fix: resolve fork PRs in bumpy ci comment

.bumpy/ci-comment-fork-pr-resolution.md

@@ -0,0 +1,5 @@
+---
+'@varlock/bumpy': patch
+---
+
+Fix `bumpy ci comment` failing to resolve the target PR for fork PRs. Under `workflow_run`, the PR was looked up via `GET commits/{head_sha}/pulls`, which only knows about commits in the base repo's own branches — for a fork PR it returns nothing, so the command exited with "Could not resolve a target PR" (defeating the whole point of the fork-safe `pull_request` + `workflow_run` split). When that lookup is empty, bumpy now scans the repo's open PRs (paginated) and matches `head.sha` against the trusted `workflow_run.head_sha`. The target still derives only from the trusted event, never from the artifact or from `workflow_run.pull_requests[]` (which GitHub leaves empty for forks).

packages/bumpy/src/commands/ci.ts

@@ -349,22 +349,54 @@ export function resolveTargetPrNumber(rootDir: string): string | null {
     const repo = process.env.GITHUB_REPOSITORY;
     // Sanitize both before they reach the gh api path: a 40-hex SHA and an owner/repo slug.
     if (headSha && /^[0-9a-f]{40}$/i.test(headSha) && repo && /^[\w.-]+\/[\w.-]+$/.test(repo)) {
-      const out = tryRunArgs(
-        ['gh', 'api', `repos/${repo}/commits/${headSha}/pulls`, '--jq', '.[] | select(.state == "open") | .number'],
-        { cwd: rootDir },
-      );
-      return (
-        out
-          ?.split('\n')
-          .map((l) => l.trim())
-          .find((l) => /^\d+$/.test(l)) ?? null
-      );
+      return findOpenPrByHeadSha(repo, headSha, rootDir);
     }
     return null;
   }
   return detectPrNumber();
 }
 
+/**
+ * Find the open PR whose head commit is `headSha`.
+ *
+ * `GET commits/{sha}/pulls` is the cheap lookup, but it only knows about commits that
+ * live in the base repo's own branches — for a PR opened from a fork the head commit
+ * isn't there, so it returns `[]`. Fall back to scanning the repo's open PRs and matching
+ * on `head.sha`. Both derive the target purely from the trusted SHA, so the security
+ * model (never trust the artifact, never trust `workflow_run.pull_requests[]`, which
+ * GitHub leaves empty for forks) is preserved.
+ */
+function findOpenPrByHeadSha(repo: string, headSha: string, rootDir: string): string | null {
+  const firstNumber = (out: string | null): string | null =>
+    out
+      ?.split('\n')
+      .map((l) => l.trim())
+      .find((l) => /^\d+$/.test(l)) ?? null;
+
+  const fromCommit = firstNumber(
+    tryRunArgs(
+      ['gh', 'api', `repos/${repo}/commits/${headSha}/pulls`, '--jq', '.[] | select(.state == "open") | .number'],
+      { cwd: rootDir },
+    ),
+  );
+  if (fromCommit) return fromCommit;
+
+  // `--paginate` follows Link headers, so repos with >100 open PRs are still covered.
+  return firstNumber(
+    tryRunArgs(
+      [
+        'gh',
+        'api',
+        '--paginate',
+        `repos/${repo}/pulls?state=open&per_page=100`,
+        '--jq',
+        `.[] | select(.head.sha == "${headSha}") | .number`,
+      ],
+      { cwd: rootDir },
+    ),
+  );
+}
+
 // ---- ci plan ----
 
 /** Path (relative to rootDir) where ci plan caches its output for ci release to reuse */

packages/bumpy/test/core/ci-comment.test.ts

@@ -59,6 +59,40 @@ describe('resolveTargetPrNumber — workflow_run', () => {
     // It must look up the PR by the event's head_sha — that's the trusted derivation.
     const apiCalls = getCallsMatching(`commits/${HEAD_SHA}/pulls`);
     expect(apiCalls).toHaveLength(1);
+    // Same-repo PR: the commits endpoint answers, so no open-PR scan is needed.
+    expect(getCallsMatching('pulls?state=open')).toHaveLength(0);
+  });
+
+  test('fork PR: falls back to scanning open PRs by head.sha when the commits endpoint is empty', () => {
+    process.env.GITHUB_EVENT_NAME = 'workflow_run';
+    process.env.GITHUB_REPOSITORY = 'owner/repo';
+    process.env.GITHUB_EVENT_PATH = writeEvent({
+      // GitHub leaves pull_requests[] empty for fork PRs — it must not be relied on.
+      workflow_run: { head_sha: HEAD_SHA, pull_requests: [] },
+    });
+    // The fork's head commit isn't in the base repo, so commits/{sha}/pulls yields nothing.
+    addMockRule({ match: /commits\/[0-9a-f]+\/pulls/, response: '' });
+    addMockRule({ match: 'pulls?state=open', response: '1075\n' });
+
+    const pr = resolveTargetPrNumber(tmp);
+
+    expect(pr).toBe('1075');
+    expect(getCallsMatching(`commits/${HEAD_SHA}/pulls`)).toHaveLength(1);
+    const scans = getCallsMatching('pulls?state=open');
+    expect(scans).toHaveLength(1);
+    // The scan matches on the trusted head_sha and paginates past 100 open PRs.
+    expect(scans[0]!.args).toContain('--paginate');
+    expect(scans[0]!.command).toContain(`select(.head.sha == "${HEAD_SHA}")`);
+  });
+
+  test('returns null when neither lookup finds an open PR for the head_sha', () => {
+    process.env.GITHUB_EVENT_NAME = 'workflow_run';
+    process.env.GITHUB_REPOSITORY = 'owner/repo';
+    process.env.GITHUB_EVENT_PATH = writeEvent({ workflow_run: { head_sha: HEAD_SHA } });
+    addMockRule({ match: /commits\/[0-9a-f]+\/pulls/, response: '' });
+    addMockRule({ match: 'pulls?state=open', response: '' });
+
+    expect(resolveTargetPrNumber(tmp)).toBeNull();
   });
 
   test('returns null when the event has no usable head_sha', () => {