fix(backend): sprint 3 post-review — migration nullable + dead code + tactic names + tests

- Migration 0003: enforce techniques NOT NULL via batch_alter_table (AC-13.1 DDL spec)
- Migration 0003: remove unused _sims table proxy and orphaned column/table imports
- mitre.py: rename _TACTIC_NAMES → TACTIC_NAMES (public); add all 12 correct display names
- mitre.py: use TACTIC_NAMES dict in _build_matrix() to fix "Command And Control" → "Command and Control"
- test_mitre.py: add T1071 fixture entry under command-and-control; assert tactic_name lowercase "and"
- test_simulations_techniques.py: real Alembic round-trip test asserting techniques NOT NULL after upgrade

backend/tests/test_simulations_techniques.py

@@ -366,3 +366,64 @@ def test_migration_backfill_logic() -> None:
     ]
     assert _backfill(None, None) == []
     assert _backfill("T1059", None) == [{"id": "T1059", "name": ""}]
+
+
+def test_migration_0003_techniques_not_null_after_upgrade() -> None:
+    """Run migration 0003 upgrade() against a real SQLite DB and assert techniques is NOT NULL."""
+    import importlib
+    import json as _json
+
+    import sqlalchemy as _sa
+    from alembic.operations import Operations
+    from alembic.runtime.migration import MigrationContext
+
+    engine = _sa.create_engine("sqlite:///:memory:")
+    with engine.begin() as conn:
+        # Create the pre-migration schema (0002 state).
+        conn.execute(_sa.text(
+            "CREATE TABLE simulations ("
+            "  id INTEGER PRIMARY KEY,"
+            "  mitre_technique_id VARCHAR(32),"
+            "  mitre_technique_name VARCHAR(255)"
+            ")"
+        ))
+        conn.execute(_sa.text(
+            "INSERT INTO simulations (id, mitre_technique_id, mitre_technique_name)"
+            " VALUES (1, 'T1059', 'Command and Scripting Interpreter')"
+        ))
+        conn.execute(_sa.text(
+            "INSERT INTO simulations (id, mitre_technique_id, mitre_technique_name)"
+            " VALUES (2, NULL, NULL)"
+        ))
+
+    # Run upgrade() via Alembic Operations context.
+    with engine.begin() as conn:
+        ctx = MigrationContext.configure(conn, opts={"as_sql": False})
+        ops = Operations(ctx)
+
+        # Patch the module-level proxy so the migration's op.* calls work.
+        import alembic.op as _op_module
+        _op_module._proxy = ops  # type: ignore[attr-defined]
+
+        spec = importlib.util.spec_from_file_location(
+            "mig_0003",
+            "/home/user/Documents/01_Projects/mimic/.claude/worktrees/sprint-3-mitre-matrix/backend/migrations/versions/0003_simulation_techniques_array.py",
+        )
+        assert spec is not None and spec.loader is not None
+        mig = importlib.util.module_from_spec(spec)
+        spec.loader.exec_module(mig)  # type: ignore[union-attr]
+        mig.upgrade()
+
+    # Verify schema: techniques column exists and is NOT NULL.
+    insp = _sa.inspect(engine)
+    cols = {c["name"]: c for c in insp.get_columns("simulations")}
+    assert "techniques" in cols, "techniques column must exist after upgrade"
+    assert cols["techniques"]["nullable"] is False, "techniques must be NOT NULL after upgrade"
+    assert "mitre_technique_id" not in cols
+    assert "mitre_technique_name" not in cols
+
+    # Verify data was backfilled correctly.
+    with engine.connect() as conn:
+        rows = conn.execute(_sa.text("SELECT id, techniques FROM simulations ORDER BY id")).fetchall()
+    assert _json.loads(rows[0][1]) == [{"id": "T1059", "name": "Command and Scripting Interpreter"}]
+    assert _json.loads(rows[1][1]) == []