Bt6 Merge Train

---
namespace: bt6-maintainer
name: bt6-merge-train
platforms: [all]
description: Run an explicitly authorized, conservative BT6 merge train that processes validated pull requests one at a time and reconciles repository, CI, evidence, and issue state after each merge.
triggers:
  - bt6 merge train
  - merge validated BT6 pull requests
  - start a maintainer merge session
  - integrate ready research tool changes
requires:
  - current-queue-audit: ready candidates with exact audited head SHAs
  - explicit-merge-authorization: operator authorizes repository, candidates, and mutation in the current context
  - tracker-write-access: configured canonical tracker actor may merge
ensures:
  - dry-run-default: no merge occurs unless explicitly authorized and dry-run is disabled
  - one-at-a-time: only one PR is merged before all relevant state is refreshed
  - current-gates: head, base, reviews, checks, risk-surface verification, and policy are rechecked immediately before merge
  - reconciliation: canonical branch, CI, linked issues, and queue state are checked after each merge
commandHint:
  argumentHint: "<pr...> [--method squash|merge|rebase] [--dry-run] [--stop-on-conflict]"
  allowedTools: Bash, Read
  model: sonnet
  category: release-management
  modelRole: reasoning
  modelTier: standard
---

# BT6 Merge Train

Use only after `bt6-queue-audit`. Apply `bt6-maintainer-guardrails`.

## Authorization preflight

Confirm the current operator explicitly authorized merging in the resolved
repository. Record:

- canonical repository/tracker and expected actor;
- candidate PR numbers and audited head SHAs;
- base branch and permitted merge method;
- whether this is dry-run or live;
- current queue-audit reference and expiration conditions.

Approval to inspect, plan, review, fix, or prepare is not merge authorization.

## Never merge

- requested-changes, draft, conflict/dirty, or ambiguous PR state;
- missing/failing required checks;
- head SHA different from the audited SHA;
- policy-disallowed merge method or unexpected base branch;
- unresolved security, privacy, citation, provenance, corpus, schema, data-loss,
  compatibility, or research-integrity finding;
- missing profile-required risk-surface verification;
- missing, stale, incomplete, or non-merge-ready external-provider assessment;
- a PR whose target repository/tracker/actor cannot be proven.

## Candidate ordering

Respect dependencies and gate-critical fixes first. For otherwise independent
work, prefer narrowly scoped docs/config, small verified defects, integrity and
compatibility fixes, then larger features. Recompute ordering after each merge.

## Per-PR procedure

1. Re-fetch PR metadata, exact head SHA, base, mergeability, reviews, required
   checks, linked issues, dependencies, and new human feedback.
2. Compare the head with the queue audit and PR-audit evidence.
3. Confirm hostile-input and all matched risk-surface checks are current.
4. Run any profile validation invalidated by base-branch movement.
5. For external-provider changes, confirm the provider assessment matches the
   exact head and its integration-complete and merge-ready verdicts are `yes`.
6. Verify the merge method is allowed and dry-run is false.
7. Merge exactly one PR through the canonical tracker.
8. Verify the resulting canonical-branch commit and post-merge CI.
9. Reconcile linked issues by observed state. Comment/close only when separately
   authorized; do not assume closing keywords worked.
10. Refresh base branch, open queue, reviews, checks, dependencies, and candidate
   ordering before considering another PR.

## Stop conditions

Stop on any merge conflict, check failure, unexpected commit, issue mismatch,
new feedback, stale audit, changed profile/policy, or ambiguous external state.
Do not skip a failed candidate and continue unless the operator's authorization
explicitly covers that behavior and remaining candidates are independent.

Use `templates/bt6-merge-train-report.md`. Record every attempted/merged PR,
exact SHA, method, checks, authorization, linked-issue outcome, and stop reason.