Support Images and PDFs (#447)

7 files changed, 552 insertions, 49 deletions

diff --git a/packages/server/src/__mocks__/fs/promises.ts b/packages/server/src/__mocks__/fs/promises.ts
new file mode 100644
index 00000000..42385911
--- /dev/null
+++ b/packages/server/src/__mocks__/fs/promises.ts
@@ -0,0 +1,48 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { vi } from 'vitest';
+import * as actualFsPromises from 'node:fs/promises';
+
+const readFileMock = vi.fn();
+
+// Export a control object so tests can access and manipulate the mock
+export const mockControl = {
+  mockReadFile: readFileMock,
+};
+
+// Export all other functions from the actual fs/promises module
+export const {
+  access,
+  appendFile,
+  chmod,
+  chown,
+  copyFile,
+  cp,
+  lchmod,
+  lchown,
+  link,
+  lstat,
+  mkdir,
+  open,
+  opendir,
+  readdir,
+  readlink,
+  realpath,
+  rename,
+  rmdir,
+  rm,
+  stat,
+  symlink,
+  truncate,
+  unlink,
+  utimes,
+  watch,
+  writeFile,
+} = actualFsPromises;
+
+// Override readFile with our mock
+export const readFile = readFileMock;
diff --git a/packages/server/src/core/geminiRequest.ts b/packages/server/src/core/geminiRequest.ts
new file mode 100644
index 00000000..e85bd51e
--- /dev/null
+++ b/packages/server/src/core/geminiRequest.ts
@@ -0,0 +1,71 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { type PartListUnion, type Part } from '@google/genai';
+
+/**
+ * Represents a request to be sent to the Gemini API.
+ * For now, it's an alias to PartListUnion as the primary content.
+ * This can be expanded later to include other request parameters.
+ */
+export type GeminiCodeRequest = PartListUnion;
+
+export function partListUnionToString(value: PartListUnion): string {
+  if (typeof value === 'string') {
+    return value;
+  }
+
+  if (Array.isArray(value)) {
+    return value.map(partListUnionToString).join('');
+  }
+
+  // Cast to Part, assuming it might contain project-specific fields
+  const part = value as Part & {
+    videoMetadata?: unknown;
+    thought?: string;
+    codeExecutionResult?: unknown;
+    executableCode?: unknown;
+  };
+
+  if (part.videoMetadata !== undefined) {
+    return `[Video Metadata]`;
+  }
+
+  if (part.thought !== undefined) {
+    return `[Thought: ${part.thought}]`;
+  }
+
+  if (part.codeExecutionResult !== undefined) {
+    return `[Code Execution Result]`;
+  }
+
+  if (part.executableCode !== undefined) {
+    return `[Executable Code]`;
+  }
+
+  // Standard Part fields
+  if (part.fileData !== undefined) {
+    return `[File Data]`;
+  }
+
+  if (part.functionCall !== undefined) {
+    return `[Function Call: ${part.functionCall.name}]`;
+  }
+
+  if (part.functionResponse !== undefined) {
+    return `[Function Response: ${part.functionResponse.name}]`;
+  }
+
+  if (part.inlineData !== undefined) {
+    return `<${part.inlineData.mimeType}>`;
+  }
+
+  if (part.text !== undefined) {
+    return part.text;
+  }
+
+  return '';
+}
diff --git a/packages/server/src/index.ts b/packages/server/src/index.ts
index 9183c2f9..c90ef2fd 100644
--- a/packages/server/src/index.ts
+++ b/packages/server/src/index.ts
@@ -11,6 +11,7 @@ export * from './config/config.js';
 export * from './core/client.js';
 export * from './core/prompts.js';
 export * from './core/turn.js';
+export * from './core/geminiRequest.js';
 // Potentially export types from turn.ts if needed externally
 // export { GeminiEventType } from './core/turn.js'; // Example
 
diff --git a/packages/server/src/tools/glob.test.ts b/packages/server/src/tools/glob.test.ts
index 3437a66e..d42e5b1c 100644
--- a/packages/server/src/tools/glob.test.ts
+++ b/packages/server/src/tools/glob.test.ts
@@ -5,6 +5,7 @@
  */
 
 import { GlobTool, GlobToolParams } from './glob.js';
+import { partListUnionToString } from '../core/geminiRequest.js';
 // import { ToolResult } from './tools.js'; // ToolResult is implicitly used by execute
 import path from 'path';
 import fs from 'fs/promises';
@@ -134,9 +135,14 @@ describe('GlobTool', () => {
     it('should correctly sort files by modification time (newest first)', async () => {
       const params: GlobToolParams = { pattern: '*.sortme' };
       const result = await globTool.execute(params, abortSignal);
-      expect(result.llmContent).toContain('Found 2 file(s)');
-      const filesListed = result.llmContent
-        .substring(result.llmContent.indexOf(':') + 1)
+      const llmContent = partListUnionToString(result.llmContent);
+
+      expect(llmContent).toContain('Found 2 file(s)');
+      // Ensure llmContent is a string for TypeScript type checking
+      expect(typeof llmContent).toBe('string');
+
+      const filesListed = llmContent
+        .substring(llmContent.indexOf(':') + 1)
         .trim()
         .split('\n');
       expect(filesListed[0]).toContain(path.join(tempRootDir, 'newer.sortme'));
diff --git a/packages/server/src/tools/read-many-files.test.ts b/packages/server/src/tools/read-many-files.test.ts
new file mode 100644
index 00000000..50156b55
--- /dev/null
+++ b/packages/server/src/tools/read-many-files.test.ts
@@ -0,0 +1,332 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { vi } from 'vitest';
+import type { Mock } from 'vitest';
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import { mockControl } from '../__mocks__/fs/promises.js';
+import { ReadManyFilesTool } from './read-many-files.js';
+import path from 'path';
+import fs from 'fs'; // Actual fs for setup
+import os from 'os';
+
+describe('ReadManyFilesTool', () => {
+  let tool: ReadManyFilesTool;
+  let tempRootDir: string;
+  let tempDirOutsideRoot: string;
+  let mockReadFileFn: Mock;
+
+  beforeEach(async () => {
+    tempRootDir = fs.mkdtempSync(
+      path.join(os.tmpdir(), 'read-many-files-root-'),
+    );
+    tempDirOutsideRoot = fs.mkdtempSync(
+      path.join(os.tmpdir(), 'read-many-files-external-'),
+    );
+    tool = new ReadManyFilesTool(tempRootDir);
+
+    mockReadFileFn = mockControl.mockReadFile;
+    mockReadFileFn.mockReset();
+
+    mockReadFileFn.mockImplementation(
+      async (filePath: fs.PathLike, options?: Record<string, unknown>) => {
+        const fp =
+          typeof filePath === 'string'
+            ? filePath
+            : (filePath as Buffer).toString();
+
+        if (fs.existsSync(fp)) {
+          const originalFs = await vi.importActual<typeof fs>('fs');
+          return originalFs.promises.readFile(fp, options);
+        }
+
+        if (fp.endsWith('nonexistent-file.txt')) {
+          const err = new Error(
+            `ENOENT: no such file or directory, open '${fp}'`,
+          );
+          (err as NodeJS.ErrnoException).code = 'ENOENT';
+          throw err;
+        }
+        if (fp.endsWith('unreadable.txt')) {
+          const err = new Error(`EACCES: permission denied, open '${fp}'`);
+          (err as NodeJS.ErrnoException).code = 'EACCES';
+          throw err;
+        }
+        if (fp.endsWith('.png'))
+          return Buffer.from([0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a]); // PNG header
+        if (fp.endsWith('.pdf')) return Buffer.from('%PDF-1.4...'); // PDF start
+        if (fp.endsWith('binary.bin'))
+          return Buffer.from([0x00, 0x01, 0x02, 0x00, 0x03]);
+
+        const err = new Error(
+          `ENOENT: no such file or directory, open '${fp}' (unmocked path)`,
+        );
+        (err as NodeJS.ErrnoException).code = 'ENOENT';
+        throw err;
+      },
+    );
+  });
+
+  afterEach(() => {
+    if (fs.existsSync(tempRootDir)) {
+      fs.rmSync(tempRootDir, { recursive: true, force: true });
+    }
+    if (fs.existsSync(tempDirOutsideRoot)) {
+      fs.rmSync(tempDirOutsideRoot, { recursive: true, force: true });
+    }
+  });
+
+  describe('validateParams', () => {
+    it('should return null for valid relative paths within root', () => {
+      const params = { paths: ['file1.txt', 'subdir/file2.txt'] };
+      expect(tool.validateParams(params)).toBeNull();
+    });
+
+    it('should return null for valid glob patterns within root', () => {
+      const params = { paths: ['*.txt', 'subdir/**/*.js'] };
+      expect(tool.validateParams(params)).toBeNull();
+    });
+
+    it('should return null for paths trying to escape the root (e.g., ../) as execute handles this', () => {
+      const params = { paths: ['../outside.txt'] };
+      expect(tool.validateParams(params)).toBeNull();
+    });
+
+    it('should return null for absolute paths as execute handles this', () => {
+      const params = { paths: [path.join(tempDirOutsideRoot, 'absolute.txt')] };
+      expect(tool.validateParams(params)).toBeNull();
+    });
+
+    it('should return error if paths array is empty', () => {
+      const params = { paths: [] };
+      expect(tool.validateParams(params)).toBe(
+        'The "paths" parameter is required and must be a non-empty array of strings/glob patterns.',
+      );
+    });
+
+    it('should return null for valid exclude and include patterns', () => {
+      const params = {
+        paths: ['src/**/*.ts'],
+        exclude: ['**/*.test.ts'],
+        include: ['src/utils/*.ts'],
+      };
+      expect(tool.validateParams(params)).toBeNull();
+    });
+  });
+
+  describe('execute', () => {
+    const createFile = (filePath: string, content = '') => {
+      const fullPath = path.join(tempRootDir, filePath);
+      fs.mkdirSync(path.dirname(fullPath), { recursive: true });
+      fs.writeFileSync(fullPath, content);
+    };
+    const createBinaryFile = (filePath: string, data: Uint8Array) => {
+      const fullPath = path.join(tempRootDir, filePath);
+      fs.mkdirSync(path.dirname(fullPath), { recursive: true });
+      fs.writeFileSync(fullPath, data);
+    };
+
+    it('should read a single specified file', async () => {
+      createFile('file1.txt', 'Content of file1');
+      const params = { paths: ['file1.txt'] };
+      const result = await tool.execute(params, new AbortController().signal);
+      expect(result.llmContent).toEqual([
+        '--- file1.txt ---\n\nContent of file1\n\n',
+      ]);
+      expect(result.returnDisplay).toContain(
+        'Successfully read and concatenated content from **1 file(s)**',
+      );
+    });
+
+    it('should read multiple specified files', async () => {
+      createFile('file1.txt', 'Content1');
+      createFile('subdir/file2.js', 'Content2');
+      const params = { paths: ['file1.txt', 'subdir/file2.js'] };
+      const result = await tool.execute(params, new AbortController().signal);
+      const content = result.llmContent as string[];
+      expect(
+        content.some((c) => c.includes('--- file1.txt ---\n\nContent1\n\n')),
+      ).toBe(true);
+      expect(
+        content.some((c) =>
+          c.includes('--- subdir/file2.js ---\n\nContent2\n\n'),
+        ),
+      ).toBe(true);
+      expect(result.returnDisplay).toContain(
+        'Successfully read and concatenated content from **2 file(s)**',
+      );
+    });
+
+    it('should handle glob patterns', async () => {
+      createFile('file.txt', 'Text file');
+      createFile('another.txt', 'Another text');
+      createFile('sub/data.json', '{}');
+      const params = { paths: ['*.txt'] };
+      const result = await tool.execute(params, new AbortController().signal);
+      const content = result.llmContent as string[];
+      expect(
+        content.some((c) => c.includes('--- file.txt ---\n\nText file\n\n')),
+      ).toBe(true);
+      expect(
+        content.some((c) =>
+          c.includes('--- another.txt ---\n\nAnother text\n\n'),
+        ),
+      ).toBe(true);
+      expect(content.find((c) => c.includes('sub/data.json'))).toBeUndefined();
+      expect(result.returnDisplay).toContain(
+        'Successfully read and concatenated content from **2 file(s)**',
+      );
+    });
+
+    it('should respect exclude patterns', async () => {
+      createFile('src/main.ts', 'Main content');
+      createFile('src/main.test.ts', 'Test content');
+      const params = { paths: ['src/**/*.ts'], exclude: ['**/*.test.ts'] };
+      const result = await tool.execute(params, new AbortController().signal);
+      const content = result.llmContent as string[];
+      expect(content).toEqual(['--- src/main.ts ---\n\nMain content\n\n']);
+      expect(
+        content.find((c) => c.includes('src/main.test.ts')),
+      ).toBeUndefined();
+      expect(result.returnDisplay).toContain(
+        'Successfully read and concatenated content from **1 file(s)**',
+      );
+    });
+
+    it('should handle non-existent specific files gracefully', async () => {
+      const params = { paths: ['nonexistent-file.txt'] };
+      const result = await tool.execute(params, new AbortController().signal);
+      expect(result.llmContent).toEqual([
+        'No files matching the criteria were found or all were skipped.',
+      ]);
+      expect(result.returnDisplay).toContain(
+        'No files were read and concatenated based on the criteria.',
+      );
+    });
+
+    it('should use default excludes', async () => {
+      createFile('node_modules/some-lib/index.js', 'lib code');
+      createFile('src/app.js', 'app code');
+      const params = { paths: ['**/*.js'] };
+      const result = await tool.execute(params, new AbortController().signal);
+      const content = result.llmContent as string[];
+      expect(content).toEqual(['--- src/app.js ---\n\napp code\n\n']);
+      expect(
+        content.find((c) => c.includes('node_modules/some-lib/index.js')),
+      ).toBeUndefined();
+      expect(result.returnDisplay).toContain(
+        'Successfully read and concatenated content from **1 file(s)**',
+      );
+    });
+
+    it('should NOT use default excludes if useDefaultExcludes is false', async () => {
+      createFile('node_modules/some-lib/index.js', 'lib code');
+      createFile('src/app.js', 'app code');
+      const params = { paths: ['**/*.js'], useDefaultExcludes: false };
+      const result = await tool.execute(params, new AbortController().signal);
+      const content = result.llmContent as string[];
+      expect(
+        content.some((c) =>
+          c.includes('--- node_modules/some-lib/index.js ---\n\nlib code\n\n'),
+        ),
+      ).toBe(true);
+      expect(
+        content.some((c) => c.includes('--- src/app.js ---\n\napp code\n\n')),
+      ).toBe(true);
+      expect(result.returnDisplay).toContain(
+        'Successfully read and concatenated content from **2 file(s)**',
+      );
+    });
+
+    it('should include images as inlineData parts if explicitly requested by extension', async () => {
+      createBinaryFile(
+        'image.png',
+        Buffer.from([0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a]),
+      );
+      const params = { paths: ['*.png'] }; // Explicitly requesting .png
+      const result = await tool.execute(params, new AbortController().signal);
+      expect(result.llmContent).toEqual([
+        {
+          inlineData: {
+            data: Buffer.from([
+              0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a,
+            ]).toString('base64'),
+            mimeType: 'image/png',
+          },
+        },
+      ]);
+      expect(result.returnDisplay).toContain(
+        'Successfully read and concatenated content from **1 file(s)**',
+      );
+    });
+
+    it('should include images as inlineData parts if explicitly requested by name', async () => {
+      createBinaryFile(
+        'myExactImage.png',
+        Buffer.from([0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a]),
+      );
+      const params = { paths: ['myExactImage.png'] }; // Explicitly requesting by full name
+      const result = await tool.execute(params, new AbortController().signal);
+      expect(result.llmContent).toEqual([
+        {
+          inlineData: {
+            data: Buffer.from([
+              0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a,
+            ]).toString('base64'),
+            mimeType: 'image/png',
+          },
+        },
+      ]);
+    });
+
+    it('should skip PDF files if not explicitly requested by extension or name', async () => {
+      createBinaryFile('document.pdf', Buffer.from('%PDF-1.4...'));
+      createFile('notes.txt', 'text notes');
+      const params = { paths: ['*'] }; // Generic glob, not specific to .pdf
+      const result = await tool.execute(params, new AbortController().signal);
+      const content = result.llmContent as string[];
+      expect(
+        content.some(
+          (c) => typeof c === 'string' && c.includes('--- notes.txt ---'),
+        ),
+      ).toBe(true);
+      expect(result.returnDisplay).toContain(
+        '**Skipped 1 item(s) (up to 5 shown):**',
+      );
+      expect(result.returnDisplay).toContain(
+        '- `document.pdf` (Reason: asset file (image/pdf) was not explicitly requested by name or extension)',
+      );
+    });
+
+    it('should include PDF files as inlineData parts if explicitly requested by extension', async () => {
+      createBinaryFile('important.pdf', Buffer.from('%PDF-1.4...'));
+      const params = { paths: ['*.pdf'] }; // Explicitly requesting .pdf files
+      const result = await tool.execute(params, new AbortController().signal);
+      expect(result.llmContent).toEqual([
+        {
+          inlineData: {
+            data: Buffer.from('%PDF-1.4...').toString('base64'),
+            mimeType: 'application/pdf',
+          },
+        },
+      ]);
+    });
+
+    it('should include PDF files as inlineData parts if explicitly requested by name', async () => {
+      createBinaryFile('report-final.pdf', Buffer.from('%PDF-1.4...'));
+      const params = { paths: ['report-final.pdf'] };
+      const result = await tool.execute(params, new AbortController().signal);
+      expect(result.llmContent).toEqual([
+        {
+          inlineData: {
+            data: Buffer.from('%PDF-1.4...').toString('base64'),
+            mimeType: 'application/pdf',
+          },
+        },
+      ]);
+    });
+  });
+});
diff --git a/packages/server/src/tools/read-many-files.ts b/packages/server/src/tools/read-many-files.ts
index 4d9d35e8..5064ae1b 100644
--- a/packages/server/src/tools/read-many-files.ts
+++ b/packages/server/src/tools/read-many-files.ts
@@ -12,6 +12,8 @@ import * as path from 'path';
 import fg from 'fast-glob';
 import { GEMINI_MD_FILENAME } from './memoryTool.js';
 
+import { PartListUnion } from '@google/genai';
+import mime from 'mime-types';
 /**
  * Parameters for the ReadManyFilesTool.
  */
@@ -82,14 +84,6 @@ const DEFAULT_EXCLUDES: string[] = [
   '**/*.bz2',
   '**/*.rar',
   '**/*.7z',
-  '**/*.png',
-  '**/*.jpg',
-  '**/*.jpeg',
-  '**/*.gif',
-  '**/*.bmp',
-  '**/*.tiff',
-  '**/*.ico',
-  '**/*.pdf',
   '**/*.doc',
   '**/*.docx',
   '**/*.xls',
@@ -188,6 +182,13 @@ Default excludes apply to common non-text files and large dependency directories
 
   validateParams(params: ReadManyFilesParams): string | null {
     if (
+      !params.paths ||
+      !Array.isArray(params.paths) ||
+      params.paths.length === 0
+    ) {
+      return 'The "paths" parameter is required and must be a non-empty array of strings/glob patterns.';
+    }
+    if (
       this.schema.parameters &&
       !SchemaValidator.validate(
         this.schema.parameters as Record<string, unknown>,
@@ -263,7 +264,7 @@ Default excludes apply to common non-text files and large dependency directories
     const filesToConsider = new Set<string>();
     const skippedFiles: Array<{ path: string; reason: string }> = [];
     const processedFilesRelativePaths: string[] = [];
-    let concatenatedContent = '';
+    const content: PartListUnion = [];
 
     const effectiveExcludes = useDefaultExcludes
       ? [...DEFAULT_EXCLUDES, ...exclude]
@@ -319,28 +320,63 @@ Default excludes apply to common non-text files and large dependency directories
         .relative(toolBaseDir, filePath)
         .replace(/\\/g, '/');
       try {
-        const contentBuffer = await fs.readFile(filePath);
-        // Basic binary detection: check for null bytes in the first 1KB
-        const sample = contentBuffer.subarray(
-          0,
-          Math.min(contentBuffer.length, 1024),
-        );
-        if (sample.includes(0)) {
-          skippedFiles.push({
-            path: relativePathForDisplay,
-            reason: 'Skipped (appears to be binary)',
+        const mimeType = mime.lookup(filePath);
+        if (
+          mimeType &&
+          (mimeType.startsWith('image/') || mimeType === 'application/pdf')
+        ) {
+          const fileExtension = path.extname(filePath);
+          const fileNameWithoutExtension = path.basename(
+            filePath,
+            fileExtension,
+          );
+          const requestedExplicitly = inputPatterns.some(
+            (pattern: string) =>
+              pattern.toLowerCase().includes(fileExtension) ||
+              pattern.includes(fileNameWithoutExtension),
+          );
+
+          if (!requestedExplicitly) {
+            skippedFiles.push({
+              path: relativePathForDisplay,
+              reason:
+                'asset file (image/pdf) was not explicitly requested by name or extension',
+            });
+            continue;
+          }
+          const contentBuffer = await fs.readFile(filePath);
+          const base64Data = contentBuffer.toString('base64');
+          content.push({
+            inlineData: {
+              data: base64Data,
+              mimeType,
+            },
           });
-          continue;
+          processedFilesRelativePaths.push(relativePathForDisplay);
+        } else {
+          const contentBuffer = await fs.readFile(filePath);
+          // Basic binary detection: check for null bytes in the first 1KB
+          const sample = contentBuffer.subarray(
+            0,
+            Math.min(contentBuffer.length, 1024),
+          );
+          if (sample.includes(0)) {
+            skippedFiles.push({
+              path: relativePathForDisplay,
+              reason: 'appears to be binary',
+            });
+            continue;
+          }
+          // Using default encoding
+          const fileContent = contentBuffer.toString(DEFAULT_ENCODING);
+          // Using default separator format
+          const separator = DEFAULT_OUTPUT_SEPARATOR_FORMAT.replace(
+            '{filePath}',
+            relativePathForDisplay,
+          );
+          content.push(`${separator}\n\n${fileContent}\n\n`);
+          processedFilesRelativePaths.push(relativePathForDisplay);
         }
-        // Using default encoding
-        const fileContent = contentBuffer.toString(DEFAULT_ENCODING);
-        // Using default separator format
-        const separator = DEFAULT_OUTPUT_SEPARATOR_FORMAT.replace(
-          '{filePath}',
-          relativePathForDisplay,
-        );
-        concatenatedContent += `${separator}\n\n${fileContent}\n\n`;
-        processedFilesRelativePaths.push(relativePathForDisplay);
       } catch (error) {
         skippedFiles.push({
           path: relativePathForDisplay,
@@ -352,18 +388,24 @@ Default excludes apply to common non-text files and large dependency directories
     let displayMessage = `### ReadManyFiles Result (Target Dir: \`${this.targetDir}\`)\n\n`;
     if (processedFilesRelativePaths.length > 0) {
       displayMessage += `Successfully read and concatenated content from **${processedFilesRelativePaths.length} file(s)**.\n`;
-      displayMessage += `\n**Processed Files:**\n`;
-      processedFilesRelativePaths
-        .slice(0, 10)
-        .forEach((p) => (displayMessage += `- \`${p}\`\n`));
-      if (processedFilesRelativePaths.length > 10) {
+      if (processedFilesRelativePaths.length <= 10) {
+        displayMessage += `\n**Processed Files:**\n`;
+        processedFilesRelativePaths.forEach(
+          (p) => (displayMessage += `- \`${p}\`\n`),
+        );
+      } else {
+        displayMessage += `\n**Processed Files (first 10 shown):**\n`;
+        processedFilesRelativePaths
+          .slice(0, 10)
+          .forEach((p) => (displayMessage += `- \`${p}\`\n`));
         displayMessage += `- ...and ${processedFilesRelativePaths.length - 10} more.\n`;
       }
-    } else {
-      displayMessage += `No files were read and concatenated based on the criteria.\n`;
     }
 
     if (skippedFiles.length > 0) {
+      if (processedFilesRelativePaths.length === 0) {
+        displayMessage += `No files were read and concatenated based on the criteria.\n`;
+      }
       displayMessage += `\n**Skipped ${skippedFiles.length} item(s) (up to 5 shown):**\n`;
       skippedFiles
         .slice(0, 5)
@@ -373,18 +415,21 @@ Default excludes apply to common non-text files and large dependency directories
       if (skippedFiles.length > 5) {
         displayMessage += `- ...and ${skippedFiles.length - 5} more.\n`;
       }
-    }
-    if (
-      concatenatedContent.length === 0 &&
-      processedFilesRelativePaths.length === 0
+    } else if (
+      processedFilesRelativePaths.length === 0 &&
+      skippedFiles.length === 0
     ) {
-      concatenatedContent =
-        'No files matching the criteria were found or all were skipped.';
+      displayMessage += `No files were read and concatenated based on the criteria.\n`;
     }
 
+    if (content.length === 0) {
+      content.push(
+        'No files matching the criteria were found or all were skipped.',
+      );
+    }
     return {
-      llmContent: concatenatedContent,
-      returnDisplay: displayMessage,
+      llmContent: content,
+      returnDisplay: displayMessage.trim(),
     };
   }
 }
diff --git a/packages/server/src/tools/tools.ts b/packages/server/src/tools/tools.ts
index de4bf287..329010bc 100644
--- a/packages/server/src/tools/tools.ts
+++ b/packages/server/src/tools/tools.ts
@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { FunctionDeclaration, Schema } from '@google/genai';
+import { FunctionDeclaration, PartListUnion, Schema } from '@google/genai';
 
 /**
  * Interface representing the base Tool functionality
@@ -152,7 +152,7 @@ export interface ToolResult {
    * Content meant to be included in LLM history.
    * This should represent the factual outcome of the tool execution.
    */
-  llmContent: string;
+  llmContent: PartListUnion;
 
   /**
    * Markdown string for user display.