fix(git): pass through --check/--exit-code/--quiet/--no-patch unfiltered

[yunaremaia]

Summary

Diagnostic modes --check, --exit-code, --quiet, and --no-patch derive their value entirely from stdout and exit code. RTK's git diff filter destroyed that signal — rtk git diff --check returned exit 2 with zero bytes of output, leaving agents and pre-commit scripts with "failure with no reason attached".

This PR adds an is_diagnostic gate that routes these flags through the existing passthrough path.

Changes

• src/cmds/git/git.rs — added is_diagnostic flag detection in run_diff, ANDed into wants_compact so diagnostic modes skip compaction
• Test: test_diagnostic_flags_skip_compaction verifies all four flags skip compaction

Verification

• cargo check passes (no new warnings)
• New test added for the gating logic
• Reproduction from rtk git diff --check emits no output at all, silently discarding every whitespace diagnostic #3984: rtk git diff --check now emits the same diagnostic lines as raw git --no-pager diff --check

Fixes #3984

[CLAassistant]

All committers have signed the CLA.

[rtk-wshm-sync-bot]

wshm · Automated triage by AI

📊 Automated PR Analysis

🐛 Type	bug-fix
🟢 Risk	low

Summary

Fixes a bug in RTK's git diff compaction where diagnostic flags (--check, --exit-code, --quiet, --no-patch) had their output filtered by the compact-diff feature, destroying the only signal these modes provide (stdout content and exit code). Adds an is_diagnostic gate that routes these flags through the existing unfiltered passthrough path, with a test covering all four flags.

Review Checklist

• Tests present
• Breaking change
• Docs updated

Linked issues: #3984

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Analyzed automatically by wshm · This is an automated analysis, not a human review.

[yunaremaia]

Thanks @rtk-wshm-sync-bot for the triage summary — the analysis matches the fix exactly: derives its value from stdout, and RTK's compaction was destroying that signal.

CLA is pending; I'll sign it now. Maintainers: this is ready for review — one-line logic change in with a dedicated test.

[yunaremaia]

Hi @rtk-ai — gentle bump on this PR (fix(git): pass through --check/--exit-code/--quiet/--no-patch unfiltered). It's mergeable and CLA is signed. Would appreciate a review when you have a moment. Thanks!

[KuSh]

Thanks for the fix and the clear reproduction. This landed on develop through #3681 (merged 2026-09-12, commit 7931993): git diff now routes --check, --exit-code and --quiet through a raw pass-through when the tokenizer sees them, and -s/--no-patch skip compaction because there is no body to compact. Checked against git 2.53 on current develop, all four flags and their combinations print exactly what raw git prints and keep its exit code, including exit 2 for --check. Closing as already fixed; if you still see a diagnostic mode that comes back empty on develop, please comment here and it can be reopened.