feat(vector): Add configurable chunk size and overlap for document embedding

Enable users to tune document chunking parameters to match their embedding
model and content type by adding DOCUMENT_CHUNK_SIZE and DOCUMENT_CHUNK_OVERLAP
environment variables.

- **config.py**: Added `document_chunk_size` (default: 512) and
  `document_chunk_overlap` (default: 50) configuration fields with validation:
  - Ensures overlap < chunk_size
  - Warns if chunk_size < 100 words
  - Prevents negative overlap values

- **processor.py**: Updated DocumentChunker instantiation to use config
  settings instead of hardcoded values (line 174-177)

- **tests/unit/test_config.py**: Added TestChunkConfigValidation class with
  9 tests covering:
  - Default values
  - Valid configurations
  - Validation errors (overlap >= chunk_size, negative overlap)
  - Warning for small chunk sizes
  - Environment variable loading

- **docs/configuration.md**: Added comprehensive "Document Chunking
  Configuration" section with:
  - Chunk size selection guidance (256-384 vs 512 vs 768-1024 words)
  - Overlap recommendations (10-20% of chunk size)
  - Configuration examples for different use cases
  - Added env vars to reference table

- **docs/semantic-search-architecture.md**: Added "Document Chunking Strategy"
  section with:
  - Chunking process explanation
  - Example showing sliding window behavior
  - Search behavior with chunks
  - Tuning recommendations

- **env.sample**: Added complete "Semantic Search & Vector Sync Configuration"
  section with:
  - Vector sync settings
  - Qdrant configuration (3 modes)
  - Ollama embedding service
  - Document chunking configuration

- **docker-compose.yml**: Added commented examples for DOCUMENT_CHUNK_SIZE and
  DOCUMENT_CHUNK_OVERLAP with usage notes

\`\`\`bash
DOCUMENT_CHUNK_SIZE=512

DOCUMENT_CHUNK_OVERLAP=50
\`\`\`

1. \`overlap\` must be less than \`chunk_size\`
2. \`overlap\` cannot be negative
3. Warning issued if \`chunk_size\` < 100 words

**Precise matching** (small notes, specific queries):
\`\`\`bash
DOCUMENT_CHUNK_SIZE=256
DOCUMENT_CHUNK_OVERLAP=25
\`\`\`

**Balanced** (default, general purpose):
\`\`\`bash
DOCUMENT_CHUNK_SIZE=512
DOCUMENT_CHUNK_OVERLAP=50
\`\`\`

**Contextual** (long documents, broader topics):
\`\`\`bash
DOCUMENT_CHUNK_SIZE=1024
DOCUMENT_CHUNK_OVERLAP=100
\`\`\`

✅ **User control** - Tune chunking to match embedding model capabilities
✅ **Experimentation** - Test different chunk sizes for optimal results
✅ **Model alignment** - Match chunk size to embedding context window
✅ **Backward compatible** - Defaults maintain existing behavior
✅ **Well validated** - Comprehensive tests prevent misconfiguration

All 22 config validation tests pass (9 new tests for chunking):
- Default values work correctly
- Validation prevents invalid configurations
- Environment variables load properly
- Warning system works as expected

With configurable chunk sizes, users can now experiment with different Ollama
embedding models and tune chunk parameters for optimal semantic search quality.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

nextcloud_mcp_server/config.py

@@ -174,6 +174,10 @@ class Settings:
     ollama_embedding_model: str = "nomic-embed-text"
     ollama_verify_ssl: bool = True
 
+    # Document chunking settings (for vector embeddings)
+    document_chunk_size: int = 512  # Words per chunk
+    document_chunk_overlap: int = 50  # Overlapping words between chunks
+
     # Observability settings
     metrics_enabled: bool = True
     metrics_port: int = 9090
@@ -209,6 +213,25 @@ class Settings:
                 "API key is only relevant for network mode and will be ignored."
             )
 
+        # Validate chunking configuration
+        if self.document_chunk_overlap >= self.document_chunk_size:
+            raise ValueError(
+                f"DOCUMENT_CHUNK_OVERLAP ({self.document_chunk_overlap}) must be less than "
+                f"DOCUMENT_CHUNK_SIZE ({self.document_chunk_size}). "
+                f"Overlap should be 10-20% of chunk size for optimal results."
+            )
+
+        if self.document_chunk_size < 100:
+            logger.warning(
+                f"DOCUMENT_CHUNK_SIZE is set to {self.document_chunk_size} words, which is quite small. "
+                f"Smaller chunks may lose context. Consider using at least 256 words."
+            )
+
+        if self.document_chunk_overlap < 0:
+            raise ValueError(
+                f"DOCUMENT_CHUNK_OVERLAP ({self.document_chunk_overlap}) cannot be negative."
+            )
+
     def get_collection_name(self) -> str:
         """
         Get Qdrant collection name.
@@ -305,6 +328,9 @@ def get_settings() -> Settings:
         ollama_base_url=os.getenv("OLLAMA_BASE_URL"),
         ollama_embedding_model=os.getenv("OLLAMA_EMBEDDING_MODEL", "nomic-embed-text"),
         ollama_verify_ssl=os.getenv("OLLAMA_VERIFY_SSL", "true").lower() == "true",
+        # Document chunking settings
+        document_chunk_size=int(os.getenv("DOCUMENT_CHUNK_SIZE", "512")),
+        document_chunk_overlap=int(os.getenv("DOCUMENT_CHUNK_OVERLAP", "50")),
         # Observability settings
         metrics_enabled=os.getenv("METRICS_ENABLED", "true").lower() == "true",
         metrics_port=int(os.getenv("METRICS_PORT", "9090")),

nextcloud_mcp_server/vector/processor.py

@@ -170,8 +170,11 @@ async def _index_document(
     else:
         raise ValueError(f"Unsupported doc_type: {doc_task.doc_type}")
 
-    # Tokenize and chunk
-    chunker = DocumentChunker(chunk_size=512, overlap=50)
+    # Tokenize and chunk (using configured chunk size and overlap)
+    chunker = DocumentChunker(
+        chunk_size=settings.document_chunk_size,
+        overlap=settings.document_chunk_overlap,
+    )
     chunks = chunker.chunk_text(content)
 
     # Generate embeddings (I/O bound - external API call)