fix: improve diff matching by handling invisible whitespace

Before normalization:
- Only collapsed multiple whitespace characters into a single space
- Only trimmed leading/trailing whitespace
- Treated different line endings (\r\n vs \n) as different
- Treated tabs and spaces as different characters
- Zero-width spaces and other invisible characters were preserved

After normalization:
- Standardizes all line endings to \n
- Converts tabs to spaces for consistent comparison
- Still collapses multiple whitespace into single space
- Removes zero-width spaces and other invisible Unicode characters
- Still trims leading/trailing whitespace

This fix applies to both:
- Single search-replace functionality (search-replace.ts)
- Multi-block diff functionality (multi-search-replace.ts)

Users will encounter fewer "No sufficiently similar match found" errors across all diff operations when the content is semantically the same but has minor formatting differences.

Author: hannesrudolph

src/core/diff/strategies/multi-search-replace.ts

@@ -12,7 +12,13 @@ function getSimilarity(original: string, search: string): number {
 	}
 
 	// Normalize strings by removing extra whitespace but preserve case
-	const normalizeStr = (str: string) => str.replace(/\s+/g, " ").trim()
+	const normalizeStr = (str: string) =>
+		str
+			.replace(/\r\n/g, "\n") // Standardize line endings
+			.replace(/\t/g, " ") // Convert tabs to spaces
+			.replace(/\s+/g, " ") // Replace all whitespace sequences with a single space
+			.replace(/\u200B/g, "") // Remove zero-width spaces
+			.trim() // Remove leading/trailing whitespace
 
 	const normalizedOriginal = normalizeStr(original)
 	const normalizedSearch = normalizeStr(search)

src/core/diff/strategies/search-replace.ts

@@ -10,7 +10,13 @@ function getSimilarity(original: string, search: string): number {
 	}
 
 	// Normalize strings by removing extra whitespace but preserve case
-	const normalizeStr = (str: string) => str.replace(/\s+/g, " ").trim()
+	const normalizeStr = (str: string) =>
+		str
+			.replace(/\r\n/g, "\n") // Standardize line endings
+			.replace(/\t/g, " ") // Convert tabs to spaces
+			.replace(/\s+/g, " ") // Replace all whitespace sequences with a single space
+			.replace(/\u200B/g, "") // Remove zero-width spaces
+			.trim() // Remove leading/trailing whitespace
 
 	const normalizedOriginal = normalizeStr(original)
 	const normalizedSearch = normalizeStr(search)