fix(debug): guarded v8.setFlagsFromString call so CPU profiler works on Bun

The CPU profiler called node:v8 setFlagsFromString("--allow-natives-syntax")
unconditionally and crashed on Bun (oven-sh/bun#1702), surfacing as
"Failed to start profiler: node:v8 setFlagsFromString is not yet
implemented in Bun". The flag is only needed for ad-hoc V8 natives such
as %GetOptimizationStatus, not for the CDP Profiler session that actually
collects samples — so swallow the error and let the inspector path run.

Added a Bun-runtime regression test that would have caught the crash:
without the guard, startCpuProfile() throws before returning a session.

Fixes #3897

packages/coding-agent/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Fixed `omp debug --profile` failing on Bun with "node:v8 setFlagsFromString is not yet implemented in Bun" by treating the optional `--allow-natives-syntax` flag as best-effort, so the CPU profiler proceeds even on runtimes that don't expose `v8.setFlagsFromString`. ([#3897](https://github.com/can1357/oh-my-pi/issues/3897))
+
 ## [16.2.8] - 2026-06-30
 
 ### Added

packages/coding-agent/src/debug/profiler.ts

@@ -114,7 +114,13 @@ function formatProfileAsMarkdown(profileJson: string): string {
  */
 export async function startCpuProfile(): Promise<ProfilerSession> {
 	const v8 = await import("node:v8");
-	v8.setFlagsFromString("--allow-natives-syntax");
+	try {
+		// Enables `%GetOptimizationStatus` and friends when V8 natives are needed
+		// for ad-hoc profiling. Best-effort: Bun does not implement
+		// `setFlagsFromString` (oven-sh/bun#1702) but the CPU profiler itself
+		// works without it, so swallow the error and continue.
+		v8.setFlagsFromString("--allow-natives-syntax");
+	} catch {}
 
 	const { Session } = await import("node:inspector/promises");
 	const session = new Session();

packages/coding-agent/test/debug/profiler.test.ts

@@ -0,0 +1,24 @@
+import { describe, expect, it } from "bun:test";
+import { startCpuProfile } from "@oh-my-pi/pi-coding-agent/debug/profiler";
+
+describe("startCpuProfile", () => {
+	// Regression: `node:v8` `setFlagsFromString` throws on Bun
+	// (oven-sh/bun#1702). The profiler used to call it unconditionally and
+	// crash before connecting the inspector session. Running this test under
+	// Bun guarantees the guard is in place — without it the call below would
+	// reject with "node:v8 setFlagsFromString is not yet implemented in Bun".
+	it("starts and stops successfully even when v8.setFlagsFromString is unavailable", async () => {
+		const session = await startCpuProfile();
+		// Run a tiny bit of work so the profile has at least one sample.
+		let acc = 0;
+		for (let i = 0; i < 10_000; i++) acc += i;
+		expect(acc).toBeGreaterThan(0);
+
+		const profile = await session.stop();
+		const parsed = JSON.parse(profile.data) as { nodes: unknown[] };
+		expect(Array.isArray(parsed.nodes)).toBe(true);
+		expect(parsed.nodes.length).toBeGreaterThan(0);
+		expect(typeof profile.markdown).toBe("string");
+		expect(profile.markdown.length).toBeGreaterThan(0);
+	});
+});