fix(server): wake idle workers on admitted work

[svonava]

Remove the idle worker's recurring 1 ms poll by waking it on successful request admission or shutdown. Keep the configured idle coalescing window (3 ms by default), normal coalescing, first-request timeout, and batch limits. Caller-formed batches continue to bypass this loop.

Refs #373 as partial progress. This preserves the existing accumulation policy and does not establish sub-millisecond idle dispatch, strict whole-burst fusion, or throughput equivalence. PR #658 remains separate with its existing human review hold and unmet qualification criteria. No GPU or performance claim is made here.

Validation: 377 CPU tests passed, including 15 new controls for wakeup races, cancellation/shutdown, and the original lone/burst coalescing behavior. Ruff lint, formatting, and type checks pass.

Summary by CodeRabbit

• Performance
  • Reduced unnecessary background activity while the worker is idle by having it wait for new work instead of repeatedly checking for it.
• Reliability
  • Improved worker wake-up behavior when work arrives or the worker stops.

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Reviewing files that changed from the base of the PR and between 118ba91 and 6dfdaaf.

📒 Files selected for processing: 2

• packages/sie_server/src/sie_server/core/worker/model_worker.py
• packages/sie_server/tests/core/test_worker_idle_wakeup.py

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📝 Walkthrough

ModelWorker now uses an event to wake its FCFS batch selector when work is submitted or the worker stops. The selector waits on the event instead of polling, then rechecks batcher queues. New tests cover admission, idle waiting, shutdown, and batch selection.

Changes: Worker idle wake-up

Layer / File(s)	Summary
Signal work and validate idle selection packages/sie_server/src/sie_server/core/worker/model_worker.py, packages/sie_server/tests/core/test_worker_idle_wakeup.py	ModelWorker sets an event after work submission and shutdown. When no batcher has pending items, the selector waits for the event, clears it, and rechecks queue state. Tests cover admission timing, idle behavior, cancellation, shutdown, and batch selection.

Suggested reviewers: krisztian-gajdar

Priority: ⬇️ Low

Merge Risk: ⚪ Minimal · up to 6dfda

No actionable risk introduced by this change remains; it is ready to merge after normal checks.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 35.29% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 17 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely describes the main change: waking idle workers when work is admitted.

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[svonava]

@coderabbitai review

Please review exact head 6dfdaaf1f128ed4e68cb31ef71d4e836658bd7d5. This replaces only idle polling with an admission event and preserves the configured coalescing policy; #373 remains partially addressed and PR #658 stays separate.

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