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/session-recovery/storage/readers-from-sdk.test.ts

@@ -1,4 +1,5 @@
 import { describe, expect, it } from "bun:test"
+import { unsafeTestValue } from "../../../../test-support/unsafe-test-value"
 async function importFreshReaders() {
   const token = `${Date.now()}-${Math.random()}`
   const [{ readMessagesFromSDK, readMessages }, { readPartsFromSDK, readParts }] = await Promise.all([
@@ -13,7 +14,7 @@ function createMockClient(handlers: {
   messages?: (sessionID: string) => unknown[]
   message?: (sessionID: string, messageID: string) => unknown
 }) {
-  return testCoerce({
+  return unsafeTestValue({
     session: {
       messages: async (opts: { path: { id: string } }) => {
         if (handlers.messages) {