fix(diff): detect renamed and deleted files correctly in diff parsing

[adlternative]

Summary

Fixes #99 — ocr review --from master --to BRANCH --format json emitted [ocr] WARNING: cannot read file <old path> at ref BRANCH: exit status 128 when a file was renamed on the target branch.

Root Cause

Two compounding bugs:

1. Broken /dev/null detection (internal/diff/parser.go): git emits --- /dev/null / +++ /dev/null without a//b/ prefixes, but the old regexes required them, so IsNew/IsDeleted were never set. Deleted files fell through to git show ref:<old path> → exit status 128.
2. Renames never handled: the parser ignored rename from / rename to extended headers, and the git diff/show call sites did not pass --find-renames, so with diff.renames=false a rename degraded to delete(old)+add(new); the delete half hit bug 1 and warned about the old path.

Changes

• Parse rename from/rename to (authoritative paths, robust for paths with spaces), new file mode, deleted file mode, and unprefixed /dev/null markers in ParseDiffText
• Pass --find-renames to all 4 git diff/show invocations so rename detection no longer depends on user git config
• Add IsRenamed to model.Diff (json: is_renamed) and prefer it in diffStatus
• New parser_test.go: rename / pure rename (100% similarity, no hunks) / deleted / new file unit tests
• New TestRangeDiffDetectsRename integration test: diff.renames=false + branch rename + small edit → exactly 1 diff, IsRenamed=true, content read at the new path

Testing

• go test -race -count=1 ./... — all packages pass
• go vet ./... and go build ./... clean

[adlternative]

End-to-End Verification Report

To confirm the fix actually resolves issue #99 (beyond unit tests), I reproduced the reported scenario and compared the pre-fix and post-fix binaries side by side.

Repro setup (mirrors the issue exactly)

git init -b master
git config diff.renames false        # key: simulates an environment where git does NOT auto-detect renames
seq 1 50 | sed 's/^/code line /' > service.go
git add . && git commit -m 'init on master'

git checkout -b SRQ-12345            # the SRQ-XXXXX branch from the issue
git mv service.go service_renamed.go # rename
sed -i 's/code line 25/code line 25 EDITED/' service_renamed.go  # small edit, like the reporter did
git add -A && git commit -m 'rename service.go'

diff.renames=false is the trigger: it makes git diff emit the rename as delete(old) + add(new), which is exactly the path that produced the warning.

Method

• Pre-fix binary: built from main @ 022800c via git worktree
• Post-fix binary: built from this branch
• Both run the same command with --preview, which skips the LLM but fully exercises the diff fetch/parse path where the warning originates (finalizeDiff in internal/diff/parser.go)

ocr review --from master --to SRQ-12345 --preview

Results

Before fix (reproduces the exact warning from the issue):

[ocr] WARNING: cannot read file service.go at ref SRQ-12345: exit status 128

Preview: 2 file(s) changed  |  +50  -50
  [M]  service.go           +0   -50     <- rename misclassified as delete + add
  [M]  service_renamed.go   +50  -0

After fix:

Preview: 1 file(s) changed  |  +1  -1
  [R]  service_renamed.go   +1   -1      <- correctly recognized as a single rename, no warning

Takeaways

• The warning is gone, and behavior is also more correct:
  • File count drops from a bogus 2 (delete + add) to 1 rename ([R] status)
  • Line stats drop from an inflated +50/-50 to the real +1/-1, avoiding feeding the entire file to the LLM as 'new' content (saves tokens and improves review accuracy)
• This manual repro is also codified as the TestRangeDiffDetectsRename integration test (same diff.renames=false setup) to guard against regressions in CI.
• go test -race -count=1 ./..., go vet ./..., and go build ./... all pass.

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