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/__tests__/perf/plugin-init-team-mode-resume-defer.test.ts

@@ -4,6 +4,7 @@ import { join } from "node:path"
 
 import type { PluginInput } from "@opencode-ai/plugin"
 import { describe, expect, it } from "bun:test"
+import { unsafeTestValue } from "../../../test-support/unsafe-test-value"
 
 const HUNG_LEAD_SESSION_ID = "ses_999999999fffeeRegrTestHang0"
 
@@ -16,7 +17,7 @@ function makeHangingClient(): {
     hangCount.value += 1
     return new Promise<never>(() => {})
   }
-  const client = testCoerce<PluginInput["client"]>({
+  const client = unsafeTestValue<PluginInput["client"]>({
     session: {
       get: sessionGet,
     },