fix: boulder continuation now respects /stop-continuation guard

Add isContinuationStopped check to atlas hook's session.idle handler
so boulder continuation stops when user runs /stop-continuation.

Previously, todo continuation and session recovery checked the guard,
but boulder continuation did not — causing work to resume after stop.

Fixes #1575

src/hooks/atlas/index.ts

@@ -399,6 +399,7 @@ const CONTINUATION_COOLDOWN_MS = 5000
 export interface AtlasHookOptions {
   directory: string
   backgroundManager?: BackgroundManager
+  isContinuationStopped?: (sessionID: string) => boolean
 }
 
 function isAbortError(error: unknown): boolean {
@@ -573,6 +574,11 @@ export function createAtlasHook(
           return
         }
 
+        if (options?.isContinuationStopped?.(sessionID)) {
+          log(`[${HOOK_NAME}] Skipped: continuation stopped for session`, { sessionID })
+          return
+        }
+
         const requiredAgent = (boulderState.agent ?? "atlas").toLowerCase()
         const lastAgent = getLastAgentFromSession(sessionID)
         if (!lastAgent || lastAgent !== requiredAgent) {