feat(config): default thinking for sessions_spawn subagents (#7372)

* feat(config): add subagent default thinking

* fix: accept config subagents.thinking + stabilize test mocks (#7372) (thanks @tyler6204)

* fix: use findLast instead of clearAllMocks in test (#7372)

* fix: correct test assertions for tool result structure (#7372)

* fix: remove unnecessary type assertion after rebase

src/config/types.agent-defaults.ts

@@ -204,6 +204,8 @@ export type AgentDefaultsConfig = {
     archiveAfterMinutes?: number;
     /** Default model selection for spawned sub-agents (string or {primary,fallbacks}). */
     model?: string | { primary?: string; fallbacks?: string[] };
+    /** Default thinking level for spawned sub-agents (e.g. "off", "low", "medium", "high"). */
+    thinking?: string;
   };
   /** Optional sandbox settings for non-main sessions. */
   sandbox?: {