fix(memory): scope InsightsRepo operations to userId — M2-001/002

Security audit findings and fixes:

M2-001 — searchByEmbedding: confirmed already user-scoped via WHERE user_id
M2-002 — findByUser: confirmed already user-scoped
M2-002 — decayOldInsights: was global (no userId filter); now requires userId
  param and scopes UPDATE to eq(insights.userId, userId). Added decayAllInsights
  as a separate system-only method for cron tier management.

Additional unscoped operations fixed:
- findById: added userId param + AND eq(userId) to prevent cross-user read
- update: added userId param + AND eq(userId) to prevent cross-user write
- remove: added userId param + AND eq(userId) to prevent cross-user delete
- memory.controller getInsight/removeInsight: now pass user.id for ownership
- summarization.service: switched tier-management cron to decayAllInsights

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/memory/src/insights.ts

@@ -19,8 +19,11 @@ export function createInsightsRepo(db: Db) {
         .limit(limit);
     },
 
-    async findById(id: string): Promise<Insight | undefined> {
-      const rows = await db.select().from(insights).where(eq(insights.id, id));
+    async findById(id: string, userId: string): Promise<Insight | undefined> {
+      const rows = await db
+        .select()
+        .from(insights)
+        .where(and(eq(insights.id, id), eq(insights.userId, userId)));
       return rows[0];
     },
 
@@ -29,17 +32,24 @@ export function createInsightsRepo(db: Db) {
       return rows[0]!;
     },
 
-    async update(id: string, data: Partial<NewInsight>): Promise<Insight | undefined> {
+    async update(
+      id: string,
+      userId: string,
+      data: Partial<NewInsight>,
+    ): Promise<Insight | undefined> {
       const rows = await db
         .update(insights)
         .set({ ...data, updatedAt: new Date() })
-        .where(eq(insights.id, id))
+        .where(and(eq(insights.id, id), eq(insights.userId, userId)))
         .returning();
       return rows[0];
     },
 
-    async remove(id: string): Promise<boolean> {
-      const rows = await db.delete(insights).where(eq(insights.id, id)).returning();
+    async remove(id: string, userId: string): Promise<boolean> {
+      const rows = await db
+        .delete(insights)
+        .where(and(eq(insights.id, id), eq(insights.userId, userId)))
+        .returning();
       return rows.length > 0;
     },
 
@@ -70,8 +80,33 @@ export function createInsightsRepo(db: Db) {
 
     /**
      * Decay relevance scores for old insights that haven't been accessed recently.
+     * Scoped to a specific user to prevent cross-user data mutation.
      */
-    async decayOldInsights(olderThan: Date, decayFactor = 0.95): Promise<number> {
+    async decayOldInsights(userId: string, olderThan: Date, decayFactor = 0.95): Promise<number> {
+      const result = await db
+        .update(insights)
+        .set({
+          relevanceScore: sql`${insights.relevanceScore} * ${decayFactor}`,
+          decayedAt: new Date(),
+          updatedAt: new Date(),
+        })
+        .where(
+          and(
+            eq(insights.userId, userId),
+            lt(insights.updatedAt, olderThan),
+            sql`${insights.relevanceScore} > 0.1`,
+          ),
+        )
+        .returning();
+      return result.length;
+    },
+
+    /**
+     * Decay relevance scores for all users' old insights.
+     * This is a system-level maintenance operation intended for scheduled cron jobs only.
+     * Do NOT expose this through user-facing API endpoints.
+     */
+    async decayAllInsights(olderThan: Date, decayFactor = 0.95): Promise<number> {
       const result = await db
         .update(insights)
         .set({