docs: add agentsgen handoff integration note

docs/AGENTSGEN_INTEGRATION.md

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+# AGENTS.md Generator Integration
+
+This document makes the `ID` and `agentsgen` relationship explicit at the repo-contract level.
+
+## Boundary
+
+- `ID` owns portable human context, freshness, privacy, and handshakes.
+- `agentsgen` owns repo-scoped agent context and command manifests.
+- `SET` can orchestrate both layers, but the bridge should also work without `SET`.
+
+## Repo-local handoff contract
+
+When a repository runs `agentsgen pack --autodetect`, it can publish `docs/ai/id-context.json`.
+
+That file is the repo-local handoff surface for `ID`-compatible workflows. It should point at the repo artifacts that matter most for execution:
+
+- `AGENTS.md`
+- `RUNBOOK.md`
+- `agents.entrypoints.json`
+- `docs/ai/how-to-run.md`
+- `docs/ai/how-to-test.md`
+- `docs/ai/architecture.md`
+- `docs/ai/data-contracts.md`
+- optional `repomap`, `graph`, `agents.knowledge.json`, and proof-loop task artifacts when present
+
+## Recommended flow
+
+1. Load the owner profile and handshake from `ID`.
+2. Load `docs/ai/id-context.json` from the active repository.
+3. Merge human context from `ID` with repo context from `agentsgen`.
+4. If orchestration is present, let `SET` call `pre_task` and `weekly_review` around the repo workflow.
+
+## Non-goals
+
+- `docs/ai/id-context.json` does not replace `profile.core.md`, `profile.extended.md`, or interop exports.
+- `agentsgen` does not own user preferences or privacy policy.
+- `ID` does not replace repo-local contracts such as `AGENTS.md`.
+
+## Practical summary
+
+Use `ID` for the human.
+Use `agentsgen` for the repository.
+Use `SET` when you want one orchestration entrypoint for both.