Closes #58. G4 of TechDevGroup/devagentic#203.

Depends on TechDevGroup/devagentic#207 (reasoningGraftCandidates GraphQL query). Merge that first.

Summary

• New plugin plugins/devagentic-lane-h/ with the same shape as the other devagentic-adjacent plugins.
• Two MCP tools registered via mcp_serve.py::_register_lane_h_tools:
  • lane_h_list(user_id?, limit?) — wraps reasoningGraftCandidates(userId, limit) GraphQL query
  • lane_h_fetch(graft_id) — wraps the existing searchDocs(query, k:1) retrieval pattern + validates the kind:reasoning-graft-candidate tag
• 31 MCP tools registered total now.

Design — no request_reasoning_graft tool

The original G4 issue proposed a requestReasoningGraft(prompt, lift_model?) MCP tool. Investigation showed Lane H is event-driven, not request-response: the cycle_tick auto-emits kind:reasoning-graft-candidate docs when a confer-result clears the Lane H confidence threshold (api.py ~line 8139 + ~line 23990, both gated on _lane_h_auto_trigger_enabled()). There is no manual-request entry point.

The actual worker flow per NousResearch#174:

worker → confer_run → high-confidence result → cycle_tick auto-emits
                                                kind:reasoning-graft-candidate
                                              ↓
                                        worker reads via lane_h_list / lane_h_fetch

So G4 ships as a read surface only. The "request" side is implicit via confer_run (G2, already shipped). Documented in the plugin README + __init__.py.

Test plan

• 12 client unit tests pass: user_id resolution + override, list happy/empty/zero-limit/network-error/graphql-error paths, fetch empty-id/happy/no-match/id-mismatch/wrong-kind paths.
• create_mcp_server() smoke-import succeeds; lane_h_list + lane_h_fetch registered alongside existing tools (31 total).
• Plugin is additive — no changes to existing modules — so no regression risk.

Notes

• lane_h_list accepts an optional user_id arg to allow operators to query other users' grafts from their own profile; defaults to the active profile when omitted.
• lane_h_fetch uses the same searchDocs retrieval pattern as devagentic-docs's get_doc (devagentic has no GET-by-id GraphQL field) but adds kind-tag validation so workers can't accidentally pull a non-Lane-H doc.
• After this lands the polynomial-explorer worker has the full hermes-native tool surface per test: add unit tests for trajectory_compressor NousResearch/hermes-agent#203 §1.3: preamble loading (G1), querySilo + confer + writeDoc + fork* (G2 + existing docs plugin), fileIssue (G3), Lane H read (G4). The remaining G2b/c/d sub-issues (G2b: assertOutput MCP tool (sub-issue of #56) #60/G2c: patchArtifact / readArtifact MCP tools (sub-issue of #56) #61/G2d: fetchUrl MCP tool (sub-issue of #56) #62) are enrichment, not blockers.