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/hooks/atlas/recent-model-resolver.test.ts

@@ -1,11 +1,12 @@
 import { describe, expect, mock, test } from "bun:test"
 import type { PluginInput } from "@opencode-ai/plugin"
 import { resolveRecentPromptContextForSession } from "./recent-model-resolver"
+import { unsafeTestValue } from "../../../test-support/unsafe-test-value"
 
 describe("resolveRecentPromptContextForSession", () => {
   test("uses message time.created rather than SDK array order for recent prompt context", async () => {
     // given
-    const ctx = testCoerce<PluginInput>({
+    const ctx = unsafeTestValue<PluginInput>({
       client: {
         session: {
           messages: mock(async () => ({