Add validateFixtures checks for turnIndex and hasToolResult

JSON fixtures bypass TypeScript's type system, so invalid values like
turnIndex: -1, turnIndex: 1.5, turnIndex: "zero", or hasToolResult: "yes"
would silently pass validation but fail to match at runtime. Add runtime
type checks for both fields and corresponding unit tests.

Author: jpr5

src/__tests__/fixture-loader.test.ts

@@ -800,6 +800,68 @@ describe("validateFixtures", () => {
     expect(validateFixtures(fixtures)).toHaveLength(0);
   });
 
+  // --- match.turnIndex / match.hasToolResult type checks ---
+
+  it("error: turnIndex is negative", () => {
+    const fixtures = [makeFixture({ match: { userMessage: "test", turnIndex: -1 } })];
+    const results = validateFixtures(fixtures);
+    expect(
+      results.some((r) => r.severity === "error" && r.message.includes("turnIndex")),
+    ).toBe(true);
+  });
+
+  it("error: turnIndex is a float", () => {
+    const fixtures = [makeFixture({ match: { userMessage: "test", turnIndex: 1.5 } })];
+    const results = validateFixtures(fixtures);
+    expect(
+      results.some((r) => r.severity === "error" && r.message.includes("turnIndex")),
+    ).toBe(true);
+  });
+
+  it("error: turnIndex is a string", () => {
+    const fixtures = [
+      makeFixture({ match: { userMessage: "test", turnIndex: "zero" as never } }),
+    ];
+    const results = validateFixtures(fixtures);
+    expect(
+      results.some((r) => r.severity === "error" && r.message.includes("turnIndex")),
+    ).toBe(true);
+  });
+
+  it("no error: turnIndex is 0 (falsy but valid)", () => {
+    const fixtures = [makeFixture({ match: { userMessage: "test", turnIndex: 0 } })];
+    const results = validateFixtures(fixtures);
+    expect(results.filter((r) => r.message.includes("turnIndex"))).toHaveLength(0);
+  });
+
+  it("no error: turnIndex is a positive integer", () => {
+    const fixtures = [makeFixture({ match: { userMessage: "test", turnIndex: 3 } })];
+    const results = validateFixtures(fixtures);
+    expect(results.filter((r) => r.message.includes("turnIndex"))).toHaveLength(0);
+  });
+
+  it("error: hasToolResult is a string", () => {
+    const fixtures = [
+      makeFixture({ match: { userMessage: "test", hasToolResult: "yes" as never } }),
+    ];
+    const results = validateFixtures(fixtures);
+    expect(
+      results.some((r) => r.severity === "error" && r.message.includes("hasToolResult")),
+    ).toBe(true);
+  });
+
+  it("no error: hasToolResult is false (falsy but valid)", () => {
+    const fixtures = [makeFixture({ match: { userMessage: "test", hasToolResult: false } })];
+    const results = validateFixtures(fixtures);
+    expect(results.filter((r) => r.message.includes("hasToolResult"))).toHaveLength(0);
+  });
+
+  it("no error: hasToolResult is true", () => {
+    const fixtures = [makeFixture({ match: { userMessage: "test", hasToolResult: true } })];
+    const results = validateFixtures(fixtures);
+    expect(results.filter((r) => r.message.includes("hasToolResult"))).toHaveLength(0);
+  });
+
   // --- Warning checks ---
 
   it("warning: duplicate userMessage", () => {

src/fixture-loader.ts

@@ -531,6 +531,28 @@ export function validateFixtures(fixtures: Fixture[]): ValidationResult[] {
       }
     }
 
+    // Match field type checks
+    if (f.match.turnIndex !== undefined) {
+      if (
+        typeof f.match.turnIndex !== "number" ||
+        f.match.turnIndex < 0 ||
+        !Number.isInteger(f.match.turnIndex)
+      ) {
+        results.push({
+          severity: "error",
+          fixtureIndex: i,
+          message: "match.turnIndex must be a non-negative integer",
+        });
+      }
+    }
+    if (f.match.hasToolResult !== undefined && typeof f.match.hasToolResult !== "boolean") {
+      results.push({
+        severity: "error",
+        fixtureIndex: i,
+        message: `match.hasToolResult must be a boolean, got ${typeof f.match.hasToolResult}`,
+      });
+    }
+
     // --- Warning checks ---
 
     // Duplicate userMessage shadowing — include turnIndex, hasToolResult, and