fix: guard against undefined path in bootstrap file entries

The session-context hook pushed bootstrap entries without the required
`path` property, causing a TypeError in buildInjectedWorkspaceFiles when
it called .replace() on undefined. Add fallback to file.name when path
is missing, and skip entries with no path in the report builder.

Also add stack trace logging to lane task errors and embedded agent
failures to make future debugging faster.

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

src/process/command-queue.ts

@@ -100,8 +100,9 @@ function drainLane(lane: string) {
           const completedCurrentGeneration = completeTask(state, taskId, taskGeneration);
           const isProbeLane = lane.startsWith("auth-probe:") || lane.startsWith("session:probe-");
           if (!isProbeLane) {
+            const stack = err instanceof Error ? err.stack : undefined;
             diag.error(
-              `lane task error: lane=${lane} durationMs=${Date.now() - startTime} error="${String(err)}"`,
+              `lane task error: lane=${lane} durationMs=${Date.now() - startTime} error="${String(err)}"${stack ? `\n${stack}` : ""}`,
             );
           }
           if (completedCurrentGeneration) {