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/category-skill-reminder/index.test.ts

@@ -3,6 +3,7 @@ import { createCategorySkillReminderHook } from "./index"
 import { updateSessionAgent, clearSessionAgent, _resetForTesting } from "../../features/claude-code-session-state"
 import type { AvailableSkill } from "../../agents/dynamic-agent-prompt-builder"
 import * as sharedModule from "../../shared"
+import { unsafeTestValue } from "../../../test-support/unsafe-test-value"
 
 describe("category-skill-reminder hook", () => {
   let logCalls: Array<{ msg: string; data?: unknown }>
@@ -21,7 +22,7 @@ describe("category-skill-reminder hook", () => {
   })
 
   function createMockPluginInput() {
-    return testCoerce({
+    return unsafeTestValue({
       client: {
         tui: {
           showToast: async () => {},