fix(core): register the custom api in the pi-ai compat registry

pi routes the main chat through the registered provider, but sibling
extensions that call streamSimple from @earendil-works/pi-ai/compat with
the active Command Code model resolve model.api through the compat
api-registry, which only knows built-in APIs. On plain pi that failed
with "No API provider registered for api: commandcode-custom".

Register commandcode-custom there and delegate to the transport router.
The registry resolves no credentials for extension providers, so fall
back to the configured Command Code key when the caller passes none.

Closes #68

(cherry picked from commit 7e9659e672771c6a9223b95938e50fb2a051a0a7)

index.ts

@@ -6,7 +6,11 @@
  */
 
 import { AssistantMessageEventStream } from "@earendil-works/pi-ai"
-import { streamSimple as streamNativeProvider } from "@earendil-works/pi-ai/compat"
+import {
+  registerApiProvider,
+  streamSimple as streamNativeProvider,
+  type ApiStreamSimpleFunction,
+} from "@earendil-works/pi-ai/compat"
 import {
   getAgentDir,
   type ExtensionAPI,
@@ -37,6 +41,9 @@ import { registerCommandCodeQuota } from "./src/quota-command.ts"
 import { createCommandCodeRuntime } from "./src/runtime.ts"
 import { createCommandCodeTransportRouter } from "./src/transport.ts"
 
+const COMMAND_CODE_API = "commandcode-custom"
+const COMPAT_SOURCE_ID = "pi-commandcode-provider"
+
 function commandCodeHeaders(): Record<string, string> | undefined {
   if (process.env.CMD_ZDR === "1" || process.env.COMMANDCODE_ZDR === "1") {
     return { "x-cmd-zdr": "1" }
@@ -54,7 +61,7 @@ function createProviderConfig(
     name: "Command Code",
     baseUrl: apiBase,
     apiKey: getConfiguredApiKey() ?? "$COMMAND_CODE_API_KEY",
-    api: "commandcode-custom",
+    api: COMMAND_CODE_API,
     streamSimple: streamCommandCode,
     headers,
     oauth: {
@@ -66,7 +73,7 @@ function createProviderConfig(
     models: models.map((model) => ({
       id: model.id,
       name: model.name,
-      api: "commandcode-custom",
+      api: COMMAND_CODE_API,
       baseUrl: baseUrlForModel(apiBase, model.api),
       reasoning: model.reasoning,
       ...(thinkingMetadataForModel(model.id) ?? {}),
@@ -120,6 +127,24 @@ export default async function (pi: ExtensionAPI) {
     streamGenerate,
   })
 
+  // pi dispatches the main chat through the registered provider, but sibling
+  // extensions that call `streamSimple` from `@earendil-works/pi-ai/compat`
+  // with a Command Code model resolve `model.api` through the compat
+  // api-registry, which knows nothing about extension providers. Register the
+  // custom api there so those calls reach the same transport. The registry
+  // resolves no credentials for extension providers, so fall back to the
+  // configured key when the caller passes none.
+  const compatStream: ApiStreamSimpleFunction = (model, context, options) =>
+    transport.stream(
+      model,
+      context,
+      options?.apiKey ? options : { ...options, apiKey: getConfiguredApiKey() },
+    ) as AssistantMessageEventStream
+  registerApiProvider(
+    { api: COMMAND_CODE_API, stream: compatStream, streamSimple: compatStream },
+    COMPAT_SOURCE_ID,
+  )
+
   pi.on("message_end", async (event, ctx) => {
     if (event.message.role !== "assistant") return
     const normalized = normalizeCommandCodeMessage(event.message, ctx.model?.provider)