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/features/background-agent/manager-session-permission.test.ts

@@ -4,6 +4,7 @@ import { tmpdir } from "node:os"
 import type { PluginInput } from "@opencode-ai/plugin"
 
 import { BackgroundManager } from "./manager"
+import { unsafeTestValue } from "../../../test-support/unsafe-test-value"
 
 describe("BackgroundManager session permission", () => {
   test("passes query directory when loading the parent session", async () => {
@@ -21,7 +22,7 @@ describe("BackgroundManager session permission", () => {
       },
     }
     const directory = tmpdir()
-    const manager = new BackgroundManager({ pluginContext: testCoerce<PluginInput>({ client, directory }) })
+    const manager = new BackgroundManager({ pluginContext: unsafeTestValue<PluginInput>({ client, directory }) })
 
     // when
     await manager.launch({
@@ -62,7 +63,7 @@ describe("BackgroundManager session permission", () => {
         abort: async () => ({}),
       },
     }
-    const manager = new BackgroundManager({ pluginContext: testCoerce<PluginInput>({ client, directory: tmpdir() }) })
+    const manager = new BackgroundManager({ pluginContext: unsafeTestValue<PluginInput>({ client, directory: tmpdir() }) })
 
     // when
     await manager.launch({