fix(atlas): await injectBoulderContinuation and handle errors

The async call was fire-and-forget with no error handling. Now properly
awaited with try/catch that logs failures and increments promptFailureCount.

src/hooks/atlas/event-handler.ts

@@ -122,7 +122,8 @@ export function createAtlasEventHandler(input: {
 
       state.lastContinuationInjectedAt = now
       const remaining = progress.total - progress.completed
-      injectBoulderContinuation({
+      try {
+        await injectBoulderContinuation({
           ctx,
           sessionID,
           planName: boulderState.plan_name,
@@ -132,6 +133,10 @@ export function createAtlasEventHandler(input: {
           backgroundManager,
           sessionState: state,
         })
+      } catch (err) {
+        log(`[${HOOK_NAME}] Failed to inject boulder continuation`, { sessionID, error: err })
+        state.promptFailureCount++
+      }
       return
     }