feat(coding-agent): set PI_CODING_AGENT=true env var at startup

closes #2868

packages/coding-agent/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Added
+
+- Set `PI_CODING_AGENT=true` environment variable at startup so sub-processes can detect they are running inside the coding agent ([#2868](https://github.com/badlogic/pi-mono/issues/2868))
+
 ## [0.66.1] - 2026-04-08
 
 ### Changed

packages/coding-agent/src/cli.ts

@@ -6,6 +6,7 @@
  * Test with: npx tsx src/cli-new.ts [args...]
  */
 process.title = "pi";
+process.env.PI_CODING_AGENT = "true";
 process.emitWarning = (() => {}) as typeof process.emitWarning;
 
 import { EnvHttpProxyAgent, setGlobalDispatcher } from "undici";