Document chunks not stored in vector store (#665)

- Schema - ChunkEmbeddings now uses chunk_id: str instead of chunk: bytes
- Schema - DocumentEmbeddingsResponse now returns chunk_ids: list[str]
  instead of chunks
- Translators - Updated to serialize/deserialize chunk_id
- Clients - DocumentEmbeddingsClient.query() returns chunk_ids
- SDK/API - flow.py, socket_client.py, bulk_client.py updated
- Document embeddings service - Stores chunk_id (document ID) instead
  of chunk text
- Storage writers - Qdrant, Milvus, Pinecone store chunk_id in payload
- Query services - Return chunk_id from vector store searches
- Gateway dispatchers - Serialize chunk_id in API responses
- Document RAG - Added librarian client to fetch chunk content from
  Garage using chunk_ids
- CLI tools - Updated all three tools:
  - invoke_document_embeddings.py - displays chunk_ids, removed
    max_chunk_length
  - save_doc_embeds.py - exports chunk_id
  - load_doc_embeds.py - imports chunk_id

docs/tech-specs/document-embeddings-chunk-id.md

@@ -0,0 +1,136 @@
+# Document Embeddings Chunk ID
+
+## Overview
+
+Document embeddings storage currently stores chunk text directly in the vector store payload, duplicating data that exists in Garage. This spec replaces chunk text storage with `chunk_id` references.
+
+## Current State
+
+```python
+@dataclass
+class ChunkEmbeddings:
+    chunk: bytes = b""
+    vectors: list[list[float]] = field(default_factory=list)
+
+@dataclass
+class DocumentEmbeddingsResponse:
+    error: Error | None = None
+    chunks: list[str] = field(default_factory=list)
+```
+
+Vector store payload:
+```python
+payload={"doc": chunk}  # Duplicates Garage content
+```
+
+## Design
+
+### Schema Changes
+
+**ChunkEmbeddings** - replace chunk with chunk_id:
+```python
+@dataclass
+class ChunkEmbeddings:
+    chunk_id: str = ""
+    vectors: list[list[float]] = field(default_factory=list)
+```
+
+**DocumentEmbeddingsResponse** - return chunk_ids instead of chunks:
+```python
+@dataclass
+class DocumentEmbeddingsResponse:
+    error: Error | None = None
+    chunk_ids: list[str] = field(default_factory=list)
+```
+
+### Vector Store Payload
+
+All stores (Qdrant, Milvus, Pinecone):
+```python
+payload={"chunk_id": chunk_id}
+```
+
+### Document RAG Changes
+
+The document RAG processor fetches chunk content from Garage:
+
+```python
+# Get chunk_ids from embeddings store
+chunk_ids = await self.rag.doc_embeddings_client.query(...)
+
+# Fetch chunk content from Garage
+docs = []
+for chunk_id in chunk_ids:
+    content = await self.rag.librarian_client.get_document_content(
+        chunk_id, self.user
+    )
+    docs.append(content)
+```
+
+### API/SDK Changes
+
+**DocumentEmbeddingsClient** returns chunk_ids:
+```python
+return resp.chunk_ids  # Changed from resp.chunks
+```
+
+**Wire format** (DocumentEmbeddingsResponseTranslator):
+```python
+result["chunk_ids"] = obj.chunk_ids  # Changed from chunks
+```
+
+### CLI Changes
+
+CLI tool displays chunk_ids (callers can fetch content separately if needed).
+
+## Files to Modify
+
+### Schema
+- `trustgraph-base/trustgraph/schema/knowledge/embeddings.py` - ChunkEmbeddings
+- `trustgraph-base/trustgraph/schema/services/query.py` - DocumentEmbeddingsResponse
+
+### Messaging/Translators
+- `trustgraph-base/trustgraph/messaging/translators/embeddings_query.py` - DocumentEmbeddingsResponseTranslator
+
+### Client
+- `trustgraph-base/trustgraph/base/document_embeddings_client.py` - return chunk_ids
+
+### Python SDK/API
+- `trustgraph-base/trustgraph/api/flow.py` - document_embeddings_query
+- `trustgraph-base/trustgraph/api/socket_client.py` - document_embeddings_query
+- `trustgraph-base/trustgraph/api/async_flow.py` - if applicable
+- `trustgraph-base/trustgraph/api/bulk_client.py` - import/export document embeddings
+- `trustgraph-base/trustgraph/api/async_bulk_client.py` - import/export document embeddings
+
+### Embeddings Service
+- `trustgraph-flow/trustgraph/embeddings/document_embeddings/embeddings.py` - pass chunk_id
+
+### Storage Writers
+- `trustgraph-flow/trustgraph/storage/doc_embeddings/qdrant/write.py`
+- `trustgraph-flow/trustgraph/storage/doc_embeddings/milvus/write.py`
+- `trustgraph-flow/trustgraph/storage/doc_embeddings/pinecone/write.py`
+
+### Query Services
+- `trustgraph-flow/trustgraph/query/doc_embeddings/qdrant/service.py`
+- `trustgraph-flow/trustgraph/query/doc_embeddings/milvus/service.py`
+- `trustgraph-flow/trustgraph/query/doc_embeddings/pinecone/service.py`
+
+### Gateway
+- `trustgraph-flow/trustgraph/gateway/dispatch/document_embeddings_query.py`
+- `trustgraph-flow/trustgraph/gateway/dispatch/document_embeddings_export.py`
+- `trustgraph-flow/trustgraph/gateway/dispatch/document_embeddings_import.py`
+
+### Document RAG
+- `trustgraph-flow/trustgraph/retrieval/document_rag/rag.py` - add librarian client
+- `trustgraph-flow/trustgraph/retrieval/document_rag/document_rag.py` - fetch from Garage
+
+### CLI
+- `trustgraph-cli/trustgraph/cli/invoke_document_embeddings.py`
+- `trustgraph-cli/trustgraph/cli/save_doc_embeds.py`
+- `trustgraph-cli/trustgraph/cli/load_doc_embeds.py`
+
+## Benefits
+
+1. Single source of truth - chunk text only in Garage
+2. Reduced vector store storage
+3. Enables query-time provenance via chunk_id