* feat: worker NDJSON monitoring, budget enforcement, PID-based stop fallback
Closes three gaps in parallel orchestration:
1. **Worker stdout monitoring** — Workers now run with `--mode json` so
they emit NDJSON events. The coordinator parses stdout line-by-line,
extracting cost/token data from `message_end` events. This keeps
per-worker cost tracking in sync with actual API spend and updates
session status files for live dashboard visibility.
2. **Budget enforcement before spawn** — `startParallel()` now checks
`isBudgetExceeded()` before each worker spawn. When the aggregate
cost across all workers reaches the configured ceiling, no new
workers are started.
3. **PID-based stop fallback** — `stopParallel()` now falls back to
`process.kill(pid, "SIGTERM")` when the ChildProcess handle is null
(e.g., after coordinator restart when handles aren't available).
Previously, orphaned workers could not be stopped.
Includes 11 new tests covering NDJSON format validation, cost
aggregation, budget ceiling comparison, and PID-based kill patterns.
All 54 existing parallel-orchestration tests still pass.
Relates to #672
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
* fix: currentUnit type must match SessionStatus interface (object | null, not string)
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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