preview-watchdog.yml

name: Preview watchdog

# Catches PR previews whose "Backend target: preview requested" comment is
# stuck because a `backend_preview_ready` or `backend_preview_failed`
# dispatch was lost (token expired, GitHub API blip, job crashed, etc.).
# Today this leaves the author staring at a stale "preview requested"
# message with no recourse. Watchdog runs every 15 minutes and nudges
# anything older than 20 minutes with a follow-up comment and link to
# re-run the upsert-preview workflow.
#
# Strictly additive — doesn't modify existing preview comments, only adds
# a sibling `mcpjam-preview-watchdog` comment. Posts once per stuck PR and
# keeps the comment updated, so it won't spam the PR thread.

on:
  schedule:
    - cron: "*/15 * * * *"
  workflow_dispatch: {}

permissions:
  contents: read
  pull-requests: write

jobs:
  scan-stuck-previews:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/github-script@v7
        with:
          script: |
            const previewMarker = "<!-- mcpjam-preview -->";
            const watchdogMarker = "<!-- mcpjam-preview-watchdog -->";
            const stuckAfterMs = 20 * 60 * 1000;

            const prs = await github.paginate(github.rest.pulls.list, {
              owner: context.repo.owner,
              repo: context.repo.repo,
              state: "open",
              per_page: 100,
            });

            for (const pr of prs) {
              const comments = await github.paginate(github.rest.issues.listComments, {
                owner: context.repo.owner,
                repo: context.repo.repo,
                issue_number: pr.number,
                per_page: 100,
              });

              const previewComment = comments.find((c) =>
                c.body?.includes(previewMarker),
              );
              if (!previewComment) continue;

              // Only nudge when the current state is "preview requested"
              // — that's the specific stuck-waiting state we can resolve.
              if (!previewComment.body?.includes("Backend target: preview requested")) {
                continue;
              }

              const updatedAt = new Date(previewComment.updated_at).getTime();
              if (Date.now() - updatedAt < stuckAfterMs) continue;

              const ageMinutes = Math.round(
                (Date.now() - updatedAt) / 60000,
              );
              const runsUrl = `https://github.com/${context.repo.owner}/${context.repo.repo}/actions/workflows/pr-preview.yml?query=branch%3A${encodeURIComponent(pr.head.ref)}`;
              const body = [
                watchdogMarker,
                "### Preview watchdog",
                `The "preview requested" state has been stuck for ~${ageMinutes} minutes.`,
                "The backend callback probably dropped (token expired, dispatch failed, or the backend job crashed).",
                "",
                `Recover: re-run the [\`upsert-preview\` workflow](${runsUrl}) for this PR, or push an empty commit.`,
                "",
                "_Watchdog runs every 15 minutes; this comment updates in place when conditions change._",
              ].join("\n");

              const existing = comments.find((c) =>
                c.body?.includes(watchdogMarker),
              );
              if (existing) {
                if (existing.body === body) continue;
                await github.rest.issues.updateComment({
                  owner: context.repo.owner,
                  repo: context.repo.repo,
                  comment_id: existing.id,
                  body,
                });
                continue;
              }

              await github.rest.issues.createComment({
                owner: context.repo.owner,
                repo: context.repo.repo,
                issue_number: pr.number,
                body,
              });
            }