoneOrder
+            ON roadmap_features(milestoneId, orderIndex, createdAt, id)
+        `);
+      });
+    }
   }
 
   /**