fix(memory): address review findings from Issue #88

Fixes based on multi-agent review:

Model Improvements:
- Remove duplicate index ix_procedures_agent_type (already indexed via Column)
- Fix postgresql_where to use text() instead of string literal in Fact model
- Add thread-safety to Procedure.success_rate property (snapshot values)

Data Integrity Constraints:
- Add CheckConstraint for Episode: importance_score 0-1, duration >= 0, tokens >= 0
- Add CheckConstraint for Fact: confidence 0-1
- Add CheckConstraint for Procedure: success_count >= 0, failure_count >= 0

Migration Updates:
- Add check constraints creation in upgrade()
- Add check constraints removal in downgrade()

Note: SQLAlchemy Column default=list is correct (callable factory pattern)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/alembic/versions/0005_add_memory_system_tables.py

@@ -361,13 +361,53 @@ def upgrade() -> None:
         unique=True,
     )
     op.create_index("ix_procedures_project_name", "procedures", ["project_id", "name"])
-    op.create_index("ix_procedures_agent_type", "procedures", ["agent_type_id"])
+    # Note: agent_type_id already indexed via ix_procedures_agent_type_id (line 354)
     op.create_index(
         "ix_procedures_success_rate",
         "procedures",
         ["success_count", "failure_count"],
     )
 
+    # =========================================================================
+    # Add check constraints for data integrity
+    # =========================================================================
+
+    # Episode constraints
+    op.create_check_constraint(
+        "ck_episodes_importance_range",
+        "episodes",
+        "importance_score >= 0.0 AND importance_score <= 1.0",
+    )
+    op.create_check_constraint(
+        "ck_episodes_duration_positive",
+        "episodes",
+        "duration_seconds >= 0.0",
+    )
+    op.create_check_constraint(
+        "ck_episodes_tokens_positive",
+        "episodes",
+        "tokens_used >= 0",
+    )
+
+    # Fact constraints
+    op.create_check_constraint(
+        "ck_facts_confidence_range",
+        "facts",
+        "confidence >= 0.0 AND confidence <= 1.0",
+    )
+
+    # Procedure constraints
+    op.create_check_constraint(
+        "ck_procedures_success_positive",
+        "procedures",
+        "success_count >= 0",
+    )
+    op.create_check_constraint(
+        "ck_procedures_failure_positive",
+        "procedures",
+        "failure_count >= 0",
+    )
+
     # =========================================================================
     # Create memory_consolidation_log table
     # Tracks consolidation jobs
@@ -432,6 +472,14 @@ def upgrade() -> None:
 def downgrade() -> None:
     """Drop Agent Memory System tables."""
 
+    # Drop check constraints first
+    op.drop_constraint("ck_procedures_failure_positive", "procedures", type_="check")
+    op.drop_constraint("ck_procedures_success_positive", "procedures", type_="check")
+    op.drop_constraint("ck_facts_confidence_range", "facts", type_="check")
+    op.drop_constraint("ck_episodes_tokens_positive", "episodes", type_="check")
+    op.drop_constraint("ck_episodes_duration_positive", "episodes", type_="check")
+    op.drop_constraint("ck_episodes_importance_range", "episodes", type_="check")
+
     # Drop tables in reverse order (dependencies first)
     op.drop_table("memory_consolidation_log")
     op.drop_table("procedures")