chore(aiwg): adopt shared BT6 maintainer workflow (#148)

* docs(policy): allow low-impact contributor courtesy cleanup

* chore(aiwg): migrate to shared BT6 maintainer plugin

* chore: reconcile delivery validation

.aiwg/plugins/bt6-maintainer/payload/templates/bt6-external-provider-assessment.md

@@ -0,0 +1,72 @@
+---
+name: bt6-external-provider-assessment
+description: Evidence-based assessment of an external provider and its BT6 repository integration boundary.
+---
+
+# BT6 External Provider Assessment
+
+Provider: `<name>`
+Repository: `<canonical repository>`
+PR / issue: `<reference>`
+Head SHA: `<sha>`
+Assessment date: `<YYYY-MM-DD>`
+
+## Verdicts
+
+| Dimension | Verdict | Evidence / limitation |
+| --- | --- | --- |
+| Service is real | `<yes/no/unclear>` | `<evidence>` |
+| Claims independently verified | `<yes/partial/no>` | `<evidence>` |
+| Trustworthy for sensitive workloads | `<yes/conditional/no/unproven>` | `<basis>` |
+| Integration complete | `<yes/no>` | `<gaps>` |
+| Merge ready | `<yes/no>` | `<gates>` |
+
+## Trust Boundary
+
+| Data / action | Destination or processor | Retention / control | Evidence or assumption |
+| --- | --- | --- | --- |
+| `<credential/prompt/output/tool/etc>` | `<destination>` | `<control>` | `<source/assumption>` |
+
+## Claim-to-Code Traceability
+
+| Claim | Code/config | Behavioral test | Result |
+| --- | --- | --- | --- |
+| `<claim>` | `<path or none>` | `<test or none>` | `<implemented/provider-only/future/unsupported>` |
+
+## Integration Completeness
+
+| Surface | Result | Evidence / required change |
+| --- | --- | --- |
+| Config, adapter, setup | `<pass/fail>` | `<evidence>` |
+| Environment templates and docs | `<pass/fail>` | `<evidence>` |
+| Secret redaction and child processes | `<pass/fail>` | `<evidence>` |
+| CLI/UI/status | `<pass/fail>` | `<evidence>` |
+| Models and fallback behavior | `<pass/fail>` | `<evidence>` |
+| HTTP/error contract tests | `<pass/fail>` | `<evidence>` |
+
+## Findings
+
+| Severity | Finding | Required change |
+| --- | --- | --- |
+| `<blocking/non-blocking>` | `<finding>` | `<change>` |
+
+## Verification
+
+- Hostile-input preflight: `<risk/result>`
+- Security discovery route: `<query/result or none>`
+- Service checks: `<non-secret checks>`
+- Local checks: `<commands/results>`
+- Hosted checks: `<checks/results>`
+- Exact-head recheck: `<sha/result>`
+
+## Residual Risk and Assumptions
+
+- `<risk or assumption>`
+
+## Maintainer Decision
+
+Decision: `<approve/request changes/comment/hold>`
+
+Rationale:
+
+- `<reason>`