# Fix: Exclude cache files from rules compilation

## Summary
Prevents system files like `.DS_Store`, `.Thumbs.db`, and other cache files from being processed as rule files in the `.roo/rules-{mode-slug}` directories.

## Changes
- Added `shouldIncludeRuleFile()` function to filter out unwanted files during rule compilation
- Modified `readTextFilesFromDirectory()` to apply file filtering before processing
- Added support for 21 common cache file patterns including `.DS_Store`, `.db`, `.bak`, `.log`, etc.
- Updated comment to reflect the new filtering behavior

## Impact
- Fixes issue where macOS `.DS_Store` files were being included in system prompts
- Prevents other cache and temporary files from polluting rule compilation
- Improves system prompt quality and reduces noise

## Additional Notes

**Why we didn't import from existing exclusion patterns:**

The existing `getCacheFilePatterns()` function in `src/services/checkpoints/excludes.ts` contains identical patterns, but we cannot import from it due to architectural constraints:

- The `custom-instructions.ts` file is imported by webview components that run in the browser
- `excludes.ts` has Node.js dependencies (`fs/promises`, `path`) that cannot be bundled for browser environments
- Importing from `excludes.ts` would cause Vite build failures in the webview

This is a necessary architectural trade-off to maintain browser compatibility while solving the cache file inclusion issue.

Resolves: #2728

Author: MuriloFP

src/core/prompts/sections/custom-instructions.ts

@@ -123,6 +123,10 @@ async function readTextFilesFromDirectory(dirPath: string): Promise<Array<{ file
 					// Check if it's a file (not a directory)
 					const stats = await fs.stat(file)
 					if (stats.isFile()) {
+						// Filter out cache files and system files that shouldn't be in rules
+						if (!shouldIncludeRuleFile(file)) {
+							return null
+						}
 						const content = await safeReadFile(file)
 						return { filename: file, content }
 					}
@@ -133,7 +137,7 @@ async function readTextFilesFromDirectory(dirPath: string): Promise<Array<{ file
 			}),
 		)
 
-		// Filter out null values (directories or failed reads)
+		// Filter out null values (directories, failed reads, or excluded files)
 		return fileContents.filter((item): item is { filename: string; content: string } => item !== null)
 	} catch (err) {
 		return []
@@ -297,3 +301,48 @@ The following additional instructions are provided by the user, and should be fo
 ${joinedSections}`
 		: ""
 }
+
+/**
+ * Check if a file should be included in rule compilation.
+ * Excludes cache files and system files that shouldn't be processed as rules.
+ */
+function shouldIncludeRuleFile(filename: string): boolean {
+	const basename = path.basename(filename)
+
+	const cachePatterns = [
+		"*.DS_Store",
+		"*.bak",
+		"*.cache",
+		"*.crdownload",
+		"*.db",
+		"*.dmp",
+		"*.dump",
+		"*.eslintcache",
+		"*.lock",
+		"*.log",
+		"*.old",
+		"*.part",
+		"*.partial",
+		"*.pyc",
+		"*.pyo",
+		"*.stackdump",
+		"*.swo",
+		"*.swp",
+		"*.temp",
+		"*.tmp",
+		"*.Thumbs.db",
+	]
+
+	for (const pattern of cachePatterns) {
+		if (pattern.startsWith("*.")) {
+			const extension = pattern.slice(1)
+			if (basename.endsWith(extension)) {
+				return false
+			}
+		} else if (basename === pattern) {
+			return false
+		}
+	}
+
+	return true
+}