From 59ecd2a4d8b488ffca1c702084f1999fd65e33d2 Mon Sep 17 00:00:00 2001
From: can1357 <me@can.ac>
Date: Mon, 13 Jul 2026 18:53:19 +0200
Subject: [PATCH] refactor(coding-agent/modes): added ACP type guards for
 elicitation narrowing

- Added `isAcceptedElicitation` in the ACP agent to narrow accepted elicitations before accessing response content.
- Added `isFormElicitation` in ACP tests and used it to narrow form-mode requests before assertions.
---
 packages/coding-agent/src/modes/acp/acp-agent.ts |  9 ++++++++-
 packages/coding-agent/test/acp-agent.test.ts     | 15 +++++++++++----
 2 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/packages/coding-agent/src/modes/acp/acp-agent.ts b/packages/coding-agent/src/modes/acp/acp-agent.ts
index 5b31ec935..3bca86ddc 100644
--- a/packages/coding-agent/src/modes/acp/acp-agent.ts
+++ b/packages/coding-agent/src/modes/acp/acp-agent.ts
@@ -351,12 +351,19 @@ async function elicitFromAcpClient(
 			finish(undefined);
 		});
 	const response = await promise;
-	if (response?.action !== "accept" || !response.content) {
+	if (!isAcceptedElicitation(response) || !response.content) {
 		return undefined;
 	}
 	return response.content.value;
 }
 
+/** Narrows a `CreateElicitationResponse` to the accepted-with-content branch; the SDK's `action: string` catch-all arm otherwise defeats literal narrowing on `action !== "accept"`. */
+function isAcceptedElicitation(
+	response: CreateElicitationResponse | undefined,
+): response is Extract<CreateElicitationResponse, { action: "accept" }> {
+	return response?.action === "accept";
+}
+
 /**
  * Build an {@link ExtensionUIContext} that translates skill/extension UI
  * requests into ACP elicitations against `connection` for the session
diff --git a/packages/coding-agent/test/acp-agent.test.ts b/packages/coding-agent/test/acp-agent.test.ts
index f8892c557..886fedb6c 100644
--- a/packages/coding-agent/test/acp-agent.test.ts
+++ b/packages/coding-agent/test/acp-agent.test.ts
@@ -2244,6 +2244,13 @@ describe("ACP agent", () => {
 			return { connection, calls };
 		}
 
+		/** Narrows `CreateElicitationRequest` to the `mode: "form"` branch; the SDK's `mode: string` catch-all arm otherwise defeats literal narrowing on `mode !== "form"`. */
+		function isFormElicitation(
+			request: CreateElicitationRequest,
+		): request is Extract<CreateElicitationRequest, { mode: "form" }> {
+			return request.mode === "form";
+		}
+
 		it("translates select to a single-property string-enum elicitation", async () => {
 			const { connection, calls } = createElicitConnection(async () => ({
 				action: "accept",
@@ -2258,7 +2265,7 @@ describe("ACP agent", () => {
 			const request = calls[0]!;
 			expect(request.mode).toBe("form");
 			expect(request.message).toBe("Pick one");
-			if (request.mode !== "form" || !("sessionId" in request)) {
+			if (!isFormElicitation(request) || !("sessionId" in request)) {
 				throw new Error("expected session-scoped form elicitation");
 			}
 			expect(request.sessionId).toBe("session-select");
@@ -2281,7 +2288,7 @@ describe("ACP agent", () => {
 			expect(result).toBe(true);
 			expect(calls).toHaveLength(1);
 			const request = calls[0]!;
-			if (request.mode !== "form") {
+			if (!isFormElicitation(request)) {
 				throw new Error("expected form-mode elicitation");
 			}
 			expect(request.message).toBe("Proceed?\n\nThis will overwrite the file.");
@@ -2301,7 +2308,7 @@ describe("ACP agent", () => {
 			expect(result).toBe("claude");
 			expect(calls).toHaveLength(1);
 			const request = calls[0]!;
-			if (request.mode !== "form") {
+			if (!isFormElicitation(request)) {
 				throw new Error("expected form-mode elicitation");
 			}
 			expect(request.message).toBe("Your name?");
@@ -2450,7 +2457,7 @@ describe("ACP agent", () => {
 
 			expect(calls).toHaveLength(1);
 			const request = calls[0]!;
-			if (request.mode !== "form") throw new Error("expected form-mode elicitation");
+			if (!isFormElicitation(request)) throw new Error("expected form-mode elicitation");
 			expect(request.requestedSchema.properties?.value).toEqual({ type: "string" });
 		});