review-checklist: exempt a just-requested reviewer from avalanche pruning (#6524)

A direct review_requested (e.g. manually re-requesting a reviewer via
the GitHub UI) adds a second currently-requested owner to that
reviewer's area — indistinguishable from an unpruned CODEOWNERS
avalanche, so the avalanche-detection pass immediately removed them
again on the same run. Carve out the login this run's review_requested
action names before running avalanche detection.

.github/scripts/review-checklist.js

@@ -450,6 +450,16 @@ async function coordinateReviewers(github, context, core, {
     }
   }
 
+  // The specific login a direct review_requested action just added, if any —
+  // see its use below in avalanche detection. A deliberate re-request must
+  // survive this same run: it lands existingRequested at two owners for that
+  // login's area (them plus whoever an earlier pruning pass already picked),
+  // which is indistinguishable from an unpruned CODEOWNERS avalanche unless
+  // this login is carved out.
+  const justRequestedLogin = (action === 'review_requested' && context.payload.requested_reviewer)
+    ? context.payload.requested_reviewer.login
+    : null;
+
   const existingRequested = new Set(
     prData.requested_reviewers.map(r => r.login).filter(Boolean).filter(l => !updatedExcluded.has(l))
   );
@@ -561,8 +571,12 @@ async function coordinateReviewers(github, context, core, {
   // synchronize-swap or additive-fill logic runs, so those paths see an already-
   // correct one-per-area baseline. (PR #6484: user pushed a commit that first
   // touched .github; GitHub assigned all 4 .github CODEOWNERS simultaneously.)
+  // justRequestedLogin's area is exempted — a human just deliberately asked
+  // for exactly that person, which looks identical to an avalanche (two
+  // owners now requested) but isn't one.
   const avalancheAreas = eligibleAreas.filter(
     area => area.owners.filter(o => existingRequested.has(o)).length > 1
+      && !(justRequestedLogin && area.owners.includes(justRequestedLogin))
   );
   if (avalancheAreas.length > 0) {
     const { selected: avalanchePruned, log: pruneLog } = chooseReviewers(avalancheAreas, {

.github/scripts/review-checklist.test.js

@@ -898,6 +898,46 @@ asyncTest('coordinateReviewers: synchronize with one owner per area does not pru
   assert.strictEqual(github.calls.removeRequestedReviewers.length, 0);
 });
 
+// ----------------------------------------------------------------
+// coordinateReviewers — a direct review_requested must survive avalanche
+// detection on the very same run (reported bug: manually re-requesting a
+// reviewer via the GitHub UI got them immediately removed again, because
+// their area now had two currently-requested owners — themselves plus
+// whichever pick an earlier ready_for_review pruning pass had already made
+// — which is indistinguishable from an unpruned CODEOWNERS avalanche unless
+// the just-requested login is carved out).
+// ----------------------------------------------------------------
+
+asyncTest('coordinateReviewers: review_requested for a specific login is not undone by avalanche pruning', async () => {
+  const github = makeGithubMock();
+  const context = {
+    eventName: 'pull_request_target',
+    payload: {
+      action: 'review_requested',
+      requested_reviewer: { login: 'jhendersonHDF' },
+      sender: { type: 'User' },
+    },
+  };
+  const args = makeCoordinateBaseArgs({
+    prData: {
+      user: { login: 'lrknox' },
+      draft: false,
+      // hyoklee is the load-balanced pick an earlier pass already made;
+      // jhendersonHDF was just manually re-requested on top of it.
+      requested_reviewers: [{ login: 'hyoklee' }, { login: 'jhendersonHDF' }],
+    },
+    // Rig the load-balancer so a fresh pick would land on hyoklee, not
+    // jhendersonHDF — proving jhendersonHDF survives because they were
+    // just requested, not because they'd have won the pick anyway.
+    reviewerLoad: { hyoklee: 0, jhendersonHDF: 99, glennsong09: 0 },
+  });
+
+  const { confirmedRequested } = await coordinateReviewers(github, context, makeCore(), args);
+
+  assert.strictEqual(github.calls.removeRequestedReviewers.length, 0, 'Nothing should be removed');
+  assert.ok(confirmedRequested.has('jhendersonHDF'), 'The just-requested reviewer must stay');
+});
+
 // ----------------------------------------------------------------
 // coordinateReviewers — bot-self-triggered review_request_removed must not
 // create a sticky exclusion (the bot's own removeUnselected/removeRequestedReviewers