diff --git a/docs/testing/plan-canvas-pdf-export.tdd.md b/docs/testing/plan-canvas-pdf-export.tdd.md
index e2bc2ca06..38e849628 100644
--- a/docs/testing/plan-canvas-pdf-export.tdd.md
+++ b/docs/testing/plan-canvas-pdf-export.tdd.md
@@ -24,9 +24,9 @@ artifact as a real PDF file without sending the plan to an external converter.
 
 - RED: the focused server suite produced 30 passes and 2 failures because the
   Canvas had no Download PDF control or PDF endpoint.
-- GREEN: renderer unit tests pass 7/7, Plan Canvas server tests pass 34/34,
-  and the end-to-end review workflow passes 12/12.
-- FULL SUITE: the final review-hardened implementation passes all 4,008
+- GREEN: renderer unit tests pass 7/7, Plan Canvas server tests pass 35/35,
+  and the end-to-end review workflow passes 13/13.
+- FULL SUITE: the final review-hardened implementation passes all 4,010
   discovered tests; hosted security reruns are recorded on PR #2894.
 - COVERAGE: `npm run coverage` passes 4,003/4,003 with 88.97% statements,
   80.58% branches, 94.22% functions, and 88.97% lines. The Plan Canvas
diff --git a/scripts/lib/plan-canvas/server.js b/scripts/lib/plan-canvas/server.js
index c93135531..7963980c7 100644
--- a/scripts/lib/plan-canvas/server.js
+++ b/scripts/lib/plan-canvas/server.js
@@ -433,8 +433,18 @@ function createPlanCanvasServer({
         });
         return sendPdf(res, pdf);
       } catch (error) {
-        const statusCode = error.code === 'PDF_BROWSER_NOT_FOUND' ? 503 : 500;
-        return sendJson(res, statusCode, { error: error.message, code: error.code || 'PDF_EXPORT_FAILED' });
+        const code = error.code || 'PDF_EXPORT_FAILED';
+        log(`[plan-canvas] PDF export failed (${code}): ${error.stack || error.message}`);
+        if (code === 'PDF_BROWSER_NOT_FOUND') {
+          return sendJson(res, 503, {
+            error: 'PDF export requires Google Chrome, Chromium, or Microsoft Edge; configure ECC_PLAN_CANVAS_CHROME_PATH if auto-discovery cannot find it',
+            code
+          });
+        }
+        return sendJson(res, 500, {
+          error: 'PDF export failed; check the Plan Canvas server log for details',
+          code: 'PDF_EXPORT_FAILED'
+        });
       } finally {
         pdfSnapshot = null;
         pdfExportActive = false;
diff --git a/scripts/plan-canvas.js b/scripts/plan-canvas.js
index 9c0a33855..195607b56 100755
--- a/scripts/plan-canvas.js
+++ b/scripts/plan-canvas.js
@@ -179,19 +179,20 @@ async function withServerStartLock(port, task, {
   const lockPort = validatePort(port);
   const startedAt = Date.now();
   let socket = null;
+  let socketError = null;
 
   while (true) {
     try {
       socket = await new Promise((resolve, reject) => {
         const candidate = dgramImpl.createSocket('udp4');
         const onError = error => {
-          candidate.close();
+          try { candidate.close(); } catch { /* failed bind has no open handle */ }
           reject(error);
         };
         candidate.once('error', onError);
         candidate.bind(lockPort, DEFAULT_HOST, () => {
           candidate.removeListener('error', onError);
-          candidate.on('error', () => {});
+          candidate.on('error', error => { socketError = error; });
           candidate.unref();
           resolve(candidate);
         });
@@ -206,11 +207,23 @@ async function withServerStartLock(port, task, {
     }
   }
 
+  let result;
   try {
-    return await task();
+    result = await task();
   } finally {
-    if (socket) socket.close();
+    if (socket) {
+      await new Promise(resolve => {
+        try { socket.close(resolve); } catch { resolve(); }
+      });
+    }
   }
+  if (socketError) {
+    const error = new Error(`Plan Canvas startup lock failed on port ${port}: ${socketError.message}`);
+    error.code = 'PLAN_CANVAS_START_LOCK_FAILED';
+    error.cause = socketError;
+    throw error;
+  }
+  return result;
 }
 
 function serverIsCompatible(health) {
diff --git a/tests/integration/plan-canvas-e2e.test.js b/tests/integration/plan-canvas-e2e.test.js
index a534e5f71..467aff10b 100644
--- a/tests/integration/plan-canvas-e2e.test.js
+++ b/tests/integration/plan-canvas-e2e.test.js
@@ -17,6 +17,7 @@
  */
 
 const assert = require('assert');
+const { EventEmitter } = require('events');
 const fs = require('fs');
 const http = require('http');
 const os = require('os');
@@ -169,6 +170,21 @@ async function main() {
       );
     });
 
+    await test('port-scoped startup lock propagates socket failures', async () => {
+      class FailingLockSocket extends EventEmitter {
+        bind(_port, _host, callback) { setImmediate(callback); }
+        unref() {}
+        close(callback) { if (callback) setImmediate(callback); }
+      }
+      const socket = new FailingLockSocket();
+      await assert.rejects(
+        withServerStartLock(port + 4, async () => {
+          socket.emit('error', new Error('simulated UDP failure'));
+        }, { dgramImpl: { createSocket: () => socket }, timeoutMs: 2000 }),
+        error => error.code === 'PLAN_CANVAS_START_LOCK_FAILED' && error.message.includes('simulated UDP failure')
+      );
+    });
+
     await test('concurrent opens serialize replacement of a same-version legacy server', async () => {
       const legacyPort = port + 1;
       const legacyStateDir = path.join(tmp, 'legacy-state');
diff --git a/tests/scripts/plan-canvas.test.js b/tests/scripts/plan-canvas.test.js
index b460e7ef7..ca3635994 100644
--- a/tests/scripts/plan-canvas.test.js
+++ b/tests/scripts/plan-canvas.test.js
@@ -104,6 +104,8 @@ async function main() {
   const pdfRequests = [];
   let holdPdfExport = false;
   let releasePdfExport = null;
+  let pdfFailure = null;
+  const serverLogs = [];
   let idleFired = false;
   const canvas = createPlanCanvasServer({
     store,
@@ -112,9 +114,11 @@ async function main() {
     idleTimeoutMs: 0,
     pdfExporter: async options => {
       pdfRequests.push(options);
+      if (pdfFailure) throw pdfFailure;
       if (holdPdfExport) await new Promise(resolve => { releasePdfExport = resolve; });
       return { buffer: Buffer.from('%PDF-1.4\n%%EOF\n'), filename: 'demo.pdf' };
     },
+    log: line => serverLogs.push(line),
     onIdleShutdown: () => {
       idleFired = true;
     }
@@ -260,22 +264,53 @@ async function main() {
     holdPdfExport = true;
     const snapshot = '<!doctype html><html><body><h1>Already rendered diagram</h1><svg><text>Local SVG</text></svg><script>fetch("https://example.invalid")</script></body></html>';
     const first = request(port, 'POST', `/api/session/${key}/pdf`, { body: { html: snapshot } });
-    await waitFor(() => typeof releasePdfExport === 'function');
-    const printable = await request(port, 'GET', `/artifact/${key}/?pdf=1`);
-    assert.ok(printable.body.includes('Already rendered diagram'));
-    assert.ok(printable.body.includes('Local SVG'));
-    assert.ok(printable.headers['content-security-policy'].includes("script-src 'none'"));
-    const overloaded = await request(port, 'GET', `/api/session/${key}/pdf`);
-    assert.strictEqual(overloaded.statusCode, 429);
-    assert.strictEqual(overloaded.headers['retry-after'], '1');
-    assert.deepStrictEqual(jsonBody(overloaded), {
-      error: 'another PDF export is already in progress',
-      code: 'PDF_EXPORT_BUSY'
-    });
-    releasePdfExport();
+    try {
+      await waitFor(() => typeof releasePdfExport === 'function');
+      const printable = await request(port, 'GET', `/artifact/${key}/?pdf=1`);
+      assert.ok(printable.body.includes('Already rendered diagram'));
+      assert.ok(printable.body.includes('Local SVG'));
+      assert.ok(printable.headers['content-security-policy'].includes("script-src 'none'"));
+      const overloaded = await request(port, 'GET', `/api/session/${key}/pdf`);
+      assert.strictEqual(overloaded.statusCode, 429);
+      assert.strictEqual(overloaded.headers['retry-after'], '1');
+      assert.deepStrictEqual(jsonBody(overloaded), {
+        error: 'another PDF export is already in progress',
+        code: 'PDF_EXPORT_BUSY'
+      });
+    } finally {
+      const release = releasePdfExport;
+      holdPdfExport = false;
+      releasePdfExport = null;
+      if (release) release();
+    }
     assert.strictEqual((await first).statusCode, 200);
-    holdPdfExport = false;
-    releasePdfExport = null;
+  })) passed++; else failed++;
+
+  if (await test('PDF failures log diagnostics without disclosing local paths', async () => {
+    try {
+      const rendererError = new Error('Chromium failed at /Users/private/browser-profile');
+      rendererError.code = 'PDF_EXPORT_FAILED';
+      pdfFailure = rendererError;
+      const failed = await request(port, 'GET', `/api/session/${key}/pdf`);
+      assert.strictEqual(failed.statusCode, 500);
+      assert.deepStrictEqual(jsonBody(failed), {
+        error: 'PDF export failed; check the Plan Canvas server log for details',
+        code: 'PDF_EXPORT_FAILED'
+      });
+      assert.ok(!failed.body.includes('/Users/private'));
+      assert.ok(serverLogs.some(line => line.includes('/Users/private/browser-profile')));
+
+      const browserError = new Error('missing override /Users/private/Chrome');
+      browserError.code = 'PDF_BROWSER_NOT_FOUND';
+      pdfFailure = browserError;
+      const missing = await request(port, 'GET', `/api/session/${key}/pdf`);
+      assert.strictEqual(missing.statusCode, 503);
+      assert.strictEqual(jsonBody(missing).code, 'PDF_BROWSER_NOT_FOUND');
+      assert.ok(jsonBody(missing).error.includes('ECC_PLAN_CANVAS_CHROME_PATH'));
+      assert.ok(!missing.body.includes('/Users/private'));
+    } finally {
+      pdfFailure = null;
+    }
   })) passed++; else failed++;
 
   if (await test('browser client uses finite polling instead of one permanent connection per canvas', async () => {