test(prompts-core): audit opencode coupling

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 +1,42 @@
+import { describe, expect, test } from "bun:test"
+import { readdir, readFile } from "node:fs/promises"
+import { dirname, join } from "node:path"
+import { fileURLToPath } from "node:url"
+
+const SOURCE_DIR = join(dirname(fileURLToPath(import.meta.url)), "../src")
+
+describe("opencode coupling audit", () => {
+  test("#given prompts-core source #then no file imports @opencode-ai packages", async () => {
+    const offenders = await findOpenCodeImports(SOURCE_DIR)
+
+    expect(offenders).toEqual([])
+  })
+})
+
+async function findOpenCodeImports(sourceDir: string): Promise<readonly string[]> {
+  const files = await collectTypeScriptFiles(sourceDir)
+  const offenders: string[] = []
+
+  for (const filePath of files) {
+    const source = await readFile(filePath, "utf8")
+    if (source.includes("@opencode-ai")) offenders.push(filePath)
+  }
+
+  return offenders
+}
+
+async function collectTypeScriptFiles(directory: string): Promise<readonly string[]> {
+  const entries = await readdir(directory, { withFileTypes: true })
+  const files: string[] = []
+
+  for (const entry of entries) {
+    const entryPath = join(directory, entry.name)
+    if (entry.isDirectory()) {
+      files.push(...(await collectTypeScriptFiles(entryPath)))
+    } else if (entry.isFile() && entry.name.endsWith(".ts")) {
+      files.push(entryPath)
+    }
+  }
+
+  return files
+}