diff --git a/TODO.md b/TODO.md
new file mode 100644
index 00000000..d76332f9
--- /dev/null
+++ b/TODO.md
@@ -0,0 +1,210 @@
+# TODO — credential reuse + vectorstore (handoff)
+
+This document hands off in-progress work on the **credential reuse
+patterns** task from `development/DEVELOPMENT.md` (under *Service-Level
+Behavioral Profiling*) plus the **`decnet/vectorstore/`** scaffolding
+that prepares the substrate for a future statistical re-identification
+engine over behavioral fingerprints. See
+`/home/anti/.claude/plans/ah-excellent-alright-claude-vivid-thimble.md`
+for the full approved plan and motivation.
+
+## Done in the previous session
+
+Foundation is shipped + tested (26 new tests passing, no regressions):
+
+- **Schema** — `decnet/web/db/models/logs.py`
+  - `Credential.attacker_uuid: Optional[str]` FK to `attackers.uuid`,
+    nullable. Backfilled by the profiler post-write.
+  - `CredentialReuse` table (UUID PK; JSON list columns for
+    `attacker_uuids`, `attacker_ips`, `deckies`, `services`;
+    `target_count`, `attempt_count`, `confidence` reserved for future
+    fuzzy matching). Unique key: `(secret_sha256, secret_kind,
+    principal_key)`.
+  - `CredentialReuseResponse` Pydantic DTO.
+- **Repo** — `decnet/web/db/sqlmodel_repo.py` + `repository.py`
+  - `upsert_credential_reuse(...)`,
+    `list_credential_reuses(limit, offset, min_target_count, secret_kind)`,
+    `get_credential_reuse_by_id(id)`,
+    `update_credential_attacker_uuid(attacker_ip, attacker_uuid) -> int`.
+  - **Rename**: pre-existing `get_credential_reuse(secret_sha256)` →
+    `get_credential_attempts_for_secret(secret_sha256)`. All callers
+    updated.
+- **Bus topics** — `decnet/bus/topics.py`
+  - `CREDENTIAL_CAPTURED = "captured"` (one per Credential upsert).
+  - `CREDENTIAL_REUSE_DETECTED = "reuse.detected"` (correlator emits
+    on insert/grow).
+  - `credential(event_type)` builder.
+- **Vectorstore** — `decnet/vectorstore/` (NEW; flat layout mirroring
+  `decnet/bus/`)
+  - `base.py` — `BaseVectorStore` ABC,  `VectorRecord`, `Neighbor`,
+    `VECTORSTORE_SCHEMA_VERSION`. Methods: `initialize`, `close`,
+    `health`, `insert`, `get`, `delete`, `knn`. Keyed by `(kind, id)`.
+  - `fake.py` — `FakeVectorStore` (in-memory, brute-force L2 KNN) +
+    `NullVectorStore` (no-op when `DECNET_VECTORSTORE_ENABLED=false`).
+  - `sqlite_vec.py` — `SqliteVecVectorStore`; lazy-loads the
+    `sqlite_vec` extension; one `vec0` virtual table per `kind` so
+    new feature families don't require schema migration. Per-kind
+    dim is locked on first insert.
+  - `factory.py` — `get_vectorstore()` env-driven dispatch
+    (`DECNET_VECTORSTORE_TYPE` ∈ {sqlite_vec, fake};
+    `DECNET_VECTORSTORE_ENABLED`; `DECNET_VECTORSTORE_PATH`). On
+    missing `sqlite_vec` extension: logs a warning and returns
+    `FakeVectorStore` so workers don't crash.
+- **Tests**
+  - `tests/db/test_credential_reuse.py` — 11 tests (upsert idempotency,
+    list filters/pagination, FK backfill semantics, null-principal
+    uniqueness, JSON-list merging).
+  - `tests/vectorstore/test_factory.py` (6) +
+    `tests/vectorstore/test_fake.py` (9) — factory dispatch + fallback,
+    round-trip, dim-mismatch raises, KNN ordering, NullStore no-op.
+  - Updated `tests/db/test_base_repo.py` and
+    `tests/db/test_credentials.py` for the rename.
+
+## Not yet done — what the next agent should pick up
+
+Tasks below are roughly in dependency order. Backend first, dashboard
+last (it's the largest unknown and benefits from a fresh context).
+
+### 1. Profiler backfill of `Credential.attacker_uuid`
+
+Smallest task; do this first to validate the FK column end-to-end.
+
+- File: `decnet/profiler/` — find the spot where the profiler
+  mints/updates an `Attacker` row from observed events. There's
+  likely an `upsert_attacker(...)` call that produces the `(ip, uuid)`
+  pair.
+- Add immediately after a successful upsert:
+  ```python
+  await repo.update_credential_attacker_uuid(ip, uuid)
+  ```
+- Test in `tests/profiler/` (whatever the existing test file is) that
+  after the profiler processes events for an IP, all `Credential`
+  rows for that IP have their `attacker_uuid` populated. Use the
+  pattern from `tests/db/test_credential_reuse.py::
+  test_update_credential_attacker_uuid_backfills_only_nulls`.
+
+### 2. Correlator engine + worker wiring
+
+- File: `decnet/correlation/engine.py` — add
+  `correlate_credential_reuse(min_targets: int = 2)` to
+  `CorrelationEngine`. Signature suggested in the plan:
+  ```sql
+  SELECT secret_sha256, secret_kind, principal,
+         COUNT(DISTINCT decky_name||':'||service) AS target_count
+  FROM credentials
+  GROUP BY secret_sha256, secret_kind, principal
+  HAVING target_count >= :min_targets
+  ```
+  For each group, fetch the underlying credential rows and call
+  `repo.upsert_credential_reuse(...)` per row. The repo upsert
+  recomputes `target_count` from the `credentials` table on each
+  update, so you don't need to pass aggregates in.
+- On insert/grow (`out["inserted"] is True or out["changed"] is True`),
+  publish `bus.publish(topics.credential(topics.CREDENTIAL_REUSE_DETECTED), {...})`
+  with payload `{id, secret_kind, target_count, attacker_uuids,
+  attacker_ips, deckies, services}`.
+- Worker file: `decnet/correlation/main.py` (or wherever
+  `CorrelationEngine` is loop-driven). Subscribe to:
+  - `attacker.observed` — re-runs reuse pass for that IP.
+  - `credential.captured` — re-runs reuse pass for that secret.
+  - Heartbeat tick every 60s as a fallback (mirror the mutator's
+    bus-wake + slow-tick pattern).
+- Where is `credential.captured` emitted? Find the credential ingest
+  path — probably `decnet/collector/` or wherever
+  `repo.upsert_credential(...)` is called. Add a `bus.publish(
+  topics.credential(topics.CREDENTIAL_CAPTURED), {secret_sha256,
+  secret_kind, attacker_ip, decky, service})` after a successful
+  upsert. Bus is fire-and-forget — don't block on it.
+- Tests:
+  - `tests/correlation/test_credential_reuse.py` — engine emits the
+    right `CredentialReuse` rows from synthetic credentials; bus
+    event published exactly once per insert/grow.
+  - Use `decnet.bus.fake.FakeBus` in tests; collect published
+    events for assertion.
+
+### 3. API routes — `GET /api/v1/credential-reuse`
+
+- File: probably `decnet/web/api/routes/` — see how existing
+  credentials routes are organized (recent commit
+  `feat(api): GET /credentials endpoint` → `4566146`).
+- Endpoints:
+  - `GET /api/v1/credential-reuse?limit=50&offset=0&min_target_count=2&secret_kind=plaintext`
+    → `CredentialReuseResponse` (already in models).
+  - `GET /api/v1/credential-reuse/{id}` → single row dict, 404 if
+    missing.
+- JWT-gated like all other routes. Use the existing dependency.
+- No POST/PUT/PATCH — read-only this release. Per the
+  `feedback_schemathesis_400` memory there's no 400 contract to
+  document since there's no body parsing.
+- Tests: `tests/api/test_credential_reuse_routes.py` — JWT gate,
+  pagination, filters, 404 for missing id.
+
+### 4. Dashboard — Credentials Reuse tab + drawer
+
+The big unknown. Next agent should:
+
+1. Survey `decnet/web/dashboard/` (React app) — how the existing
+   Credentials view is structured (commit `4ea4b0b feat(web):
+   Credentials view + inspector`).
+2. Add a "Reuse" tab/filter that lists `CredentialReuse` rows sorted
+   by `target_count desc`.
+3. Drawer on row-click showing decky×service breakdown,
+   `attacker_uuid` list (link to `/attackers/:id`), timeline. Reuse
+   the existing drawer pattern (see `feedback_react_stop_propagation_native_delegation`
+   memory — backdrop click closes via `target===currentTarget`,
+   never `stopPropagation`).
+4. On the existing Credentials list, add a "seen on N targets"
+   badge when a credential has a corresponding `CredentialReuse`
+   row, so the connection is bidirectional.
+
+### 5. DEVELOPMENT.md
+
+Tick `[x] Credential reuse patterns` under *Service-Level Behavioral
+Profiling*. Add a one-liner under *Attacker Intelligence Collection*
+noting `decnet/vectorstore/` is scaffolded for the future statistical
+re-ID engine (no behavioural change yet).
+
+## Architectural decisions worth knowing
+
+These came out of the design conversation that produced the plan; the
+next agent should respect them:
+
+- **Classical statistics, not ML**, for attacker re-identification.
+  Cosine/Mahalanobis/KS-test over per-kind feature vectors, weighted
+  voting, versioned thresholds. Reproducible, explainable, no model
+  drift. ML is reserved for a future *advisory* layer behind the
+  factory, never primary.
+- **Provider factory pattern is mandatory** for any new pluggable
+  backend (storage, transport, similarity). Mirror `decnet/web/db/`
+  and `decnet/bus/` — never let workers import concrete backends.
+- **`kind` discriminator is the extension point** for new feature
+  families. Adding `kind="cmd_ngram"` later does not require schema
+  changes — the `vec_<kind>` table is created lazily on first insert.
+- **`Credential.attacker_uuid` is nullable on write** by design — the
+  credential capture path runs before the profiler mints `Attacker`,
+  so coupling them would create a chicken-and-egg ordering bug. The
+  profiler backfills.
+- **`CredentialReuse.confidence` is always 1.0 today** (exact-secret
+  match). The column exists so a future fuzzy-credential pass
+  (`hunter2` ≈ `hunter22`) can write 0.x rows without schema work.
+
+## Verification checklist for the next agent
+
+After finishing each chunk:
+
+- `pytest tests/<area> --timeout=30 --timeout-method=thread` — must
+  be green before moving on.
+- Don't run fuzz/bench/live/stress in the dev loop (memory:
+  `feedback_skip_heavy_tests`).
+- Don't pre-clear with custom bandit/ruff flags (memory:
+  `feedback_trust_git_hooks`) — the pre-commit hook is authoritative.
+- Commit per task, not batched (memory: `feedback_commit_per_task`).
+  Don't add Co-Authored-By to commit messages.
+
+## Open questions to surface to ANTI before tackling §4
+
+- Should the dashboard "Reuse" surface live as a tab on the existing
+  Credentials page, or as a sibling page? (The plan said tab, but
+  worth confirming once you've seen the code.)
+- Pagination size for the reuse list — match the existing Credentials
+  view default, or use a smaller page since the rows are wider?
diff --git a/decnet/bus/topics.py b/decnet/bus/topics.py
index 9c4566af..ccd9d7a0 100644
--- a/decnet/bus/topics.py
+++ b/decnet/bus/topics.py
@@ -14,6 +14,8 @@ Token structure (NATS-style, dot-separated):
     attacker.scored
     attacker.session.started
     attacker.session.ended
+    credential.captured
+    credential.reuse.detected
     system.log
     system.bus.health
     system.{worker}.health
@@ -32,6 +34,7 @@ TOPOLOGY = "topology"
 DECKY = "decky"
 ATTACKER = "attacker"
 SYSTEM = "system"
+CREDENTIAL = "credential"
 
 
 # ─── Leaf event-type constants (the last segment of each topic) ──────────────
@@ -75,6 +78,15 @@ ATTACKER_FINGERPRINTED = "fingerprinted"
 ATTACKER_SESSION_STARTED = "session.started"
 ATTACKER_SESSION_ENDED = "session.ended"
 
+# Credential event types (second/third tokens under ``credential``).
+# ``credential.captured`` fires once per upserted Credential row — the
+# correlator listens for it and runs the cred-reuse query in response,
+# so reuse detection latency is sub-second after a fresh capture.
+# ``credential.reuse.detected`` fires when the correlator inserts a new
+# CredentialReuse row or grows an existing one (added decky/service/IP).
+CREDENTIAL_CAPTURED = "captured"
+CREDENTIAL_REUSE_DETECTED = "reuse.detected"
+
 # System event types.
 SYSTEM_LOG = "log"
 SYSTEM_BUS_HEALTH = "bus.health"
@@ -143,6 +155,19 @@ def system(event_type: str) -> str:
     return f"{SYSTEM}.{event_type}"
 
 
+def credential(event_type: str) -> str:
+    """Build ``credential.<event_type>``.
+
+    *event_type* is typically one of :data:`CREDENTIAL_CAPTURED` or
+    :data:`CREDENTIAL_REUSE_DETECTED`. Dotted leaves
+    (``reuse.detected``) are permitted — same rationale as
+    :func:`system`.
+    """
+    if not event_type:
+        raise ValueError("credential topic requires a non-empty event_type")
+    return f"{CREDENTIAL}.{event_type}"
+
+
 def attacker(event_type: str) -> str:
     """Build ``attacker.<event_type>``.
 
diff --git a/decnet/vectorstore/__init__.py b/decnet/vectorstore/__init__.py
new file mode 100644
index 00000000..0a1f0f86
--- /dev/null
+++ b/decnet/vectorstore/__init__.py
@@ -0,0 +1,27 @@
+"""Vector store substrate for behavioral fingerprint similarity search.
+
+Provider-pluggable storage for ``(kind, id, vector)`` triples used by the
+future statistical re-identification engine. ``kind`` discriminates
+feature families (``ja3``, ``hassh``, ``keystroke``, ``cmd_ngram``, ...)
+so new feature types are additive — no schema migration required when
+adding a new extractor.
+
+Use :func:`get_vectorstore` from :mod:`decnet.vectorstore.factory`; never
+import concrete implementations directly. Mirrors the same factory
+discipline as :mod:`decnet.bus` and :mod:`decnet.web.db`.
+"""
+from decnet.vectorstore.base import (
+    BaseVectorStore,
+    Neighbor,
+    VectorRecord,
+    VECTORSTORE_SCHEMA_VERSION,
+)
+from decnet.vectorstore.factory import get_vectorstore
+
+__all__ = [
+    "BaseVectorStore",
+    "Neighbor",
+    "VectorRecord",
+    "VECTORSTORE_SCHEMA_VERSION",
+    "get_vectorstore",
+]
diff --git a/decnet/vectorstore/base.py b/decnet/vectorstore/base.py
new file mode 100644
index 00000000..ad6d27fa
--- /dev/null
+++ b/decnet/vectorstore/base.py
@@ -0,0 +1,114 @@
+"""Vector-store abstractions: :class:`BaseVectorStore` ABC + record types.
+
+Every backend (sqlite-vec, in-memory fake, future pgvector / Qdrant)
+speaks this contract. The store is keyed by ``(kind, id)`` where:
+
+* ``kind`` is a short discriminator (``ja3``, ``hassh``,
+  ``keystroke_dwell``, ``cmd_ngram``, ...) — vectors are only ever
+  compared **within the same kind**, so adding a new feature family is
+  a non-event for the store.
+* ``id`` is a stable identifier owned by the caller — typically the
+  ``session_id`` or ``attacker_uuid``. The store does not interpret it.
+* ``extractor_version`` is recorded alongside the vector so v1 vs v2 of
+  the same kind never get cross-compared by accident — a similarity
+  scorer that respects versioning is the consumer's responsibility, but
+  the data it needs is here.
+
+The contract is intentionally minimal (insert/get/knn/delete/health) so
+backends with different physical layouts can implement it
+straightforwardly. No batch APIs in v1 — sub-millisecond per-vector
+overhead at honeypot scales (≤ 100k vectors per kind) makes batching
+unnecessary, and the loop-over-singles pattern keeps the contract small.
+"""
+from __future__ import annotations
+
+import abc
+from dataclasses import dataclass
+from typing import Optional, Sequence
+
+# Bumped when the wire/ABI shape of records changes incompatibly.
+# Backends MAY refuse to load older data when this changes, but the
+# pre-v1 expectation is to migrate forward in the same release.
+VECTORSTORE_SCHEMA_VERSION = 1
+
+
+@dataclass(frozen=True)
+class VectorRecord:
+    """One stored vector, returned by :meth:`BaseVectorStore.get`."""
+
+    kind: str
+    id: str
+    vector: Sequence[float]
+    dim: int
+    extractor_version: int = 1
+
+
+@dataclass(frozen=True)
+class Neighbor:
+    """One similarity-search hit, returned by :meth:`BaseVectorStore.knn`.
+
+    ``distance`` is whatever the backend's native metric reports —
+    cosine distance for sqlite-vec's default index, L2 for the in-memory
+    fake. Smaller is more similar in both cases. Consumers that need
+    a uniform metric should configure the backend explicitly.
+    """
+
+    kind: str
+    id: str
+    distance: float
+
+
+class BaseVectorStore(abc.ABC):
+    """Async interface for a kind-discriminated vector store.
+
+    Implementations MAY be transactional (sqlite) or not (pure
+    in-memory). All methods are async to match the rest of the DECNET
+    storage layer; trivial backends can ``await`` no-op coroutines.
+    """
+
+    @abc.abstractmethod
+    async def initialize(self) -> None:
+        """One-shot setup (open files, load extensions, create tables)."""
+
+    @abc.abstractmethod
+    async def close(self) -> None:
+        """Release resources. Idempotent."""
+
+    @abc.abstractmethod
+    async def health(self) -> dict:
+        """Liveness + capability probe.
+
+        Returns a dict like ``{"ok": True, "backend": "sqlite_vec",
+        "kinds": 4, "vectors": 12_345}``. Used by ``/api/v1/health`` and
+        diagnostics; never raises — backends that can't determine a
+        field set it to None.
+        """
+
+    @abc.abstractmethod
+    async def insert(
+        self,
+        kind: str,
+        id: str,
+        vector: Sequence[float],
+        *,
+        extractor_version: int = 1,
+    ) -> None:
+        """Insert or replace ``(kind, id)``. Vector dim is fixed per kind
+        the first time a kind is seen; mismatched dims raise.
+        """
+
+    @abc.abstractmethod
+    async def get(self, kind: str, id: str) -> Optional[VectorRecord]:
+        """Fetch one record, or None if absent."""
+
+    @abc.abstractmethod
+    async def delete(self, kind: str, id: str) -> bool:
+        """Delete one record. Returns True if a row was removed."""
+
+    @abc.abstractmethod
+    async def knn(
+        self, kind: str, vector: Sequence[float], k: int = 10
+    ) -> list[Neighbor]:
+        """Return up to *k* nearest neighbors of ``vector`` within
+        ``kind``. Empty list if the kind is unknown or empty.
+        """
diff --git a/decnet/vectorstore/factory.py b/decnet/vectorstore/factory.py
new file mode 100644
index 00000000..a75ee1fb
--- /dev/null
+++ b/decnet/vectorstore/factory.py
@@ -0,0 +1,73 @@
+"""Vectorstore factory — selects a :class:`BaseVectorStore` implementation.
+
+Dispatch keys:
+
+* ``DECNET_VECTORSTORE_ENABLED`` — ``"false"`` short-circuits to
+  :class:`~decnet.vectorstore.fake.NullVectorStore`. Default ``"true"``.
+* ``DECNET_VECTORSTORE_TYPE`` — ``"sqlite_vec"`` (default) or
+  ``"fake"``.
+* ``DECNET_VECTORSTORE_PATH`` — sqlite file path. Defaults to
+  ``/var/lib/decnet/vectors.sqlite`` if writable, else
+  ``~/.decnet/vectors.sqlite``.
+
+Mirrors :mod:`decnet.bus.factory` and :mod:`decnet.web.db.factory`:
+lazy imports inside each branch, env-driven dispatch, callers MUST go
+through :func:`get_vectorstore` rather than instantiating backends.
+
+If ``sqlite_vec`` is requested but the extension is unavailable on
+this host, the factory logs a warning and returns the fake backend
+instead — the caller's code path stays valid (``insert`` no-ops, etc.)
+without crashing the worker on a missing optional dependency.
+"""
+from __future__ import annotations
+
+import logging
+import os
+from typing import Any
+
+from decnet.vectorstore.base import BaseVectorStore
+
+LOG = logging.getLogger(__name__)
+
+
+def get_vectorstore(**kwargs: Any) -> BaseVectorStore:
+    if os.environ.get("DECNET_VECTORSTORE_ENABLED", "true").lower() == "false":
+        from decnet.vectorstore.fake import NullVectorStore
+        return NullVectorStore()
+
+    backend = os.environ.get("DECNET_VECTORSTORE_TYPE", "sqlite_vec").lower()
+
+    if backend == "fake":
+        from decnet.vectorstore.fake import FakeVectorStore
+        return FakeVectorStore()
+
+    if backend == "sqlite_vec":
+        # Probe extension availability up front so the factory can fall
+        # back cleanly. Construction is cheap, but the extension load
+        # only happens in initialize(); without this probe the caller
+        # sees the failure too late to substitute a backend.
+        try:
+            import sqlite_vec  # noqa: F401
+        except ImportError as e:
+            LOG.warning(
+                "sqlite_vec not installed (%s); falling back to FakeVectorStore. "
+                "Install the sqlite-vec package or set "
+                "DECNET_VECTORSTORE_TYPE=fake to silence this warning.", e,
+            )
+            from decnet.vectorstore.fake import FakeVectorStore
+            return FakeVectorStore()
+        from decnet.vectorstore.sqlite_vec import SqliteVecVectorStore
+        db_path = kwargs.pop("db_path", None) or _default_db_path()
+        return SqliteVecVectorStore(db_path=db_path)
+
+    raise ValueError(f"Unsupported vectorstore type: {backend}")
+
+
+def _default_db_path() -> str:
+    explicit = os.environ.get("DECNET_VECTORSTORE_PATH")
+    if explicit:
+        return explicit
+    runtime_dir = "/var/lib/decnet"
+    if os.path.isdir(runtime_dir) and os.access(runtime_dir, os.W_OK):
+        return f"{runtime_dir}/vectors.sqlite"
+    return os.path.expanduser("~/.decnet/vectors.sqlite")
diff --git a/decnet/vectorstore/fake.py b/decnet/vectorstore/fake.py
new file mode 100644
index 00000000..93c64694
--- /dev/null
+++ b/decnet/vectorstore/fake.py
@@ -0,0 +1,131 @@
+"""In-memory vector store backend.
+
+Two flavors:
+
+* :class:`FakeVectorStore` — a real, working in-memory store. Used by
+  tests and by dev environments that want similarity search without
+  any native extension on the box. KNN is brute-force L2 — fine up to
+  a few thousand vectors per kind.
+* :class:`NullVectorStore` — a no-op store returned by the factory
+  when ``DECNET_VECTORSTORE_ENABLED=false``. Every method succeeds
+  trivially; ``get`` and ``knn`` return None / [] respectively. Lets
+  workers run unaffected when the operator hasn't opted into vector
+  features yet.
+"""
+from __future__ import annotations
+
+import math
+from typing import Optional, Sequence
+
+from decnet.vectorstore.base import BaseVectorStore, Neighbor, VectorRecord
+
+
+class FakeVectorStore(BaseVectorStore):
+    """Pure-python in-memory vector store, brute-force KNN.
+
+    Suitable for tests and small-scale dev (≤ a few thousand vectors
+    per kind). Not persistent — every process restart drops state.
+    """
+
+    def __init__(self) -> None:
+        # {kind: {id: VectorRecord}}
+        self._store: dict[str, dict[str, VectorRecord]] = {}
+        # {kind: dim} — locked the first time a kind is written.
+        self._dims: dict[str, int] = {}
+
+    async def initialize(self) -> None:
+        return None
+
+    async def close(self) -> None:
+        return None
+
+    async def health(self) -> dict:
+        total = sum(len(by_id) for by_id in self._store.values())
+        return {
+            "ok": True,
+            "backend": "fake",
+            "kinds": len(self._store),
+            "vectors": total,
+        }
+
+    async def insert(
+        self,
+        kind: str,
+        id: str,
+        vector: Sequence[float],
+        *,
+        extractor_version: int = 1,
+    ) -> None:
+        dim = len(vector)
+        existing_dim = self._dims.get(kind)
+        if existing_dim is None:
+            self._dims[kind] = dim
+        elif existing_dim != dim:
+            raise ValueError(
+                f"vector dim mismatch for kind={kind!r}: "
+                f"expected {existing_dim}, got {dim}"
+            )
+        rec = VectorRecord(
+            kind=kind, id=id, vector=tuple(float(x) for x in vector),
+            dim=dim, extractor_version=int(extractor_version),
+        )
+        self._store.setdefault(kind, {})[id] = rec
+
+    async def get(self, kind: str, id: str) -> Optional[VectorRecord]:
+        return self._store.get(kind, {}).get(id)
+
+    async def delete(self, kind: str, id: str) -> bool:
+        bucket = self._store.get(kind)
+        if bucket is None or id not in bucket:
+            return False
+        del bucket[id]
+        return True
+
+    async def knn(
+        self, kind: str, vector: Sequence[float], k: int = 10
+    ) -> list[Neighbor]:
+        bucket = self._store.get(kind)
+        if not bucket:
+            return []
+        q = tuple(float(x) for x in vector)
+        if len(q) != self._dims.get(kind, len(q)):
+            raise ValueError(
+                f"query dim {len(q)} != stored dim {self._dims[kind]} "
+                f"for kind={kind!r}"
+            )
+        scored: list[Neighbor] = []
+        for rid, rec in bucket.items():
+            d = math.sqrt(sum((a - b) ** 2 for a, b in zip(q, rec.vector)))
+            scored.append(Neighbor(kind=kind, id=rid, distance=d))
+        scored.sort(key=lambda n: n.distance)
+        return scored[: max(0, int(k))]
+
+
+class NullVectorStore(BaseVectorStore):
+    """No-op vector store. Returned when vectorstore is disabled."""
+
+    async def initialize(self) -> None:
+        return None
+
+    async def close(self) -> None:
+        return None
+
+    async def health(self) -> dict:
+        return {"ok": True, "backend": "null", "kinds": 0, "vectors": 0}
+
+    async def insert(
+        self, kind: str, id: str, vector: Sequence[float],
+        *, extractor_version: int = 1,
+    ) -> None:
+        return None
+
+    async def get(self, kind: str, id: str) -> Optional[VectorRecord]:
+        return None
+
+    async def delete(self, kind: str, id: str) -> bool:
+        return False
+
+    async def knn(
+        self, kind: str, vector: Sequence[float], k: int = 10
+    ) -> list[Neighbor]:
+        return []
diff --git a/decnet/vectorstore/sqlite_vec.py b/decnet/vectorstore/sqlite_vec.py
new file mode 100644
index 00000000..b38c414d
--- /dev/null
+++ b/decnet/vectorstore/sqlite_vec.py
@@ -0,0 +1,285 @@
+"""SQLite + sqlite-vec backend.
+
+Lazy-imports the ``sqlite_vec`` extension. If the extension isn't
+available (the package isn't installed, or the host's libsqlite3 is too
+old to load loadable extensions), construction raises
+:class:`SqliteVecUnavailable`; the factory catches that and falls back
+to :class:`~decnet.vectorstore.fake.FakeVectorStore` with a warning.
+
+Schema:
+
+    CREATE TABLE vectors (
+        kind TEXT NOT NULL,
+        id   TEXT NOT NULL,
+        extractor_version INTEGER NOT NULL DEFAULT 1,
+        dim  INTEGER NOT NULL,
+        PRIMARY KEY (kind, id)
+    );
+    CREATE VIRTUAL TABLE vec_<kind> USING vec0(
+        embedding float[<dim>]
+    );
+
+A vec0 virtual table is created lazily per-kind on first insert
+(distinct ``kind`` values get distinct vec0 tables because vec0's dim
+is a schema-time constant). The ``vectors`` row is the source of truth
+for metadata (extractor_version, dim) and for the (kind, id) → rowid
+mapping; vec0 stores only the embedding, keyed by an INTEGER rowid.
+"""
+from __future__ import annotations
+
+import asyncio
+import logging
+import sqlite3
+import threading
+from pathlib import Path
+from typing import Optional, Sequence
+
+from decnet.vectorstore.base import BaseVectorStore, Neighbor, VectorRecord
+
+LOG = logging.getLogger(__name__)
+
+
+class SqliteVecUnavailable(RuntimeError):
+    """sqlite_vec couldn't be loaded (extension missing / too-old sqlite3)."""
+
+
+def _load_sqlite_vec(conn: sqlite3.Connection) -> None:
+    try:
+        import sqlite_vec  # type: ignore[import-untyped]
+    except ImportError as e:
+        raise SqliteVecUnavailable("sqlite_vec package not installed") from e
+    try:
+        conn.enable_load_extension(True)
+    except (AttributeError, sqlite3.NotSupportedError) as e:
+        raise SqliteVecUnavailable(
+            "system sqlite3 was built without loadable-extension support"
+        ) from e
+    try:
+        sqlite_vec.load(conn)
+    except sqlite3.OperationalError as e:
+        raise SqliteVecUnavailable(f"sqlite_vec load failed: {e}") from e
+    finally:
+        try:
+            conn.enable_load_extension(False)
+        except sqlite3.NotSupportedError:
+            pass
+
+
+class SqliteVecVectorStore(BaseVectorStore):
+    """sqlite-vec backed vector store. Single-file, async-friendly via
+    :func:`asyncio.to_thread`. Keep one instance per process.
+    """
+
+    def __init__(self, db_path: str) -> None:
+        self._db_path = db_path
+        self._conn: Optional[sqlite3.Connection] = None
+        self._lock = threading.Lock()
+        # {kind: dim} cached after first insert/probe.
+        self._kinds: dict[str, int] = {}
+
+    async def initialize(self) -> None:
+        await asyncio.to_thread(self._init_sync)
+
+    def _init_sync(self) -> None:
+        Path(self._db_path).parent.mkdir(parents=True, exist_ok=True)
+        conn = sqlite3.connect(self._db_path, check_same_thread=False)
+        _load_sqlite_vec(conn)  # raises SqliteVecUnavailable on failure
+        conn.execute("PRAGMA journal_mode=WAL")
+        conn.execute(
+            """
+            CREATE TABLE IF NOT EXISTS vectors (
+                kind TEXT NOT NULL,
+                id   TEXT NOT NULL,
+                extractor_version INTEGER NOT NULL DEFAULT 1,
+                dim  INTEGER NOT NULL,
+                rowid_in_vec INTEGER NOT NULL,
+                PRIMARY KEY (kind, id)
+            )
+            """
+        )
+        conn.execute(
+            "CREATE INDEX IF NOT EXISTS ix_vectors_kind ON vectors(kind)"
+        )
+        conn.commit()
+        # Re-hydrate kind→dim cache from any existing rows so a process
+        # restart doesn't accept a mismatched dim on the first insert.
+        for row in conn.execute("SELECT kind, dim FROM vectors GROUP BY kind"):
+            self._kinds[row[0]] = int(row[1])
+        self._conn = conn
+
+    async def close(self) -> None:
+        await asyncio.to_thread(self._close_sync)
+
+    def _close_sync(self) -> None:
+        with self._lock:
+            if self._conn is not None:
+                self._conn.close()
+                self._conn = None
+
+    async def health(self) -> dict:
+        return await asyncio.to_thread(self._health_sync)
+
+    def _health_sync(self) -> dict:
+        if self._conn is None:
+            return {"ok": False, "backend": "sqlite_vec", "reason": "not initialized"}
+        try:
+            row = self._conn.execute("SELECT COUNT(*) FROM vectors").fetchone()
+            return {
+                "ok": True,
+                "backend": "sqlite_vec",
+                "kinds": len(self._kinds),
+                "vectors": int(row[0]) if row else 0,
+            }
+        except sqlite3.Error as e:
+            return {"ok": False, "backend": "sqlite_vec", "reason": str(e)}
+
+    @staticmethod
+    def _vec_table(kind: str) -> str:
+        # Validate the kind so it can't break out of the table name.
+        # Allowed: ascii letters, digits, underscore. Anything else =
+        # programmer error; raise loudly.
+        if not kind or not all(c.isalnum() or c == "_" for c in kind):
+            raise ValueError(f"invalid kind {kind!r}: ascii [a-z0-9_] only")
+        return f"vec_{kind}"
+
+    def _ensure_kind_table(self, kind: str, dim: int) -> None:
+        assert self._conn is not None  # nosec B101
+        existing = self._kinds.get(kind)
+        if existing is None:
+            # vec_<kind> identifier is validated by _vec_table() to be
+            # ascii [a-z0-9_] only, and dim is int-cast — no injection
+            # vector. The f-string is the only way to interpolate a
+            # virtual-table name; placeholders aren't allowed for DDL.
+            ddl = (  # nosec B608
+                f"CREATE VIRTUAL TABLE IF NOT EXISTS {self._vec_table(kind)} "
+                f"USING vec0(embedding float[{int(dim)}])"
+            )
+            self._conn.execute(ddl)
+            self._conn.commit()
+            self._kinds[kind] = dim
+        elif existing != dim:
+            raise ValueError(
+                f"vector dim mismatch for kind={kind!r}: "
+                f"expected {existing}, got {dim}"
+            )
+
+    async def insert(
+        self, kind: str, id: str, vector: Sequence[float],
+        *, extractor_version: int = 1,
+    ) -> None:
+        await asyncio.to_thread(
+            self._insert_sync, kind, id, list(vector), int(extractor_version)
+        )
+
+    def _insert_sync(
+        self, kind: str, id: str, vector: list[float], extractor_version: int,
+    ) -> None:
+        with self._lock:
+            assert self._conn is not None  # nosec B101
+            dim = len(vector)
+            self._ensure_kind_table(kind, dim)
+            vec_table = self._vec_table(kind)
+            cur = self._conn.cursor()
+            existing = cur.execute(
+                "SELECT rowid_in_vec FROM vectors WHERE kind=? AND id=?",
+                (kind, id),
+            ).fetchone()
+            if existing is not None:
+                rowid = int(existing[0])
+                # vec_table is validated; rowid is bound. Safe.
+                cur.execute(f"DELETE FROM {vec_table} WHERE rowid=?", (rowid,))  # nosec B608
+            import struct
+            blob = struct.pack(f"{dim}f", *vector)
+            cur.execute(f"INSERT INTO {vec_table}(embedding) VALUES (?)", (blob,))  # nosec B608
+            new_rowid = cur.lastrowid
+            cur.execute(
+                "INSERT OR REPLACE INTO vectors"
+                "(kind, id, extractor_version, dim, rowid_in_vec) "
+                "VALUES (?, ?, ?, ?, ?)",
+                (kind, id, extractor_version, dim, new_rowid),
+            )
+            self._conn.commit()
+
+    async def get(self, kind: str, id: str) -> Optional[VectorRecord]:
+        return await asyncio.to_thread(self._get_sync, kind, id)
+
+    def _get_sync(self, kind: str, id: str) -> Optional[VectorRecord]:
+        with self._lock:
+            assert self._conn is not None  # nosec B101
+            row = self._conn.execute(
+                "SELECT extractor_version, dim, rowid_in_vec "
+                "FROM vectors WHERE kind=? AND id=?",
+                (kind, id),
+            ).fetchone()
+            if row is None:
+                return None
+            ext_v, dim, rowid = int(row[0]), int(row[1]), int(row[2])
+            vec_table = self._vec_table(kind)
+            blob_row = self._conn.execute(f"SELECT embedding FROM {vec_table} WHERE rowid=?", (rowid,)).fetchone()  # nosec B608
+            if blob_row is None:
+                return None
+            import struct
+            vec = list(struct.unpack(f"{dim}f", blob_row[0]))
+            return VectorRecord(
+                kind=kind, id=id, vector=vec, dim=dim,
+                extractor_version=ext_v,
+            )
+
+    async def delete(self, kind: str, id: str) -> bool:
+        return await asyncio.to_thread(self._delete_sync, kind, id)
+
+    def _delete_sync(self, kind: str, id: str) -> bool:
+        with self._lock:
+            assert self._conn is not None  # nosec B101
+            row = self._conn.execute(
+                "SELECT rowid_in_vec FROM vectors WHERE kind=? AND id=?",
+                (kind, id),
+            ).fetchone()
+            if row is None:
+                return False
+            rowid = int(row[0])
+            vec_table = self._vec_table(kind)
+            self._conn.execute(f"DELETE FROM {vec_table} WHERE rowid=?", (rowid,))  # nosec B608
+            self._conn.execute(
+                "DELETE FROM vectors WHERE kind=? AND id=?", (kind, id)
+            )
+            self._conn.commit()
+            return True
+
+    async def knn(
+        self, kind: str, vector: Sequence[float], k: int = 10,
+    ) -> list[Neighbor]:
+        return await asyncio.to_thread(self._knn_sync, kind, list(vector), int(k))
+
+    def _knn_sync(self, kind: str, vector: list[float], k: int) -> list[Neighbor]:
+        with self._lock:
+            assert self._conn is not None  # nosec B101
+            existing_dim = self._kinds.get(kind)
+            if existing_dim is None:
+                return []
+            if len(vector) != existing_dim:
+                raise ValueError(
+                    f"query dim {len(vector)} != stored dim {existing_dim} "
+                    f"for kind={kind!r}"
+                )
+            vec_table = self._vec_table(kind)
+            import struct
+            qblob = struct.pack(f"{existing_dim}f", *vector)
+            knn_sql = f"SELECT rowid, distance FROM {vec_table} WHERE embedding MATCH ? ORDER BY distance LIMIT ?"  # nosec B608
+            rows = self._conn.execute(knn_sql, (qblob, max(0, k))).fetchall()
+            if not rows:
+                return []
+            id_map = {
+                int(r[0]): r[1]
+                for r in self._conn.execute(
+                    "SELECT rowid_in_vec, id FROM vectors WHERE kind=?",
+                    (kind,),
+                )
+            }
+            out: list[Neighbor] = []
+            for rowid, dist in rows:
+                rid = id_map.get(int(rowid))
+                if rid is None:
+                    continue
+                out.append(Neighbor(kind=kind, id=rid, distance=float(dist)))
+            return out
diff --git a/decnet/web/db/models/__init__.py b/decnet/web/db/models/__init__.py
index 6de83d61..c55f99ac 100644
--- a/decnet/web/db/models/__init__.py
+++ b/decnet/web/db/models/__init__.py
@@ -49,6 +49,8 @@ from .logs import (
     Bounty,
     BountyResponse,
     Credential,
+    CredentialReuse,
+    CredentialReuseResponse,
     CredentialsResponse,
     Log,
     LogsResponse,
@@ -170,6 +172,8 @@ __all__ = [
     "Bounty",
     "BountyResponse",
     "Credential",
+    "CredentialReuse",
+    "CredentialReuseResponse",
     "CredentialsResponse",
     "Log",
     "LogsResponse",
diff --git a/decnet/web/db/models/logs.py b/decnet/web/db/models/logs.py
index af5ce93d..779819cd 100644
--- a/decnet/web/db/models/logs.py
+++ b/decnet/web/db/models/logs.py
@@ -3,7 +3,7 @@ from datetime import datetime, timezone
 from typing import Any, List, Optional
 
 from pydantic import BaseModel
-from sqlalchemy import Column, Index, Text
+from sqlalchemy import Column, Index, Text, UniqueConstraint
 from sqlmodel import Field, SQLModel
 
 from ._base import _BIG_TEXT
@@ -54,9 +54,13 @@ class Credential(SQLModel, table=True):
     LDAP. Nullable for principal-less mechanisms (Redis AUTH, bearer
     tokens). Fully service-specific keys ride in ``fields`` JSON.
 
-    Dedup contract: same (attacker_uuid, decky, service, secret_sha256,
+    Dedup contract: same (attacker_ip, decky, service, secret_sha256,
     principal_or_empty) tuple → upsert, bumps ``attempt_count`` and
     ``last_seen``. Different secret or different principal → new row.
+
+    ``attacker_uuid`` is backfilled by the profiler once an Attacker row
+    has been minted for the source IP. It is nullable on first write so
+    the credential ingest path stays decoupled from the profiler.
     """
     __tablename__ = "credentials"
     __table_args__ = (
@@ -64,11 +68,15 @@ class Credential(SQLModel, table=True):
         Index("ix_credentials_principal_service", "principal", "service"),
     )
     id: Optional[int] = Field(default=None, primary_key=True)
-    # Keyed by attacker IP (not attackers.uuid) to match Bounty's pattern
-    # and avoid the chicken-and-egg of writing a credential row before
-    # the profiler has minted the Attacker. Index covers the join path
-    # cred_reuse → Attacker.ip.
+    # Keyed by attacker IP (not attackers.uuid) on the write path to
+    # avoid the chicken-and-egg of landing a credential before the
+    # profiler has minted the Attacker. The profiler backfills
+    # ``attacker_uuid`` once it knows the IP, so cross-IP reuse queries
+    # eventually have an indexed FK to traverse.
     attacker_ip: str = Field(index=True)
+    attacker_uuid: Optional[str] = Field(
+        default=None, foreign_key="attackers.uuid", index=True
+    )
     decky_name: str = Field(index=True)
     service: str = Field(index=True)
     principal: Optional[str] = Field(default=None, index=True, max_length=256)
@@ -107,6 +115,77 @@ class Credential(SQLModel, table=True):
     attempt_count: int = Field(default=1)
 
 
+class CredentialReuse(SQLModel, table=True):
+    """One observed credential reuse pattern across deckies and/or services.
+
+    A row here is a *finding* produced by the correlator: the same
+    ``(secret_sha256, secret_kind, principal)`` tuple was observed
+    against ``target_count`` distinct decky×service pairs. Upserted on
+    that natural key — the row accumulates new deckies/services/IPs
+    over time as the credential is reused.
+
+    The ``confidence`` column is reserved for a future fuzzy-match pass
+    (credential variants, e.g. ``hunter2`` vs ``hunter22``); rows
+    written by the exact-secret correlator are always 1.0.
+    """
+    __tablename__ = "credential_reuse"
+    __table_args__ = (
+        UniqueConstraint(
+            "secret_sha256", "secret_kind", "principal_key",
+            name="uq_credential_reuse_secret_principal",
+        ),
+    )
+    id: str = Field(primary_key=True, max_length=36)
+    secret_sha256: str = Field(index=True, max_length=64)
+    secret_kind: str = Field(index=True, max_length=32)
+    # Optional human-readable principal (e.g. "root"). Nullable — for
+    # cross-principal reuse rows we leave this null, but we still need
+    # a unique constraint, so ``principal_key`` is the non-null
+    # canonicalised form ("" when principal is null) used in the
+    # uniqueness tuple. SQLite's NULLs-distinct-in-UNIQUE behaviour
+    # would otherwise let duplicate null-principal rows through.
+    principal: Optional[str] = Field(default=None, max_length=256)
+    principal_key: str = Field(default="", max_length=256)
+    attacker_uuids: str = Field(
+        default="[]",
+        sa_column=Column("attacker_uuids", _BIG_TEXT, nullable=False, default="[]"),
+    )  # JSON list[str]
+    attacker_ips: str = Field(
+        default="[]",
+        sa_column=Column("attacker_ips", _BIG_TEXT, nullable=False, default="[]"),
+    )  # JSON list[str]
+    deckies: str = Field(
+        default="[]",
+        sa_column=Column("deckies", _BIG_TEXT, nullable=False, default="[]"),
+    )  # JSON list[str]
+    services: str = Field(
+        default="[]",
+        sa_column=Column("services", _BIG_TEXT, nullable=False, default="[]"),
+    )  # JSON list[str]
+    # COUNT(DISTINCT decky||':'||service). The discriminative scalar
+    # for ranking and filtering — a credential seen on 12 targets is
+    # far more interesting than one seen on 2.
+    target_count: int = Field(default=0, index=True)
+    attempt_count: int = Field(default=0)
+    confidence: float = Field(default=1.0)
+    first_seen: datetime = Field(
+        default_factory=lambda: datetime.now(timezone.utc), index=True
+    )
+    last_seen: datetime = Field(
+        default_factory=lambda: datetime.now(timezone.utc), index=True
+    )
+    updated_at: datetime = Field(
+        default_factory=lambda: datetime.now(timezone.utc), index=True
+    )
+
+
+class CredentialReuseResponse(BaseModel):
+    total: int
+    limit: int
+    offset: int
+    data: List[dict[str, Any]]
+
+
 class State(SQLModel, table=True):
     __tablename__ = "state"
     key: str = Field(primary_key=True)
diff --git a/decnet/web/db/repository.py b/decnet/web/db/repository.py
index 22d0ea02..fcb0c030 100644
--- a/decnet/web/db/repository.py
+++ b/decnet/web/db/repository.py
@@ -153,12 +153,59 @@ class BaseRepository(ABC):
         pass
 
     @abstractmethod
-    async def get_credential_reuse(
+    async def get_credential_attempts_for_secret(
         self, secret_sha256: str
     ) -> list[dict[str, Any]]:
         """Every (attacker, decky, service, principal) row sharing this secret hash."""
         pass
 
+    @abstractmethod
+    async def upsert_credential_reuse(
+        self,
+        *,
+        secret_sha256: str,
+        secret_kind: str,
+        principal: Optional[str],
+        attacker_uuid: Optional[str],
+        attacker_ip: str,
+        decky: str,
+        service: str,
+        attempt_count: int,
+        ts: Optional[Any] = None,
+    ) -> Optional[dict[str, Any]]:
+        """Upsert one credential-reuse finding. Returns the row dict (with
+        ``inserted: bool`` mixed in) on insert/update, or None if the row
+        is below the reuse threshold and shouldn't be persisted yet.
+        """
+        pass
+
+    @abstractmethod
+    async def list_credential_reuses(
+        self,
+        limit: int = 50,
+        offset: int = 0,
+        min_target_count: int = 2,
+        secret_kind: Optional[str] = None,
+    ) -> tuple[int, list[dict[str, Any]]]:
+        """Paged list of credential-reuse findings ordered by target_count desc."""
+        pass
+
+    @abstractmethod
+    async def get_credential_reuse_by_id(
+        self, reuse_id: str
+    ) -> Optional[dict[str, Any]]:
+        """One credential-reuse finding by UUID, or None."""
+        pass
+
+    @abstractmethod
+    async def update_credential_attacker_uuid(
+        self, attacker_ip: str, attacker_uuid: str
+    ) -> int:
+        """Backfill ``attacker_uuid`` on every Credential row matching the IP
+        whose ``attacker_uuid`` is currently null. Returns rows updated.
+        """
+        pass
+
     @abstractmethod
     async def get_state(self, key: str) -> Optional[dict[str, Any]]:
         """Retrieve a specific state entry by key."""
diff --git a/decnet/web/db/sqlmodel_repo.py b/decnet/web/db/sqlmodel_repo.py
index 256959bc..f4b1e964 100644
--- a/decnet/web/db/sqlmodel_repo.py
+++ b/decnet/web/db/sqlmodel_repo.py
@@ -32,6 +32,7 @@ from decnet.web.db.models import (
     Log,
     Bounty,
     Credential,
+    CredentialReuse,
     State,
     Attacker,
     AttackerBehavior,
@@ -684,7 +685,7 @@ class SQLModelRepository(BaseRepository):
                 out.append(d)
             return out
 
-    async def get_credential_reuse(
+    async def get_credential_attempts_for_secret(
         self, secret_sha256: str
     ) -> List[dict[str, Any]]:
         """Every (attacker_ip, decky, service, principal) row sharing this
@@ -706,6 +707,197 @@ class SQLModelRepository(BaseRepository):
                 out.append(d)
             return out
 
+    # ─── credential reuse (findings) ──────────────────────────────────────
+
+    async def update_credential_attacker_uuid(
+        self, attacker_ip: str, attacker_uuid: str
+    ) -> int:
+        """Backfill ``attacker_uuid`` on every Credential row matching the
+        given IP whose ``attacker_uuid`` is currently null. Run by the
+        profiler after it mints/updates an Attacker row.
+        """
+        async with self._session() as session:
+            result = await session.execute(
+                update(Credential)
+                .where(
+                    Credential.attacker_ip == attacker_ip,
+                    Credential.attacker_uuid.is_(None),
+                )
+                .values(attacker_uuid=attacker_uuid)
+            )
+            await session.commit()
+            return int(result.rowcount or 0)
+
+    @staticmethod
+    def _merge_unique(existing_json: str, value: Optional[str]) -> tuple[str, bool]:
+        """Append ``value`` to a JSON list[str] column if not present.
+        Returns (new_json, changed). None values and duplicates are skipped.
+        """
+        if value is None:
+            return existing_json, False
+        try:
+            current = json.loads(existing_json) if existing_json else []
+            if not isinstance(current, list):
+                current = []
+        except (json.JSONDecodeError, TypeError):
+            current = []
+        if value in current:
+            return existing_json, False
+        current.append(value)
+        return json.dumps(current, ensure_ascii=True), True
+
+    async def upsert_credential_reuse(
+        self,
+        *,
+        secret_sha256: str,
+        secret_kind: str,
+        principal: Optional[str],
+        attacker_uuid: Optional[str],
+        attacker_ip: str,
+        decky: str,
+        service: str,
+        attempt_count: int,
+        ts: Optional[datetime] = None,
+    ) -> Optional[dict[str, Any]]:
+        """Upsert a credential-reuse finding.
+
+        The row is keyed by ``(secret_sha256, secret_kind, principal_key)``
+        — ``principal_key`` is the canonicalised non-null form ("" when
+        principal is null) so the unique constraint behaves the same on
+        SQLite and MySQL.
+
+        Returns the row dict augmented with ``inserted: bool`` and
+        ``changed: bool`` so the correlator can decide whether to publish
+        a bus event.
+        """
+        principal_key = principal or ""
+        now = ts or datetime.now(timezone.utc)
+        async with self._session() as session:
+            existing = (await session.execute(
+                select(CredentialReuse).where(
+                    CredentialReuse.secret_sha256 == secret_sha256,
+                    CredentialReuse.secret_kind == secret_kind,
+                    CredentialReuse.principal_key == principal_key,
+                )
+            )).scalar_one_or_none()
+
+            if existing is None:
+                row = CredentialReuse(
+                    id=str(uuid.uuid4()),
+                    secret_sha256=secret_sha256,
+                    secret_kind=secret_kind,
+                    principal=principal,
+                    principal_key=principal_key,
+                    attacker_uuids=json.dumps(
+                        [attacker_uuid] if attacker_uuid else [], ensure_ascii=True
+                    ),
+                    attacker_ips=json.dumps([attacker_ip], ensure_ascii=True),
+                    deckies=json.dumps([decky], ensure_ascii=True),
+                    services=json.dumps([service], ensure_ascii=True),
+                    target_count=1,
+                    attempt_count=int(attempt_count),
+                    confidence=1.0,
+                    first_seen=now,
+                    last_seen=now,
+                    updated_at=now,
+                )
+                session.add(row)
+                await session.commit()
+                await session.refresh(row)
+                d = row.model_dump(mode="json")
+                d["inserted"] = True
+                d["changed"] = True
+                return d
+
+            changed = False
+            new_uuids, c1 = self._merge_unique(existing.attacker_uuids, attacker_uuid)
+            new_ips, c2 = self._merge_unique(existing.attacker_ips, attacker_ip)
+            new_deckies, c3 = self._merge_unique(existing.deckies, decky)
+            new_services, c4 = self._merge_unique(existing.services, service)
+            existing.attacker_uuids = new_uuids
+            existing.attacker_ips = new_ips
+            if c3 or c4:
+                existing.deckies = new_deckies
+                existing.services = new_services
+                # Recount target tuples from the underlying credentials
+                # table — a (decky, service) tuple only counts when both
+                # were observed together, which the JSON lists alone
+                # can't tell us.
+                stmt = (
+                    select(func.count(func.distinct(
+                        Credential.decky_name + ":" + Credential.service
+                    )))
+                    .where(
+                        Credential.secret_sha256 == secret_sha256,
+                        Credential.secret_kind == secret_kind,
+                        (Credential.principal == principal) if principal is not None
+                        else Credential.principal.is_(None),
+                    )
+                )
+                target_count = (await session.execute(stmt)).scalar() or 0
+                existing.target_count = int(target_count)
+            existing.attempt_count = (existing.attempt_count or 0) + int(attempt_count)
+            existing.last_seen = now
+            existing.updated_at = now
+            if c1 or c2 or c3 or c4:
+                changed = True
+            session.add(existing)
+            await session.commit()
+            await session.refresh(existing)
+            d = existing.model_dump(mode="json")
+            d["inserted"] = False
+            d["changed"] = changed
+            return d
+
+    async def list_credential_reuses(
+        self,
+        limit: int = 50,
+        offset: int = 0,
+        min_target_count: int = 2,
+        secret_kind: Optional[str] = None,
+    ) -> tuple[int, List[dict[str, Any]]]:
+        async with self._session() as session:
+            base = select(CredentialReuse).where(
+                CredentialReuse.target_count >= min_target_count
+            )
+            if secret_kind:
+                base = base.where(CredentialReuse.secret_kind == secret_kind)
+            total_stmt = select(func.count()).select_from(base.subquery())
+            total = (await session.execute(total_stmt)).scalar() or 0
+            list_stmt = (
+                base.order_by(desc(CredentialReuse.target_count),
+                              desc(CredentialReuse.last_seen))
+                .offset(offset).limit(limit)
+            )
+            rows = (await session.execute(list_stmt)).scalars().all()
+            out: List[dict[str, Any]] = []
+            for r in rows:
+                d = r.model_dump(mode="json")
+                for key in ("attacker_uuids", "attacker_ips", "deckies", "services"):
+                    try:
+                        d[key] = json.loads(d[key])
+                    except (json.JSONDecodeError, TypeError):
+                        d[key] = []
+                out.append(d)
+            return int(total), out
+
+    async def get_credential_reuse_by_id(
+        self, reuse_id: str
+    ) -> Optional[dict[str, Any]]:
+        async with self._session() as session:
+            row = (await session.execute(
+                select(CredentialReuse).where(CredentialReuse.id == reuse_id)
+            )).scalar_one_or_none()
+            if row is None:
+                return None
+            d = row.model_dump(mode="json")
+            for key in ("attacker_uuids", "attacker_ips", "deckies", "services"):
+                try:
+                    d[key] = json.loads(d[key])
+                except (json.JSONDecodeError, TypeError):
+                    d[key] = []
+            return d
+
     async def get_state(self, key: str) -> Optional[dict[str, Any]]:
         async with self._session() as session:
             statement = select(State).where(State.key == key)
diff --git a/tests/db/test_base_repo.py b/tests/db/test_base_repo.py
index 52121d68..c4c74c71 100644
--- a/tests/db/test_base_repo.py
+++ b/tests/db/test_base_repo.py
@@ -23,7 +23,11 @@ class DummyRepo(BaseRepository):
     async def get_credentials(self, **kw): await super().get_credentials(**kw)
     async def get_total_credentials(self, **kw): await super().get_total_credentials(**kw)
     async def get_credentials_for_attacker(self, ip): await super().get_credentials_for_attacker(ip)
-    async def get_credential_reuse(self, h): await super().get_credential_reuse(h)
+    async def get_credential_attempts_for_secret(self, h): await super().get_credential_attempts_for_secret(h)
+    async def upsert_credential_reuse(self, **kw): await super().upsert_credential_reuse(**kw); return None
+    async def list_credential_reuses(self, **kw): await super().list_credential_reuses(**kw); return (0, [])
+    async def get_credential_reuse_by_id(self, i): await super().get_credential_reuse_by_id(i)
+    async def update_credential_attacker_uuid(self, ip, u): await super().update_credential_attacker_uuid(ip, u); return 0
     async def get_state(self, k): await super().get_state(k)
     async def set_state(self, k, v): await super().set_state(k, v)
     async def get_max_log_id(self): await super().get_max_log_id()
@@ -73,7 +77,15 @@ async def test_base_repo_coverage():
     await dr.get_credentials()
     await dr.get_total_credentials()
     await dr.get_credentials_for_attacker("1.2.3.4")
-    await dr.get_credential_reuse("abc")
+    await dr.get_credential_attempts_for_secret("abc")
+    await dr.upsert_credential_reuse(
+        secret_sha256="x", secret_kind="plaintext", principal=None,
+        attacker_uuid=None, attacker_ip="1.2.3.4", decky="d", service="ssh",
+        attempt_count=1, ts=None,
+    )
+    await dr.list_credential_reuses()
+    await dr.get_credential_reuse_by_id("a")
+    await dr.update_credential_attacker_uuid("1.2.3.4", "u")
     await dr.get_state("k")
     await dr.set_state("k", "v")
     await dr.get_max_log_id()
diff --git a/tests/db/test_credential_reuse.py b/tests/db/test_credential_reuse.py
new file mode 100644
index 00000000..4c857032
--- /dev/null
+++ b/tests/db/test_credential_reuse.py
@@ -0,0 +1,226 @@
+"""CredentialReuse repo tests — upsert idempotency, list pagination, FK backfill."""
+from __future__ import annotations
+
+import hashlib
+from pathlib import Path
+
+import pytest
+
+from decnet.web.db.factory import get_repository
+
+
+@pytest.fixture
+async def repo(tmp_path: Path):
+    r = get_repository(db_path=str(tmp_path / "reuse.db"))
+    await r.initialize()
+    return r
+
+
+def _sha256(s: str) -> str:
+    return hashlib.sha256(s.encode("utf-8")).hexdigest()
+
+
+async def _seed_credential(repo, **overrides):
+    base = {
+        "attacker_ip": "10.0.0.5",
+        "decky_name": "decky-01",
+        "service": "ssh",
+        "principal": "root",
+        "secret_sha256": _sha256("hunter2"),
+        "secret_b64": "aHVudGVyMg==",
+        "secret_printable": "hunter2",
+        "fields": {},
+    }
+    base.update(overrides)
+    return await repo.upsert_credential(base)
+
+
+@pytest.mark.anyio
+async def test_upsert_inserts_first_observation(repo) -> None:
+    sha = _sha256("hunter2")
+    out = await repo.upsert_credential_reuse(
+        secret_sha256=sha, secret_kind="plaintext", principal="root",
+        attacker_uuid=None, attacker_ip="10.0.0.5",
+        decky="decky-01", service="ssh", attempt_count=1,
+    )
+    assert out is not None
+    assert out["inserted"] is True
+    assert out["target_count"] == 1
+    assert out["confidence"] == 1.0
+
+
+@pytest.mark.anyio
+async def test_upsert_grows_target_count_across_services(repo) -> None:
+    """Same secret on two distinct (decky, service) pairs → target_count=2.
+
+    target_count is recomputed from the credentials table, so the test
+    must seed actual Credential rows first.
+    """
+    sha = _sha256("p4ssw0rd")
+    await _seed_credential(repo, secret_sha256=sha, decky_name="d1", service="ssh")
+    await _seed_credential(repo, secret_sha256=sha, decky_name="d2", service="ftp")
+
+    await repo.upsert_credential_reuse(
+        secret_sha256=sha, secret_kind="plaintext", principal="root",
+        attacker_uuid=None, attacker_ip="10.0.0.5",
+        decky="d1", service="ssh", attempt_count=1,
+    )
+    out = await repo.upsert_credential_reuse(
+        secret_sha256=sha, secret_kind="plaintext", principal="root",
+        attacker_uuid=None, attacker_ip="10.0.0.5",
+        decky="d2", service="ftp", attempt_count=1,
+    )
+    assert out["inserted"] is False
+    assert out["changed"] is True
+    assert out["target_count"] == 2
+
+
+@pytest.mark.anyio
+async def test_upsert_dedups_same_decky_service(repo) -> None:
+    """Repeated upserts for the same (decky, service) don't grow target_count."""
+    sha = _sha256("samepw")
+    await _seed_credential(repo, secret_sha256=sha)
+    for _ in range(3):
+        await repo.upsert_credential_reuse(
+            secret_sha256=sha, secret_kind="plaintext", principal="root",
+            attacker_uuid=None, attacker_ip="10.0.0.5",
+            decky="decky-01", service="ssh", attempt_count=1,
+        )
+    rows = (await repo.list_credential_reuses(min_target_count=1))[1]
+    assert len(rows) == 1
+    assert rows[0]["target_count"] == 1
+    assert rows[0]["attempt_count"] == 3
+
+
+@pytest.mark.anyio
+async def test_upsert_merges_attacker_lists(repo) -> None:
+    """Distinct attacker_uuid/ip values accumulate into the JSON lists."""
+    sha = _sha256("shared")
+    await _seed_credential(repo, secret_sha256=sha, attacker_ip="1.1.1.1")
+    await _seed_credential(
+        repo, secret_sha256=sha, attacker_ip="2.2.2.2", decky_name="d2",
+    )
+    await repo.upsert_credential_reuse(
+        secret_sha256=sha, secret_kind="plaintext", principal="root",
+        attacker_uuid="uuid-A", attacker_ip="1.1.1.1",
+        decky="decky-01", service="ssh", attempt_count=1,
+    )
+    await repo.upsert_credential_reuse(
+        secret_sha256=sha, secret_kind="plaintext", principal="root",
+        attacker_uuid="uuid-B", attacker_ip="2.2.2.2",
+        decky="d2", service="ssh", attempt_count=1,
+    )
+    rows = (await repo.list_credential_reuses(min_target_count=1))[1]
+    assert set(rows[0]["attacker_uuids"]) == {"uuid-A", "uuid-B"}
+    assert set(rows[0]["attacker_ips"]) == {"1.1.1.1", "2.2.2.2"}
+
+
+@pytest.mark.anyio
+async def test_null_principal_uniqueness(repo) -> None:
+    """Two upserts with principal=None go to the same row, not two rows."""
+    sha = _sha256("redis-auth")
+    await _seed_credential(repo, secret_sha256=sha, service="redis", principal=None)
+    for _ in range(2):
+        await repo.upsert_credential_reuse(
+            secret_sha256=sha, secret_kind="plaintext", principal=None,
+            attacker_uuid=None, attacker_ip="1.1.1.1",
+            decky="decky-01", service="redis", attempt_count=1,
+        )
+    rows = (await repo.list_credential_reuses(min_target_count=1))[1]
+    assert len(rows) == 1
+    assert rows[0]["principal"] is None
+
+
+@pytest.mark.anyio
+async def test_list_filters_by_min_target_count(repo) -> None:
+    """min_target_count=2 hides 1-target findings."""
+    sha = _sha256("only-once")
+    await _seed_credential(repo, secret_sha256=sha)
+    await repo.upsert_credential_reuse(
+        secret_sha256=sha, secret_kind="plaintext", principal="root",
+        attacker_uuid=None, attacker_ip="1.1.1.1",
+        decky="decky-01", service="ssh", attempt_count=1,
+    )
+    total, rows = await repo.list_credential_reuses(min_target_count=2)
+    assert total == 0
+    assert rows == []
+    total, _ = await repo.list_credential_reuses(min_target_count=1)
+    assert total == 1
+
+
+@pytest.mark.anyio
+async def test_list_pagination_orders_by_target_count_desc(repo) -> None:
+    sha_a = _sha256("a")
+    sha_b = _sha256("b")
+    # secret a → 1 target
+    await _seed_credential(repo, secret_sha256=sha_a)
+    await repo.upsert_credential_reuse(
+        secret_sha256=sha_a, secret_kind="plaintext", principal="root",
+        attacker_uuid=None, attacker_ip="1.1.1.1",
+        decky="d1", service="ssh", attempt_count=1,
+    )
+    # secret b → 2 targets
+    await _seed_credential(repo, secret_sha256=sha_b, service="ssh")
+    await _seed_credential(repo, secret_sha256=sha_b, service="ftp", decky_name="d2")
+    await repo.upsert_credential_reuse(
+        secret_sha256=sha_b, secret_kind="plaintext", principal="root",
+        attacker_uuid=None, attacker_ip="1.1.1.1",
+        decky="decky-01", service="ssh", attempt_count=1,
+    )
+    await repo.upsert_credential_reuse(
+        secret_sha256=sha_b, secret_kind="plaintext", principal="root",
+        attacker_uuid=None, attacker_ip="1.1.1.1",
+        decky="d2", service="ftp", attempt_count=1,
+    )
+    total, rows = await repo.list_credential_reuses(min_target_count=1)
+    assert total == 2
+    assert rows[0]["secret_sha256"] == sha_b  # higher target_count first
+
+
+@pytest.mark.anyio
+async def test_get_by_id_roundtrip(repo) -> None:
+    sha = _sha256("rt")
+    await _seed_credential(repo, secret_sha256=sha)
+    out = await repo.upsert_credential_reuse(
+        secret_sha256=sha, secret_kind="plaintext", principal="root",
+        attacker_uuid=None, attacker_ip="1.1.1.1",
+        decky="decky-01", service="ssh", attempt_count=1,
+    )
+    fetched = await repo.get_credential_reuse_by_id(out["id"])
+    assert fetched is not None
+    assert fetched["id"] == out["id"]
+    assert fetched["secret_sha256"] == sha
+    assert isinstance(fetched["deckies"], list)
+
+
+@pytest.mark.anyio
+async def test_get_by_id_missing_returns_none(repo) -> None:
+    assert await repo.get_credential_reuse_by_id("nope") is None
+
+
+@pytest.mark.anyio
+async def test_update_credential_attacker_uuid_backfills_only_nulls(repo) -> None:
+    """The profiler hook must backfill attacker_uuid only on rows where it
+    is currently null — pre-existing UUIDs must not be overwritten."""
+    sha = _sha256("backfill")
+    await _seed_credential(repo, secret_sha256=sha, attacker_ip="9.9.9.9")
+    await _seed_credential(
+        repo, secret_sha256=sha, attacker_ip="9.9.9.9",
+        service="ftp", decky_name="d2",
+    )
+    # Backfill: both null, both should update.
+    n = await repo.update_credential_attacker_uuid("9.9.9.9", "uuid-9")
+    assert n == 2
+
+    # Second call: both already set, nothing should change.
+    n2 = await repo.update_credential_attacker_uuid("9.9.9.9", "uuid-other")
+    assert n2 == 0
+
+    rows = await repo.get_credentials_for_attacker("9.9.9.9")
+    assert all(r["attacker_uuid"] == "uuid-9" for r in rows)
+
+
+@pytest.mark.anyio
+async def test_update_credential_attacker_uuid_no_match(repo) -> None:
+    n = await repo.update_credential_attacker_uuid("0.0.0.0", "uuid-x")
+    assert n == 0
diff --git a/tests/db/test_credentials.py b/tests/db/test_credentials.py
index 958959df..f426ea0b 100644
--- a/tests/db/test_credentials.py
+++ b/tests/db/test_credentials.py
@@ -101,7 +101,7 @@ async def test_cross_service_reuse_query(repo) -> None:
             "secret_printable": secret,
             "fields": {},
         })
-    reuse = await repo.get_credential_reuse(sha)
+    reuse = await repo.get_credential_attempts_for_secret(sha)
     assert {r["service"] for r in reuse} == {"ssh", "ftp", "smtp"}
 
 
diff --git a/tests/vectorstore/__init__.py b/tests/vectorstore/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/tests/vectorstore/test_factory.py b/tests/vectorstore/test_factory.py
new file mode 100644
index 00000000..5cdbc053
--- /dev/null
+++ b/tests/vectorstore/test_factory.py
@@ -0,0 +1,66 @@
+"""Tests for :func:`decnet.vectorstore.factory.get_vectorstore` dispatch."""
+from __future__ import annotations
+
+import os
+
+import pytest
+
+from decnet.vectorstore.factory import _default_db_path, get_vectorstore
+from decnet.vectorstore.fake import FakeVectorStore, NullVectorStore
+
+
+def test_disabled_returns_null(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setenv("DECNET_VECTORSTORE_ENABLED", "false")
+    monkeypatch.setenv("DECNET_VECTORSTORE_TYPE", "sqlite_vec")  # ignored when disabled
+    s = get_vectorstore()
+    assert isinstance(s, NullVectorStore)
+
+
+def test_fake_dispatch(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setenv("DECNET_VECTORSTORE_ENABLED", "true")
+    monkeypatch.setenv("DECNET_VECTORSTORE_TYPE", "fake")
+    s = get_vectorstore()
+    assert isinstance(s, FakeVectorStore)
+
+
+def test_sqlite_vec_falls_back_to_fake_when_extension_missing(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """The factory must degrade gracefully when sqlite_vec isn't installed:
+    log a warning, return FakeVectorStore. Workers stay alive instead of
+    crashing on a missing optional dep."""
+    monkeypatch.setenv("DECNET_VECTORSTORE_ENABLED", "true")
+    monkeypatch.setenv("DECNET_VECTORSTORE_TYPE", "sqlite_vec")
+    # Force the import to fail regardless of what's actually installed,
+    # so this test is deterministic on dev boxes that have the extension.
+    import builtins
+    real_import = builtins.__import__
+
+    def _fake_import(name, *a, **kw):  # noqa: ANN001
+        if name == "sqlite_vec":
+            raise ImportError("forced")
+        return real_import(name, *a, **kw)
+
+    monkeypatch.setattr(builtins, "__import__", _fake_import)
+    s = get_vectorstore()
+    assert isinstance(s, FakeVectorStore)
+
+
+def test_unknown_type_raises(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setenv("DECNET_VECTORSTORE_ENABLED", "true")
+    monkeypatch.setenv("DECNET_VECTORSTORE_TYPE", "qdrant")
+    with pytest.raises(ValueError, match="Unsupported vectorstore type"):
+        get_vectorstore()
+
+
+def test_default_db_path_honors_env(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setenv("DECNET_VECTORSTORE_PATH", "/tmp/explicit.sqlite")
+    assert _default_db_path() == "/tmp/explicit.sqlite"
+
+
+def test_default_db_path_falls_back_to_home(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.delenv("DECNET_VECTORSTORE_PATH", raising=False)
+    monkeypatch.setattr("os.path.isdir", lambda p: False)
+    p = _default_db_path()
+    assert p.endswith(".decnet/vectors.sqlite")
+    assert p.startswith(os.path.expanduser("~"))
diff --git a/tests/vectorstore/test_fake.py b/tests/vectorstore/test_fake.py
new file mode 100644
index 00000000..4c132823
--- /dev/null
+++ b/tests/vectorstore/test_fake.py
@@ -0,0 +1,113 @@
+"""Tests for :class:`FakeVectorStore` and :class:`NullVectorStore`.
+
+The fake is the reference implementation of the BaseVectorStore
+contract — every behavior assertion here doubles as a contract test
+that any future backend must satisfy.
+"""
+from __future__ import annotations
+
+import pytest
+
+from decnet.vectorstore.fake import FakeVectorStore, NullVectorStore
+
+
+@pytest.mark.anyio
+async def test_fake_round_trip() -> None:
+    s = FakeVectorStore()
+    await s.initialize()
+    await s.insert("ja3", "sess-1", [1.0, 0.0, 0.0])
+    await s.insert("ja3", "sess-2", [0.9, 0.1, 0.0])
+    await s.insert("ja3", "sess-3", [0.0, 1.0, 0.0])
+
+    rec = await s.get("ja3", "sess-1")
+    assert rec is not None
+    assert rec.kind == "ja3"
+    assert rec.id == "sess-1"
+    assert rec.dim == 3
+    assert tuple(rec.vector) == (1.0, 0.0, 0.0)
+
+
+@pytest.mark.anyio
+async def test_fake_knn_orders_by_distance() -> None:
+    s = FakeVectorStore()
+    await s.initialize()
+    await s.insert("ja3", "near", [1.0, 0.0])
+    await s.insert("ja3", "far", [0.0, 1.0])
+    await s.insert("ja3", "exact", [0.99, 0.01])
+
+    n = await s.knn("ja3", [1.0, 0.0], k=3)
+    assert [x.id for x in n] == ["near", "exact", "far"]
+    assert n[0].distance == 0.0
+    assert n[2].distance > n[1].distance
+
+
+@pytest.mark.anyio
+async def test_fake_knn_unknown_kind_returns_empty() -> None:
+    s = FakeVectorStore()
+    await s.initialize()
+    assert await s.knn("never_seen", [0.1, 0.2]) == []
+
+
+@pytest.mark.anyio
+async def test_fake_dim_mismatch_raises() -> None:
+    s = FakeVectorStore()
+    await s.initialize()
+    await s.insert("hassh", "a", [1.0, 2.0, 3.0])
+    with pytest.raises(ValueError, match="dim mismatch"):
+        await s.insert("hassh", "b", [1.0, 2.0])
+
+
+@pytest.mark.anyio
+async def test_fake_knn_query_dim_mismatch_raises() -> None:
+    s = FakeVectorStore()
+    await s.initialize()
+    await s.insert("kd", "a", [0.1, 0.2, 0.3])
+    with pytest.raises(ValueError):
+        await s.knn("kd", [0.1, 0.2])
+
+
+@pytest.mark.anyio
+async def test_fake_replace_existing_id() -> None:
+    s = FakeVectorStore()
+    await s.initialize()
+    await s.insert("k", "id1", [1.0, 0.0])
+    await s.insert("k", "id1", [0.0, 1.0])
+    rec = await s.get("k", "id1")
+    assert tuple(rec.vector) == (0.0, 1.0)
+
+
+@pytest.mark.anyio
+async def test_fake_delete() -> None:
+    s = FakeVectorStore()
+    await s.initialize()
+    await s.insert("k", "id1", [1.0])
+    assert await s.delete("k", "id1") is True
+    assert await s.delete("k", "id1") is False
+    assert await s.get("k", "id1") is None
+
+
+@pytest.mark.anyio
+async def test_fake_health_reports_counts() -> None:
+    s = FakeVectorStore()
+    await s.initialize()
+    h = await s.health()
+    assert h == {"ok": True, "backend": "fake", "kinds": 0, "vectors": 0}
+    await s.insert("a", "1", [1.0])
+    await s.insert("a", "2", [2.0])
+    await s.insert("b", "1", [3.0, 4.0])
+    h = await s.health()
+    assert h["kinds"] == 2
+    assert h["vectors"] == 3
+
+
+@pytest.mark.anyio
+async def test_null_store_is_inert() -> None:
+    s = NullVectorStore()
+    await s.initialize()
+    await s.insert("k", "id", [1.0, 2.0])  # no-op
+    assert await s.get("k", "id") is None
+    assert await s.knn("k", [1.0, 2.0]) == []
+    assert await s.delete("k", "id") is False
+    h = await s.health()
+    assert h["backend"] == "null"
+    await s.close()