refactor: hook infrastructure DRY cleanup (debug bootstrap + log init helpers)

[dean0x]

Overview

Three related boilerplate patterns in hook scripts block smooth hook maintenance and create tight coupling. This issue consolidates tech debt from PR #228.

Items

1. Debug boilerplate (4 lines, 7 hooks)

   • Repeated across: sidecar-capture, sidecar-dispatch, sidecar-evaluate, session-start-context, session-start-memory, pre-compact-memory, preamble
   • Risk: any debug protocol change requires editing 7 files
   • Solution: extract to devflow_debug_bootstrap helper

2. log() function definition (4 lines, 5 hooks)

   • Repeated across: sidecar-capture, sidecar-dispatch, sidecar-evaluate, session-start-context, session-start-memory
   • Risk: logging API inconsistencies, maintenance burden
   • Solution: extract to devflow_log_init helper

3. Dual logging system message overlap (design concern)

   • dbg() (debug-toggle) and log() (always-on) both write to logs
   • Deliberate by design but worth revisiting in follow-up

Implementation Plan

• Move 4-line debug init sequence to scripts/hooks/lib/debug-bootstrap.cjs
• Move 4-line log function definition to scripts/hooks/lib/log-init.cjs
• Update 7 hooks to source debug-bootstrap
• Update 5 hooks to source log-init
• Test all hooks with DEVFLOW_HOOK_DEBUG on/off

References

• PR fix(hooks): stop hook field rename + debug tracing system #228 introduced repeated patterns
• Related: refactor: decompose init.ts action handler into phase functions #139 (decompose init.ts)