refactor: unify tool reason requirements

tests/opencode/toolReason.test.ts

@@ -0,0 +1,14 @@
+import { describe, expect, it } from "bun:test";
+import { optionalToolReason, toolReason } from "../../.opencode/tool-reason.js";
+
+describe("tool reason contract", () => {
+  it("allows omitted purpose but requires a nonblank business reason", () => {
+    expect(optionalToolReason.parse(undefined)).toBeUndefined();
+    expect(toolReason.safeParse(undefined).success).toBeFalse();
+    for (const schema of [optionalToolReason, toolReason]) {
+      expect(schema.parse("  核验压力异常  ")).toBe("核验压力异常");
+      expect(schema.safeParse("   ").success).toBeFalse();
+      expect(schema.safeParse("x".repeat(2001)).success).toBeFalse();
+    }
+  });
+});