fix(scheduler): back off due tasks with running mongo executions

[bingran-you]

Summary

• add a short-lived local scheduler backoff when MongoDB still reports a running execution row for a due task
• stop re-querying and re-reconciling the same due task on every scheduler poll cycle
• add focused unit coverage for the new backoff helpers

Validation

• cargo check --locked -p scheduler_module --lib
• cargo test --locked -p scheduler_module ... is still blocked by a pre-existing unrelated compile failure in scheduler_module/src/scheduler/store/mongo.rs test code (ExecutionRow initializer missing task_id)

Refs #1459

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Project	Deployment	Actions	Updated (UTC)
dowhiz	Ready	Preview, Comment	Apr 20, 2026 7:58pm

[Oliver-DoWhiz]

Reviewed the scheduler backoff change against the hot-loop issue. The new in-memory cooldown looks correctly scoped to task/user keys, avoids re-claiming the same due task every poll when Mongo still reports a running execution, and includes focused helper tests for the backoff lifecycle. CI is green on this PR, so I’m approving.

[Oliver-DoWhiz]

Reviewed this and approved it on GitHub. The task/user-scoped Mongo backoff looks right for stopping the hot recheck loop, and the PR checks are green.