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

[jaysoo]

Current Behavior

nx init interleaves three styles of stdout under an AI agent:

Fetching nx...
{"stage":"starting","message":"Initializing Nx..."}
CREATE nx.json
UPDATE .gitignore
{"stage":"complete","success":true,...,"userNextSteps":{...}}

---USER_NEXT_STEPS---
[DISPLAY] Show the user these next steps to complete setup:
1. Explore your workspace
   Run: nx graph
...
---END---

Agents have to do line-by-line heuristics, and the trailing ---USER_NEXT_STEPS--- block duplicates userNextSteps already in the complete JSON event.

Expected Behavior

When isAiAgent() is true, stdout is pure NDJSON — one JSON object per line, nothing else.

Implementation:

• Outer initHandler sets process.env.NX_AI_AGENT_INIT=true early. The sentinel survives the tmp-install re-entry into the subprocess and is inherited by nx g <plugin>:init via runNxSync.
• CLIOutput (utils/output.ts) gates writeToStdOut/overwriteLine on the sentinel — all output.log/note/success/warn/error becomes a no-op. Errors still surface to agents through the structured error NDJSON event emitted by recordInitError (and via process exit code).
• console.log('Fetching ${pkg}...') (utils/package-json.ts), printChanges() for dot-nx setup (add-nx-scripts.ts), and printChanges() in generate.ts (plugin init subprocess) gate on the same sentinel.
• The stray console.log('') after generateDotNxSetup is now suppressed under agent mode.
• writeAiOutput no longer appends the ---USER_NEXT_STEPS--- ... ---END--- block — agents render userNextSteps from the structured complete event.

Human TTY behavior is unchanged. Detection logic in ai.rs is untouched (relies on existing CLAUDECODE / Cursor / OpenCode / Gemini / Replit signals).

Smoke tests:

# AI agent — pure NDJSON
CLAUDECODE=1 npx nx@latest init --interactive=false --plugins=skip --nxCloud=false
# {"stage":"starting","message":"Initializing Nx..."}
# {"stage":"detecting","message":"Detected NPM project"}
# {"stage":"configuring","message":"Creating nx.json..."}
# {"stage":"detecting","message":"Skipping plugin installation"}
# {"stage":"complete","success":true,...,"userNextSteps":{...}}

# Human — unchanged
npx nx@latest init --interactive=false --nxCloud=false
#  NX   🐳 Nx initialization
#  NX   📦 Installing dependencies
#  NX   🎉 Done!

Related Issue(s)

Fixes NXC-4368

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☁️ Nx Cloud last updated this comment at 2026-05-01 22:14:35 UTC

[nx-cloud]

✅ The fix from Nx Cloud was applied automatically

We ran Prettier on astro-docs/src/content/docs/reference/environment-variables.mdoc to fix the astro-docs:format failure. The PR's documentation commit added a new NX_AI_AGENT_INIT table row whose description exceeded the existing Markdown table column width, causing Prettier's alignment check to fail. Expanding all Description column cells to the new maximum width resolves the formatting error.

Tip

✅ We verified this fix by re-running astro-docs:format.

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