feat: migration 009 — temporal edge schema for production

Replaces old memory_edge (child_sha/parent_sha node graph) with
temporal edge schema (Zep §2.2.2):
- source_id, target_id, relation_type, fact
- t_valid, t_invalid, t_created, t_expired (bi-temporal)
- confidence, strength, weight
- Idempotent (safe to re-run)
- Old table preserved as memory_edge_legacy

Applied to production CNPG cluster. Schema verified matching code.

crates/mem-store/migrations/009_temporal_edge_migration.sql

@@ -0,0 +1,55 @@
+-- Migration 009: Temporal edge schema (Zep paper §2.2.2)
+-- Replaces old memory_edge (child_sha/parent_sha node graph)
+-- with temporal edge schema supporting relation types, facts, and validity periods.
+-- Idempotent: safe to run multiple times.
+
+-- Rename old table if it still exists (skip if already migrated)
+DO $$
+BEGIN
+    IF EXISTS (SELECT 1 FROM information_schema.tables WHERE table_name = 'memory_edge'
+               AND EXISTS (SELECT 1 FROM information_schema.columns 
+                          WHERE table_name = 'memory_edge' AND column_name = 'child_sha'))
+    THEN
+        ALTER TABLE memory_edge RENAME TO memory_edge_legacy;
+    END IF;
+END $$;
+
+-- Create temporal edge table
+CREATE TABLE IF NOT EXISTS memory_edge (
+    id TEXT PRIMARY KEY,
+    project_id TEXT NOT NULL DEFAULT 'default',
+    source_id TEXT NOT NULL,
+    target_id TEXT NOT NULL,
+    relation_type TEXT NOT NULL DEFAULT '',
+    fact TEXT NOT NULL DEFAULT '',
+    weight REAL NOT NULL DEFAULT 1.0,
+    strength REAL DEFAULT 1.0,
+    confidence REAL DEFAULT 0.8,
+    t_valid TIMESTAMPTZ,
+    t_invalid TIMESTAMPTZ,
+    t_created TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    t_expired TIMESTAMPTZ,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    episode_id TEXT,
+    deleted_at TIMESTAMPTZ
+);
+
+-- Ensure app user owns the table
+DO $$ BEGIN
+    IF EXISTS (SELECT 1 FROM pg_roles WHERE rolname = 'app') THEN
+        ALTER TABLE memory_edge OWNER TO app;
+    END IF;
+END $$;
+
+CREATE INDEX IF NOT EXISTS idx_memory_edge_source ON memory_edge(source_id);
+CREATE INDEX IF NOT EXISTS idx_memory_edge_target ON memory_edge(target_id);
+CREATE INDEX IF NOT EXISTS idx_memory_edge_project ON memory_edge(project_id);
+CREATE INDEX IF NOT EXISTS idx_memory_edge_relation ON memory_edge(relation_type);
+
+-- Ensure memory_entity has deleted_at for BFS soft-delete queries
+ALTER TABLE memory_entity ADD COLUMN IF NOT EXISTS deleted_at TIMESTAMPTZ;
+
+-- ROLLBACK instructions:
+-- DROP TABLE IF EXISTS memory_edge;
+-- ALTER TABLE IF EXISTS memory_edge_legacy RENAME TO memory_edge;