diff --git a/decnet/correlation/attribution_worker.py b/decnet/correlation/attribution_worker.py
index 653fbccd..38487c88 100644
--- a/decnet/correlation/attribution_worker.py
+++ b/decnet/correlation/attribution_worker.py
@@ -26,12 +26,25 @@ from decnet.bus import topics as _topics
 from decnet.bus.base import BaseBus
 from decnet.bus.factory import get_bus
 from decnet.bus.publish import (
+    publish_safely,
     run_control_listener_signal as _run_control_listener_signal,
     run_health_heartbeat as _run_health_heartbeat,
 )
+from decnet.correlation.attribution.aggregate import aggregate_observations
 from decnet.logging import get_logger
 from decnet.web.db.repository import BaseRepository
 
+try:
+    from decnet_behave_shell.spec import (
+        PRIMITIVE_REGISTRY,
+        ValueKind,
+    )
+    _BEHAVE_REGISTRY_AVAILABLE = True
+except ImportError:  # pragma: no cover
+    PRIMITIVE_REGISTRY = {}
+    ValueKind = None
+    _BEHAVE_REGISTRY_AVAILABLE = False
+
 log = get_logger("correlation.attribution_worker")
 
 _WORKER_NAME = "attribution"
@@ -156,13 +169,103 @@ async def handle_observation_event(
             attacker_uuid,
         )
         return
-    # Phase 4 will run the merger here and emit
-    # ``attribution.profile.state_changed`` on transition. Phase 1
-    # ends with stub materialisation only.
-    log.debug(
-        "attribution worker: stub identity=%s for attacker=%s primitive=%s",
-        identity_uuid, attacker_uuid, primitive,
+    primitive_str = str(primitive)
+
+    # Load the full per-(identity, primitive) observation series.
+    # v0 with 1:1 stub identities, this is the single attacker's
+    # series; v1's clusterer makes it a cross-attacker union.
+    observations = await repo.observations_for_identity_primitive(
+        identity_uuid, primitive_str,
     )
+    if not observations:
+        log.debug(
+            "attribution worker: no observations yet for identity=%s "
+            "primitive=%s (race with upsert)",
+            identity_uuid, primitive_str,
+        )
+        return
+
+    # Run merger.
+    value_kind = _value_kind_for(primitive_str)
+    new_state = aggregate_observations(observations, value_kind=value_kind)
+
+    # Load prior state to detect transitions.
+    prior = await repo.get_attribution_state(identity_uuid, primitive_str)
+    state_changed = prior is None or prior.get("state") != new_state.state
+
+    # Persist. last_change_ts is locked to the prior row when state is
+    # unchanged so the dashboard's "stable since" timestamp doesn't
+    # reset on every observation.
+    if prior is not None and not state_changed:
+        last_change_ts = float(prior.get("last_change_ts", new_state.last_observation_ts))
+    else:
+        last_change_ts = new_state.last_observation_ts
+    await repo.upsert_attribution_state({
+        "identity_uuid": identity_uuid,
+        "primitive": primitive_str,
+        "current_value": new_state.current_value,
+        "state": new_state.state,
+        "confidence": new_state.confidence,
+        "observation_count": new_state.observation_count,
+        "last_change_ts": last_change_ts,
+        "last_observation_ts": new_state.last_observation_ts,
+    })
+
+    # Emit state_changed only on transition. Idempotent re-runs (same
+    # observations, same merger output) produce no event — matches
+    # the loop-prevention invariant that ttp.tagged uses.
+    if state_changed and bus is not None:
+        await publish_safely(
+            bus,
+            _topics.attribution(_topics.ATTRIBUTION_PROFILE_STATE_CHANGED),
+            {
+                "identity_uuid": identity_uuid,
+                "primitive": primitive_str,
+                "old_state": prior.get("state") if prior else None,
+                "new_state": new_state.state,
+                "current_value": new_state.current_value,
+                "confidence": new_state.confidence,
+                "observation_count": new_state.observation_count,
+                "ts": new_state.last_observation_ts,
+            },
+            event_type=_topics.ATTRIBUTION_PROFILE_STATE_CHANGED,
+        )
+        log.info(
+            "attribution worker: identity=%s primitive=%s %s -> %s confidence=%.2f",
+            identity_uuid, primitive_str,
+            (prior or {}).get("state") or "<new>", new_state.state,
+            new_state.confidence,
+        )
+
+
+def _value_kind_for(primitive: str) -> str:
+    """Resolve a BEHAVE primitive name to the merger's ValueKind tag.
+
+    Maps the BEHAVE registry's ``ValueKind`` enum onto the three
+    mergers the engine ships:
+
+    * ``CATEGORICAL`` / ``BOOL`` / ``FREE_STRING`` / ``ARRAY`` →
+      ``"categorical"`` (BOOL is a 2-cardinality categorical;
+      FREE_STRING and ARRAY collapse to opaque-token categorical
+      until a v1 specialised merger lands)
+    * ``NUMERIC`` → ``"numeric"``
+    * ``HASH``    → ``"hash"``
+
+    Unknown primitives (registry miss) default to categorical — the
+    safest fallback because the categorical merger is one-outlier-
+    tolerant and won't lie about confidence on noisy categorical
+    data the way a numeric merger would on non-numeric values.
+    """
+    if not _BEHAVE_REGISTRY_AVAILABLE:
+        return "categorical"
+    spec = PRIMITIVE_REGISTRY.get(primitive)
+    if spec is None or ValueKind is None:
+        return "categorical"
+    if spec.kind is ValueKind.NUMERIC:
+        return "numeric"
+    if spec.kind is ValueKind.HASH:
+        return "hash"
+    return "categorical"
 
 
 def _payload_of(event: Any) -> dict[str, Any]:
diff --git a/decnet/web/db/repository.py b/decnet/web/db/repository.py
index 29b6e4a9..b051c3fd 100644
--- a/decnet/web/db/repository.py
+++ b/decnet/web/db/repository.py
@@ -341,6 +341,20 @@ class BaseRepository(ABC):
         ordered by ``ts`` ASC. Empty list when none."""
         raise NotImplementedError
 
+    @abstractmethod
+    async def observations_for_identity_primitive(
+        self, identity_uuid: str, primitive: str,
+    ) -> list[dict[str, Any]]:
+        """Every observation of ``primitive`` across all attackers
+        rolling up to ``identity_uuid``, ordered by ``ts`` ASC.
+
+        Empty list when the identity has no observations of this
+        primitive. v0 with 1:1 stub identities returns the same set
+        as ``observations_time_series(attacker_uuid, primitive)``;
+        v1's clusterer makes the union meaningful.
+        """
+        raise NotImplementedError
+
     @abstractmethod
     async def has_observations_for_evidence(self, evidence_ref: str) -> bool:
         """True iff any observation row carries this ``evidence_ref``.
diff --git a/decnet/web/db/sqlmodel_repo/observations.py b/decnet/web/db/sqlmodel_repo/observations.py
index dc103e1f..2a90c9f7 100644
--- a/decnet/web/db/sqlmodel_repo/observations.py
+++ b/decnet/web/db/sqlmodel_repo/observations.py
@@ -25,7 +25,7 @@ from typing import Any, Optional
 from sqlalchemy import desc, func, select
 from sqlmodel import col
 
-from decnet.web.db.models import ObservationRow
+from decnet.web.db.models import Attacker, ObservationRow
 from decnet.web.db.sqlmodel_repo._helpers import _MixinBase
 
 
@@ -164,6 +164,34 @@ class ObservationsMixin(_MixinBase):
                 return None
             return row.model_dump(mode="json")
 
+    async def observations_for_identity_primitive(
+        self, identity_uuid: str, primitive: str,
+    ) -> list[dict[str, Any]]:
+        """Union of every observation of *primitive* across the
+        attackers rolling up to *identity_uuid*, ordered ``ts`` ASC.
+
+        v0 with 1:1 stub identities returns the same set as
+        ``observations_time_series(attacker_uuid, primitive)``.
+        v1's clusterer makes the union load-bearing — multiple
+        attackers point at the same identity_id and this query is
+        what gives the merger a cross-attacker view.
+        """
+        async with self._session() as session:
+            stmt = (
+                select(ObservationRow)
+                .join(Attacker, ObservationRow.attacker_uuid == Attacker.uuid)
+                .where(
+                    Attacker.identity_id == identity_uuid,
+                    ObservationRow.primitive == primitive,
+                )
+                .order_by(ObservationRow.ts)
+            )
+            rows = (await session.execute(stmt)).scalars().all()
+            return [
+                {"ts": row.ts, "value": row.value, "confidence": row.confidence}
+                for row in rows
+            ]
+
     async def has_observations_for_evidence(
         self, evidence_ref: str,
     ) -> bool:
diff --git a/tests/correlation/attribution/test_aggregate_categorical.py b/tests/correlation/attribution/test_aggregate_categorical.py
index a00d994e..1262dbb6 100644
--- a/tests/correlation/attribution/test_aggregate_categorical.py
+++ b/tests/correlation/attribution/test_aggregate_categorical.py
@@ -165,11 +165,12 @@ def test_dispatcher_routes_categorical() -> None:
     assert a == b == c
 
 
-def test_dispatcher_rejects_unimplemented_kinds() -> None:
-    """numeric / hash kinds land in Phase 3; surface the gap loudly
-    so a misuse doesn't silently fall through to categorical."""
+def test_dispatcher_rejects_unknown_value_kind() -> None:
+    """Unknown ValueKind tags surface as ValueError so misuse doesn't
+    silently fall through to categorical. Phase 3 wired numeric +
+    hash; the rejection is for typos and v1 kinds that haven't
+    landed yet."""
     import pytest
-    obs = _pad(value=5000.0, count=5)
-    for kind in ("numeric", "hash"):
-        with pytest.raises(NotImplementedError):
-            aggregate_observations(obs, value_kind=kind)
+    obs = _pad(value="typed", count=5)
+    with pytest.raises(ValueError):
+        aggregate_observations(obs, value_kind="bogus_kind")
diff --git a/tests/correlation/attribution/test_attribution_worker_phase4.py b/tests/correlation/attribution/test_attribution_worker_phase4.py
new file mode 100644
index 00000000..3edbb239
--- /dev/null
+++ b/tests/correlation/attribution/test_attribution_worker_phase4.py
@@ -0,0 +1,275 @@
+"""Phase 4 — end-to-end worker wiring.
+
+Observation event → stub identity → load series → merger → upsert
+state → emit ``attribution.profile.state_changed`` on transition.
+
+Phase 1 covered stub-only wiring; this file pins the merger /
+persist / publish path against an in-memory SQLite + FakeBus.
+"""
+from __future__ import annotations
+
+from datetime import datetime, timezone
+from pathlib import Path
+from typing import Any
+
+import pytest
+
+from decnet.bus import topics as _topics
+from decnet.bus.fake import FakeBus
+from decnet.correlation import attribution_worker as _aw
+from decnet.web.db.factory import get_repository
+
+
+@pytest.fixture
+async def repo(tmp_path: Path):
+    r = get_repository(db_path=str(tmp_path / "phase4.db"))
+    await r.initialize()
+    return r
+
+
+@pytest.fixture
+async def attacker_uuid(repo) -> str:
+    now = datetime.now(timezone.utc)
+    return await repo.upsert_attacker({
+        "ip": "10.0.0.5",
+        "first_seen": now,
+        "last_seen": now,
+    })
+
+
+def _envelope(
+    *,
+    primitive: str,
+    value: Any,
+    attacker_uuid: str,
+    evidence_ref: str,
+    ts: float,
+    confidence: float = 0.9,
+) -> dict[str, Any]:
+    return {
+        "id": f"obs-{evidence_ref}-{primitive}",
+        "primitive": primitive,
+        "value": value,
+        "confidence": confidence,
+        "window_start_ts": ts,
+        "window_end_ts": ts,
+        "source": "test",
+        "evidence_ref": evidence_ref,
+        "envelope_v": 1,
+        "ts": ts,
+        "attacker_uuid": attacker_uuid,
+    }
+
+
+def _bus_event(payload: dict[str, Any]) -> dict[str, Any]:
+    """Worker reads payload via getattr(.payload, fallback to dict)."""
+    return payload
+
+
+async def _seed_observations(
+    repo, attacker_uuid: str, primitive: str, values: list[Any],
+    *, start_ts: float = 1714000000.0,
+) -> None:
+    for i, v in enumerate(values):
+        ts = start_ts + i * 60.0
+        # ts in evidence_ref so repeated calls with overlapping i but
+        # distinct start_ts produce distinct rows.
+        await repo.upsert_observation(_envelope(
+            primitive=primitive,
+            value=v,
+            attacker_uuid=attacker_uuid,
+            evidence_ref=f"shard:test#{primitive}-{ts}",
+            ts=ts,
+        ))
+
+
+@pytest.mark.anyio
+async def test_handler_writes_unknown_below_threshold(
+    repo, attacker_uuid: str,
+) -> None:
+    """Two observations for one primitive → state row written with
+    state='unknown' (< MIN_OBSERVATIONS_FOR_STATE)."""
+    bus = FakeBus()
+    await bus.connect()
+    await _seed_observations(
+        repo, attacker_uuid, "motor.input_modality", ["typed", "typed"],
+    )
+    await _aw.handle_observation_event(bus, repo, _bus_event({
+        "attacker_uuid": attacker_uuid,
+        "primitive": "motor.input_modality",
+    }))
+
+    attacker = await repo.get_attacker_by_uuid(attacker_uuid)
+    assert attacker is not None
+    identity_uuid = attacker["identity_id"]
+    state = await repo.get_attribution_state(
+        identity_uuid, "motor.input_modality",
+    )
+    assert state is not None
+    assert state["state"] == "unknown"
+    await bus.close()
+
+
+@pytest.mark.anyio
+async def test_handler_emits_state_changed_on_transition(
+    repo, attacker_uuid: str, monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """As observations cross MIN_OBSERVATIONS_FOR_STATE, the worker
+    fires <new>→unknown then unknown→stable; idempotent re-runs in
+    between fire nothing."""
+    bus = FakeBus()
+    await bus.connect()
+
+    captured: list[dict[str, Any]] = []
+
+    async def _capture(_bus, topic, payload, *, event_type=""):
+        captured.append({"topic": topic, "payload": payload})
+
+    monkeypatch.setattr(_aw, "publish_safely", _capture)
+
+    for i in range(5):
+        await _seed_observations(
+            repo, attacker_uuid, "motor.input_modality",
+            ["typed"], start_ts=1714000000.0 + i * 60.0,
+        )
+        await _aw.handle_observation_event(bus, repo, _bus_event({
+            "attacker_uuid": attacker_uuid,
+            "primitive": "motor.input_modality",
+        }))
+
+    states_seen = [c["payload"]["new_state"] for c in captured]
+    assert states_seen == ["unknown", "stable"], states_seen
+    # The transition payload carries old + new + the observation that
+    # caused the flip.
+    assert captured[0]["payload"]["old_state"] is None
+    assert captured[1]["payload"]["old_state"] == "unknown"
+    await bus.close()
+
+
+@pytest.mark.anyio
+async def test_handler_no_event_when_state_unchanged(
+    repo, attacker_uuid: str,
+) -> None:
+    """Re-running the merger over an unchanged observation set must
+    not emit a duplicate state_changed event (loop-prevention)."""
+    bus = FakeBus()
+    await bus.connect()
+
+    captured: list[Any] = []
+    sub = bus.subscribe(
+        _topics.attribution(_topics.ATTRIBUTION_PROFILE_STATE_CHANGED),
+    )
+
+    import asyncio
+
+    async def drain() -> None:
+        try:
+            async with sub:
+                async for ev in sub:
+                    captured.append(ev)
+        except Exception:
+            pass
+
+    drain_task = asyncio.create_task(drain())
+    await asyncio.sleep(0)
+
+    await _seed_observations(
+        repo, attacker_uuid, "motor.input_modality",
+        ["typed"] * 5,
+    )
+    # First run: <new> → stable, fires event.
+    await _aw.handle_observation_event(bus, repo, _bus_event({
+        "attacker_uuid": attacker_uuid,
+        "primitive": "motor.input_modality",
+    }))
+    await asyncio.sleep(0.05)
+    first_count = len(captured)
+
+    # Re-run with no new observations: state stays "stable", no event.
+    for _ in range(3):
+        await _aw.handle_observation_event(bus, repo, _bus_event({
+            "attacker_uuid": attacker_uuid,
+            "primitive": "motor.input_modality",
+        }))
+    await asyncio.sleep(0.05)
+
+    drain_task.cancel()
+    assert len(captured) == first_count, (
+        "state didn't change; no additional events should fire"
+    )
+    await bus.close()
+
+
+@pytest.mark.anyio
+async def test_handler_locks_last_change_ts_when_unchanged(
+    repo, attacker_uuid: str,
+) -> None:
+    """When the state doesn't change, last_change_ts must NOT advance —
+    that's what tells the dashboard 'stable since X', not 'stable
+    since most-recent-observation'."""
+    bus = FakeBus()
+    await bus.connect()
+    await _seed_observations(
+        repo, attacker_uuid, "motor.input_modality",
+        ["typed"] * 5,
+    )
+    await _aw.handle_observation_event(bus, repo, _bus_event({
+        "attacker_uuid": attacker_uuid,
+        "primitive": "motor.input_modality",
+    }))
+    attacker = await repo.get_attacker_by_uuid(attacker_uuid)
+    assert attacker is not None
+    identity_uuid = attacker["identity_id"]
+    first = await repo.get_attribution_state(
+        identity_uuid, "motor.input_modality",
+    )
+    assert first is not None
+    locked_ts = first["last_change_ts"]
+
+    # Add another stable observation, re-run.
+    await _seed_observations(
+        repo, attacker_uuid, "motor.input_modality",
+        ["typed"], start_ts=1714010000.0,
+    )
+    await _aw.handle_observation_event(bus, repo, _bus_event({
+        "attacker_uuid": attacker_uuid,
+        "primitive": "motor.input_modality",
+    }))
+    second = await repo.get_attribution_state(
+        identity_uuid, "motor.input_modality",
+    )
+    assert second is not None
+    assert second["last_change_ts"] == locked_ts
+    # last_observation_ts DID advance.
+    assert second["last_observation_ts"] > locked_ts
+    await bus.close()
+
+
+@pytest.mark.anyio
+async def test_handler_routes_numeric_primitive(
+    repo, attacker_uuid: str,
+) -> None:
+    """Worker dispatches to the numeric merger when the primitive
+    registry kind is NUMERIC."""
+    bus = FakeBus()
+    await bus.connect()
+    # toolchain.c2.beacon_interval_ms is registered NUMERIC in BEHAVE.
+    primitive = "toolchain.c2.beacon_interval_ms"
+    await _seed_observations(
+        repo, attacker_uuid, primitive,
+        [5000.0, 5050.0, 4980.0, 5020.0, 5010.0],
+    )
+    await _aw.handle_observation_event(bus, repo, _bus_event({
+        "attacker_uuid": attacker_uuid,
+        "primitive": primitive,
+    }))
+    attacker = await repo.get_attacker_by_uuid(attacker_uuid)
+    assert attacker is not None
+    state = await repo.get_attribution_state(
+        attacker["identity_id"], primitive,
+    )
+    assert state is not None
+    # Numeric merger returns a smoothed mean, not a string.
+    assert isinstance(state["current_value"], float)
+    assert state["state"] == "stable"
+    await bus.close()
diff --git a/tests/db/test_base_repo.py b/tests/db/test_base_repo.py
index 1a0245ca..72156e5f 100644
--- a/tests/db/test_base_repo.py
+++ b/tests/db/test_base_repo.py
@@ -42,6 +42,24 @@ class DummyRepo(BaseRepository):
     async def upsert_observation(self, data): await super().upsert_observation(data); return ""
     async def latest_observation_per_primitive(self, attacker_uuid): await super().latest_observation_per_primitive(attacker_uuid); return {}
     async def observations_time_series(self, attacker_uuid, primitive): await super().observations_time_series(attacker_uuid, primitive); return []
+    async def observations_for_identity_primitive(self, identity_uuid, primitive):
+        await super().observations_for_identity_primitive(identity_uuid, primitive)
+        return []
+    # Attribution engine v0 (ATTRIBUTION-ENGINE.md Phase 1)
+    async def ensure_stub_identity_for_attacker(self, attacker_uuid):
+        await super().ensure_stub_identity_for_attacker(attacker_uuid)
+        return None
+    async def upsert_attribution_state(self, data):
+        await super().upsert_attribution_state(data)
+    async def get_attribution_state(self, identity_uuid, primitive):
+        await super().get_attribution_state(identity_uuid, primitive)
+        return None
+    async def get_attribution_state_for_identity(self, identity_uuid):
+        await super().get_attribution_state_for_identity(identity_uuid)
+        return []
+    async def list_multi_actor_identities(self):
+        await super().list_multi_actor_identities()
+        return []
     async def increment_smtp_target(self, u, d): await super().increment_smtp_target(u, d)
     async def list_smtp_targets(self, u): await super().list_smtp_targets(u)
     async def get_attacker_stored_mail(self, u): await super().get_attacker_stored_mail(u)
@@ -86,6 +104,38 @@ class DummyRepo(BaseRepository):
     async def set_identity_campaign_id(self, i, c): await super().set_identity_campaign_id(i, c)
     async def list_all_campaigns(self): await super().list_all_campaigns(); return []
     async def update_campaign_merged_into(self, u, w): await super().update_campaign_merged_into(u, w)
+    # Pre-existing abstract surface that DummyRepo never stubbed —
+    # added here so the coverage test exercises the full BaseRepository
+    # contract.
+    async def get_log_histogram(self, *a, **kw):
+        await super().get_log_histogram(*a, **kw); return []
+    async def has_observations_for_evidence(self, evidence_ref):
+        await super().has_observations_for_evidence(evidence_ref); return False
+    async def get_attacker_uuid_by_ip(self, ip):
+        await super().get_attacker_uuid_by_ip(ip); return None
+    # TTP rollup surface (TTP_TAGGING.md)
+    async def insert_tags(self, rows): await super().insert_tags(rows); return 0
+    async def list_techniques_by_identity(self, uuid):
+        await super().list_techniques_by_identity(uuid); return []
+    async def list_techniques_by_attacker(self, uuid):
+        await super().list_techniques_by_attacker(uuid); return []
+    async def list_techniques_by_campaign(self, uuid):
+        await super().list_techniques_by_campaign(uuid); return []
+    async def list_techniques_by_session(self, sid):
+        await super().list_techniques_by_session(sid); return []
+    async def list_tags_by_scope_and_technique(self, **kw):
+        await super().list_tags_by_scope_and_technique(**kw); return []
+    async def list_distinct_techniques(self):
+        await super().list_distinct_techniques(); return []
+    # Iter helpers — async generators, can't `await super()` on them
+    # because the base raises in the body before any yield. Just yield
+    # nothing so the consumer's ``async for`` exits cleanly.
+    async def iter_attacker_commands_since(self, since):
+        return
+        yield  # unreachable, marks the function as a generator
+    async def iter_canary_triggers_since(self, since):
+        return
+        yield
 
 @pytest.mark.asyncio
 async def test_base_repo_coverage():
@@ -127,9 +177,26 @@ async def test_base_repo_coverage():
     await dr.upsert_attacker_behavior("a", {})
     await dr.get_attacker_behavior("a")
     await dr.get_behaviors_for_ips({"1.1.1.1"})
-    await dr.upsert_observation({})
-    await dr.latest_observation_per_primitive("a")
-    await dr.observations_time_series("a", "motor.input_modality")
+    # Observation surface — bases raise NotImplementedError.
+    with pytest.raises(NotImplementedError):
+        await dr.upsert_observation({})
+    with pytest.raises(NotImplementedError):
+        await dr.latest_observation_per_primitive("a")
+    with pytest.raises(NotImplementedError):
+        await dr.observations_time_series("a", "motor.input_modality")
+    # observations_for_identity_primitive + attribution engine v0
+    with pytest.raises(NotImplementedError):
+        await dr.observations_for_identity_primitive("i", "motor.input_modality")
+    with pytest.raises(NotImplementedError):
+        await dr.ensure_stub_identity_for_attacker("a")
+    with pytest.raises(NotImplementedError):
+        await dr.upsert_attribution_state({})
+    with pytest.raises(NotImplementedError):
+        await dr.get_attribution_state("i", "motor.input_modality")
+    with pytest.raises(NotImplementedError):
+        await dr.get_attribution_state_for_identity("i")
+    with pytest.raises(NotImplementedError):
+        await dr.list_multi_actor_identities()
     await dr.increment_smtp_target("uuid", "corp.com")
     await dr.list_smtp_targets("uuid")
     await dr.get_attacker_stored_mail("uuid")
@@ -174,6 +241,37 @@ async def test_base_repo_coverage():
     await dr.update_campaign_merged_into("c", "d")
     await dr.update_campaign_merged_into("c", None)
 
+    # Pre-existing abstract surface. get_log_histogram's base body
+    # is ``pass`` (returns None), the rest raise NotImplementedError.
+    from datetime import datetime, timezone
+    await dr.get_log_histogram()
+    with pytest.raises(NotImplementedError):
+        await dr.has_observations_for_evidence("shard:x#1")
+    with pytest.raises(NotImplementedError):
+        await dr.get_attacker_uuid_by_ip("1.1.1.1")
+    with pytest.raises(NotImplementedError):
+        await dr.insert_tags([])
+    with pytest.raises(NotImplementedError):
+        await dr.list_techniques_by_identity("i")
+    with pytest.raises(NotImplementedError):
+        await dr.list_techniques_by_attacker("a")
+    with pytest.raises(NotImplementedError):
+        await dr.list_techniques_by_campaign("c")
+    with pytest.raises(NotImplementedError):
+        await dr.list_techniques_by_session("s")
+    with pytest.raises(NotImplementedError):
+        await dr.list_tags_by_scope_and_technique(
+            scope="identity", uuid="i", technique_id="T1059",
+        )
+    with pytest.raises(NotImplementedError):
+        await dr.list_distinct_techniques()
+    # Iter helpers: just consume the empty generator.
+    now = datetime.now(timezone.utc)
+    async for _ in dr.iter_attacker_commands_since(now):
+        pass
+    async for _ in dr.iter_canary_triggers_since(now):
+        pass
+
     # Swarm methods: default NotImplementedError on BaseRepository.  Covering
     # them here keeps the coverage contract honest for the swarm CRUD surface.
     for coro, args in [