docs(agents): install merge-train snippet

AGENTS.md

@@ -197,3 +197,43 @@ Rules for agents touching this repo:
 
 See also: `AgentWorkforce/cloud` → `AGENTS.md` "RelayAuth ↔ Cloud Separation"
 for the mirror rule on the cloud side.
+
+<!-- prpm:snippet:start @agent-relay/merge-train-snippet@1.0.0 -->
+## Merging: `trunk` + the `mergeable` label
+
+CI does **not** run on feature branches. It runs only on the `trunk` → `main`
+pull request and on pushes to `main`. (Repos whose default branch is not
+`main`, e.g. `master`, use that branch wherever this says `main`.) A merge
+agent batches ready PRs into `trunk`, gets that one PR green, and merges it.
+
+**When you open a PR**
+1. Branch from `trunk` and open the PR with **base `trunk`**, not `main`.
+   A PR into `main` from any other branch fails the `Trunk guard` check.
+2. No CI runs on your PR, so verify locally before calling it ready: run the
+   typecheck, tests and lint this repo uses, and list the exact commands and
+   results in the PR body.
+
+**When the PR is ready**
+3. Add the label **`mergeable`** once all of these are true:
+   - The change is complete and the local checks above pass.
+   - Review feedback (human and bot) is addressed or answered.
+   - It is not a draft and does not depend on an unmerged PR.
+4. Remove `mergeable` if the PR stops being ready (new work, a failing check, a
+   blocking question). The label is read live from GitHub on every sweep.
+
+**What you must not do**
+- Do not merge your own PR, and never merge into or push to `trunk` or `main`
+  directly.
+- Do not re-enable CI for feature branches or edit the `trunk` gates in
+  `.github/workflows/`.
+
+**The merge agent** sweeps open `mergeable` PRs with base `trunk` about every
+10 minutes. It reads each PR's linked sessions (the `Agent Relay sessions`
+block in the PR body, then the session summary) for context, merges them into
+`trunk`, opens or updates the `trunk` → `main` PR, fixes CI there, merges when
+green, and posts a summary. If your PR conflicts with `trunk`, it may ask you
+to rebase on `trunk`; do so and keep the label.
+
+> Interim: the sweep worker is not deployed yet. Until it is, a human or a
+> designated agent performs the merge-agent steps manually. Labelling is unchanged.
+<!-- prpm:snippet:end @agent-relay/merge-train-snippet@1.0.0 -->

prpm.lock

@@ -149,9 +149,26 @@
       "sourceFormat": "claude",
       "sourceSubtype": "skill",
       "installedPath": ".opencode/skills/running-headless-orchestrator/SKILL.md"
+    },
+    "@agent-relay/merge-train-snippet#agents.md:AGENTS.md": {
+      "version": "1.0.0",
+      "resolved": "https://registry.prpm.dev/api/v1/packages/%40agent-relay%2Fmerge-train-snippet/1.0.0.tar.gz",
+      "integrity": "sha256-a85e34747a332452ab6d8d7f814c828d404a3a77dd724f16878d26b91fb7d5bb",
+      "format": "agents.md",
+      "subtype": "snippet",
+      "sourceFormat": "generic",
+      "sourceSubtype": "snippet",
+      "installedPath": "AGENTS.md",
+      "snippetMetadata": {
+        "targetPath": "AGENTS.md",
+        "config": {
+          "target": "AGENTS.md",
+          "position": "append"
+        }
+      }
     }
   },
-  "generated": "2026-04-21T08:06:00.023Z",
+  "generated": "2026-10-08T22:48:21.322Z",
   "collections": {
     "agent-relay-starter": {
       "name_slug": "agent-relay-starter",