feat: use tool calls for answer extraction

tests/answer-extraction.test.ts

@@ -2,6 +2,9 @@ import assert from "node:assert/strict";
 import test from "node:test";
 import {
 	collectExtractionBusinessIssues,
+	createExtractionContext,
+	extractionCandidateFromContent,
+	parseExtractionCandidate,
 	repairExtractionParams,
 	selectExtractionModel,
 } from "../src/answer-extraction.ts";
@@ -124,3 +127,111 @@ test("selectExtractionModel validates fallback model auth", async () => {
 		error: "No auth for fallback chat model: fallback/c.",
 	});
 });
+
+test("extraction context includes the tool and preceding turn", () => {
+	const context = createExtractionContext({
+		assistantText: "Which direction: A or B?",
+		attempt: 0,
+		lastError: "",
+		lastResponse: "",
+		previousUserText: "Choose an implementation direction.",
+	});
+
+	assert.equal(context.tools?.[0]?.name, "ask_user");
+	assert.equal(context.tools?.length, 1);
+	const prompt = JSON.stringify(context.messages[0]?.content);
+	assert.equal(prompt.includes("Choose an implementation direction."), true);
+	assert.equal(prompt.includes("Which direction: A or B?"), true);
+});
+
+test("tool-call arguments become the extraction candidate", () => {
+	const candidate = extractionCandidateFromContent([
+		{ type: "thinking", thinking: "ignored" },
+		{
+			type: "toolCall",
+			id: "call-1",
+			name: "ask_user",
+			arguments: {
+				title: "Direction",
+				questions: [
+					{
+						id: "direction",
+						prompt: "Which direction?",
+						options: [{ value: "a", label: "A" }],
+					},
+				],
+			},
+		},
+	] as never);
+	const result = parseExtractionCandidate(candidate);
+
+	assert.equal(result.ok, true);
+	if (result.ok) {
+		assert.equal(result.params.title, "Direction");
+	}
+});
+
+test("tool-call arguments take precedence over text", () => {
+	const candidate = extractionCandidateFromContent([
+		{ type: "text", text: "not JSON" },
+		{
+			type: "toolCall",
+			id: "call-1",
+			name: "ask_user",
+			arguments: { questions: [] },
+		},
+	] as never);
+
+	assert.equal(parseExtractionCandidate(candidate).ok, true);
+});
+
+test("multiple tool calls are rejected", () => {
+	const candidate = extractionCandidateFromContent([
+		{
+			type: "toolCall",
+			id: "call-1",
+			name: "ask_user",
+			arguments: { questions: [] },
+		},
+		{
+			type: "toolCall",
+			id: "call-2",
+			name: "ask_user",
+			arguments: { questions: [] },
+		},
+	] as never);
+
+	assert.equal(parseExtractionCandidate(candidate).ok, false);
+});
+
+test("fenced text remains a fallback", () => {
+	const result = parseExtractionCandidate('```json\n{"questions":[]}\n```');
+	assert.equal(result.ok, true);
+});
+
+test("semantic validation issues are returned for retry feedback", () => {
+	const result = parseExtractionCandidate(
+		JSON.stringify({
+			questions: [
+				{
+					id: "duplicate",
+					prompt: "First?",
+					options: [{ value: "a", label: "A" }],
+				},
+				{
+					id: "duplicate",
+					prompt: "Second?",
+					options: [{ value: "b", label: "B" }],
+				},
+			],
+		})
+	);
+
+	assert.equal(result.ok, true);
+	if (result.ok) {
+		assert.equal(
+			result.issues.some((issue) => issue.includes("duplicate")),
+			true
+		);
+	}
+});