fix(opencode): isHealthy() must reject 401 to prevent stale-orphan adoption

The previous semantic 'response.statusCode === 401 || isHealthResponse(body)' allowed isHealthy() to return true even when the server rejected the manager's password. On IDE restart, this caused the new manager (with a fresh password Y2) to falsely adopt an orphan opencode-serve from the previous IDE session that was still running with the old password Y1. The SPA proxy then forwarded requests with Y2; opencode rejected with 401; the user saw 'Error: Unauthorized' loading the chat UI.

Fix: only treat the server as healthy when it returns a parseable health body (200 OK with {healthy:true, version:...}). 401 now returns false so doStart() falls through to killStaleServer(), which SIGKILLs the orphan and spawns a fresh opencode-serve with the current password.

If a future test or user genuinely needs 'adopt an external server with unknown password' semantic, the right path is to read the password from that external server's data dir / env, not to ignore auth failures.

Author: cpkt9762

src/vs/workbench/contrib/opencode/electron-main/opencodeServeManager.ts

@@ -394,7 +394,7 @@ export class OpencodeServeManager
 	): Promise<boolean> {
 		try {
 			const response = await this.readHealth(url, password);
-			return response.statusCode === 401 || isHealthResponse(response.body);
+			return isHealthResponse(response.body);
 		} catch {
 			return false;
 		}

src/vs/workbench/contrib/opencode/test/electron-main/opencodeServeManager.test.ts

@@ -421,11 +421,11 @@ suite('OpencodeServeManager / health checks', () => {
 		assert.strictEqual(await internals(manager).isHealthy(`http://127.0.0.1:${backend.port}`, undefined), true);
 	});
 
-	test('isHealthy returns true on HTTP 401 (auth required = server alive)', async () => {
+	test('isHealthy returns false on HTTP 401 (auth required but wrong credentials)', async () => {
 		backend = await mockBackend({ status: 401 });
 		manager = new TestableOpencodeServeManager(configuration(), new NullLogService());
 
-		assert.strictEqual(await internals(manager).isHealthy(`http://127.0.0.1:${backend.port}`, undefined), true);
+		assert.strictEqual(await internals(manager).isHealthy(`http://127.0.0.1:${backend.port}`, undefined), false);
 	});
 
 	test('isHealthy returns false on HTTP 500', async () => {