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

The injection was 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.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: TyceHerrman

src/patches/agentsMd.test.ts

@@ -0,0 +1,65 @@
+import { describe, it, expect } from 'vitest';
+import { writeAgentsMd } from './agentsMd';
+
+const mockFunction =
+  'function _t7(A,q){try{let K=x1();' +
+  'if(!K.existsSync(A)||!K.statSync(A).isFile())return null;' +
+  'let Y=UL9(A).toLowerCase();' +
+  'if(Y&&!dL9.has(Y))' +
+  'return(I(`Skipping non-text file in @include: ${A}`),null);' +
+  'let z=K.readFileSync(A,{encoding:"utf-8"}),' +
+  '{content:w,paths:H}=cL9(z);' +
+  'return{path:A,type:q,content:w,globs:H};' +
+  '}catch(K){' +
+  'if(K instanceof Error&&K.message.includes("EACCES"))' +
+  'n("tengu_claude_md_permission_error",{is_access_error:1});' +
+  '}return null;}';
+
+const altNames = ['AGENTS.md', 'GEMINI.md', 'QWEN.md'];
+
+describe('agentsMd', () => {
+  describe('writeAgentsMd', () => {
+    it('should inject fallback at early return null when CLAUDE.md is missing', () => {
+      const result = writeAgentsMd(mockFunction, altNames);
+      expect(result).not.toBeNull();
+      expect(result).toContain('didReroute');
+      expect(result).toContain('endsWith("/CLAUDE.md")');
+      expect(result).toContain('AGENTS.md');
+      expect(result).toMatch(/\.isFile\(\)\)\{.*?return null;\}/);
+    });
+
+    it('should preserve CLAUDE.md content when present', () => {
+      const result = writeAgentsMd(mockFunction, altNames)!;
+      const returnIdx = result.indexOf('return{path:');
+      expect(returnIdx).toBeGreaterThan(-1);
+      const beforeReturn = result.slice(Math.max(0, returnIdx - 50), returnIdx);
+      expect(beforeReturn).not.toContain('didReroute');
+    });
+
+    it('should pass didReroute=true in recursive calls', () => {
+      const result = writeAgentsMd(mockFunction, altNames)!;
+      expect(result).toContain('return _t7(altPath,q,true)');
+    });
+
+    it('should return null when no alternatives are found', () => {
+      const result = writeAgentsMd(mockFunction, altNames)!;
+      expect(result).toMatch(/\}return null;\}/);
+    });
+
+    it('should add didReroute parameter to function signature', () => {
+      const result = writeAgentsMd(mockFunction, altNames)!;
+      expect(result).toContain('function _t7(A,q,didReroute)');
+    });
+
+    it('should use the correct fs expression', () => {
+      const result = writeAgentsMd(mockFunction, altNames)!;
+      expect(result).toContain('K.existsSync(altPath)');
+      expect(result).toContain('K.statSync(altPath)');
+    });
+
+    it('should return null when function pattern is not found', () => {
+      const result = writeAgentsMd('not a valid file', altNames);
+      expect(result).toBeNull();
+    });
+  });
+});

src/patches/agentsMd.ts

@@ -4,12 +4,13 @@ import { showDiff } from './index';
 
 /**
  * Patches the CLAUDE.md file reading function to also check for alternative
- * filenames (e.g., AGENTS.md).
+ * filenames (e.g., AGENTS.md) when CLAUDE.md doesn't exist.
  *
  * This finds the function that reads CLAUDE.md files and modifies it to:
  * 1. Add a `didReroute` parameter to the function
- * 2. Right before the `return {` statement, check if the path ends with
- *    CLAUDE.md and try alternative names (unless didReroute is true)
+ * 2. At the early `return null` (when the file doesn't exist), check if the
+ *    path ends with CLAUDE.md and try alternative names (unless didReroute
+ *    is true)
  * 3. Recursive calls pass didReroute=true to avoid infinite loops
  *
  * CC 2.1.62 (approx. by Claude):
@@ -18,19 +19,22 @@ import { showDiff } from './index';
  * +function _t7(A, q, didReroute) {
  *    try {
  *      let K = x1();
- *      if (!K.existsSync(A) || !K.statSync(A).isFile()) return null;
+ * -    if (!K.existsSync(A) || !K.statSync(A).isFile()) return null;
+ * +    if (!K.existsSync(A) || !K.statSync(A).isFile()) {
+ * +      if (!didReroute && (A.endsWith("/CLAUDE.md") || A.endsWith("\\CLAUDE.md"))) {
+ * +        for (let alt of ["AGENTS.md", "GEMINI.md", "QWEN.md"]) {
+ * +          let altPath = A.slice(0, -9) + alt;
+ * +          if (K.existsSync(altPath) && K.statSync(altPath).isFile())
+ * +            return _t7(altPath, q, true);
+ * +        }
+ * +      }
+ * +      return null;
+ * +    }
  *      let Y = UL9(A).toLowerCase();
  *      if (Y && !dL9.has(Y))
  *        return (I(`Skipping non-text file in @include: ${A}`), null);
  *      let z = K.readFileSync(A, { encoding: "utf-8" }),
  *        { content: w, paths: H } = cL9(z);
- * +    if (!didReroute && (A.endsWith("/CLAUDE.md") || A.endsWith("\\CLAUDE.md"))) {
- * +      for (let alt of ["AGENTS.md", "GEMINI.md", "QWEN.md"]) {
- * +        let altPath = A.slice(0, -9) + alt;
- * +        if (K.existsSync(altPath) && K.statSync(altPath).isFile())
- * +          return _t7(altPath, q, true);
- * +      }
- * +    }
  *      return { path: A, type: q, content: w, globs: H };
  *    } catch (K) {
  *      if (K instanceof Error && K.message.includes("EACCES"))
@@ -48,7 +52,7 @@ export const writeAgentsMd = (
   altNames: string[]
 ): string | null => {
   const funcPattern =
-    /(function ([$\w]+)\(([$\w]+),([^)]+?))\)(?:.|\n){0,500}Skipping non-text file in @include(?:.|\n){0,500}return\{path:[$\w]+,.{0,20}?content:[$\w]+/;
+    /(function ([$\w]+)\(([$\w]+),([^)]+?))\)(?:.|\n){0,500}Skipping non-text file in @include/;
 
   const funcMatch = file.match(funcPattern);
   if (!funcMatch || funcMatch.index === undefined) {
@@ -71,33 +75,36 @@ export const writeAgentsMd = (
 
   const altNamesJson = JSON.stringify(altNames);
 
+  // Step 1: Add didReroute parameter to function signature
   const sigIndex = funcStart + upToFuncParamsClosingParen.length;
   let newFile = file.slice(0, sigIndex) + ',didReroute' + file.slice(sigIndex);
 
   showDiff(file, newFile, ',didReroute', sigIndex, sigIndex);
 
-  // Step 2: Inject rerouting code right before the `return {`
-  const returnPattern = /return\{path:[$\w]+,.{0,20}?content:[$\w]+/;
-  const returnMatch = newFile.slice(funcStart).match(returnPattern);
+  // Step 2: Inject fallback at the early return null (when file doesn't exist)
+  const earlyReturnPattern = /\.isFile\(\)\)return null/;
+  const funcBody = newFile.slice(funcStart);
+  const earlyReturnMatch = funcBody.match(earlyReturnPattern);
 
-  if (!returnMatch || returnMatch.index === undefined) {
+  if (!earlyReturnMatch || earlyReturnMatch.index === undefined) {
     console.error(
-      'patch: agentsMd: failed to find return statement for injection'
+      'patch: agentsMd: failed to find early return null for injection'
     );
     return null;
   }
 
-  const injection = `if(!didReroute&&(${firstParam}.endsWith("/CLAUDE.md")||${firstParam}.endsWith("\\\\CLAUDE.md"))){for(let alt of ${altNamesJson}){let altPath=${firstParam}.slice(0,-9)+alt;if(${fsExpr}.existsSync(altPath)&&${fsExpr}.statSync(altPath).isFile())return ${functionName}(altPath,${restParams},true);}}`;
+  const fallback = `if(!didReroute&&(${firstParam}.endsWith("/CLAUDE.md")||${firstParam}.endsWith("\\\\CLAUDE.md"))){for(let alt of ${altNamesJson}){let altPath=${firstParam}.slice(0,-9)+alt;if(${fsExpr}.existsSync(altPath)&&${fsExpr}.statSync(altPath).isFile())return ${functionName}(altPath,${restParams},true);}}`;
 
-  const returnStart = funcStart + returnMatch.index;
-  const replacement = injection + returnMatch[0];
+  const earlyReturnStart = funcStart + earlyReturnMatch.index;
+  const oldStr = earlyReturnMatch[0];
+  const newStr = `.isFile()){${fallback}return null;}`;
 
   newFile =
-    newFile.slice(0, returnStart) +
-    replacement +
-    newFile.slice(returnStart + returnMatch[0].length);
+    newFile.slice(0, earlyReturnStart) +
+    newStr +
+    newFile.slice(earlyReturnStart + oldStr.length);
 
-  showDiff(file, newFile, replacement, returnStart, returnStart);
+  showDiff(file, newFile, newStr, earlyReturnStart, earlyReturnStart);
 
   return newFile;
 };