Partial close of #56. G2 foundation. Follow-up sub-issues filed: #60 (assertOutput), #61 (patchArtifact/readArtifact), #62 (fetchUrl).

Summary

• New plugin plugins/devagentic-mutations/ with the same shape as devagentic-canvas / devagentic-docs.
• Two new MCP tools registered via mcp_serve.py::_register_devagentic_mutation_tools:
  • silo_query(name, prompt, role_override?) — wraps querySilo GraphQL field
  • confer_run(user_id, candidate_id) — wraps runConferLoop mutation
• All transport mirrors existing devagentic-adjacent plugins: same env vars, same X-User-Id auto-binding, same fail-soft contract.

Why

Under devagentic#203 §1.2, worker sessions must call devagentic ops through hermes-native tools — not shell out to python api.py. G2 closes the missing read + confer surfaces (writeDoc + forkContext were already shipped via _register_docs_tools).

Scope decision (partial close)

The original #56 enumerated 6+ tools (querySilo, writeDoc, confer, forkContext, assertOutput, patchArtifact). Discovered during implementation:

• writeDoc already shipped as doc_write in plugins/devagentic-docs/ + _register_docs_tools.
• forkContext family already shipped as fork_open / fork_decorate / fork_get / fork_render in same.
• querySilo + confer were genuinely missing — shipped here.
• assertOutput / patchArtifact / readArtifact / fetchUrl filed as G2b/c/d (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) — each has its own design surface (e.g. assertOutput's ExpectationInput shape mapping).

Per devagentic#203 broadcast: "don't try to land all four at once" — applying the same principle within G2.

Test plan

• 12 client unit tests pass (tests/plugins/devagentic-mutations/test_client.py): user_id resolution, empty-args guards, happy paths for both tools, network errors, GraphQL errors, invalid JSON, null-data handling.
• create_mcp_server() smoke-import succeeds; new tools silo_query + confer_run registered alongside existing canvas_* / doc_* / fork_* (28 tools total).
• Plugin is additive — no changes to existing client modules — so no regression risk to existing canvas / docs / fork flows.

Notes

• confer_run requires a kind:finding-candidate doc id, which a fresh worker won't have on day 1. The tool is foundational for established workers running through the Lane F confer-loop; first-day workers will use silo_query + doc_write predominantly.
• last_error_text() populated on the client to surface actionable diagnostics in MCP error JSON.