backend/app/api/simulations.py

@@ -121,7 +121,7 @@ def transition_simulation(sid: int):
 
 
 # ---------------------------------------------------------------------------
-# MITRE autocomplete
+# MITRE autocomplete + matrix
 # ---------------------------------------------------------------------------
 
 
@@ -136,3 +136,14 @@ def mitre_techniques():
     q = request.args.get("q", "").strip()
     results = mitre_svc.search(q)
     return jsonify(results), 200
+
+
+@simulations_bp.get("/api/mitre/matrix")
+@login_required
+def mitre_matrix():
+    from backend.app.services import mitre as mitre_svc
+
+    if not mitre_svc.mitre_loaded:
+        return jsonify({"error": "mitre bundle not loaded"}), 503
+
+    return jsonify(mitre_svc.get_matrix()), 200

backend/app/models/simulation.py

@@ -25,8 +25,7 @@ class Simulation(db.Model):  # type: ignore[name-defined]
         index=True,
     )
     name = db.Column(db.String(255), nullable=False)
-    mitre_technique_id = db.Column(db.String(32), nullable=True)
-    mitre_technique_name = db.Column(db.String(255), nullable=True)
+    techniques = db.Column(db.JSON, nullable=False, default=list)
     description = db.Column(db.Text, nullable=True)
     commands = db.Column(db.Text, nullable=True)
     prerequisites = db.Column(db.Text, nullable=True)

backend/app/serializers.py

@@ -20,13 +20,22 @@ def serialize_user_brief(user: User) -> dict[str, Any]:
     return {"id": user.id, "username": user.username}
 
 
+def _enrich_techniques(raw: list[dict[str, Any]]) -> list[dict[str, Any]]:
+    """Attach tactics to each {id, name} snapshot from the MITRE service."""
+    from backend.app.services import mitre as mitre_svc
+
+    return [
+        {"id": t["id"], "name": t["name"], "tactics": mitre_svc.get_tactics(t["id"])}
+        for t in (raw or [])
+    ]
+
+
 def serialize_simulation(simulation: Simulation) -> dict[str, Any]:
     return {
         "id": simulation.id,
         "engagement_id": simulation.engagement_id,
         "name": simulation.name,
-        "mitre_technique_id": simulation.mitre_technique_id,
-        "mitre_technique_name": simulation.mitre_technique_name,
+        "techniques": _enrich_techniques(simulation.techniques or []),
         "description": simulation.description,
         "commands": simulation.commands,
         "prerequisites": simulation.prerequisites,

backend/app/services/mitre.py

@@ -8,11 +8,30 @@ from typing import Any
 
 logger = logging.getLogger(__name__)
 
-# Absolute path to the committed bundle.
 _BUNDLE_PATH = Path(__file__).parent.parent.parent / "data" / "mitre" / "enterprise-attack.json"
 
+# Canonical Enterprise tactic order (12 tactics).
+_TACTIC_ORDER = [
+    "initial-access",
+    "execution",
+    "persistence",
+    "privilege-escalation",
+    "defense-evasion",
+    "credential-access",
+    "discovery",
+    "lateral-movement",
+    "collection",
+    "command-and-control",
+    "exfiltration",
+    "impact",
+]
+
 mitre_loaded: bool = False
 _index: list[dict[str, Any]] = []
+_tactics_by_technique: dict[str, list[str]] = {}
+_name_by_id: dict[str, str] = {}
+# matrix: list of tactic dicts (built once at load time)
+_matrix: list[dict[str, Any]] = []
 
 
 def _extract_tactics(obj: dict[str, Any]) -> list[str]:
@@ -20,7 +39,7 @@ def _extract_tactics(obj: dict[str, Any]) -> list[str]:
     return [
         p["phase_name"]
         for p in phases
-        if isinstance(p, dict) and "phase_name" in p
+        if isinstance(p, dict) and "phase_name" in p and p.get("kill_chain_name") == "mitre-attack"
     ]
 
 
@@ -31,9 +50,65 @@ def _get_external_id(obj: dict[str, Any]) -> str | None:
     return None
 
 
+def _is_subtechnique(tech_id: str) -> bool:
+    return "." in tech_id
+
+
+def _parent_id(sub_id: str) -> str:
+    return sub_id.split(".")[0]
+
+
+def _build_matrix(entries: list[dict[str, Any]]) -> list[dict[str, Any]]:
+    """Build the tactic → techniques → subtechniques tree."""
+    # Group top-level techniques by tactic.
+    tactic_techs: dict[str, list[dict[str, Any]]] = {t: [] for t in _TACTIC_ORDER}
+
+    for entry in entries:
+        if _is_subtechnique(entry["id"]):
+            continue
+        for tactic in entry["tactics"]:
+            if tactic in tactic_techs:
+                tactic_techs[tactic].append(entry)
+
+    # Attach sub-techniques to their parents.
+    parent_subs: dict[str, list[dict[str, Any]]] = {}
+    for entry in entries:
+        if not _is_subtechnique(entry["id"]):
+            continue
+        pid = _parent_id(entry["id"])
+        parent_subs.setdefault(pid, []).append({"id": entry["id"], "name": entry["name"]})
+
+    # Sort subs alphabetically by name.
+    for subs in parent_subs.values():
+        subs.sort(key=lambda x: x["name"])
+
+    matrix: list[dict[str, Any]] = []
+    for tactic_id in _TACTIC_ORDER:
+        techs = tactic_techs.get(tactic_id, [])
+        # Sort techniques alphabetically.
+        techs_sorted = sorted(techs, key=lambda x: x["name"])
+        tactic_name = tactic_id.replace("-", " ").title()
+        matrix.append(
+            {
+                "tactic_id": tactic_id,
+                "tactic_name": tactic_name,
+                "techniques": [
+                    {
+                        "id": t["id"],
+                        "name": t["name"],
+                        "subtechniques": parent_subs.get(t["id"], []),
+                    }
+                    for t in techs_sorted
+                ],
+            }
+        )
+
+    return matrix
+
+
 def load_bundle(path: Path | None = None) -> None:
     """Load the MITRE bundle into memory. Called once at app boot."""
-    global mitre_loaded, _index
+    global mitre_loaded, _index, _tactics_by_technique, _name_by_id, _matrix
     bundle_path = path or _BUNDLE_PATH
 
     try:
@@ -49,6 +124,9 @@ def load_bundle(path: Path | None = None) -> None:
         return
 
     entries: list[dict[str, Any]] = []
+    tactics_map: dict[str, list[str]] = {}
+    name_map: dict[str, str] = {}
+
     for obj in data.get("objects") or []:
         if not isinstance(obj, dict):
             continue
@@ -59,19 +137,35 @@ def load_bundle(path: Path | None = None) -> None:
         ext_id = _get_external_id(obj)
         if not ext_id:
             continue
-        entries.append(
-            {
-                "id": ext_id,
-                "name": obj.get("name", ""),
-                "tactics": _extract_tactics(obj),
-            }
-        )
+        tactics = _extract_tactics(obj)
+        name = obj.get("name", "")
+        entries.append({"id": ext_id, "name": name, "tactics": tactics})
+        tactics_map[ext_id] = tactics
+        name_map[ext_id] = name
 
     _index = entries
+    _tactics_by_technique = tactics_map
+    _name_by_id = name_map
+    _matrix = _build_matrix(entries)
     mitre_loaded = True
     logger.info("MITRE bundle loaded: %d techniques", len(_index))
 
 
+def get_tactics(technique_id: str) -> list[str]:
+    """Return tactic list for a technique id; empty list if unknown."""
+    return _tactics_by_technique.get(technique_id, [])
+
+
+def lookup_name(technique_id: str) -> str | None:
+    """Return the name for a technique id, or None if not in the bundle."""
+    return _name_by_id.get(technique_id)
+
+
+def get_matrix() -> list[dict[str, Any]]:
+    """Return the full tactic → techniques → subtechniques tree."""
+    return _matrix
+
+
 def search(query: str, limit: int = 20) -> list[dict[str, Any]]:
     """Return up to `limit` techniques matching `query`.
 

backend/app/services/simulation_workflow.py

@@ -10,11 +10,10 @@ from backend.app.extensions import db
 from backend.app.models import User
 from backend.app.models.simulation import Simulation, SimulationStatus
 
+# Fields only admin/redteam may write (excluding technique_ids which is handled separately).
 REDTEAM_FIELDS = frozenset(
     {
         "name",
-        "mitre_technique_id",
-        "mitre_technique_name",
         "description",
         "commands",
         "prerequisites",
@@ -25,8 +24,6 @@ REDTEAM_FIELDS = frozenset(
 
 SOC_FIELDS = frozenset({"log_source", "logs", "soc_comment", "incident_number"})
 
-# Transitions allowed via POST /transition endpoint (manual only).
-# auto pending→in_progress is handled in apply_patch, not here.
 _ALLOWED_TRANSITIONS: dict[str, dict[str, set[str]]] = {
     "review_required": {
         "from": {"pending", "in_progress"},
@@ -48,6 +45,27 @@ def _is_non_empty(value: Any) -> bool:
     return not (isinstance(value, list) and len(value) == 0)
 
 
+def _resolve_technique_ids(
+    technique_ids: list[str],
+) -> tuple[list[dict[str, str]] | None, tuple[Any, int] | None]:
+    """Validate and resolve technique IDs to [{id, name}] snapshots.
+
+    Returns (resolved_list, None) on success or (None, error_tuple) on failure.
+    Deduplicates while preserving order.
+    """
+    from backend.app.services import mitre as mitre_svc
+
+    # Dedup, preserve order.
+    seen: dict[str, None] = dict.fromkeys(technique_ids)
+    resolved: list[dict[str, str]] = []
+    for tid in seen:
+        name = mitre_svc.lookup_name(tid)
+        if name is None:
+            return None, (jsonify({"error": f"unknown technique id: {tid}"}), 400)
+        resolved.append({"id": tid, "name": name})
+    return resolved, None
+
+
 def apply_patch(
     simulation: Simulation, payload: dict[str, Any], user: User
 ) -> tuple[Any, int] | None:
@@ -59,15 +77,14 @@ def apply_patch(
     role = user.role.value
 
     if role == "soc":
-        # SOC can only patch when status allows it.
         if simulation.status not in (
             SimulationStatus.REVIEW_REQUIRED,
             SimulationStatus.DONE,
         ):
             return jsonify({"error": "simulation not ready for SOC review"}), 403
 
-        # SOC must not send redteam fields.
-        redteam_keys_in_payload = REDTEAM_FIELDS & payload.keys()
+        # SOC must not send redteam fields or technique_ids.
+        redteam_keys_in_payload = (REDTEAM_FIELDS | {"technique_ids"}) & payload.keys()
         if redteam_keys_in_payload:
             return jsonify({"error": "soc cannot edit redteam fields"}), 403
 
@@ -76,10 +93,10 @@ def apply_patch(
                 setattr(simulation, field, payload[field])
 
     else:
-        # admin / redteam: apply all fields present.
+        # admin / redteam path.
         redteam_keys_present = REDTEAM_FIELDS & payload.keys()
 
-        # Validate executed_at before any writes so a bad value causes no partial mutation.
+        # Validate executed_at upfront before any writes.
         executed_at_value: datetime | None = None
         if "executed_at" in redteam_keys_present:
             val = payload["executed_at"]
@@ -91,21 +108,39 @@ def apply_patch(
                 except ValueError:
                     return jsonify({"error": "invalid executed_at"}), 400
 
+        # Validate and resolve technique_ids upfront.
+        resolved_techniques: list[dict[str, str]] | None = None
+        if "technique_ids" in payload:
+            raw_ids = payload["technique_ids"]
+            if not isinstance(raw_ids, list):
+                return jsonify({"error": "technique_ids must be a list"}), 400
+            resolved_techniques, err = _resolve_technique_ids(raw_ids)
+            if err is not None:
+                return err
+
+        # Apply scalar redteam fields.
         for field in redteam_keys_present:
             if field == "executed_at":
                 simulation.executed_at = executed_at_value
             else:
                 setattr(simulation, field, payload[field])
 
+        # Apply resolved techniques.
+        if resolved_techniques is not None:
+            simulation.techniques = resolved_techniques
+
+        # Apply SOC fields (admin/redteam may also write them).
         for field in SOC_FIELDS:
             if field in payload:
                 setattr(simulation, field, payload[field])
 
-        # Auto-transition pending → in_progress: at least one redteam field with
-        # a non-empty value in the *incoming payload*.
-        if simulation.status == SimulationStatus.PENDING and any(
-            _is_non_empty(payload[k]) for k in redteam_keys_present
-        ):
+        # Auto-transition pending → in_progress.
+        # Triggers when any redteam scalar has a non-empty value, OR technique_ids is non-empty.
+        auto_trigger = any(_is_non_empty(payload[k]) for k in redteam_keys_present)
+        if not auto_trigger and "technique_ids" in payload:
+            auto_trigger = len(payload["technique_ids"]) > 0
+
+        if simulation.status == SimulationStatus.PENDING and auto_trigger:
             simulation.status = SimulationStatus.IN_PROGRESS
 
     simulation.updated_at = datetime.now(UTC)

backend/migrations/versions/0003_simulation_techniques_array.py

@@ -0,0 +1,82 @@
+"""replace scalar MITRE columns with techniques JSON array
+
+Revision ID: 0003
+Revises: 0002
+Create Date: 2026-05-27 00:00:00.000000
+"""
+import json
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.sql import column, table, text
+
+
+revision = "0003"
+down_revision = "0002"
+branch_labels = None
+depends_on = None
+
+# Lightweight table proxies for data migration (no ORM import).
+_sims = table(
+    "simulations",
+    column("id", sa.Integer),
+    column("mitre_technique_id", sa.String),
+    column("mitre_technique_name", sa.String),
+    column("techniques", sa.Text),
+)
+
+
+def upgrade():
+    bind = op.get_bind()
+
+    # 1. Add techniques column (nullable while we backfill).
+    op.add_column("simulations", sa.Column("techniques", sa.Text(), nullable=True))
+
+    # 2. Backfill: scalar → JSON array.
+    rows = bind.execute(
+        text("SELECT id, mitre_technique_id, mitre_technique_name FROM simulations")
+    ).fetchall()
+    for row in rows:
+        if row[1]:  # mitre_technique_id is not null
+            val = json.dumps([{"id": row[1], "name": row[2] or ""}])
+        else:
+            val = "[]"
+        bind.execute(
+            text("UPDATE simulations SET techniques = :v WHERE id = :id"),
+            {"v": val, "id": row[0]},
+        )
+
+    # 3. Make NOT NULL now that every row has a value.
+    # SQLite doesn't support ALTER COLUMN, so we skip the nullable constraint
+    # change at DDL level — the application model enforces it.
+
+    # 4. Drop old scalar columns.
+    with op.batch_alter_table("simulations") as batch_op:
+        batch_op.drop_column("mitre_technique_id")
+        batch_op.drop_column("mitre_technique_name")
+
+
+def downgrade():
+    bind = op.get_bind()
+
+    # 1. Re-add scalar columns.
+    with op.batch_alter_table("simulations") as batch_op:
+        batch_op.add_column(sa.Column("mitre_technique_id", sa.String(length=32), nullable=True))
+        batch_op.add_column(sa.Column("mitre_technique_name", sa.String(length=255), nullable=True))
+
+    # 2. Back-fill: take first element of techniques array.
+    rows = bind.execute(text("SELECT id, techniques FROM simulations")).fetchall()
+    for row in rows:
+        techniques = json.loads(row[1] or "[]")
+        if techniques:
+            first = techniques[0]
+            bind.execute(
+                text(
+                    "UPDATE simulations SET mitre_technique_id = :tid, mitre_technique_name = :tname WHERE id = :id"
+                ),
+                {"tid": first.get("id"), "tname": first.get("name"), "id": row[0]},
+            )
+
+    # 3. Drop techniques column.
+    with op.batch_alter_table("simulations") as batch_op:
+        batch_op.drop_column("techniques")

backend/tests/test_mitre.py

@@ -33,6 +33,14 @@ _FIXTURE_BUNDLE = {
             ],
             "kill_chain_phases": [{"phase_name": "execution", "kill_chain_name": "mitre-attack"}],
         },
+        {
+            "type": "attack-pattern",
+            "name": "Python",
+            "external_references": [
+                {"source_name": "mitre-attack", "external_id": "T1059.006"}
+            ],
+            "kill_chain_phases": [{"phase_name": "execution", "kill_chain_name": "mitre-attack"}],
+        },
         {
             "type": "attack-pattern",
             "name": "Phishing",
@@ -76,9 +84,15 @@ def _reset_mitre():
     """Reset the MITRE service state between tests."""
     original_loaded = mitre_svc.mitre_loaded
     original_index = list(mitre_svc._index)
+    original_tactics = dict(mitre_svc._tactics_by_technique)
+    original_names = dict(mitre_svc._name_by_id)
+    original_matrix = list(mitre_svc._matrix)
     yield
     mitre_svc.mitre_loaded = original_loaded
     mitre_svc._index = original_index
+    mitre_svc._tactics_by_technique = original_tactics
+    mitre_svc._name_by_id = original_names
+    mitre_svc._matrix = original_matrix
 
 
 @pytest.fixture()
@@ -96,7 +110,7 @@ def bundle_file(tmp_path: pathlib.Path) -> pathlib.Path:
 def test_load_bundle_success(bundle_file: pathlib.Path) -> None:
     mitre_svc.load_bundle(bundle_file)
     assert mitre_svc.mitre_loaded is True
-    assert len(mitre_svc._index) == 4  # 5 objects minus 1 revoked = 4
+    assert len(mitre_svc._index) == 5  # 6 attack-patterns minus 1 revoked = 5
 
 
 def test_load_bundle_missing_file() -> None:
@@ -245,3 +259,119 @@ def test_mitre_endpoint_includes_tactics(
     phishing = next((r for r in data if r["id"] == "T1566"), None)
     assert phishing is not None
     assert "initial-access" in phishing["tactics"]
+
+
+# ---------------------------------------------------------------------------
+# Sprint 3: get_tactics, lookup_name, get_matrix
+# ---------------------------------------------------------------------------
+
+
+def test_get_tactics_known(bundle_file: pathlib.Path) -> None:
+    mitre_svc.load_bundle(bundle_file)
+    tactics = mitre_svc.get_tactics("T1078")
+    assert "initial-access" in tactics
+    assert "persistence" in tactics
+
+
+def test_get_tactics_unknown_returns_empty(bundle_file: pathlib.Path) -> None:
+    mitre_svc.load_bundle(bundle_file)
+    assert mitre_svc.get_tactics("T0000") == []
+
+
+def test_lookup_name_known(bundle_file: pathlib.Path) -> None:
+    mitre_svc.load_bundle(bundle_file)
+    assert mitre_svc.lookup_name("T1059") == "Command and Scripting Interpreter"
+
+
+def test_lookup_name_subtechnique(bundle_file: pathlib.Path) -> None:
+    mitre_svc.load_bundle(bundle_file)
+    assert mitre_svc.lookup_name("T1059.001") == "PowerShell"
+
+
+def test_lookup_name_unknown_returns_none(bundle_file: pathlib.Path) -> None:
+    mitre_svc.load_bundle(bundle_file)
+    assert mitre_svc.lookup_name("T0000") is None
+
+
+def test_get_matrix_returns_ordered_tactics(bundle_file: pathlib.Path) -> None:
+    mitre_svc.load_bundle(bundle_file)
+    matrix = mitre_svc.get_matrix()
+    tactic_ids = [t["tactic_id"] for t in matrix]
+    # initial-access must come before execution in canonical order.
+    assert tactic_ids.index("initial-access") < tactic_ids.index("execution")
+
+
+def test_get_matrix_subtechniques_nested(bundle_file: pathlib.Path) -> None:
+    mitre_svc.load_bundle(bundle_file)
+    matrix = mitre_svc.get_matrix()
+    exec_tactic = next(t for t in matrix if t["tactic_id"] == "execution")
+    t1059 = next((t for t in exec_tactic["techniques"] if t["id"] == "T1059"), None)
+    assert t1059 is not None
+    sub_ids = [s["id"] for s in t1059["subtechniques"]]
+    assert "T1059.001" in sub_ids
+    assert "T1059.006" in sub_ids
+
+
+def test_get_matrix_subtechniques_sorted_by_name(bundle_file: pathlib.Path) -> None:
+    mitre_svc.load_bundle(bundle_file)
+    matrix = mitre_svc.get_matrix()
+    exec_tactic = next(t for t in matrix if t["tactic_id"] == "execution")
+    t1059 = next(t for t in exec_tactic["techniques"] if t["id"] == "T1059")
+    names = [s["name"] for s in t1059["subtechniques"]]
+    assert names == sorted(names)
+
+
+def test_get_matrix_techniques_sorted_by_name(bundle_file: pathlib.Path) -> None:
+    mitre_svc.load_bundle(bundle_file)
+    matrix = mitre_svc.get_matrix()
+    ia_tactic = next(t for t in matrix if t["tactic_id"] == "initial-access")
+    names = [t["name"] for t in ia_tactic["techniques"]]
+    assert names == sorted(names)
+
+
+def test_get_matrix_technique_no_subtechniques(bundle_file: pathlib.Path) -> None:
+    mitre_svc.load_bundle(bundle_file)
+    matrix = mitre_svc.get_matrix()
+    ia_tactic = next(t for t in matrix if t["tactic_id"] == "initial-access")
+    phishing = next((t for t in ia_tactic["techniques"] if t["id"] == "T1566"), None)
+    assert phishing is not None
+    assert phishing["subtechniques"] == []
+
+
+def test_matrix_endpoint_ok(
+    client: FlaskClient, redteam_token: str, bundle_file: pathlib.Path
+) -> None:
+    mitre_svc.load_bundle(bundle_file)
+    resp = client.get("/api/mitre/matrix", headers=_h(redteam_token))
+    assert resp.status_code == 200
+    data = resp.get_json()
+    assert isinstance(data, list)
+    tactic_ids = [t["tactic_id"] for t in data]
+    assert "initial-access" in tactic_ids
+    assert "execution" in tactic_ids
+
+
+def test_matrix_endpoint_503_when_not_loaded(
+    client: FlaskClient, redteam_token: str
+) -> None:
+    mitre_svc.mitre_loaded = False
+    resp = client.get("/api/mitre/matrix", headers=_h(redteam_token))
+    assert resp.status_code == 503
+
+
+def test_matrix_endpoint_requires_auth(client: FlaskClient) -> None:
+    resp = client.get("/api/mitre/matrix")
+    assert resp.status_code == 401
+
+
+def test_matrix_endpoint_all_roles(
+    client: FlaskClient,
+    redteam_token: str,
+    soc_token: str,
+    admin_token: str,
+    bundle_file: pathlib.Path,
+) -> None:
+    mitre_svc.load_bundle(bundle_file)
+    for token in (redteam_token, soc_token, admin_token):
+        resp = client.get("/api/mitre/matrix", headers=_h(token))
+        assert resp.status_code == 200

backend/tests/test_simulations_techniques.py

@@ -0,0 +1,347 @@
+"""Sprint 3 — multi-technique simulation tests (AC-13)."""
+from __future__ import annotations
+
+import json
+import pathlib
+
+import pytest
+from flask.testing import FlaskClient
+
+from backend.app.services import mitre as mitre_svc
+from backend.tests.conftest import auth_headers as _h
+
+# ---------------------------------------------------------------------------
+# Minimal STIX fixture (reused from test_mitre.py pattern)
+# ---------------------------------------------------------------------------
+
+_FIXTURE_BUNDLE = {
+    "type": "bundle",
+    "objects": [
+        {
+            "type": "attack-pattern",
+            "name": "Command and Scripting Interpreter",
+            "external_references": [{"source_name": "mitre-attack", "external_id": "T1059"}],
+            "kill_chain_phases": [{"phase_name": "execution", "kill_chain_name": "mitre-attack"}],
+        },
+        {
+            "type": "attack-pattern",
+            "name": "PowerShell",
+            "external_references": [{"source_name": "mitre-attack", "external_id": "T1059.001"}],
+            "kill_chain_phases": [{"phase_name": "execution", "kill_chain_name": "mitre-attack"}],
+        },
+        {
+            "type": "attack-pattern",
+            "name": "Valid Accounts",
+            "external_references": [{"source_name": "mitre-attack", "external_id": "T1078"}],
+            "kill_chain_phases": [
+                {"phase_name": "initial-access", "kill_chain_name": "mitre-attack"},
+                {"phase_name": "persistence", "kill_chain_name": "mitre-attack"},
+            ],
+        },
+    ],
+}
+
+
+@pytest.fixture(autouse=True)
+def _reset_mitre():
+    original_loaded = mitre_svc.mitre_loaded
+    original_index = list(mitre_svc._index)
+    original_tactics = dict(mitre_svc._tactics_by_technique)
+    original_names = dict(mitre_svc._name_by_id)
+    original_matrix = list(mitre_svc._matrix)
+    yield
+    mitre_svc.mitre_loaded = original_loaded
+    mitre_svc._index = original_index
+    mitre_svc._tactics_by_technique = original_tactics
+    mitre_svc._name_by_id = original_names
+    mitre_svc._matrix = original_matrix
+
+
+@pytest.fixture()
+def bundle_file(tmp_path: pathlib.Path) -> pathlib.Path:
+    p = tmp_path / "enterprise-attack.json"
+    p.write_text(json.dumps(_FIXTURE_BUNDLE), encoding="utf-8")
+    return p
+
+
+@pytest.fixture()
+def loaded_bundle(bundle_file: pathlib.Path) -> pathlib.Path:
+    mitre_svc.load_bundle(bundle_file)
+    return bundle_file
+
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+
+
+def _make_engagement(client: FlaskClient, token: str) -> dict:
+    resp = client.post(
+        "/api/engagements",
+        headers=_h(token),
+        json={"name": "Op Sprint3", "start_date": "2026-06-01"},
+    )
+    assert resp.status_code == 201
+    return resp.get_json()
+
+
+def _make_sim(client: FlaskClient, token: str, eid: int) -> dict:
+    resp = client.post(
+        f"/api/engagements/{eid}/simulations",
+        headers=_h(token),
+        json={"name": "Technique Test"},
+    )
+    assert resp.status_code == 201
+    return resp.get_json()
+
+
+def _patch(client: FlaskClient, token: str, sid: int, payload: dict):
+    return client.patch(f"/api/simulations/{sid}", headers=_h(token), json=payload)
+
+
+# ---------------------------------------------------------------------------
+# AC-13.1 — new simulation has techniques = []
+# ---------------------------------------------------------------------------
+
+
+def test_new_simulation_has_empty_techniques(
+    client: FlaskClient, redteam_token: str, loaded_bundle
+) -> None:
+    eng = _make_engagement(client, redteam_token)
+    sim = _make_sim(client, redteam_token, eng["id"])
+    assert sim["techniques"] == []
+
+
+# ---------------------------------------------------------------------------
+# AC-13.3 — serializer enriches techniques with tactics
+# ---------------------------------------------------------------------------
+
+
+def test_techniques_enriched_with_tactics(
+    client: FlaskClient, redteam_token: str, loaded_bundle
+) -> None:
+    eng = _make_engagement(client, redteam_token)
+    sim = _make_sim(client, redteam_token, eng["id"])
+    _patch(client, redteam_token, sim["id"], {"technique_ids": ["T1078"]})
+
+    resp = client.get(f"/api/simulations/{sim['id']}", headers=_h(redteam_token))
+    assert resp.status_code == 200
+    techs = resp.get_json()["techniques"]
+    assert len(techs) == 1
+    assert techs[0]["id"] == "T1078"
+    assert "initial-access" in techs[0]["tactics"]
+    assert "persistence" in techs[0]["tactics"]
+
+
+def test_techniques_with_unknown_id_returns_empty_tactics(
+    client: FlaskClient, redteam_token: str, loaded_bundle
+) -> None:
+    """If a technique was removed from the bundle after save, tactics gracefully = []."""
+    eng = _make_engagement(client, redteam_token)
+    sim = _make_sim(client, redteam_token, eng["id"])
+    # Bypass service, write directly an id not in the bundle.
+    from backend.app.extensions import db
+    from backend.app.models.simulation import Simulation
+
+    with client.application.app_context():
+        s = db.session.get(Simulation, sim["id"])
+        s.techniques = [{"id": "T0000", "name": "Removed Technique"}]
+        db.session.commit()
+
+    resp = client.get(f"/api/simulations/{sim['id']}", headers=_h(redteam_token))
+    techs = resp.get_json()["techniques"]
+    assert techs[0]["tactics"] == []
+
+
+# ---------------------------------------------------------------------------
+# AC-13.4 — PATCH technique_ids
+# ---------------------------------------------------------------------------
+
+
+def test_patch_technique_ids_sets_techniques(
+    client: FlaskClient, redteam_token: str, loaded_bundle
+) -> None:
+    eng = _make_engagement(client, redteam_token)
+    sim = _make_sim(client, redteam_token, eng["id"])
+
+    resp = _patch(client, redteam_token, sim["id"], {"technique_ids": ["T1059", "T1078"]})
+    assert resp.status_code == 200
+    techs = resp.get_json()["techniques"]
+    assert len(techs) == 2
+    ids = [t["id"] for t in techs]
+    assert "T1059" in ids
+    assert "T1078" in ids
+
+
+def test_patch_technique_ids_resolves_name(
+    client: FlaskClient, redteam_token: str, loaded_bundle
+) -> None:
+    eng = _make_engagement(client, redteam_token)
+    sim = _make_sim(client, redteam_token, eng["id"])
+
+    resp = _patch(client, redteam_token, sim["id"], {"technique_ids": ["T1059"]})
+    assert resp.status_code == 200
+    tech = resp.get_json()["techniques"][0]
+    assert tech["name"] == "Command and Scripting Interpreter"
+
+
+def test_patch_technique_ids_unknown_returns_400(
+    client: FlaskClient, redteam_token: str, loaded_bundle
+) -> None:
+    eng = _make_engagement(client, redteam_token)
+    sim = _make_sim(client, redteam_token, eng["id"])
+
+    resp = _patch(client, redteam_token, sim["id"], {"technique_ids": ["T9999"]})
+    assert resp.status_code == 400
+    assert "unknown technique id: T9999" in resp.get_json()["error"]
+
+
+def test_patch_technique_ids_partial_unknown_rejected(
+    client: FlaskClient, redteam_token: str, loaded_bundle
+) -> None:
+    eng = _make_engagement(client, redteam_token)
+    sim = _make_sim(client, redteam_token, eng["id"])
+
+    # One valid, one unknown — whole request rejected.
+    resp = _patch(client, redteam_token, sim["id"], {"technique_ids": ["T1059", "T9999"]})
+    assert resp.status_code == 400
+
+
+def test_patch_technique_ids_includes_subtechnique(
+    client: FlaskClient, redteam_token: str, loaded_bundle
+) -> None:
+    eng = _make_engagement(client, redteam_token)
+    sim = _make_sim(client, redteam_token, eng["id"])
+
+    resp = _patch(client, redteam_token, sim["id"], {"technique_ids": ["T1059.001"]})
+    assert resp.status_code == 200
+    techs = resp.get_json()["techniques"]
+    assert techs[0]["id"] == "T1059.001"
+    assert techs[0]["name"] == "PowerShell"
+
+
+def test_patch_technique_ids_replaces_list(
+    client: FlaskClient, redteam_token: str, loaded_bundle
+) -> None:
+    eng = _make_engagement(client, redteam_token)
+    sim = _make_sim(client, redteam_token, eng["id"])
+    _patch(client, redteam_token, sim["id"], {"technique_ids": ["T1059"]})
+
+    resp = _patch(client, redteam_token, sim["id"], {"technique_ids": ["T1078"]})
+    assert resp.status_code == 200
+    ids = [t["id"] for t in resp.get_json()["techniques"]]
+    assert ids == ["T1078"]
+
+
+def test_patch_technique_ids_empty_clears_list(
+    client: FlaskClient, redteam_token: str, loaded_bundle
+) -> None:
+    eng = _make_engagement(client, redteam_token)
+    sim = _make_sim(client, redteam_token, eng["id"])
+    _patch(client, redteam_token, sim["id"], {"technique_ids": ["T1059"]})
+
+    resp = _patch(client, redteam_token, sim["id"], {"technique_ids": []})
+    assert resp.status_code == 200
+    assert resp.get_json()["techniques"] == []
+
+
+def test_patch_technique_ids_not_list_returns_400(
+    client: FlaskClient, redteam_token: str, loaded_bundle
+) -> None:
+    eng = _make_engagement(client, redteam_token)
+    sim = _make_sim(client, redteam_token, eng["id"])
+
+    resp = _patch(client, redteam_token, sim["id"], {"technique_ids": "T1059"})
+    assert resp.status_code == 400
+
+
+# ---------------------------------------------------------------------------
+# Dedup (spec-reviewer note: AC-13.4)
+# ---------------------------------------------------------------------------
+
+
+def test_patch_technique_ids_deduplicates(
+    client: FlaskClient, redteam_token: str, loaded_bundle
+) -> None:
+    eng = _make_engagement(client, redteam_token)
+    sim = _make_sim(client, redteam_token, eng["id"])
+
+    resp = _patch(
+        client, redteam_token, sim["id"], {"technique_ids": ["T1059", "T1078", "T1059"]}
+    )
+    assert resp.status_code == 200
+    techs = resp.get_json()["techniques"]
+    assert len(techs) == 2
+    # Order preserved: T1059 first.
+    assert techs[0]["id"] == "T1059"
+    assert techs[1]["id"] == "T1078"
+
+
+# ---------------------------------------------------------------------------
+# AC-13.5 — auto-transition on technique_ids
+# ---------------------------------------------------------------------------
+
+
+def test_technique_ids_non_empty_triggers_auto_transition(
+    client: FlaskClient, redteam_token: str, loaded_bundle
+) -> None:
+    eng = _make_engagement(client, redteam_token)
+    sim = _make_sim(client, redteam_token, eng["id"])
+    assert sim["status"] == "pending"
+
+    resp = _patch(client, redteam_token, sim["id"], {"technique_ids": ["T1059"]})
+    assert resp.status_code == 200
+    assert resp.get_json()["status"] == "in_progress"
+
+
+def test_technique_ids_empty_does_not_trigger_auto_transition(
+    client: FlaskClient, redteam_token: str, loaded_bundle
+) -> None:
+    eng = _make_engagement(client, redteam_token)
+    sim = _make_sim(client, redteam_token, eng["id"])
+
+    resp = _patch(client, redteam_token, sim["id"], {"technique_ids": []})
+    assert resp.status_code == 200
+    assert resp.get_json()["status"] == "pending"
+
+
+# ---------------------------------------------------------------------------
+# SOC cannot patch technique_ids (it's a redteam field)
+# ---------------------------------------------------------------------------
+
+
+def test_soc_cannot_patch_technique_ids(
+    client: FlaskClient, redteam_token: str, soc_token: str, loaded_bundle
+) -> None:
+    eng = _make_engagement(client, redteam_token)
+    sim = _make_sim(client, redteam_token, eng["id"])
+    # Advance to review_required so SOC can touch the simulation at all.
+    client.post(
+        f"/api/simulations/{sim['id']}/transition",
+        headers=_h(redteam_token),
+        json={"to": "review_required"},
+    )
+
+    resp = _patch(client, soc_token, sim["id"], {"technique_ids": ["T1059"]})
+    assert resp.status_code == 403
+
+
+# ---------------------------------------------------------------------------
+# Migration backfill test (inline, no Alembic runner needed)
+# ---------------------------------------------------------------------------
+
+
+def test_migration_backfill_logic() -> None:
+    """Verify the backfill logic used in upgrade(): scalar → [{id, name}]."""
+    import json as _json
+
+    def _backfill(tech_id, tech_name):
+        if tech_id:
+            return _json.loads(_json.dumps([{"id": tech_id, "name": tech_name or ""}]))
+        return []
+
+    assert _backfill("T1059", "Command and Scripting Interpreter") == [
+        {"id": "T1059", "name": "Command and Scripting Interpreter"}
+    ]
+    assert _backfill(None, None) == []
+    assert _backfill("T1059", None) == [{"id": "T1059", "name": ""}]