From 0b187b9f62f1e1a7a67a74d1abb5a9fb34e19dc2 Mon Sep 17 00:00:00 2001
From: Mikael Hugo <mikkihugo@users.noreply.github.com>
Date: Fri, 15 May 2026 20:12:00 +0200
Subject: [PATCH] fix(headless): remove legacy v1 fallback path

---
 src/headless.ts                         | 38 +++++++++++--------------
 src/tests/headless-v2-migration.test.ts | 22 +++-----------
 2 files changed, 20 insertions(+), 40 deletions(-)

diff --git a/src/headless.ts b/src/headless.ts
index 2a069e0e6..dc924b79a 100644
--- a/src/headless.ts
+++ b/src/headless.ts
@@ -105,7 +105,6 @@ import {
 } from "./resources/extensions/sf/trace-collector.js";
 
 const HEADLESS_HEARTBEAT_INTERVAL_MS = 60_000;
-const HEADLESS_LEGACY_FALLBACK_ENV = "SF_HEADLESS_ALLOW_V1_FALLBACK";
 
 interface HeadlessTimeoutSolverEvalRecord {
 	runId: string;
@@ -1983,27 +1982,22 @@ async function runHeadlessOnce(
 		process.exit(1);
 	}
 
-		// v2 protocol negotiation — attempt init for structured completion events
-		let _v2Enabled = false;
-		try {
-			await client.init({ clientId: "sf-headless" });
-			_v2Enabled = true;
-		} catch (initErr) {
-			const reason = initErr instanceof Error ? initErr.message : String(initErr);
-			if (process.env[HEADLESS_LEGACY_FALLBACK_ENV] !== "1") {
-				process.stderr.write(
-					`[headless] v2 init failed (${reason}); refusing legacy v1 string-matching fallback. Set ${HEADLESS_LEGACY_FALLBACK_ENV}=1 only for explicit recovery.\n`,
-				);
-				await client.stop().catch(() => {});
-				if (timeoutTimer) clearTimeout(timeoutTimer);
-				if (idleTimer) clearTimeout(idleTimer);
-				if (heartbeatTimer) clearInterval(heartbeatTimer);
-				process.exit(EXIT_ERROR);
-			}
-			process.stderr.write(
-				`[headless] Warning: v2 init failed (${reason}), falling back to v1 string-matching because ${HEADLESS_LEGACY_FALLBACK_ENV}=1\n`,
-			);
-		}
+	// v2 protocol negotiation — attempt init for structured completion events
+	let _v2Enabled = false;
+	try {
+		await client.init({ clientId: "sf-headless" });
+		_v2Enabled = true;
+	} catch (initErr) {
+		const reason = initErr instanceof Error ? initErr.message : String(initErr);
+		process.stderr.write(
+			`[headless] v2 init failed (${reason}); refusing legacy v1 string-matching fallback.\n`,
+		);
+		await client.stop().catch(() => {});
+		if (timeoutTimer) clearTimeout(timeoutTimer);
+		if (idleTimer) clearTimeout(idleTimer);
+		if (heartbeatTimer) clearInterval(heartbeatTimer);
+		process.exit(EXIT_ERROR);
+	}
 
 	clientStarted = true;
 
diff --git a/src/tests/headless-v2-migration.test.ts b/src/tests/headless-v2-migration.test.ts
index 76a6d8db8..45e9a29a3 100644
--- a/src/tests/headless-v2-migration.test.ts
+++ b/src/tests/headless-v2-migration.test.ts
@@ -97,17 +97,13 @@ class MockRpcClient {
 
 async function negotiateV2ForTest(
 	client: MockRpcClient,
-	allowLegacyFallback = false,
-): Promise<"v2" | "legacy" | "fatal"> {
+): Promise<"v2" | "fatal"> {
 	try {
 		await client.init({ clientId: "sf-headless" });
 		return "v2";
 	} catch {
-		if (!allowLegacyFallback) {
-			await client.stop();
-			return "fatal";
-		}
-		return "legacy";
+		await client.stop();
+		return "fatal";
 	}
 }
 
@@ -526,7 +522,7 @@ test("v2 init success sets v2Enabled", async () => {
 		await client.init({ clientId: "sf-headless" });
 		v2Enabled = true;
 	} catch {
-		// fall back to v1
+		await client.stop();
 	}
 
 	assert.equal(client.initCalled, true);
@@ -543,16 +539,6 @@ test("v2 init failure is fatal by default", async () => {
 	assert.equal(mode, "fatal");
 });
 
-test("v2 init failure uses v1 only with explicit legacy fallback opt-in", async () => {
-	const client = new MockRpcClient();
-	client.initShouldFail = true;
-	const mode = await negotiateV2ForTest(client, true);
-
-	assert.equal(client.initCalled, true);
-	assert.equal(client.stopCalled, false);
-	assert.equal(mode, "legacy");
-});
-
 // ─── injector adapter ───────────────────────────────────────────────────────
 
 test("injector adapter parses serialized JSONL and calls sendUIResponse", () => {