fix(worker): reclaim expired processing task leases

[Cybercommanders]

Summary

• add HINDSIGHT_API_WORKER_TASK_LEASE_SECONDS with nonnegative validation
• let workers periodically reset stale processing rows from dead workers back to pending
• keep payload-less parent rows and locally active tasks untouched

Verification

• uv run pytest tests/test_worker.py::TestWorkerLeaseReaper tests/test_worker_retry_knobs.py::test_worker_task_lease_seconds_env_var tests/test_worker_retry_knobs.py::test_worker_task_lease_seconds_rejects_negative -q
• uv run ruff check hindsight_api/worker/poller.py hindsight_api/config.py hindsight_api/api/http.py hindsight_api/worker/main.py tests/test_worker.py tests/test_worker_retry_knobs.py
• uv run ty check hindsight_api/worker/poller.py hindsight_api/config.py hindsight_api/api/http.py hindsight_api/worker/main.py tests/test_worker.py tests/test_worker_retry_knobs.py
• ./scripts/hooks/lint.sh
• git diff --check

[Copilot]

Pull request overview

This PR introduces a worker “lease reaper” mechanism to reclaim async_operations rows stuck in processing when their heartbeat (updated_at) is stale, controlled via a new HINDSIGHT_API_WORKER_TASK_LEASE_SECONDS config/env var (with nonnegative validation). This helps recover work from dead/unreachable workers without incrementing retry counts.

Changes:

• Add HINDSIGHT_API_WORKER_TASK_LEASE_SECONDS (default 3600, 0 disables) to config, docs, and env templates.
• Implement periodic lease reaping in WorkerPoller to reset stale processing tasks back to pending while excluding payload-less parent rows and locally active tasks.
• Add regression tests covering lease reaping and config parsing/validation.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
hindsight-api-slim/hindsight_api/worker/poller.py	Adds lease reaper implementation and integrates it into the poll loop.
hindsight-api-slim/hindsight_api/config.py	Introduces the new env var constant/default, config field, and validation.
hindsight-api-slim/hindsight_api/worker/main.py	Threads the new config value into worker CLI poller construction.
hindsight-api-slim/hindsight_api/api/http.py	Threads the new config value into in-process worker poller construction.
hindsight-api-slim/tests/test_worker.py	Adds tests ensuring stale leases are reclaimed and “disabled when zero” behavior.
hindsight-api-slim/tests/test_worker_retry_knobs.py	Adds tests for env parsing and negative-value rejection for the new knob.
hindsight-docs/docs/developer/configuration.md	Documents the new configuration variable and semantics.
.env.example	Adds the new env var to the root env template.
hindsight-embed/hindsight_embed/env.example	Mirrors the root env template update for embed mode.

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[Cybercommanders]

Closing at maintainer/requester direction.