Extract utility functions (stripEmptyPlanBlock, stripMarkdownFences,
buildMessageXML, copyMessages, countMessagesTokens, reviewModeString,
detectGitBranch) into util.go and all compression logic into compression.go
to improve readability (agent.go: 1489 → 1114 lines).
Fix pre-existing compression bugs from commit 14adf6f:
- Return unmodified messages on compression failure instead of truncating
to frozen zone (which discarded all conversation context)
- Check error in async compression goroutine to avoid applying failed results
- Track snapshot length to append post-snapshot messages when applying async
compression, preventing silent message loss
- Strip old <previous_review_summary> before appending new one to prevent
cumulative frozen zone bloat across multiple compressions
- Guard pendingJob cleanup to only clear when it matches the completed job,
preventing accidental clearing of a newly scheduled job
- Add context.Context and 5s timeout to detectGitBranch
- Deep copy ToolCalls in copyMessages to match session/history.go
- Reuse finalCount in addNextMessage to avoid redundant token counting
2f3ed41009