test: make unsafe test coercion explicit

Move test coercion out of a hidden global and require each test to import the helper so review tools and runtime scripts can see the unsafe boundary.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/tools/delegate-task/metadata-await.test.ts

@@ -2,6 +2,7 @@ const { describe, test, expect } = require("bun:test")
 
 import { executeBackgroundTask } from "./executor"
 import type { DelegateTaskArgs, ToolContextWithMetadata } from "./types"
+import { unsafeTestValue } from "../../../test-support/unsafe-test-value"
 
 describe("task tool metadata awaiting", () => {
   test("executeBackgroundTask awaits ctx.metadata before returning", async () => {
@@ -28,7 +29,7 @@ describe("task tool metadata awaiting", () => {
       subagent_type: "explore",
     }
 
-    const executorCtx = testCoerce({
+    const executorCtx = unsafeTestValue({
       manager: {
         launch: async () => ({
           id: "task_1",