feat: implement GEWU service and local agent workflows

docs/architecture/ARCHITECTURE.md

@@ -114,6 +114,8 @@ Every content query carries scope. Resolve registered projects and their explici
 
 Search runs scope-filtered FTS and vector candidates, merges them with reciprocal rank fusion, and performs bounded typed-edge expansion. Start with a maximum one-hop expansion and explicit candidate/edge caps in the public contract. Return ranking explanations separately from evidence status. Related suggestions never become accepted relationships by indexing.
 
+The local service stays in keyword mode unless `GEWU_EMBEDDING_MODEL_PATH` and `GEWU_EMBEDDING_MODEL_SHA256` are both set. The configured path must point to an already-installed model tree; inference is local-only with remote code disabled. `GEWU_EMBEDDING_MODEL_ID` defaults to the pinned multilingual E5 candidate and `GEWU_EMBEDDING_DIMENSIONS` defaults to 384. Install the `retrieval` extra to enable the optional runtime. Missing or failed vector generations produce a labeled keyword response. See the [probe and setup evidence](../acceptance/2026-10-14-hybrid-probe.md). This opt-in runtime is not a full-v1 acceptance claim.
+
 Use normalized English token search plus language fixtures. `unicode61` alone is not a claim of Chinese word segmentation; test CJK queries and use a documented segmentation or trigram adapter when needed. Evaluate short queries separately. Search acceptance is the PRD's labeled per-project question set, not a synthetic speed result.
 
 Index updates publish all node/edge/FTS/vector changes for a chosen Git revision in one SQLite transaction. Queries use a read transaction pinned to an index revision. A model change builds a separate index generation, with model ID, artifact hash, dimensions, normalization, chunking and parser versions. Publish the new generation only after integrity and retrieval gates pass. Avoid replacing an open database file on Windows: switch the service's generation pointer and retire old connections before cleanup. The acceptance contract specifies the immutable extraction artifact and rebuild watermark procedure.
@@ -166,5 +168,5 @@ Checked 12 October 2026. These sources establish available mechanisms, not GEWU
 - [FastAPI process workers](https://fastapi.tiangolo.com/deployment/server-workers/): multiple workers are separate processes; an in-process lock cannot serialize their writes.
 - [Pydantic strict validation](https://docs.pydantic.dev/latest/concepts/strict_mode/), [Vite](https://vite.dev/guide/), [TanStack Query](https://tanstack.com/query/latest/docs/framework/react/overview): typed boundaries, static assets and server-state tooling supporting the choices above.
 - [pypdf extraction limitations](https://pypdf.readthedocs.io/en/stable/user/extract-text.html): extraction and OCR are different capabilities; quality must be measured.
-- [Sentence Transformers model loading](https://www.sbert.net/docs/package_reference/sentence_transformer/model.html) supports pinned revisions and local-only loading. The [multilingual-e5-small model card](https://huggingface.co/intfloat/multilingual-e5-small) was available in search results; direct retrieval failed, so its full configuration/license remains a mandatory probe rather than a verified selection.
+- [Sentence Transformers model loading](https://www.sbert.net/docs/package_reference/sentence_transformer/model.html) supports pinned revisions and local-only loading. A disposable Linux/Python 3.14 CPU probe loaded the pinned [multilingual-e5-small model card](https://huggingface.co/intfloat/multilingual-e5-small/blob/614241f622f53c4eeff9890bdc4f31cfecc418b3/README.md) snapshot and sqlite-vec 0.1.9; see the [probe record](../acceptance/2026-10-14-hybrid-probe.md). The adapter is implemented, but vector storage/fusion, offline distribution, native cross-platform compatibility and labeled recall remain unqualified. sqlite-vec remains pre-v1 and is not yet approved as the production index backend.
 - [tiktoken](https://github.com/openai/tiktoken) provides named encodings for a reproducible budget convention. [Git update-ref](https://git-scm.com/docs/git-update-ref.html) supports an expected-old object check for publication.