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48c13245c5
User audit caught three gaps that prevented DiffCompressor from being
invoked even when the input was a real diff. These complement the four
emit-time bugs fixed in the previous commit — those fixes only kick in
once DiffCompressor receives the input. Without these gap fixes, real
merge-commit diffs and `git log -p` outputs with long commit messages
were misrouted away from DiffCompressor entirely.
# The three gaps (each fixed in Python; gap 3 also fixed in Rust)
1. Detector scan window was hardcoded to first 50 lines.
`_try_detect_diff` in content_detector.py only inspected
`content.split("\n")[:50]`. `git log -p` outputs commonly have
commit messages longer than 50 lines (releases, squashed commits,
bots), pushing the `diff --git` header out of the detection window.
Result: input was returned with `content_type=PLAIN_TEXT` and routed
to the text compressor, never reaching DiffCompressor. Fix: window
widened to 500 lines.
2. Detector regex didn't recognize merge-commit headers.
`_DIFF_HEADER_PATTERN` matched `diff --git`, `--- a/`, and the
regular `@@ -A,B +C,D @@` hunk header. Merge-commit diffs from
`git log -p` use `diff --combined <path>`, `diff --cc <path>`, and
combined-diff hunk headers `@@@+`. The shared `--- a/` line still
triggered the detector with low confidence, but only barely. Fix:
extended the regex to recognize all four merge-shaped header forms.
3. DiffCompressor parser only matched `^diff --git`.
Even after fixing detection, the parser's `_DIFF_GIT_PATTERN`
wouldn't match `diff --combined` or `diff --cc`, so merge diffs
reached DiffCompressor and were treated as one giant pre-diff blob —
passed through unchanged after the previous PR's pre-diff
preservation fix. Fix: added `_DIFF_COMBINED_PATTERN` and
`_DIFF_CC_PATTERN`; `_parse_diff` starts a new file section on any
of the three header forms. Mirrored in Rust as `is_diff_header`
helper that checks all three regexes.
# Why this matters end-to-end
DiffCompressor's value comes from being routed to. Detection +
parser-level coverage are upstream of the compressor — without them,
the compressor never sees the input. The previous PR's four bug fixes
(rename, combined-diff hunks, no-newline marker, pre-diff content) are
correct and necessary, but for merge commits and long-preamble diffs,
they were only firing on the rare cases where the detector misclicked
into DiffCompressor anyway. With these three gaps closed, the
ContentRouter→DiffCompressor pipeline actually engages on:
- `git log -p` outputs of any commit-message length
- Merge-commit diffs (`diff --combined`, `diff --cc`)
- Combined-diff snippets (`@@@`+ hunk-only inputs)
# New fixtures (3 added to the existing 24)
- `066bc82…` — `diff --combined` merge diff (3-way)
- `5d950a94…` — `diff --cc` merge diff (alternate form)
- `66c86f64…` — long pre-diff content (60-line commit message)
followed by a rename diff (exercises detector scan widening +
pre-diff preservation in tandem)
Parity: total=27 matched=27 skipped=0 diffed=0.
# Tests
- Python: 4 new tests across 2 new test classes —
`TestRoutingGapMergeDiffs` (combined / cc parser) and
`TestRoutingGapDetectorScanWindow` (long preamble detection +
combined-diff regex recognition).
- Rust: 2 new tests covering combined / cc parser sections.
# Verification
- 27/27 parity fixtures byte-equal.
- Python: 41/41 tests pass (was 37).
- Rust: 18/18 transforms tests; 62/62 workspace; 5/5 proptests.
- `cargo fmt --check` clean; `cargo clippy --workspace --all-targets
-- -D warnings` clean.
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