Atlas continuation only treated running background tasks as active work. When a delegated subagent had been launched but was still waiting for session creation, the task remained pending and Atlas could inject another continuation too early.
Treat pending tasks as active background work in the continuation injector and add regression coverage for the pending-session-creation race so delegated work is allowed to acquire a session before Atlas resumes the plan.
Tests: bun test src/hooks/atlas/boulder-continuation-injector.test.ts src/hooks/atlas/index.test.ts; bun run typecheck
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
tw-yshuang
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