test(prompts-core): audit OpenCode coupling boundary

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

packages/prompts-core/test/opencode-coupling-audit.test.ts

@@ -0,0 +1,63 @@
+import { describe, expect, test } from "bun:test"
+import { readdir, readFile } from "node:fs/promises"
+import { dirname, extname, join } from "node:path"
+import { fileURLToPath } from "node:url"
+
+type CouplingMatch = {
+  readonly filePath: string
+  readonly lineNumber: number
+  readonly line: string
+}
+
+const forbiddenImportPatterns = [/from\s+["']@opencode-ai\//, /from\s+["']\.\.\/opencode\//] as const
+
+async function collectTypeScriptFiles(directory: string): Promise<readonly string[]> {
+  const entries = await readdir(directory, { withFileTypes: true })
+  const files: string[] = []
+
+  for (const entry of entries) {
+    const childPath = join(directory, entry.name)
+    if (entry.isDirectory()) {
+      files.push(...(await collectTypeScriptFiles(childPath)))
+      continue
+    }
+
+    if (entry.isFile() && extname(entry.name) === ".ts") {
+      files.push(childPath)
+    }
+  }
+
+  return files
+}
+
+function findForbiddenImports(filePath: string, content: string): readonly CouplingMatch[] {
+  const matches: CouplingMatch[] = []
+  const lines = content.split(/\r?\n/)
+
+  for (const [index, line] of lines.entries()) {
+    if (!forbiddenImportPatterns.some((pattern) => pattern.test(line))) continue
+    matches.push({ filePath, lineNumber: index + 1, line })
+  }
+
+  return matches
+}
+
+describe("opencode coupling audit", () => {
+  test("#given prompts-core source #when scanning imports #then no OpenCode adapter imports exist", async () => {
+    // given
+    const packageRoot = dirname(dirname(fileURLToPath(import.meta.url)))
+    const srcRoot = join(packageRoot, "src")
+    const sourceFiles = await collectTypeScriptFiles(srcRoot)
+    const matches: CouplingMatch[] = []
+
+    // when
+    for (const filePath of sourceFiles) {
+      const content = await readFile(filePath, "utf8")
+      matches.push(...findForbiddenImports(filePath, content))
+    }
+
+    // then
+    console.info("opencode coupling matches:", JSON.stringify(matches))
+    expect(matches).toEqual([])
+  })
+})