diff --git a/tests/fixtures/compat-caller-extension.ts b/tests/fixtures/compat-caller-extension.ts
index 214533f..a028299 100644
--- a/tests/fixtures/compat-caller-extension.ts
+++ b/tests/fixtures/compat-caller-extension.ts
@@ -2,12 +2,45 @@
  * Test fixture: a sibling extension that streams through the pi-ai compat
  * entrypoint with the active session model, the way background-agent
  * extensions do. Registers `/compat-call` so the test can drive it over RPC.
+ *
+ * Types are declared inline so the fixture has no typecheck dependency on the
+ * optional pi peer packages; the host's extension loader resolves the import.
  */
 
-import { streamSimple } from "@earendil-works/pi-ai/compat"
-import type { ExtensionAPI } from "@earendil-works/pi-coding-agent"
+// @ts-expect-error pi resolves this peer package at load time.
+import * as compatModule from "@earendil-works/pi-ai/compat"
 
-export default function (pi: ExtensionAPI) {
+interface CompatTextPart {
+  type: string
+  text?: string
+}
+
+interface CompatStreamResult {
+  result(): Promise<{ content: readonly CompatTextPart[] }>
+}
+
+interface CompatModule {
+  streamSimple(model: unknown, context: unknown): CompatStreamResult
+}
+
+interface CompatCallerContext {
+  model?: unknown
+  ui: { notify(message: string, level: "info" | "error"): void }
+}
+
+interface CompatCallerExtensionApi {
+  registerCommand(
+    name: string,
+    command: {
+      description: string
+      handler: (args: string, ctx: CompatCallerContext) => Promise<void>
+    },
+  ): void
+}
+
+const compat = compatModule as CompatModule
+
+export default function (pi: CompatCallerExtensionApi) {
   pi.registerCommand("compat-call", {
     description: "Stream through @earendil-works/pi-ai/compat with the session model",
     handler: async (_args, ctx) => {
@@ -17,12 +50,14 @@ export default function (pi: ExtensionAPI) {
         return
       }
       try {
-        const message = await streamSimple(model, {
-          messages: [{ role: "user", content: "say mock token", timestamp: Date.now() }],
-        }).result()
+        const message = await compat
+          .streamSimple(model, {
+            messages: [{ role: "user", content: "say mock token", timestamp: Date.now() }],
+          })
+          .result()
         const text = message.content
-          .filter((part): part is { type: "text"; text: string } => part.type === "text")
-          .map((part) => part.text)
+          .filter((part) => part.type === "text")
+          .map((part) => part.text ?? "")
           .join("")
         ctx.ui.notify(`compat-call ok: ${text}`, "info")
       } catch (error) {