diff --git a/src/filesystem/__tests__/structured-content.test.ts b/src/filesystem/__tests__/structured-content.test.ts
index 4b8f92b0a3..8f1bb7b16d 100644
--- a/src/filesystem/__tests__/structured-content.test.ts
+++ b/src/filesystem/__tests__/structured-content.test.ts
@@ -4,7 +4,6 @@ import * as path from 'path';
 import * as os from 'os';
 import { Client } from '@modelcontextprotocol/sdk/client/index.js';
 import { StdioClientTransport } from '@modelcontextprotocol/sdk/client/stdio.js';
-import { spawn } from 'child_process';
 
 /**
  * Integration tests to verify that tool handlers return structuredContent
@@ -13,6 +12,8 @@ import { spawn } from 'child_process';
  * These tests address issues #3110, #3106, #3093 where tools were returning
  * structuredContent: { content: [contentBlock] } (array) instead of
  * structuredContent: { content: string } as declared in outputSchema.
+ *
+ * Coverage: all 14 tools registered by the filesystem MCP server.
  */
 describe('structuredContent schema compliance', () => {
   let client: Client;
@@ -50,26 +51,172 @@ describe('structuredContent schema compliance', () => {
     await fs.rm(testDir, { recursive: true, force: true });
   });
 
-  describe('directory_tree', () => {
-    it('should return structuredContent.content as a string, not an array', async () => {
+  // ── Tools with outputSchema { content: z.string() } ──────────────
+
+  describe('read_text_file', () => {
+    it('should return structuredContent.content as a string', async () => {
       const result = await client.callTool({
-        name: 'directory_tree',
-        arguments: { path: testDir }
+        name: 'read_text_file',
+        arguments: { path: path.join(testDir, 'test.txt') }
+      });
+
+      expect(result.structuredContent).toBeDefined();
+      const sc = result.structuredContent as { content: unknown };
+      expect(typeof sc.content).toBe('string');
+      expect(Array.isArray(sc.content)).toBe(false);
+      expect(sc.content).toContain('test content');
+    });
+  });
+
+  describe('read_file (deprecated, back-compat)', () => {
+    it('should return structuredContent.content as a string, matching read_text_file', async () => {
+      const result = await client.callTool({
+        name: 'read_file',
+        arguments: { path: path.join(testDir, 'test.txt') }
       });
 
-      // The result should have structuredContent
       expect(result.structuredContent).toBeDefined();
+      const sc = result.structuredContent as { content: unknown };
+      expect(typeof sc.content).toBe('string');
+      expect(Array.isArray(sc.content)).toBe(false);
+      expect(sc.content).toContain('test content');
+    });
+  });
 
-      // structuredContent.content should be a string (matching outputSchema: { content: z.string() })
-      const structuredContent = result.structuredContent as { content: unknown };
-      expect(typeof structuredContent.content).toBe('string');
+  describe('read_multiple_files', () => {
+    it('should return structuredContent.content as a string containing both paths', async () => {
+      const file1 = path.join(testDir, 'test.txt');
+      const file2 = path.join(testDir, 'subdir', 'nested.txt');
 
-      // It should NOT be an array
-      expect(Array.isArray(structuredContent.content)).toBe(false);
+      const result = await client.callTool({
+        name: 'read_multiple_files',
+        arguments: { paths: [file1, file2] }
+      });
 
-      // The content should be valid JSON representing the tree
-      const treeData = JSON.parse(structuredContent.content as string);
-      expect(Array.isArray(treeData)).toBe(true);
+      expect(result.structuredContent).toBeDefined();
+      const sc = result.structuredContent as { content: unknown };
+      expect(typeof sc.content).toBe('string');
+      expect(Array.isArray(sc.content)).toBe(false);
+      expect(sc.content).toContain('test.txt');
+      expect(sc.content).toContain('nested.txt');
+    });
+  });
+
+  describe('write_file', () => {
+    it('should return structuredContent.content as a string and persist data', async () => {
+      const targetPath = path.join(testDir, 'written.txt');
+
+      const result = await client.callTool({
+        name: 'write_file',
+        arguments: { path: targetPath, content: 'hello world' }
+      });
+
+      expect(result.structuredContent).toBeDefined();
+      const sc = result.structuredContent as { content: unknown };
+      expect(typeof sc.content).toBe('string');
+      expect(Array.isArray(sc.content)).toBe(false);
+      expect(sc.content).toContain('Successfully wrote');
+
+      // Verify the file was actually written
+      const onDisk = await fs.readFile(targetPath, 'utf-8');
+      expect(onDisk).toBe('hello world');
+    });
+  });
+
+  describe('edit_file', () => {
+    it('should return structuredContent.content as a string with diff output', async () => {
+      const filePath = path.join(testDir, 'editable.txt');
+      await fs.writeFile(filePath, 'line one\nline two\nline three\n');
+
+      const result = await client.callTool({
+        name: 'edit_file',
+        arguments: {
+          path: filePath,
+          edits: [{ oldText: 'line two', newText: 'LINE TWO REPLACED' }],
+          dryRun: false
+        }
+      });
+
+      expect(result.structuredContent).toBeDefined();
+      const sc = result.structuredContent as { content: unknown };
+      expect(typeof sc.content).toBe('string');
+      expect(Array.isArray(sc.content)).toBe(false);
+
+      // Verify actual file was edited
+      const onDisk = await fs.readFile(filePath, 'utf-8');
+      expect(onDisk).toContain('LINE TWO REPLACED');
+    });
+
+    it('should return structuredContent.content as a string in dryRun mode without modifying the file', async () => {
+      const filePath = path.join(testDir, 'dryrun.txt');
+      await fs.writeFile(filePath, 'alpha\nbeta\ngamma\n');
+
+      const result = await client.callTool({
+        name: 'edit_file',
+        arguments: {
+          path: filePath,
+          edits: [{ oldText: 'beta', newText: 'BETA' }],
+          dryRun: true
+        }
+      });
+
+      expect(result.structuredContent).toBeDefined();
+      const sc = result.structuredContent as { content: unknown };
+      expect(typeof sc.content).toBe('string');
+      expect(Array.isArray(sc.content)).toBe(false);
+
+      // File should be unchanged after dry run
+      const onDisk = await fs.readFile(filePath, 'utf-8');
+      expect(onDisk).toContain('beta');
+      expect(onDisk).not.toContain('BETA');
+    });
+  });
+
+  describe('create_directory', () => {
+    it('should return structuredContent.content as a string and create the directory', async () => {
+      const dirPath = path.join(testDir, 'newdir');
+
+      const result = await client.callTool({
+        name: 'create_directory',
+        arguments: { path: dirPath }
+      });
+
+      expect(result.structuredContent).toBeDefined();
+      const sc = result.structuredContent as { content: unknown };
+      expect(typeof sc.content).toBe('string');
+      expect(Array.isArray(sc.content)).toBe(false);
+      expect(sc.content).toContain('Successfully created directory');
+
+      // Verify the directory exists
+      const stat = await fs.stat(dirPath);
+      expect(stat.isDirectory()).toBe(true);
+    });
+
+    it('should succeed idempotently when called twice on the same path', async () => {
+      const dirPath = path.join(testDir, 'idem');
+
+      await client.callTool({ name: 'create_directory', arguments: { path: dirPath } });
+      const result = await client.callTool({ name: 'create_directory', arguments: { path: dirPath } });
+
+      expect(result.structuredContent).toBeDefined();
+      const sc = result.structuredContent as { content: unknown };
+      expect(typeof sc.content).toBe('string');
+    });
+  });
+
+  describe('list_directory', () => {
+    it('should return structuredContent.content as a string with [FILE] and [DIR] markers', async () => {
+      const result = await client.callTool({
+        name: 'list_directory',
+        arguments: { path: testDir }
+      });
+
+      expect(result.structuredContent).toBeDefined();
+      const sc = result.structuredContent as { content: unknown };
+      expect(typeof sc.content).toBe('string');
+      expect(Array.isArray(sc.content)).toBe(false);
+      expect(sc.content).toContain('[FILE]');
+      expect(sc.content).toContain('[DIR]');
     });
   });
 
@@ -80,79 +227,139 @@ describe('structuredContent schema compliance', () => {
         arguments: { path: testDir }
       });
 
-      // The result should have structuredContent
       expect(result.structuredContent).toBeDefined();
+      const sc = result.structuredContent as { content: unknown };
+      expect(typeof sc.content).toBe('string');
+      expect(Array.isArray(sc.content)).toBe(false);
+      expect(sc.content).toContain('[FILE]');
+    });
+  });
 
-      // structuredContent.content should be a string (matching outputSchema: { content: z.string() })
-      const structuredContent = result.structuredContent as { content: unknown };
-      expect(typeof structuredContent.content).toBe('string');
+  describe('directory_tree', () => {
+    it('should return structuredContent.content as a string, not an array', async () => {
+      const result = await client.callTool({
+        name: 'directory_tree',
+        arguments: { path: testDir }
+      });
 
-      // It should NOT be an array
-      expect(Array.isArray(structuredContent.content)).toBe(false);
+      expect(result.structuredContent).toBeDefined();
+      const sc = result.structuredContent as { content: unknown };
+      expect(typeof sc.content).toBe('string');
+      expect(Array.isArray(sc.content)).toBe(false);
 
-      // The content should contain directory listing info
-      expect(structuredContent.content).toContain('[FILE]');
+      // The content should be valid JSON representing the tree
+      const treeData = JSON.parse(sc.content as string);
+      expect(Array.isArray(treeData)).toBe(true);
     });
   });
 
   describe('move_file', () => {
-    it('should return structuredContent.content as a string, not an array', async () => {
+    it('should return structuredContent.content as a string and move the file', async () => {
       const sourcePath = path.join(testDir, 'test.txt');
       const destPath = path.join(testDir, 'moved.txt');
 
       const result = await client.callTool({
         name: 'move_file',
-        arguments: {
-          source: sourcePath,
-          destination: destPath
-        }
+        arguments: { source: sourcePath, destination: destPath }
       });
 
-      // The result should have structuredContent
       expect(result.structuredContent).toBeDefined();
+      const sc = result.structuredContent as { content: unknown };
+      expect(typeof sc.content).toBe('string');
+      expect(Array.isArray(sc.content)).toBe(false);
+      expect(sc.content).toContain('Successfully moved');
 
-      // structuredContent.content should be a string (matching outputSchema: { content: z.string() })
-      const structuredContent = result.structuredContent as { content: unknown };
-      expect(typeof structuredContent.content).toBe('string');
+      // Verify source is gone and destination exists
+      await expect(fs.access(sourcePath)).rejects.toThrow();
+      const destContent = await fs.readFile(destPath, 'utf-8');
+      expect(destContent).toBe('test content');
+    });
+  });
 
-      // It should NOT be an array
-      expect(Array.isArray(structuredContent.content)).toBe(false);
+  describe('search_files', () => {
+    it('should return structuredContent.content as a string with matching paths', async () => {
+      const result = await client.callTool({
+        name: 'search_files',
+        arguments: { path: testDir, pattern: '*.txt' }
+      });
 
-      // The content should contain success message
-      expect(structuredContent.content).toContain('Successfully moved');
+      expect(result.structuredContent).toBeDefined();
+      const sc = result.structuredContent as { content: unknown };
+      expect(typeof sc.content).toBe('string');
+      expect(Array.isArray(sc.content)).toBe(false);
+      expect(sc.content).toContain('test.txt');
     });
   });
 
-  describe('list_directory (control - already working)', () => {
-    it('should return structuredContent.content as a string', async () => {
+  describe('get_file_info', () => {
+    it('should return structuredContent.content as a string with metadata', async () => {
       const result = await client.callTool({
-        name: 'list_directory',
-        arguments: { path: testDir }
+        name: 'get_file_info',
+        arguments: { path: path.join(testDir, 'test.txt') }
       });
 
       expect(result.structuredContent).toBeDefined();
+      const sc = result.structuredContent as { content: unknown };
+      expect(typeof sc.content).toBe('string');
+      expect(Array.isArray(sc.content)).toBe(false);
+      expect(sc.content).toContain('size');
+    });
+  });
 
-      const structuredContent = result.structuredContent as { content: unknown };
-      expect(typeof structuredContent.content).toBe('string');
-      expect(Array.isArray(structuredContent.content)).toBe(false);
+  describe('list_allowed_directories', () => {
+    it('should return structuredContent.content as a string listing the allowed directories', async () => {
+      const result = await client.callTool({
+        name: 'list_allowed_directories',
+        arguments: {}
+      });
+
+      expect(result.structuredContent).toBeDefined();
+      const sc = result.structuredContent as { content: unknown };
+      expect(typeof sc.content).toBe('string');
+      expect(Array.isArray(sc.content)).toBe(false);
+      expect(sc.content).toContain('Allowed directories');
     });
   });
 
-  describe('search_files (control - already working)', () => {
-    it('should return structuredContent.content as a string', async () => {
+  // ── Tool with outputSchema { content: z.array(...) } ─────────────
+
+  describe('read_media_file', () => {
+    it('should return structuredContent.content as an array matching its outputSchema', async () => {
+      // Write a minimal valid PNG (1x1 pixel, transparent)
+      const pngHeader = Buffer.from([
+        0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A, // PNG signature
+        0x00, 0x00, 0x00, 0x0D, 0x49, 0x48, 0x44, 0x52, // IHDR chunk
+        0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x01, // 1x1
+        0x08, 0x02, 0x00, 0x00, 0x00, 0x90, 0x77, 0x53, // 8-bit RGB
+        0xDE, 0x00, 0x00, 0x00, 0x0C, 0x49, 0x44, 0x41, // IDAT chunk
+        0x54, 0x08, 0xD7, 0x63, 0xF8, 0xCF, 0xC0, 0x00,
+        0x00, 0x00, 0x02, 0x00, 0x01, 0xE2, 0x21, 0xBC,
+        0x33, 0x00, 0x00, 0x00, 0x00, 0x49, 0x45, 0x4E, // IEND chunk
+        0x44, 0xAE, 0x42, 0x60, 0x82,
+      ]);
+      const imgPath = path.join(testDir, 'pixel.png');
+      await fs.writeFile(imgPath, pngHeader);
+
       const result = await client.callTool({
-        name: 'search_files',
-        arguments: {
-          path: testDir,
-          pattern: '*.txt'
-        }
+        name: 'read_media_file',
+        arguments: { path: imgPath }
       });
 
       expect(result.structuredContent).toBeDefined();
+      const sc = result.structuredContent as { content: unknown };
+
+      // read_media_file's outputSchema declares content as an array of
+      // { type, data, mimeType } objects — unlike every other tool which
+      // declares content as a plain string.
+      expect(Array.isArray(sc.content)).toBe(true);
 
-      const structuredContent = result.structuredContent as { content: unknown };
-      expect(typeof structuredContent.content).toBe('string');
-      expect(Array.isArray(structuredContent.content)).toBe(false);
+      const items = sc.content as Array<{ type: string; data: string; mimeType: string }>;
+      expect(items.length).toBeGreaterThanOrEqual(1);
+      expect(items[0].type).toBe('image');
+      expect(items[0].mimeType).toBe('image/png');
+      expect(typeof items[0].data).toBe('string'); // base64
+      // TODO: see WRG case-study F-006 — envelope reconciliation pending in separate PR
+      // (https://github.com/yakuphanycl/wrg-skills/blob/main/docs/case-studies/filesystem-mcp-2026-04-26.md#F-006)
     });
   });
 });