Skip no-op search/replace blocks in Squiggle AI edits

internal-packages/ai/__tests__/searchReplace_test.ts

@@ -18,6 +18,44 @@ Goodbye, world!
       expect(result.value).toBe("Goodbye, world!");
     });
 
+    test("should skip no-op blocks when other blocks make changes", () => {
+      const originalText = "first line\nsecond line";
+      const promptResponse = `
+<<<<<<< SEARCH
+first line
+=======
+first line
+>>>>>>> REPLACE
+
+<<<<<<< SEARCH
+second line
+=======
+changed line
+>>>>>>> REPLACE
+      `;
+
+      const result = processSearchReplaceResponse(originalText, promptResponse);
+
+      expect(result.success).toBe(true);
+      expect(result.value).toBe("first line\nchanged line");
+    });
+
+    test("should fail when all blocks are no-ops", () => {
+      const originalText = "Hello, world!";
+      const promptResponse = `
+<<<<<<< SEARCH
+Hello, world!
+=======
+Hello, world!
+>>>>>>> REPLACE
+      `;
+
+      const result = processSearchReplaceResponse(originalText, promptResponse);
+
+      expect(result.success).toBe(false);
+      expect(result.value).toContain("no-ops");
+    });
+
     test("should handle empty prompt response", () => {
       const originalText = "Hello, world!";
       const promptResponse = "";

internal-packages/ai/src/squiggle/searchReplace.ts

@@ -50,15 +50,16 @@ function applySearchReplaceBlocks(
   blocks: Array<{ search: string; replace: string }>
 ): { success: boolean; value: string } {
   let updatedText = originalText;
+  // LLMs sometimes emit blocks where search === replace (e.g. an unchanged
+  // context block alongside real edits). Those are harmless no-ops — skip
+  // them instead of failing the whole edit. We only fail if *no* block
+  // changes anything, so the model gets feedback and retries.
+  let appliedBlocks = 0;
 
   try {
     for (const block of blocks) {
-      // Check if search and replace are identical
       if (block.search === block.replace) {
-        return {
-          success: false,
-          value: `Error: Search and replace texts are identical: \n\`\`\`\n${block.search}\n\`\`\``,
-        };
+        continue;
       }
 
       if (block.search === "") {
@@ -81,6 +82,15 @@ function applySearchReplaceBlocks(
           block.replace +
           updatedText.slice(match.index + match[0].length);
       }
+      appliedBlocks++;
+    }
+
+    if (appliedBlocks === 0) {
+      return {
+        success: false,
+        value:
+          "Error: All search/replace blocks were no-ops (SEARCH and REPLACE texts are identical), so the code was not changed. Put the modified text in the REPLACE section.",
+      };
     }
 
     return { success: true, value: updatedText };