feat(logging): migrate from debug_log to tracing with production logging

[svarlamov]

Summary

• Migrate entire codebase from hand-rolled debug_log() to the tracing crate with proper log levels (tracing::error!, tracing::warn!, tracing::info!, tracing::debug!)
• Add production-visible logging for daemon operations that was previously invisible outside debug mode: git write ops, checkpoints, auto-updater, auto-restart, panics, socket failures
• Add custom SentryLayer that automatically routes tracing::error!() events to Sentry via the existing telemetry worker pipeline — no manual dual-calls needed at error sites
• Remove debug_log infrastructure entirely from utils.rs — one call pattern (tracing::*!()) across the entire codebase

What gets logged in production (INFO level):

• Daemon started/shutdown with PID, version, OS, arch
• Git write ops completed: commit, rebase, merge, cherry-pick, am, stash, reset, push
• Checkpoint start/done with kind, repo, and duration
• Auto-updater: check started, result (update available / no update), install result
• Auto-restart trigger (24.5h uptime exceeded)
• Shutdown reasons

What gets logged as errors (ERROR → Sentry):

• All panic catches (trace ingest, command side-effect, checkpoint)
• Socket listener failures (control, trace)
• Log file setup failures

What stays debug-only:

• All existing verbose output (authorship details, trace normalization, family state transitions)
• Git read ops (status, diff, log, show, fetch)
• Detailed checkpoint state dumps

Changes

• 53 files changed, ~1400 insertions, ~1300 deletions
• 581 debug_log() + 15 debug_performance_log() + 2 debug_performance_log_structured() calls converted
• 16 observability::log_error() calls in daemon.rs replaced by tracing::error!() with structured context fields (SentryLayer handles forwarding)
• New file: src/daemon/sentry_layer.rs — custom tracing Layer for Sentry error forwarding
• New deps: tracing 0.1, tracing-subscriber 0.3 (with env-filter feature)

Test plan

• cargo check passes
• cargo test — all unit tests pass
• cargo test --test daemon_mode — all 54 daemon integration tests pass
• Zero remaining debug_log / debug_performance_log references in codebase
• Manual: run daemon, trigger a commit, verify log file at ~/.git-ai/internal/daemon/logs/{PID}.log shows INFO-level output
• Manual: verify git-ai bg tail shows formatted log output

Follow-up items

• Migrate to official sentry crate with sentry-tracing Layer (replaces custom SentryLayer + custom SentryClient)
• Convert TelemetryEnvelope::Performance events to tracing spans for standard Sentry performance monitoring
• Add tracing subscriber initialization for non-daemon processes (CLI wrapper) for local debugging
• Consider structured JSON log output option for machine parsing
• Consider log rotation by size in addition to current pruning by age

🤖 Generated with Claude Code

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

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