fix(cancel-poll): use ctx.authToken instead of process.env for cancel polling

The cancel poll was sending empty Authorization headers because
PAPERCLIP_API_KEY is not set on the Paperclip server pod. Use the
per-run authToken from ctx instead, which is the JWT issued by Paperclip
for this execution. PAPERCLIP_DEV_API_KEY still overrides for dev instances.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/server/execute.ts

@@ -569,9 +569,9 @@ async function streamAndAwaitJob(
         await new Promise<void>((resolve) => setTimeout(resolve, KEEPALIVE_INTERVAL_MS));
         if (logStopSignal.stopped || cancelSignal.cancelled) break;
         try {
-          // Prefer PAPERCLIP_DEV_API_KEY if set (allows dev instance key to be
-          // distinct from the main-instance run JWT in PAPERCLIP_API_KEY).
-          const apiKey = process.env.PAPERCLIP_DEV_API_KEY ?? process.env.PAPERCLIP_API_KEY ?? "";
+          // Prefer PAPERCLIP_DEV_API_KEY if set (dev override), otherwise use
+          // the per-run authToken issued by Paperclip for this execution.
+          const apiKey = process.env.PAPERCLIP_DEV_API_KEY ?? ctx.authToken ?? "";
           const resp = await fetch(`${apiUrl}/api/issues/${issueId}`, {
             headers: { Authorization: `Bearer ${apiKey}` },
           });