fix(drive): reject ambient fixture config

.changeset/isolated-config-root.md

@@ -0,0 +1,5 @@
+---
+"opencode-drive": patch
+---
+
+Reject artifact roots beneath ambient OpenCode configuration instead of silently contaminating isolated fixtures.

packages/drive/src/instance/instance.ts

@@ -1,6 +1,6 @@
-import { mkdir } from "node:fs/promises"
+import { mkdir, stat } from "node:fs/promises"
 import { tmpdir } from "node:os"
-import { join, resolve } from "node:path"
+import { dirname, join, resolve } from "node:path"
 import * as Effect from "effect/Effect"
 import { createScriptFileSystem } from "../script/filesystem.js"
 import {
@@ -20,6 +20,11 @@ export function artifactDirectory() {
 }
 
 export async function initializeInstance(name?: string) {
+  const ambient = await ambientConfigSource(artifactDirectory())
+  if (ambient)
+    throw new Error(
+      `Drive's isolated project would inherit ambient OpenCode configuration from ${ambient}; use a neutral TMPDIR`,
+    )
   const artifacts = resolve(
     join(artifactDirectory(), `run-${crypto.randomUUID()}`),
   )
@@ -53,6 +58,20 @@ export async function initializeInstance(name?: string) {
   return artifacts
 }
 
+async function ambientConfigSource(root: string) {
+  const names = [".opencode", ".claude", ".agents", "opencode.json", "opencode.jsonc"]
+  let directory = dirname(root)
+  while (true) {
+    for (const name of names) {
+      const source = join(directory, name)
+      if (await stat(source).then(() => true, () => false)) return source
+    }
+    const parent = dirname(directory)
+    if (parent === directory) return undefined
+    directory = parent
+  }
+}
+
 export const prepareInstanceProject = Effect.fn("OpenCodeInstance.prepareProject")(function* (options: {
   readonly artifacts: string
     readonly project?: Project

packages/drive/test/cli/integration.test.ts

@@ -154,6 +154,17 @@ describe("opencode-drive", () => {
     })
   })
 
+  test("rejects an artifact root beneath ambient OpenCode configuration", async () => {
+    const root = await temporary()
+    await mkdir(join(root, ".opencode", "skills", "ambient"), { recursive: true })
+    const child = spawn(["init", "--name", "ambient-config"], root)
+    const [status, stderr] = await Promise.all([child.exited, new Response(child.stderr).text()])
+
+    expect(status).toBe(1)
+    expect(stderr).toContain(`would inherit ambient OpenCode configuration from ${join(root, ".opencode")}`)
+    expect(stderr).toContain("use a neutral TMPDIR")
+  })
+
   test("starts, drives, prints dir, restarts, and stops a named detached instance", async () => {
     const root = await temporary()
     const name = "detached-test"