Temp [ improve worker observability ]

[bKP451]

don’t give crayons to more kids than the box has.

Summary

Improve Delayed::Worker#work_off observability and failure handling around worker thread setup.

What Changed

• Add debug-level logs around job reservation, batch dispatch, thread waiting, and batch completion inside work_off
• Include job name and id when a queued job is handed off for thread execution
• Include job context in the thread crash log by using job_say
• Distinguish thread crashes that happen before perform from those that happen after it starts
• Route pre-perform thread crashes through normal job error handling instead of only logging them
• Cap the worker thread pool size based on the Active Record connection pool so a batch does not fan out beyond available connections

Why

The worker previously had two observability gaps:

• work_off did not log enough detail to show where a batch was in the reserve and dispatch flow
• thread setup failures could be logged without enough job context, and pre-perform crashes were not handled through the normal job failure path

This change makes worker execution easier to trace and improves behavior when a thread fails before the job body starts running.

Behavior

• Adds new debug-level logs for the work_off loop
• Preserves existing handling for crashes that happen after perform has started
• Changes pre-perform thread crashes so they are treated like job failures instead of being logged and dropped
• Limits thread fan-out per batch to reduce the chance of exhausting the Active Record connection pool