refactor(@angular/cli): implement native stream line-buffering & VT removal for MCP logs

Refactor the process log capturing mechanism in host.ts and devserver.ts to natively line-buffer and sanitize process stdout and stderr streams using Node's native readline `createInterface` API and `util.stripVTControlCharacters`. This ensures all command and devserver logs are cleanly line-split, trimmed, and stripped of VT/ANSI color sequences and carriage returns.

Author: clydin

packages/angular/cli/src/commands/mcp/devserver.ts

@@ -7,7 +7,7 @@
  */
 
 import type { ChildProcess } from 'child_process';
-import type { Host } from './host';
+import { type Host, processStreamLines } from './host';
 
 // Log messages that we want to catch to identify the build status.
 
@@ -122,13 +122,10 @@ export class LocalDevserver implements Devserver {
       stdio: 'pipe',
       cwd: this.workspacePath,
     });
-    this.devserverProcess.stdout?.on('data', (data) => {
-      this.addLog(data.toString());
-    });
-    this.devserverProcess.stderr?.on('data', (data) => {
-      this.addLog(data.toString());
-    });
-    this.devserverProcess.stderr?.on('close', () => {
+    processStreamLines(this.devserverProcess.stdout, (line) => this.addLog(line));
+    processStreamLines(this.devserverProcess.stderr, (line) => this.addLog(line));
+
+    this.devserverProcess.on('close', () => {
       this.stop();
     });
     this.buildInProgress = true;

packages/angular/cli/src/commands/mcp/host.ts

@@ -20,6 +20,8 @@ import { glob as nodeGlob, readFile as nodeReadFile, stat } from 'node:fs/promis
 import { createRequire } from 'node:module';
 import { createServer } from 'node:net';
 import { dirname, isAbsolute, join, relative, resolve } from 'node:path';
+import { createInterface } from 'node:readline';
+import { stripVTControlCharacters } from 'node:util';
 
 /**
  * An error thrown when a command fails to execute.
@@ -191,8 +193,8 @@ export const LocalWorkspaceHost: Host = {
       });
 
       const logs: string[] = [];
-      childProcess.stdout?.on('data', (data) => logs.push(data.toString()));
-      childProcess.stderr?.on('data', (data) => logs.push(data.toString()));
+      processStreamLines(childProcess.stdout, (line) => logs.push(line));
+      processStreamLines(childProcess.stderr, (line) => logs.push(line));
 
       childProcess.on('close', (code) => {
         if (code === 0) {
@@ -381,3 +383,25 @@ export function createRootRestrictedHost(
     },
   };
 }
+
+/**
+ * Binds a readline interface to the given stream to process each line.
+ * Sanitizes lines by removing VT/ANSI control characters, trimming trailing whitespace,
+ * and preserving leading indentation.
+ */
+export function processStreamLines(
+  stream: NodeJS.ReadableStream | undefined | null,
+  lineCallback: (line: string) => void,
+): void {
+  if (!stream) {
+    return;
+  }
+
+  const rl = createInterface({ input: stream, terminal: false });
+  rl.on('line', (line) => {
+    const cleanLine = stripVTControlCharacters(line).trimEnd();
+    if (cleanLine.length > 0) {
+      lineCallback(cleanLine);
+    }
+  });
+}

packages/angular/cli/src/commands/mcp/tools/devserver/devserver_spec.ts

@@ -18,9 +18,14 @@ import { startDevserver } from './devserver-start';
 import { stopDevserver } from './devserver-stop';
 import { WATCH_DELAY, waitForDevserverBuild } from './devserver-wait-for-build';
 
+class MockStream extends EventEmitter {
+  resume = jasmine.createSpy('resume').and.returnValue(this);
+  pause = jasmine.createSpy('pause').and.returnValue(this);
+}
+
 class MockChildProcess extends EventEmitter {
-  stdout = new EventEmitter();
-  stderr = new EventEmitter();
+  stdout = new MockStream();
+  stderr = new MockStream();
   kill = jasmine.createSpy('kill');
 }
 
@@ -95,10 +100,10 @@ describe('Serve Tools', () => {
     const waitPromise = waitForDevserverBuild({ timeout: 10 }, mockContext);
 
     // Simulate build logs.
-    mockProcess.stdout.emit('data', '... building ...');
-    mockProcess.stdout.emit('data', '✔ Changes detected. Rebuilding...');
-    mockProcess.stdout.emit('data', '... more logs ...');
-    mockProcess.stdout.emit('data', 'Application bundle generation complete.');
+    mockProcess.stdout.emit('data', '... building ...\n');
+    mockProcess.stdout.emit('data', '✔ Changes detected. Rebuilding...\n');
+    mockProcess.stdout.emit('data', '... more logs ...\n');
+    mockProcess.stdout.emit('data', 'Application bundle generation complete.\n');
 
     const waitResult = await waitPromise;
     expect(waitResult.structuredContent.status).toBe('success');
@@ -161,7 +166,7 @@ describe('Serve Tools', () => {
     await startDevserver({ project: 'crash-app' }, mockContext);
 
     // Simulate a crash with exit code 1
-    mockProcess.stdout.emit('data', 'Fatal error.');
+    mockProcess.stdout.emit('data', 'Fatal error.\n');
     mockProcess.emit('close', 1);
 
     const stopResult = await stopDevserver({ project: 'crash-app' }, mockContext);
@@ -185,7 +190,7 @@ describe('Serve Tools', () => {
       await startDevserver({}, mockContext);
 
       // Immediately simulate a build starting so isBuilding() is true.
-      mockProcess.stdout.emit('data', '❯ Changes detected. Rebuilding...');
+      mockProcess.stdout.emit('data', '❯ Changes detected. Rebuilding...\n');
 
       const waitPromise = waitForDevserverBuild({ timeout: 5 * WATCH_DELAY }, mockContext);
 
@@ -199,7 +204,7 @@ describe('Serve Tools', () => {
       jasmine.clock().tick(WATCH_DELAY + 1);
 
       // Now finish the build.
-      mockProcess.stdout.emit('data', 'Application bundle generation complete.');
+      mockProcess.stdout.emit('data', 'Application bundle generation complete.\n');
 
       // Tick past another debounce to exit the loop.
       jasmine.clock().tick(WATCH_DELAY + 1);