fix(linear): skip uploads.linear.app images in description pre-fetch

Markdown image URLs from Linear's CDN (`uploads.linear.app`) require the
workspace's OAuth token to fetch — the orchestrator's URL-resolver runs
unauthenticated and was 401ing, killing every Linear-with-image task
before the agent ever started:

 Hydration failed: AttachmentResolutionError: URL attachment fetch
 failed with status 401: https://uploads.linear.app/…

Filter Linear-hosted URLs out of the pre-fetch list. The agent picks
these up at runtime via `mcp__linear-server__extract_images` (which
mints fresh signed URLs the agent can fetch with `WebFetch`), so
removing them from the pre-fetch path doesn't lose coverage — it just
shifts the fetch from "Lambda with no auth" to "agent with the OAuth
token."

Trade-off: those bytes skip the input-Guardrail screening pass that
runs at task-creation time. The description text is still screened.

(cherry picked from commit f3bcc8e)

Author: isadeks

cdk/src/handlers/linear-webhook-processor.ts

@@ -1133,29 +1133,58 @@ function buildTaskDescription(issue: LinearIssueEvent['data'], contextHint: stri
  * Scans for standard markdown image references: `![alt](url)`.
  * Only HTTPS URLs are included (security: no HTTP, no data: URIs).
  * Capped at 10 images per issue to stay within attachment limits.
+ *
+ * Linear-hosted upload URLs (`uploads.linear.app`) are SKIPPED because
+ * they require the workspace's OAuth token to fetch — the orchestrator's
+ * URL-resolver runs unauthenticated and would fail closed with 401,
+ * killing the task before the agent ever starts. The agent picks these
+ * up at runtime via `mcp__linear-server__extract_images` (which mints
+ * fresh signed URLs) per the on-demand prompt addendum, so dropping
+ * them from the pre-fetch path doesn't lose coverage — it just shifts
+ * the fetch from "Lambda with no auth" to "agent with the OAuth token."
+ *
+ * Trade-off: Linear-hosted images skip the Bedrock Guardrail screening
+ * pass that runs at task-creation time. The description text itself is
+ * still screened via the input guardrail; the bytes are not. Acceptable
+ * for now — the agent treats those images as untrusted input anyway.
  */
 function extractImageUrlAttachments(description: string | undefined): Attachment[] {
   if (!description) return [];
 
   const imagePattern = /!\[[^\]]*\]\((https:\/\/[^)]+)\)/g;
   const attachments: Attachment[] = [];
+  let skippedLinearUploads = 0;
   let match: RegExpExecArray | null;
 
   while ((match = imagePattern.exec(description)) !== null) {
     if (attachments.length >= 10) break;
     const url = match[1];
+    if (isLinearUploadsUrl(url)) {
+      skippedLinearUploads += 1;
+      continue;
+    }
     attachments.push({ type: 'url', url });
   }
 
-  if (attachments.length > 0) {
+  if (attachments.length > 0 || skippedLinearUploads > 0) {
     logger.info('Extracted image URL attachments from Linear issue description', {
       count: attachments.length,
+      skipped_linear_uploads: skippedLinearUploads,
     });
   }
 
   return attachments;
 }
 
+function isLinearUploadsUrl(url: string): boolean {
+  try {
+    const host = new URL(url).hostname.toLowerCase();
+    return host === 'uploads.linear.app' || host.endsWith('.uploads.linear.app');
+  } catch {
+    return false;
+  }
+}
+
 async function lookupPlatformUser(workspaceId: string, userId: string): Promise<string | null> {
   const key = `${workspaceId}#${userId}`;
   const result = await ddb.send(new GetCommand({

cdk/test/handlers/linear-webhook-processor.test.ts

@@ -508,6 +508,39 @@ describe('linear-webhook-processor handler', () => {
       const [reqBody] = createTaskCoreMock.mock.calls[0];
       expect(reqBody.attachments).toBeUndefined();
     });
+
+    test('skips uploads.linear.app images so the unauthenticated URL resolver does not 401', async () => {
+      // Linear's CDN requires the workspace OAuth token to fetch, which the
+      // orchestrator's URL-resolver does NOT have. The agent picks these up
+      // at runtime via mcp__linear-server__extract_images instead, per the
+      // Linear-channel prompt addendum.
+      const payload = issue();
+      const data = payload.data as Record<string, unknown>;
+      data.description = [
+        '![paste](https://uploads.linear.app/15d12f61/090e5ce6/938f90d7)',
+        '![public](https://i.imgur.com/abc.png)',
+      ].join('\n');
+
+      await handler(eventWith(payload));
+
+      expect(createTaskCoreMock).toHaveBeenCalledTimes(1);
+      const [reqBody] = createTaskCoreMock.mock.calls[0];
+      // Only the public image survives the filter.
+      expect(reqBody.attachments).toHaveLength(1);
+      expect(reqBody.attachments[0].url).toBe('https://i.imgur.com/abc.png');
+    });
+
+    test('drops attachments entirely when only uploads.linear.app images are present', async () => {
+      const payload = issue();
+      const data = payload.data as Record<string, unknown>;
+      data.description = '![only](https://uploads.linear.app/x/y/z)';
+
+      await handler(eventWith(payload));
+
+      expect(createTaskCoreMock).toHaveBeenCalledTimes(1);
+      const [reqBody] = createTaskCoreMock.mock.calls[0];
+      expect(reqBody.attachments).toBeUndefined();
+    });
   });
 
   // ─── Linear issue context probe (paperclip attachments + project docs) ──────