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/tools/hashline-edit/normalize-edits.test.ts

@@ -1,5 +1,6 @@
 import { describe, expect, it } from "bun:test"
 import { normalizeHashlineEdits, type RawHashlineEdit } from "./normalize-edits"
+import { unsafeTestValue } from "../../../test-support/unsafe-test-value"
 
 describe("normalizeHashlineEdits", () => {
   it("maps replace with pos to replace", () => {
@@ -51,7 +52,7 @@ describe("normalizeHashlineEdits", () => {
 
   it("rejects legacy payload without op", () => {
     //#given
-    const input = testCoerce<Parameters<
+    const input = unsafeTestValue<Parameters<
       typeof normalizeHashlineEdits
     >[0]>([{ type: "set_line", line: "2#VK", text: "updated" }])
 

src/tools/hashline-edit/tools.test.ts

@@ -6,9 +6,10 @@ import { canonicalizeFileText } from "./file-text-canonicalization"
 import * as fs from "node:fs"
 import * as os from "node:os"
 import * as path from "node:path"
+import { unsafeTestValue } from "../../../test-support/unsafe-test-value"
 
 function createMockContext(): ToolContext {
-  return testCoerce<ToolContext>({
+  return unsafeTestValue<ToolContext>({
     sessionID: "test",
     messageID: "test",
     agent: "test",