chat/app.py

@@ -94,9 +94,15 @@ async def lifespan(app: FastAPI):
     # Phase 4's pseudo-embedding path is local so the worker doesn't need
     # an LLM client; we still pass one so the Phase 4.5 swap to a real
     # model is a one-line change.
+    # T112 (Phase 4.5): the embedding model is now configurable via
+    # ``Settings.embedding_model``. Default ``"pseudo-sha256-384"``
+    # keeps the local-only path; swapping to a real model routes
+    # through ``client.embed(...)`` and falls back to a zero vector
+    # plus warning if the provider doesn't support embeddings.
     embedding_worker = EmbeddingWorker(
         conn_factory=lambda: open_db(settings.db_path),
         client=_factory(),
+        model=settings.embedding_model,
     )
     await embedding_worker.start()
     app.state.embedding_worker = embedding_worker

chat/config.py

@@ -39,6 +39,14 @@ class Settings(BaseModel):
     data_dir: Path = REPO_ROOT / "data"
     bind_host: str = "127.0.0.1"
     bind_port: int = 8000
+    # T112 (Phase 4.5): embedding model identifier. Default is the
+    # deterministic local pseudo (semantically meaningless but keeps the
+    # vector pipeline structurally valid). Swap to a real model name
+    # (e.g. "bge-small-en-v1.5") once the LLMClient implementation
+    # supports embed() — currently FeatherlessClient does NOT, so a
+    # non-default value will trigger the zero-vector fallback path
+    # plus a T107 warning until a different provider is wired in.
+    embedding_model: str = "pseudo-sha256-384"
 
 def load_settings() -> Settings:
     config_path = Path(os.environ.get("CHAT_CONFIG_PATH", DEFAULT_CONFIG))

chat/llm/mock.py

@@ -4,8 +4,23 @@ from .client import Message
 
 
 class MockLLMClient:
-    def __init__(self, canned: list[str]):
+    """In-memory LLMClient for tests.
+
+    ``canned`` feeds ``generate``/``stream`` (one entry per call, popped
+    from the front). ``canned_embeddings`` (T112, Phase 4.5) feeds
+    ``embed`` the same way — each call pops the next vector. An empty
+    queue raises ``IndexError`` so misconfigured tests fail loudly
+    rather than returning ``None`` or hanging.
+    """
+
+    def __init__(
+        self,
+        canned: list[str],
+        *,
+        canned_embeddings: list[list[float]] | None = None,
+    ):
         self._canned = list(canned)
+        self._canned_embeddings: list[list[float]] = list(canned_embeddings or [])
 
     async def generate(self, messages: Sequence[Message], *, model: str, **params) -> str:
         return self._canned.pop(0)
@@ -14,3 +29,8 @@ class MockLLMClient:
         text = self._canned.pop(0)
         for ch in text:
             yield ch
+
+    async def embed(self, text: str, *, model: str) -> list[float]:
+        # Mirrors the canned-queue pattern; empty queue raises so
+        # misconfigured tests surface clearly instead of returning None.
+        return self._canned_embeddings.pop(0)

chat/services/embeddings.py

@@ -95,19 +95,27 @@ async def generate_embedding(
         # Pure-local pseudo path — no LLMClient call.
         return EmbeddingResult(vector=_pseudo_embed(text, dim), model=model, dim=dim)
 
-    # Future: real embedding via client.embed(...). Phase 4.5 work.
-    # For Phase 4, any non-default model falls through to fallback —
-    # warn so misconfigured callers (e.g., a real-model swap that isn't
-    # wired up yet) don't silently degrade to a zero vector.
-    _log.warning(
-        "generate_embedding: non-default model %r returned fallback "
-        "(model client.embed() not yet implemented in Phase 4.5+); "
-        "downstream search will degrade silently. Configure a supported model.",
-        model,
-    )
-    return EmbeddingResult(
-        vector=[0.0] * dim, model=FALLBACK_EMBEDDING_MODEL, dim=dim
-    )
+    # T112 (Phase 4.5): non-default model — route through the client's
+    # ``embed()`` method. On any failure (including ``NotImplementedError``
+    # from providers that don't expose embeddings, e.g. Featherless today),
+    # fall back to the zero vector and re-fire the T107 warning so
+    # misconfigured callers see the issue in logs rather than silently
+    # producing useless cosine results.
+    try:
+        vector = await client.embed(text, model=model)
+        return EmbeddingResult(vector=list(vector), model=model, dim=len(vector))
+    except Exception as exc:  # noqa: BLE001 — any failure must degrade gracefully
+        _log.warning(
+            "generate_embedding: non-default model %r returned fallback "
+            "(client.embed() raised %s: %s); "
+            "downstream search will degrade silently. Configure a supported model.",
+            model,
+            type(exc).__name__,
+            exc,
+        )
+        return EmbeddingResult(
+            vector=[0.0] * dim, model=FALLBACK_EMBEDDING_MODEL, dim=dim
+        )
 
 
 __all__ = [

tests/test_config.py

@@ -24,3 +24,25 @@ def test_chat_db_path_env_overrides_default(tmp_path, monkeypatch):
     (tmp_path / "config.toml").write_text('featherless_api_key = "x"\n')
     s = load_settings()
     assert s.db_path == tmp_path / "alt.db"
+
+
+def test_embedding_model_defaults_to_pseudo(tmp_path, monkeypatch):
+    """T112: ``embedding_model`` defaults to the deterministic pseudo
+    so existing zero-config installs keep the Phase 4 behavior."""
+    monkeypatch.setenv("CHAT_CONFIG_PATH", str(tmp_path / "config.toml"))
+    (tmp_path / "config.toml").write_text('featherless_api_key = "x"\n')
+    s = load_settings()
+    assert s.embedding_model == "pseudo-sha256-384"
+
+
+def test_embedding_model_overridable_via_toml(tmp_path, monkeypatch):
+    """T112: operators swap the embedding model by editing config.toml.
+    The new value flows through to the embedding worker at startup."""
+    cfg = tmp_path / "config.toml"
+    cfg.write_text(
+        'featherless_api_key = "x"\n'
+        'embedding_model = "bge-small-en-v1.5"\n'
+    )
+    monkeypatch.setenv("CHAT_CONFIG_PATH", str(cfg))
+    s = load_settings()
+    assert s.embedding_model == "bge-small-en-v1.5"

tests/test_embeddings.py

@@ -120,3 +120,51 @@ async def test_generate_embedding_default_model_does_not_warn(caplog):
     await generate_embedding(_client(), text="hello")
     warnings = [r for r in caplog.records if r.levelno == logging.WARNING]
     assert warnings == []
+
+
+@pytest.mark.asyncio
+async def test_embed_routes_to_client_when_non_default_model():
+    """T112: when a non-default ``model`` is requested, generate_embedding
+    routes through ``client.embed(text, model=...)`` and wraps the
+    returned vector in an EmbeddingResult tagged with the requested
+    model (NOT the fallback sentinel)."""
+    canned = [0.1, 0.2, 0.3, 0.4]
+    client = MockLLMClient(canned=[], canned_embeddings=[canned])
+
+    result = await generate_embedding(
+        client, text="hello world", model="bge-small-en-v1.5"
+    )
+    assert result.vector == canned
+    assert result.model == "bge-small-en-v1.5"
+    assert result.dim == len(canned)
+
+
+@pytest.mark.asyncio
+async def test_embed_falls_back_on_client_failure(caplog):
+    """T112: when ``client.embed`` raises (e.g. NotImplementedError on
+    Featherless, or a transient network error), generate_embedding logs
+    the existing T107 warning and returns the zero-vector fallback so
+    callers detect the sentinel and skip indexing."""
+
+    class _FailingClient:
+        async def generate(self, messages, *, model, **params):  # pragma: no cover
+            raise AssertionError("generate must not be called")
+
+        def stream(self, messages, *, model, **params):  # pragma: no cover
+            raise AssertionError("stream must not be called")
+
+        async def embed(self, text, *, model):
+            raise NotImplementedError("provider does not expose embeddings")
+
+    caplog.set_level(logging.WARNING, logger="chat.services.embeddings")
+    result = await generate_embedding(
+        _FailingClient(), text="hello", model="bge-small-en-v1.5"
+    )
+
+    assert result.model == FALLBACK_EMBEDDING_MODEL == "fallback"
+    assert len(result.vector) == DEFAULT_EMBEDDING_DIM
+    assert all(x == 0.0 for x in result.vector)
+
+    # Existing T107 warning fires (re-used from the new exception branch).
+    warnings = [r for r in caplog.records if r.levelno == logging.WARNING]
+    assert any("bge-small-en-v1.5" in r.getMessage() for r in warnings)

tests/test_llm_mock.py

@@ -19,3 +19,28 @@ async def test_mock_streams_tokens():
     async for chunk in client.stream(msgs, model="any"):
         chunks.append(chunk)
     assert "".join(chunks) == "abcd"
+
+
+@pytest.mark.asyncio
+async def test_mock_llm_client_embed_pops_canned():
+    """T112: MockLLMClient.embed() pops a canned vector from the front
+    of ``canned_embeddings`` (mirrors the existing ``canned`` queue
+    pattern for generate/stream)."""
+    v1 = [0.1, 0.2, 0.3]
+    v2 = [0.4, 0.5, 0.6]
+    client = MockLLMClient(canned=[], canned_embeddings=[v1, v2])
+
+    out1 = await client.embed("first", model="bge-small-en-v1.5")
+    out2 = await client.embed("second", model="bge-small-en-v1.5")
+    assert out1 == v1
+    assert out2 == v2
+
+
+@pytest.mark.asyncio
+async def test_mock_llm_client_embed_empty_queue_raises():
+    """When the canned_embeddings queue is empty, ``embed`` must raise
+    a clear failure (IndexError) so misconfigured tests don't silently
+    return None or hang."""
+    client = MockLLMClient(canned=[])
+    with pytest.raises(IndexError):
+        await client.embed("text", model="any")