Closes #55. G1 of TechDevGroup/devagentic#203 (canonical fusion contract).

Depends on TechDevGroup/devagentic#205 (verticalContext GraphQL query). Merge that first.

Summary

• New plugin plugins/devagentic-vertical-preamble/ with the same shape as the existing devagentic-canvas plugin.
• pre_llm_call hook auto-loads the active hermes profile's vertical context — kind:vertical-spec + kind:grafted-context + kind:worker-guardrails docs — and injects them as ephemeral preamble on the first LLM call of the process.
• Per-process gate: once a user_id is loaded (or returns empty), no re-injection or re-fetch. Vertical docs are session-stable; paying token cost per turn would be waste.

Why

Under NousResearch#203 §1.2, worker sessions must not read genesis/doc.jsonl directly or shell out to python api.py. This plugin is the hermes-native path that lands the vertical's manifest + grafted material + guardrails in the worker's context on session boot.

Plugin shape

• __init__.py — entrypoint + module docstring
• plugin.yaml — registers pre_llm_call hook
• client.py — thin GraphQL client mirroring agent/devagentic_memory.py transport (same env vars, same X-User-Id resolution, same fail-soft contract)
• preamble.py — the hook + renderer (caps: 2KB per graft, 8 grafts shown, 32KB total)
• README.md — operator docs

Test plan

• 12 new tests cover: no-user_id gate, default-profile gate, empty-rollup gate (with re-fetch suppression), populated rollup, load-once semantics, per-graft truncation, max-grafts rendering, fetch exception → None, resolve exception → None, env-override user_id, missing-profile path, empty-user_id client guard.
• All 12 pass under hermes' pytest config (tests/plugins/devagentic-vertical-preamble/).
• Plugin is additive — no changes to existing modules — so no regression risk to existing flows.

Notes

• Failure semantics: any failure returns None; turn proceeds without preamble. Same contract as the canvas preamble.
• Long-running daemon embeddings (e.g. gateway) would need session-keyed state instead of the per-process set. Noted in the plugin docstring as a follow-up if it ever applies; today every hermes CLI invocation is its own process.