Changelog

All notable changes to this project will be documented in this file.

The format is based on Keep a Changelog, and this project adheres to Semantic Versioning.

[Unreleased]

Worker isolation mode: CONDUCTOR_WORKER_ISOLATION=thread runs every worker as a thread instead of a multiprocessing.Process (default process is unchanged — spawn remains the start method). For environments where multiprocessing's fork+exec bootstraps (spawn children, resource_tracker) fail, e.g. Firecracker microVM guests. Thread-mode tradeoffs: no per-worker force-kill (shutdown is cooperative), CPU-bound workers share the GIL, and signal.signal becomes a no-op off the main thread. Implementation: the Windows-only Process→Thread shim moved to conductor.client.automator.worker_isolation (the private worker_manager._patch_conductor_use_threads_on_windows helper is removed — the Windows gate calls apply_thread_isolation() directly) and now also swaps the logging-relay Queue for a plain queue.Queue
Canonical metrics mode: opt-in harmonized metric surface via WORKER_CANONICAL_METRICS=true -- details
MetricsSettings gains clean_directory and clean_dead_pids for opt-in stale .db file cleanup (both default to False)
SchedulerClient now carries the schedule lifecycle operations itself: pause(reason=), resume, delete, run_now, preview_next, reconcile (declarative tri-state sync) — with typed errors (ScheduleNotFound, InvalidCronExpression, ...). pause_schedule gains an optional reason= (stored by OSS Conductor servers; ignored by Orkes servers)

Multiprocessing start method now defaults to spawn on all platforms (was fork everywhere except Windows). fork caused silently-restarting SIGSEGV worker subprocesses on macOS (exitcode -11) and fork-with-held-lock deadlocks on POSIX.
Legacy metrics emit unchanged by default; no env var required
metrics_collector.py is now a compatibility shim; from conductor.client.telemetry.metrics_collector import MetricsCollector continues to work
get_schedule returns a typed WorkflowSchedule (or None for missing schedules) instead of a raw camelCase dict, matching its declared annotation and docs/SCHEDULE.md; dict-consumers should switch to attribute access or to_dict()

@worker_task workers are now picklable, making the decorator path work with the spawn/forkserver start methods (fixes TypeError: cannot pickle '_thread.lock' object and PicklingError: it's not the same object as ...; issues #264, #271): Worker.api_client is created lazily in the worker process, runtime state (locks, pending async tasks, background loop) is excluded from pickling and rebuilt in the child, and decorated functions are pickled as importable references resolved in the child
TaskHandler.start_processes() no longer hangs the interpreter when a worker fails to start (e.g., unpicklable state under spawn); it now cleans up already-started subprocesses and raises with actionable guidance
Worker processes killed by a signal now log a diagnostic hint (signal number, PYTHONFAULTHANDLER=1 guidance) instead of restarting silently
Per-schedule pause/resume now work on both Conductor server families: the client sends PUT (the OSS Conductor dialect — the spec-generated GET failed there) and transparently falls back to GET on a 405 for Orkes servers