fix(core): emit only NDJSON from nx init when running under an AI agent

`nx init` mixes NDJSON events with `Fetching nx...`, `CREATE`/`UPDATE`
file lines, `output.log` titles, and a trailing `---USER_NEXT_STEPS---`
block — agents must parse stdout line-by-line with brittle heuristics.

Under any agent detected by `isAiAgent()`, stdout is pure NDJSON. Sets
`NX_AI_AGENT_INIT=1` early in `initHandler` so it survives the
tmp-install re-entry and the `nx g <plugin>:init` subprocess. `output.*`
methods, `printChanges()` (dot-nx + generate), and the `Fetching ${pkg}`
log all gate on it. `userNextSteps` already lives in the `complete`
event, so the trailing human block is dropped. Human TTY behavior
unchanged.

Fixes NXC-4368

Author: jaysoo

packages/nx/src/command-line/generate/generate.ts

@@ -416,7 +416,7 @@ export async function generate(args: { [k: string]: any }) {
 
       const changes = host.listChanges();
 
-      if (!opts.quiet) {
+      if (!opts.quiet && process.env.NX_AI_AGENT_INIT !== 'true') {
         printChanges(changes);
       }
       if (!opts.dryRun) {

packages/nx/src/command-line/init/implementation/dot-nx/add-nx-scripts.ts

@@ -61,7 +61,9 @@ export function generateDotNxSetup(version?: string) {
     mode: FsConstants.S_IXUSR | FsConstants.S_IRUSR | FsConstants.S_IWUSR,
   });
   const changes = host.listChanges();
-  printChanges(changes);
+  if (process.env.NX_AI_AGENT_INIT !== 'true') {
+    printChanges(changes);
+  }
   flushChanges(host.root, changes);
   // Ensure that the dot-nx installation is available.
   // This is needed when using a global nx with dot-nx, otherwise running any nx command using global command will fail due to missing modules.

packages/nx/src/command-line/init/init-v2.ts

@@ -67,6 +67,13 @@ export async function initHandler(
   options: InitArgs,
   inner = false
 ): Promise<void> {
+  // Set early so all subsequent in-process and subprocess writes (e.g. the
+  // tmp-install fetch log, nx generate output from plugin init generators)
+  // honor NDJSON-only mode.
+  if (isAiAgent()) {
+    process.env.NX_AI_AGENT_INIT = 'true';
+  }
+
   // Use environment variable to force local execution
   if (process.env.NX_USE_LOCAL === 'true' || inner) {
     return await initHandlerImpl(options);
@@ -307,7 +314,9 @@ async function runInit(
       logProgress('detecting', 'Detected non-JavaScript project');
     }
     generateDotNxSetup(version);
-    console.log('');
+    if (!aiMode) {
+      console.log('');
+    }
   } else {
     if (aiMode) {
       logProgress('detecting', 'Detected NPM project');

packages/nx/src/utils/output.ts

@@ -56,6 +56,19 @@ class CLIOutput {
   cliName = 'NX';
   formatCommand = (taskId: string) => `${pc.dim('nx run')} ${taskId}`;
 
+  /**
+   * When running `nx init` under an AI agent we emit only NDJSON on stdout.
+   * All human-formatted output via this class becomes a no-op so the stdout
+   * stream is parseable line-by-line. Callers that need to surface failures
+   * to agents must do so through the structured error event emitted by the
+   * init command (see `writeAiOutput(buildErrorResult(...))`); silent
+   * `output.error` here is intentional — agents check exit code plus the
+   * final NDJSON event, not human-formatted text.
+   */
+  private get isSilenced(): boolean {
+    return process.env.NX_AI_AGENT_INIT === 'true';
+  }
+
   /**
    * Longer dash character which forms more of a continuous line when place side to side
    * with itself, unlike the standard dash character
@@ -86,10 +99,12 @@ class CLIOutput {
   dim = pc.dim;
 
   private writeToStdOut(str: string) {
+    if (this.isSilenced) return;
     process.stdout.write(str);
   }
 
   overwriteLine(lineText: string = '') {
+    if (this.isSilenced) return;
     // Ensure we always start writing from column 0.
     readline.cursorTo(process.stdout, 0);
     // this replaces the existing text up to the new line length

packages/nx/src/utils/package-json.ts

@@ -382,7 +382,9 @@ function preparePackageInstallation(pkg: string, requiredVersion: string) {
     cleanup: () => {},
   };
 
-  console.log(`Fetching ${pkg}...`);
+  if (process.env.NX_AI_AGENT_INIT !== 'true') {
+    console.log(`Fetching ${pkg}...`);
+  }
   const packageManager = detectPackageManager();
   const isVerbose = process.env.NX_VERBOSE_LOGGING === 'true';
   generatePackageManagerFiles(tempDir, packageManager);