fix(runtime): derive unattributed cost from usage status

tests/unit/worker-message-schema.test.ts

@@ -0,0 +1,43 @@
+import { describe, expect, it } from "vitest";
+import { workerMessageSchema } from "../../src/main/worker/entry/types";
+
+const RUN_ID = "00000000-0000-4000-8000-000000000001";
+
+describe("worker message schema", () => {
+  it("accepts run-finished messages keyed by usage status", () => {
+    expect(
+      workerMessageSchema.safeParse({
+        type: "run-finished",
+        runId: RUN_ID,
+        status: "failed",
+        summary: null,
+        errorMessage: "Agent stopped with error.",
+        exitCode: null,
+        signal: null,
+        model: "gpt-5.4",
+        usageStatus: "error_stop",
+        inputTokens: 12,
+        outputTokens: 1,
+      }).success,
+    ).toBe(true);
+  });
+
+  it("rejects legacy unattributed-cost truth in run-finished messages", () => {
+    expect(
+      workerMessageSchema.safeParse({
+        type: "run-finished",
+        runId: RUN_ID,
+        status: "failed",
+        summary: null,
+        errorMessage: "Agent stopped with error.",
+        exitCode: null,
+        signal: null,
+        model: "gpt-5.4",
+        usageStatus: "error_stop",
+        unattributedCost: false,
+        inputTokens: 12,
+        outputTokens: 1,
+      }).success,
+    ).toBe(false);
+  });
+});