fix: show print mode liveness

packages/coding-agent/src/modes/print-mode.test.ts

@@ -1,6 +1,7 @@
 import assert from "node:assert/strict";
 import { test } from "vitest";
 import {
+	createPrintModeLivenessReporter,
 	PrintModeTimeoutError,
 	promptWithPrintTimeout,
 	resolvePrintModeTimeoutMs,
@@ -79,3 +80,61 @@ test("runPrintMode_when_extension_startup_hangs_still_runs_prompt", async () =>
 		console.log = originalLog;
 	}
 });
+
+test("createPrintModeLivenessReporter_in_text_mode_reports_progress_to_stderr_once", () => {
+	const writes: string[] = [];
+	const originalWrite = process.stderr.write;
+	process.stderr.write = ((chunk: string | Uint8Array) => {
+		writes.push(String(chunk));
+		return true;
+	}) as typeof process.stderr.write;
+	try {
+		const report = createPrintModeLivenessReporter("text");
+		report({ type: "message_start" });
+		report({
+			type: "message_update",
+			assistantMessageEvent: { type: "thinking_start" },
+		});
+		report({
+			type: "message_update",
+			assistantMessageEvent: { type: "thinking_delta" },
+		});
+		report({
+			type: "message_update",
+			assistantMessageEvent: { type: "text_start" },
+		});
+		report({
+			type: "message_update",
+			assistantMessageEvent: { type: "text_delta" },
+		});
+
+		assert.deepEqual(writes, [
+			"[forge] model responding...\n",
+			"[forge] thinking...\n",
+			"[forge] writing response...\n",
+		]);
+	} finally {
+		process.stderr.write = originalWrite;
+	}
+});
+
+test("createPrintModeLivenessReporter_in_json_mode_keeps_stderr_quiet", () => {
+	const writes: string[] = [];
+	const originalWrite = process.stderr.write;
+	process.stderr.write = ((chunk: string | Uint8Array) => {
+		writes.push(String(chunk));
+		return true;
+	}) as typeof process.stderr.write;
+	try {
+		const report = createPrintModeLivenessReporter("json");
+		report({ type: "message_start" });
+		report({
+			type: "message_update",
+			assistantMessageEvent: { type: "thinking_start" },
+		});
+
+		assert.deepEqual(writes, []);
+	} finally {
+		process.stderr.write = originalWrite;
+	}
+});

packages/coding-agent/src/modes/print-mode.ts

@@ -126,6 +126,7 @@ export async function runPrintMode(
 	// Print mode intentionally skips extension session_start binding. One-shot
 	// automation needs bounded prompt output; startup hooks are interactive/RPC
 	// lifecycle work and have previously blocked `sf -p` before the prompt ran.
+	const liveness = createPrintModeLivenessReporter(mode);
 
 	// Always subscribe to enable session persistence via _handleAgentEvent
 	const unsubscribe = session.subscribe((event) => {
@@ -133,6 +134,7 @@ export async function runPrintMode(
 		if (mode === "json") {
 			console.log(JSON.stringify(event));
 		}
+		liveness(event);
 	});
 
 	let exitCode = 0;
@@ -232,3 +234,36 @@ export async function runPrintMode(
 		process.exit(exitCode);
 	}
 }
+
+export function createPrintModeLivenessReporter(
+	mode: "text" | "json",
+): (event: { type: string; assistantMessageEvent?: { type: string } }) => void {
+	if (mode !== "text") return () => {};
+	let sawAssistant = false;
+	let sawThinking = false;
+	let sawText = false;
+	return (event) => {
+		if (event.type === "message_start" && !sawAssistant) {
+			sawAssistant = true;
+			process.stderr.write("[forge] model responding...\n");
+			return;
+		}
+		if (event.type !== "message_update") return;
+		const streamType = event.assistantMessageEvent?.type;
+		if (
+			(streamType === "thinking_start" || streamType === "thinking_delta") &&
+			!sawThinking
+		) {
+			sawThinking = true;
+			process.stderr.write("[forge] thinking...\n");
+			return;
+		}
+		if (
+			(streamType === "text_start" || streamType === "text_delta") &&
+			!sawText
+		) {
+			sawText = true;
+			process.stderr.write("[forge] writing response...\n");
+		}
+	};
+}