fix(coding-agent,ai): fallback to /proc/self/environ in Bun sandbox (#3801)

Bun compiled binaries have an empty process.env when running inside
sandbox environments (e.g. nono on Linux/macOS). This broke API key
detection and model discovery because all process.env.* lookups returned
undefined.

- Add restoreSandboxEnv() helper that reads /proc/self/environ when Bun
  is detected and process.env is empty, populating process.env before
  any other code runs (coding-agent/src/bun/cli.ts entry point)
- Add getProcEnv() fallback in env-api-keys.ts for direct @mariozechner/pi-ai
  consumers that may not go through the coding-agent entry point
- Add unit tests for restoreSandboxEnv

packages/coding-agent/src/bun/cli.ts

@@ -4,5 +4,9 @@ import { APP_NAME } from "../config.js";
 process.title = APP_NAME;
 process.emitWarning = (() => {}) as typeof process.emitWarning;
 
+import { restoreSandboxEnv } from "./restore-sandbox-env.js";
+
+restoreSandboxEnv();
+
 await import("./register-bedrock.js");
 await import("../cli.js");

packages/coding-agent/src/bun/restore-sandbox-env.ts

@@ -0,0 +1,32 @@
+/**
+ * Workaround for https://github.com/oven-sh/bun/issues/27802
+ *
+ * Bun compiled binaries have an empty `process.env` when running inside
+ * sandbox environments (e.g. nono on Linux/macOS). On Linux we can recover
+ * the environment from `/proc/self/environ`.
+ */
+
+import { readFileSync } from "node:fs";
+
+/**
+ * Restore environment variables from `/proc/self/environ` when running
+ * inside a sandbox where Bun's `process.env` is empty.
+ */
+export function restoreSandboxEnv(): void {
+	if (!process.versions?.bun) return;
+
+	// If process.env already has entries, nothing to fix.
+	if (Object.keys(process.env).length > 0) return;
+
+	try {
+		const data = readFileSync("/proc/self/environ", "utf-8");
+		for (const entry of data.split("\0")) {
+			const idx = entry.indexOf("=");
+			if (idx > 0) {
+				process.env[entry.slice(0, idx)] = entry.slice(idx + 1);
+			}
+		}
+	} catch {
+		// /proc/self/environ may not be readable; ignore.
+	}
+}