fix(core): harden unified tool runtime (#31171)

packages/core/test/public-tool.test.ts

@@ -0,0 +1,13 @@
+import { describe, expect, it } from "bun:test"
+import { Tool } from "@opencode-ai/core/public"
+import { Effect } from "effect"
+
+describe("public Tool API", () => {
+  it("keeps the public registration capability narrow", () => {
+    const tools = {
+      register: () => Effect.void,
+    } satisfies Tool.Interface
+
+    expect(Object.keys(tools)).toEqual(["register"])
+  })
+})