Clarify PR-reopen flow and fix label-race that broke auto-reopen (#4518)

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
Co-authored-by: Claude <noreply@anthropic.com>

.github/scripts/triage-label.sh

@@ -0,0 +1,73 @@
+#!/usr/bin/env bash
+# Locked-down label helper for the Marvin triage workflow.
+#
+# Marvin runs on untrusted issue/PR bodies from non-write users, so it must
+# NOT be handed raw `gh api` (that would expose every endpoint the app token
+# can reach). This helper is the ONLY GitHub write it is allowed to perform:
+# it adds or removes repository labels on the one issue/PR being triaged.
+#
+# The target repo and number come from the environment set by the workflow —
+# never from the model — and the operation is fixed to the additive labels
+# endpoint (POST/DELETE /repos/{repo}/issues/{n}/labels), which works for both
+# issues and PRs and cannot clobber labels applied by other workflows.
+set -euo pipefail
+
+repo="${TRIAGE_REPO:?TRIAGE_REPO not set}"
+number="${TRIAGE_NUMBER:?TRIAGE_NUMBER not set}"
+
+if [[ ! "$number" =~ ^[0-9]+$ ]]; then
+  echo "TRIAGE_NUMBER must be numeric, got: $number" >&2
+  exit 1
+fi
+
+op="${1:-}"
+shift || true
+case "$op" in
+  add) method=POST ;;
+  remove) method=DELETE ;;
+  *)
+    echo "usage: triage-label.sh <add|remove> <label>..." >&2
+    exit 1
+    ;;
+esac
+
+if [[ "$#" -eq 0 ]]; then
+  echo "no labels given" >&2
+  exit 1
+fi
+
+# Reject anything that isn't a plausible label name. Notably blocks '/' so a
+# crafted value can't turn the DELETE path into a different endpoint.
+label_re="^[A-Za-z0-9 ._'-]+$"
+for label in "$@"; do
+  if [[ ! "$label" =~ $label_re ]]; then
+    echo "refusing suspicious label name: $label" >&2
+    exit 1
+  fi
+done
+
+# Never let triage add or remove the Require Issue Link control labels. Those
+# govern PR enforcement (bypass-issue-check / trusted-contributor are sticky
+# exemptions) and reopening (missing-issue-link is how closed PRs are found),
+# so a prompt-injected triage run must not be able to grant an exemption or
+# break recovery. Enforced here — in code — not merely in the prompt.
+protected=" missing-issue-link bypass-issue-check trusted-contributor "
+for label in "$@"; do
+  lower="${label,,}"
+  if [[ "$protected" == *" $lower "* ]]; then
+    echo "refusing to touch protected control label: $label" >&2
+    exit 1
+  fi
+done
+
+if [[ "$method" == POST ]]; then
+  args=()
+  for label in "$@"; do
+    args+=(-f "labels[]=$label")
+  done
+  gh api --method POST "/repos/${repo}/issues/${number}/labels" "${args[@]}"
+else
+  for label in "$@"; do
+    gh api --method DELETE "/repos/${repo}/issues/${number}/labels/${label}"
+  done
+fi

.github/workflows/marvin-label-triage.yml

@@ -49,13 +49,16 @@ jobs:
           PROMPT<<PROMPT_END
           You're an issue triage assistant for FastMCP, a Python framework for building Model Context Protocol servers and clients. Your task is to analyze issues/PRs and apply appropriate labels.
 
-          IMPORTANT: Your primary action should be to apply labels using mcp__github__update_issue. DO NOT post comments EXCEPT when applying the too-long label (see below).
+          IMPORTANT: Your primary action should be to apply labels using the locked-down helper `.github/scripts/triage-label.sh`. DO NOT post comments EXCEPT when applying the too-long label (see below).
 
           CRITICAL — LABEL MECHANICS:
-          - `mcp__github__update_issue` REPLACES all labels on the issue — it does not add to them.
-          - Before applying labels, read the issue's current labels with `mcp__github__get_issue`.
-          - Always include any existing labels you want to keep alongside the new ones.
+          - Apply labels ONLY through the helper, which adds or removes repository labels on THIS issue/PR. It already knows the target repo and number (from the workflow environment) — you never pass them:
+            add:    `bash .github/scripts/triage-label.sh add "label1" "label2"`
+            remove: `bash .github/scripts/triage-label.sh remove "label1"`
+          - The helper uses the additive REST labels endpoint, so it works for both issues and PRs and never clobbers labels applied by other workflows — notably the Require Issue Link workflow's `missing-issue-link` control label, which must survive or an auto-closed PR won't reopen when its author is assigned.
+          - The helper is your ONLY GitHub write access. Do NOT use raw `gh api`, `gh issue edit`, `gh pr edit`, or any other mutation — they are not available to you.
           - Only apply labels that exist in the repository (from `gh label list` in step 1). Never invent labels.
+          - Use `remove` only to correct a label you believe is wrong, and never remove the control labels `missing-issue-link`, `bypass-issue-check`, or `trusted-contributor`.
 
           Issue/PR Information:
           - REPO: ${{ github.repository }}
@@ -131,7 +134,7 @@ jobs:
           - DON'T MERGE: Only if PR author explicitly states it's not ready
 
           4. Apply selected labels:
-             Use mcp__github__update_issue to apply your selected labels
+             Add them with `bash .github/scripts/triage-label.sh add "label1" "label2"`.
              DO NOT post any comments unless applying too-long (see above)
           PROMPT_END
           EOF
@@ -149,11 +152,13 @@ jobs:
           allowed_non_write_users: "*"
           allowed_bots: "marvin-context-protocol"
           claude_args: |
-            --allowedTools Bash(gh label list),mcp__github__get_issue,mcp__github__get_issue_comments,mcp__github__update_issue,mcp__github__add_issue_comment,mcp__github__get_pull_request_files
+            --allowedTools Bash(gh label list),Bash(bash .github/scripts/triage-label.sh:*),mcp__github__get_issue,mcp__github__get_issue_comments,mcp__github__add_issue_comment,mcp__github__get_pull_request_files
           settings: |
             {
               "model": "claude-sonnet-4-6",
               "env": {
-                "GH_TOKEN": "${{ steps.marvin-token.outputs.token }}"
+                "GH_TOKEN": "${{ steps.marvin-token.outputs.token }}",
+                "TRIAGE_REPO": "${{ github.repository }}",
+                "TRIAGE_NUMBER": "${{ github.event.issue.number || github.event.pull_request.number || inputs.issue_number }}"
               }
             }

.github/workflows/require-issue-link.yml

@@ -354,29 +354,30 @@ jobs:
             async function enforceFailure(kind) {
               await addLabel();
 
-              const intro = kind === 'no-link'
-                ? '**This PR has been automatically closed** because its description does not reference a tracked issue.'
-                : '**This PR has been automatically closed** because you are not assigned to the issue it references.';
+              const reason = kind === 'no-link'
+                ? "it doesn't reference a tracked issue assigned to you"
+                : "you aren't assigned to the issue it references";
               const steps = kind === 'no-link'
                 ? [
-                    `1. Find or [open an issue](https://github.com/${owner}/${repo}/issues/new/choose) describing the change.`,
-                    '2. Comment on the issue to ask a maintainer to assign it to you.',
-                    '3. Add `Fixes #<issue>`, `Closes #<issue>`, or `Resolves #<issue>` to the PR description.',
-                    '4. Once you are assigned and the link is present, the PR reopens automatically.',
+                    `1. Find or [open an issue](https://github.com/${owner}/${repo}/issues/new/choose) describing the change — if you open it, you have first claim on it.`,
+                    "2. Add `Fixes #<issue>`, `Closes #<issue>`, or `Resolves #<issue>` to **this** PR's description — edit it in place, don't open a new PR.",
                   ]
                 : [
-                    '1. Comment on the linked issue to ask a maintainer to assign it to you.',
-                    '2. Once a maintainer assigns you, the PR reopens automatically.',
+                    "1. If you opened the linked issue, a maintainer will assign you when they pick it up and this PR reopens automatically. If someone else opened it, the PR reopens only if a maintainer chooses to assign it to you — please don't comment to ask.",
                   ];
 
               const commentBody = [
                 MARKER,
-                intro,
+                "**Don't open a new pull request — this one reopens on its own.** It's closed for " +
+                  `now because ${reason}, but the moment that's fixed it reopens automatically. Keep this ` +
+                  'PR and edit it; opening a fresh duplicate just starts you over and creates more to triage.',
                 '',
-                `Per [CONTRIBUTING.md](https://github.com/${owner}/${repo}/blob/main/CONTRIBUTING.md), an external PR must reference an issue that is assigned to its author. To proceed:`,
+                `Per [CONTRIBUTING.md](https://github.com/${owner}/${repo}/blob/main/CONTRIBUTING.md), an external PR must reference an issue that's assigned to its author. To get there:`,
                 '',
                 ...steps,
                 '',
+                "Once you're assigned and the link is present, this PR reopens automatically — no further action needed.",
+                '',
                 `*Maintainers: reopen this PR or remove the \`${LABEL}\` label to bypass this check.*`,
               ].join('\n');