diff --git a/.github/workflows/calibrate.yml b/.github/workflows/calibrate.yml
index 43b3949..01a82e4 100644
--- a/.github/workflows/calibrate.yml
+++ b/.github/workflows/calibrate.yml
@@ -124,6 +124,26 @@ jobs:
             const fn = await import(`${process.env.GITHUB_WORKSPACE}/scripts/post-calibration-comment.mjs`);
             await fn.default(github, context, '/tmp/aggregate.json');
 
+      # The gate must go RED when calibration measured nothing (0 apps booted) or
+      # any wired kind falls below threshold. Previously the job passed green on an
+      # empty aggregate (precision=1/recall=1) — a false-assurance bug. Runs after
+      # the comment so the PR still shows why it failed.
+      - name: Enforce calibration actually ran
+        run: |
+          node -e "
+            const a = require('/tmp/aggregate.json');
+            if (a.calibrationRan === false || (a.appsIncluded || []).length === 0) {
+              console.error('::error::Calibration produced NO data — 0 bench apps came up (health-check timeout / SurfaceMCP not started). The gate must not pass green on zero data.');
+              process.exit(1);
+            }
+            const v = a.thresholdViolations || [];
+            if (v.length > 0) {
+              console.error('::error::Calibration threshold violations: ' + v.join(', '));
+              process.exit(1);
+            }
+            console.log('Calibration ran: ' + (a.appsIncluded || []).join(', ') + ' (tp=' + a.overall.tp + ' fp=' + a.overall.fp + ' fn=' + a.overall.fn + ')');
+          "
+
       - name: Update README calibration block (push to main only)
         if: github.event_name == 'push' && github.ref == 'refs/heads/main'
         run: |
diff --git a/scripts/aggregate-calibration.mjs b/scripts/aggregate-calibration.mjs
index 0707f81..6cdf068 100644
--- a/scripts/aggregate-calibration.mjs
+++ b/scripts/aggregate-calibration.mjs
@@ -38,18 +38,21 @@ for (const p of reportPaths) {
   }
 }
 if (reports.length === 0) {
-  // Every bench app failed (likely health-check timeout or threshold violation
-  // upstream in BugHunter-bench). Emit a vacuous aggregate so the workflow can
-  // continue and upload the artifact showing which apps failed; exit cleanly so
-  // CI doesn't go red on bench-app flake.
-  process.stderr.write('All bench apps failed; emitting empty aggregate.\n');
+  // Every bench app failed to produce a report (health-check timeout, missing
+  // SurfaceMCP, etc.). This is NOT a pass — the gate measured nothing. Flag
+  // `calibrationRan: false` with null precision/recall (never 1.0 — that false
+  // green is the bug this replaces) so the comment renders a failure and the
+  // calibrate.yml "Enforce calibration ran" step turns the check red. We still
+  // exit 0 so the artifact uploads and the PR comment posts.
+  process.stderr.write('All bench apps failed to produce a report — calibration did NOT run.\n');
   process.stdout.write(JSON.stringify({
     version: 1,
     schemaVersion: 'v0.44.0',
     generatedAt: new Date().toISOString(),
+    calibrationRan: false,
     appsIncluded: [],
     appsFailed,
-    overall: { totalClusters: 0, totalGoldEntries: 0, tp: 0, fp: 0, fn: 0, tn: 0, precision: 1.0, recall: 1.0, f1: 0 },
+    overall: { totalClusters: 0, totalGoldEntries: 0, tp: 0, fp: 0, fn: 0, tn: 0, precision: null, recall: null, f1: null },
     perKind: {},
     thresholdViolations: [],
   }, null, 2) + '\n');
@@ -124,6 +127,7 @@ const aggregate = {
   version: 1,
   schemaVersion: 'v0.44.0',
   generatedAt: new Date().toISOString(),
+  calibrationRan: true,
   bughunterVersion: reports[0]?.bughunterVersion ?? 'unknown',
   bughunterCommit: reports[0]?.bughunterCommit ?? 'unknown',
   appsIncluded: reports.map(r => r.benchAppId),
diff --git a/scripts/post-calibration-comment.mjs b/scripts/post-calibration-comment.mjs
index ab5c6e9..a07ae94 100644
--- a/scripts/post-calibration-comment.mjs
+++ b/scripts/post-calibration-comment.mjs
@@ -13,6 +13,21 @@ export default async function postCalibrationComment(github, context, aggregateP
   const agg = JSON.parse(fs.readFileSync(aggregatePath, 'utf-8'));
   const { overall, perKind, thresholdViolations, appsIncluded, generatedAt } = agg;
 
+  // Calibration did not run — no bench app produced a report. Render a loud
+  // failure instead of a green ✅ with vacuous precision=1/recall=1.
+  if (agg.calibrationRan === false || (appsIncluded?.length ?? 0) === 0) {
+    const failed = (agg.appsFailed ?? []).map(f => `\`${f.path?.split('/').slice(-2, -1)[0] ?? f.path}\` (${f.reason})`).join(', ');
+    const failBody =
+      `❌ **BugHunter Calibration DID NOT RUN** | ${generatedAt?.slice(0, 10)}\n\n` +
+      `**0 bench apps produced a report** — the calibration gate measured nothing ` +
+      `(no precision/recall data). This is a failure, not a pass.\n\n` +
+      (failed ? `Failed: ${failed}\n\n` : '') +
+      `Likely cause: bench apps did not boot (health-check timeout) or SurfaceMCP ` +
+      `was not started. See the calibrate job log.\n`;
+    await upsertComment(github, context, failBody);
+    return;
+  }
+
   const statusIcon = thresholdViolations.length === 0 ? '✅' : '❌';
   const headerLine = `${statusIcon} **BugHunter Calibration** | ${appsIncluded?.join(', ')} | ${generatedAt?.slice(0, 10)}`;
 
@@ -41,23 +56,19 @@ export default async function postCalibrationComment(github, context, aggregateP
   const body =
     `${headerLine}\n\n${overallLine}\n\n${table}${violationsSection}\n`;
 
+  await upsertComment(github, context, body);
+}
+
+// Create or update the single "BugHunter Calibration" PR comment.
+async function upsertComment(github, context, body) {
   const { data: comments } = await github.rest.issues.listComments({
     ...context.repo,
     issue_number: context.issue.number,
   });
-
   const existing = comments.find(c => c.body?.includes('BugHunter Calibration'));
   if (existing) {
-    await github.rest.issues.updateComment({
-      ...context.repo,
-      comment_id: existing.id,
-      body,
-    });
+    await github.rest.issues.updateComment({ ...context.repo, comment_id: existing.id, body });
   } else {
-    await github.rest.issues.createComment({
-      ...context.repo,
-      issue_number: context.issue.number,
-      body,
-    });
+    await github.rest.issues.createComment({ ...context.repo, issue_number: context.issue.number, body });
   }
 }