fix(langchain): keyword_search raises on gRPC UNIMPLEMENTED, README missing methods

[polaz]

Problem

CoordinodeGraph.keyword_search() raises an uncaught exception when the server returns StatusCode.UNIMPLEMENTED (i.e. older CoordiNode versions without the TextSearch endpoint). The docstring says it should return [] in this case, but only handles AttributeError (method not found), not gRPC errors.

Fix

• Wrap text_search() call in try/except Exception with logger.debug(...) — same pattern used in refresh_schema()
• Add regression test test_returns_empty_when_text_search_raises

Also

• Add keyword_search, similarity_search, structured_schema to the API table in langchain-coordinode/README.md (were missing after feat(langchain): add CoordinodeGraph.keyword_search() #41)

Closes part of the work from #22.

[coderabbitai]

🔗 Related PRs

#15 - fix: CoordiNode Cypher compatibility — add_graph_documents, type/label, MATCH+CREATE [merged]
#27 - feat: similarity_search() for LangChain + upsert_relations() idempotency test [merged]
#41 - feat(langchain): add CoordinodeGraph.keyword_search() [closed]

---

📝 Issue Planner

_{Check the box below or use the @coderabbitai plan command to generate an implementation plan and prompts that you can use with your favorite coding assistant.}

• Create Plan

---

🧪 Issue enrichment is currently in open beta.

You can configure auto-planning by selecting labels in the issue_enrichment configuration.

To disable automatic issue enrichment, add the following to your .coderabbit.yaml:

issue_enrichment:
  auto_enrich:
    enabled: false

💬 Have feedback or questions? Drop into our discord!