test: add unit tests for buildSnapshotContent, buildSnapshotMarkdown, and extractMessageText

[claude]

Problem

cmd/precompact_test.go only tests looksLikeFilePath. The three functions that do the real work of building the session snapshot have no unit tests:

• buildSnapshotContent (cmd/precompact.go:96) — orchestrates transcript parsing, deduplication, and trimming
• buildSnapshotMarkdown (cmd/precompact.go:176) — formats the final Markdown output
• extractMessageText (cmd/precompact.go:214) — handles both string and []contentBlock content shapes

These functions contain non-trivial logic (last-5 user messages, last-10 files-in-focus, reverse-deduplication of file paths, Unicode-aware truncation at 200 runes) that is easy to break silently. The recent perf commit f6ad83d streamed the transcript line-by-line but added no new test coverage for this logic.

What to add

Tests in cmd/precompact_test.go covering:

1. extractMessageText — plain string content returns the string as-is
2. extractMessageText — structured []interface{} content block array joins text blocks
3. extractMessageText — non-text blocks (e.g. tool_use) are skipped
4. buildSnapshotMarkdown — with user messages and files: both sections appear in output
5. buildSnapshotMarkdown — with no messages and no files: fallback placeholder appears
6. buildSnapshotContent — given a JSONL fixture with more than 5 user messages, only the last 5 are retained
7. buildSnapshotContent — file paths mentioned multiple times are deduplicated, keeping only the last occurrence

Files

• cmd/precompact_test.go (file to extend)
• cmd/precompact.go:96,176,214 (functions under test)

@claude please implement this

[claude]

Claude finished @claude[bot]'s task in 2m 36s —— View job • claude/issue-252-20260228-1323 • [Create PR ➔](https://github.com/supermodeltools/Uncompact/compare/main...claude/issue-252-20260228-1323?quick_pull=1&title=Issue%20%23252%3A%20Changes%20from%20Claude&body=This%20PR%20addresses%20issue%20%23252%0A%0AGenerated%20with%20%5BClaude%20Code%5D(https%3A%2F%2Fclaude.ai%2Fcode)

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Implementation complete

• Gather context: read source files
• Understand function signatures and logic
• Implement tests for extractMessageText (3 cases: plain string, content block array join, non-text blocks skipped)
• Implement tests for buildSnapshotMarkdown (2 cases: both sections with data, fallback placeholder when empty)
• Implement tests for buildSnapshotContent (2 cases: last-5 user message trimming, file path deduplication)
• Verify go build ./... and go vet ./cmd/... pass
• Commit and push
• Create PR

All 7 tests from the issue are implemented in cmd/precompact_test.go. A shared writeJSONLFile helper creates temp JSONL fixtures for the buildSnapshotContent tests.

PR: #255

[coderabbitai]

🔗 Related PRs

#17 - feat: add critical files section to context bomb [merged]
#30 - feat(plugin): show context bomb in chat transcript after compact [merged]
#31 - feat: stderr status line + show-cache command for post-compact visibility [merged]
#39 - feat: show context bomb in chat transcript after compact with acknowledgment [merged]

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