Fix AGENTS.md patch replacing CLAUDE.md content instead of falling back

[TyceHerrman]

Summary

• The agentsMd patch injected fallback logic at the wrong location — before return { content }, which runs after CLAUDE.md is successfully read, unconditionally replacing its content with AGENTS.md
• Moved injection to the early return null (after existsSync/statSync check) so alternatives are only tried when CLAUDE.md doesn't exist
• Added 7 unit tests covering fallback behavior, CLAUDE.md preservation, recursion guard, and error cases

Test plan

• pnpm build passes (no type errors)
• pnpm test passes (169 tests, including 7 new ones)
• Manual: apply tweakcc to a Claude Code installation, verify that in a project with both CLAUDE.md and AGENTS.md, the CLAUDE.md content is used (not replaced)

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes

  • Improved handling of missing configuration files with automatic fallback to alternative file names.

• Tests

  • Added comprehensive test coverage for file routing and fallback logic.

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR adds a comprehensive test suite for the agentsMd module and refactors its routing logic. The implementation introduces a didReroute parameter to handle fallback paths when CLAUDE.md is unavailable, checking alternative filenames (AGENTS.md, GEMINI.md, QWEN.md) and rerouting accordingly before returning null.

Changes

Cohort / File(s)	Summary
Test Suite src/patches/agentsMd.test.ts	New test suite verifying writeAgentsMd behavior including early fallback handling, CLAUDE.md preservation, didReroute propagation, null returns, function signature changes, and filesystem checks.
Core Implementation src/patches/agentsMd.ts	Refactored routing logic to move alternative-name fallback to early-exit path; added didReroute parameter to function signature; updated injection point from final return to early return null; adjusted matching patterns and error messages; reworked fallback construction logic.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~22 minutes

Possibly related PRs

• Fix patching errors for CC 2.1.50+ and remove the swarm mode patch #532 — Modifies function-detection logic for writeAgentsMd while this PR rewrites early-return fallback mechanism and adds didReroute propagation.
• Fix React var and AGENTS.md patching 2.1.62 #563 — Also modifies agentsMd.ts to add/propagate didReroute parameter and changes CLAUDE.md rerouting logic with overlapping function signatures and injection points.
• AGENTS.md support for Claude Code #459 — Makes direct overlapping changes to agentsMd.ts adding writeAgentsMd implementation and alternative-filename fallback/reroute logic.

Suggested reviewers

• bl-ue

Poem

🐰 A rabbit hops through fallback paths so true,
When CLAUDE's gone, we know just what to do—
Check AGENTS, GEMINI, QWEN in the fray,
didReroute guides us on our way! ✨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and specifically describes the main fix: correcting the AGENTS.md patch behavior to fall back rather than replace CLAUDE.md content.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[coderabbitai]

🧹 Nitpick comments (3)

src/patches/agentsMd.ts (2)

107-107: Use the intermediate buffer as showDiff’s old content in step 2.

Passing file again in the second showDiff mixes step 1 + step 2 changes and
can offset context around the replacement site.

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@src/patches/agentsMd.ts` at line 107, The second call to showDiff currently
reuses `file` as the "old" content which mixes step-1 and step-2 changes;
replace the first-steps result with the intermediate buffer (the variable
holding the file content after step 1 — e.g., `newFile` or the actual
intermediate buffer name used in this scope) as the oldContent argument when
calling showDiff(file, newFile, newStr, earlyReturnStart, earlyReturnStart) so
the second diff shows only step-2 changes; update the second invocation of
showDiff to pass that intermediate buffer instead of `file` (refer to the
showDiff call and the intermediate buffer/newFile variable in this file).

---

78-84: Remove the inline “Step” comments to match repository TS rules.

The function body is clear without these comments, and the added comments violate
the repo convention for TS/JS files.

As per coding guidelines, “Do not add comments unless explicitly requested.”

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@src/patches/agentsMd.ts` around lines 78 - 84, Remove the inline "Step"
comments added in this patch: delete the comment lines starting with "// Step 1:
Add didReroute parameter to function signature" and "// Step 2: Inject fallback
at the early return null (when file doesn't exist)" so only the actual code
mutations remain (the insertion of ',didReroute' via sigIndex/newFile and the
showDiff call); ensure no other inline "Step" comments remain in the same block
around the symbols sigIndex, newFile, file.slice, or showDiff so the file
conforms to the repository TS/JS comment policy.

src/patches/agentsMd.test.ts (1)

44-47: Test title is misleading for what this assertion actually validates.

This test currently checks that generated code contains a return null branch,
not runtime behavior when no alternatives are found.

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@src/patches/agentsMd.test.ts` around lines 44 - 47, The test title is
misleading: the spec for writeAgentsMd(mockFunction, altNames) is asserting
generated source contains a "return null" branch, not actual runtime behavior.
Update the test either by renaming it to something like "should generate code
with a return null branch when no alternatives are found" to reflect the
string/assertion, or change the assertion to execute the generated function and
assert it returns null at runtime (invoke the code produced by writeAgentsMd and
call the resulting function); reference writeAgentsMd and the existing
mockFunction/altNames symbols when making the change.

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Nitpick comments:
In `@src/patches/agentsMd.test.ts`:
- Around line 44-47: The test title is misleading: the spec for
writeAgentsMd(mockFunction, altNames) is asserting generated source contains a
"return null" branch, not actual runtime behavior. Update the test either by
renaming it to something like "should generate code with a return null branch
when no alternatives are found" to reflect the string/assertion, or change the
assertion to execute the generated function and assert it returns null at
runtime (invoke the code produced by writeAgentsMd and call the resulting
function); reference writeAgentsMd and the existing mockFunction/altNames
symbols when making the change.

In `@src/patches/agentsMd.ts`:
- Line 107: The second call to showDiff currently reuses `file` as the "old"
content which mixes step-1 and step-2 changes; replace the first-steps result
with the intermediate buffer (the variable holding the file content after step 1
— e.g., `newFile` or the actual intermediate buffer name used in this scope) as
the oldContent argument when calling showDiff(file, newFile, newStr,
earlyReturnStart, earlyReturnStart) so the second diff shows only step-2
changes; update the second invocation of showDiff to pass that intermediate
buffer instead of `file` (refer to the showDiff call and the intermediate
buffer/newFile variable in this file).
- Around line 78-84: Remove the inline "Step" comments added in this patch:
delete the comment lines starting with "// Step 1: Add didReroute parameter to
function signature" and "// Step 2: Inject fallback at the early return null
(when file doesn't exist)" so only the actual code mutations remain (the
insertion of ',didReroute' via sigIndex/newFile and the showDiff call); ensure
no other inline "Step" comments remain in the same block around the symbols
sigIndex, newFile, file.slice, or showDiff so the file conforms to the
repository TS/JS comment policy.

---

ℹ️ Review info

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 3cea938 and dd71619.

📒 Files selected for processing (2)

• src/patches/agentsMd.test.ts
• src/patches/agentsMd.ts

[bl-ue]

Thank you!