fix(core): truncate excessively long lines in grep search output (#21147)

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: gundermanc

packages/core/src/tools/grep-utils.ts

@@ -6,6 +6,7 @@
 
 import fsPromises from 'node:fs/promises';
 import { debugLogger } from '../utils/debugLogger.js';
+import { MAX_LINE_LENGTH_TEXT_FILE } from '../utils/constants.js';
 
 /**
  * Result object for a single grep match
@@ -198,7 +199,14 @@ export async function formatGrepResults(
       // If isContext is undefined, assume it's a match (false)
       const separator = match.isContext ? '-' : ':';
       // trimEnd to avoid double newlines if line has them, but we want to preserve indentation
-      llmContent += `L${match.lineNumber}${separator} ${match.line.trimEnd()}\n`;
+      let lineContent = match.line.trimEnd();
+      const graphemes = Array.from(lineContent);
+      if (graphemes.length > MAX_LINE_LENGTH_TEXT_FILE) {
+        lineContent =
+          graphemes.slice(0, MAX_LINE_LENGTH_TEXT_FILE).join('') +
+          '... [truncated]';
+      }
+      llmContent += `L${match.lineNumber}${separator} ${lineContent}\n`;
     });
     llmContent += '---\n';
   }

packages/core/src/tools/grep.test.ts

@@ -562,6 +562,22 @@ describe('GrepTool', () => {
       // Verify context after
       expect(result.llmContent).toContain('L60- Line 60');
     });
+
+    it('should truncate excessively long lines', async () => {
+      const longString = 'a'.repeat(3000);
+      await fs.writeFile(
+        path.join(tempRootDir, 'longline.txt'),
+        `Target match ${longString}`,
+      );
+
+      const params: GrepToolParams = { pattern: 'Target match' };
+      const invocation = grepTool.build(params);
+      const result = await invocation.execute(abortSignal);
+
+      // MAX_LINE_LENGTH_TEXT_FILE is 2000. It should be truncated.
+      expect(result.llmContent).toContain('... [truncated]');
+      expect(result.llmContent).not.toContain(longString);
+    });
   });
 
   describe('getDescription', () => {

packages/core/src/tools/ripGrep.test.ts

@@ -2028,6 +2028,32 @@ describe('RipGrepTool', () => {
       expect(result.llmContent).not.toContain('fileB.txt');
       expect(result.llmContent).toContain('Copyright 2025 Google LLC');
     });
+
+    it('should truncate excessively long lines', async () => {
+      const longString = 'a'.repeat(3000);
+      mockSpawn.mockImplementation(
+        createMockSpawn({
+          outputData:
+            JSON.stringify({
+              type: 'match',
+              data: {
+                path: { text: 'longline.txt' },
+                line_number: 1,
+                lines: { text: `Target match ${longString}\n` },
+              },
+            }) + '\n',
+          exitCode: 0,
+        }),
+      );
+
+      const params: RipGrepToolParams = { pattern: 'Target match', context: 0 };
+      const invocation = grepTool.build(params);
+      const result = await invocation.execute(abortSignal);
+
+      // MAX_LINE_LENGTH_TEXT_FILE is 2000. It should be truncated.
+      expect(result.llmContent).toContain('... [truncated]');
+      expect(result.llmContent).not.toContain(longString);
+    });
   });
 });