diff --git a/CHANGELOG.md b/CHANGELOG.md
index 38b745e..ab77472 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,9 @@
 
 ## Unreleased
 
+- Register the `commandcode-custom` API in the `@earendil-works/pi-ai/compat` registry so sibling extensions that stream with the active Command Code model no longer fail with `No API provider registered for api: commandcode-custom` on plain pi.
+- Assert structural catalog invariants in the model tests so the daily catalog sync no longer fails on every upstream change.
+- Display the monthly renewal date and remaining days in `/commandcode-quota`.
 - Stop silently dropping `role: "developer"` messages (for example OMP advisor steering notes, reminders, and nudges). `/alpha/generate` only accepts `user`, `assistant`, and `tool` roles, so developer messages are now forwarded as `user` messages with identical content in the same chronological position instead of disappearing from the request.
 - Add `Qwen/Qwen3.8-Flash` and `z-ai/glm-5.3-flash` with their verified reasoning efforts (`low, medium, xhigh` and `low, high, max`) and display pricing.
 - Refresh static model capabilities from `command-code@1.40.1`, adding `claude-fable-5-1`, `deepseek/deepseek-v4-flash-fast`, and `tencent/hy4-preview` with their reasoning efforts, adding `moonshotai/Kimi-K3` efforts and the `z-ai/glm-5.3-flash` output limit, and dropping the retired `stealth/ox-alpha` and `minimax/minimax-m3-free`.
diff --git a/README.md b/README.md
index 32a54d2..25be44c 100644
--- a/README.md
+++ b/README.md
@@ -31,6 +31,10 @@ omp plugin install pi-commandcode-provider
 
 Restart OMP or run `/reload`, then use `/login` and select **Use a subscription** followed by **Command Code**.
 
+## Other extensions
+
+Command Code models are registered under the custom `commandcode-custom` API. The provider also registers that API in the `@earendil-works/pi-ai/compat` registry, so sibling extensions that stream through `streamSimple` from that entrypoint with the active session model (background agents, memory workers, and similar) reach the same Command Code transport instead of failing with `No API provider registered for api: commandcode-custom`. When such a call passes no API key, the provider uses the configured Command Code credentials.
+
 ## Authentication
 
 ### Login dialog
diff --git a/index.ts b/index.ts
index 09222bd..6dce140 100644
--- a/index.ts
+++ b/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)
diff --git a/tests/fixtures/compat-caller-extension.ts b/tests/fixtures/compat-caller-extension.ts
new file mode 100644
index 0000000..214533f
--- /dev/null
+++ b/tests/fixtures/compat-caller-extension.ts
@@ -0,0 +1,34 @@
+/**
+ * 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.
+ */
+
+import { streamSimple } from "@earendil-works/pi-ai/compat"
+import type { ExtensionAPI } from "@earendil-works/pi-coding-agent"
+
+export default function (pi: ExtensionAPI) {
+  pi.registerCommand("compat-call", {
+    description: "Stream through @earendil-works/pi-ai/compat with the session model",
+    handler: async (_args, ctx) => {
+      const model = ctx.model
+      if (!model) {
+        ctx.ui.notify("compat-call: no active model", "error")
+        return
+      }
+      try {
+        const message = await 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)
+          .join("")
+        ctx.ui.notify(`compat-call ok: ${text}`, "info")
+      } catch (error) {
+        const detail = error instanceof Error ? error.message : String(error)
+        ctx.ui.notify(`compat-call failed: ${detail}`, "error")
+      }
+    },
+  })
+}
diff --git a/tests/test-pi-local.mjs b/tests/test-pi-local.mjs
index 3bce2c8..9908653 100644
--- a/tests/test-pi-local.mjs
+++ b/tests/test-pi-local.mjs
@@ -15,6 +15,12 @@ import { fileURLToPath } from "node:url"
 const __dirname = dirname(fileURLToPath(import.meta.url))
 const PROJECT_DIR = resolve(__dirname, "..")
 const EXT_PATH = resolve(PROJECT_DIR, "index.ts")
+const COMPAT_CALLER_EXT_PATH = resolve(
+  PROJECT_DIR,
+  "tests",
+  "fixtures",
+  "compat-caller-extension.ts",
+)
 const TEST_MODEL = "gpt-5.4"
 const CLAUDE_TEST_MODEL = "claude-sonnet-4-6"
 
@@ -486,6 +492,75 @@ async function runRpcExtensionCommands(timeoutMs = 30_000) {
   }
 }
 
+async function runRpcCompatCall(timeoutMs = 30_000) {
+  const child = spawn(
+    PI_BIN,
+    [
+      "--no-extensions",
+      "--mode",
+      "rpc",
+      "-e",
+      EXT_PATH,
+      "-e",
+      COMPAT_CALLER_EXT_PATH,
+      "--provider",
+      "commandcode",
+      "--model",
+      TEST_MODEL,
+    ],
+    {
+      cwd: PROJECT_DIR,
+      env,
+      stdio: ["pipe", "pipe", "pipe"],
+    },
+  )
+
+  let buffer = ""
+  let stderr = ""
+
+  const notification = new Promise((resolve, reject) => {
+    const timer = setTimeout(
+      () => reject(new Error(`compat-call timeout. stderr: ${stderr.slice(-500)}`)),
+      timeoutMs,
+    )
+    child.stdout.on("data", (chunk) => {
+      buffer += chunk.toString("utf-8")
+      const lines = buffer.split("\n")
+      buffer = lines.pop() ?? ""
+      for (const line of lines) {
+        if (!line.trim()) continue
+        let event
+        try {
+          event = JSON.parse(line)
+        } catch {
+          continue
+        }
+        if (
+          event.type === "extension_ui_request" &&
+          event.method === "notify" &&
+          typeof event.message === "string" &&
+          event.message.startsWith("compat-call")
+        ) {
+          clearTimeout(timer)
+          resolve(event.message)
+        }
+      }
+    })
+    child.stderr.on("data", (chunk) => {
+      stderr += chunk.toString("utf-8")
+    })
+  })
+
+  try {
+    child.stdin.write(
+      `${JSON.stringify({ id: "compat", type: "prompt", message: "/compat-call" })}\n`,
+    )
+    return { message: await notification, stderr }
+  } finally {
+    child.kill()
+  }
+}
+
 async function runRpcOverflowRecovery(timeoutMs = 60_000) {
   const child = spawn(
     PI_BIN,
@@ -797,6 +872,18 @@ try {
     JSON.stringify(imageContent),
   )
 
+  console.log("[pi-local] sibling extension streams through the pi-ai compat registry")
+  requestCount = 0
+  const compatCall = await runRpcCompatCall()
+  assert.equal(compatCall.message, "compat-call ok: mock-pi-ok", compatCall.stderr)
+  assert.equal(requestCount, 1)
+  assert.equal(lastRequestBody?.model, TEST_MODEL)
+  assert.ok(
+    typeof lastRequestHeaders.authorization === "string" &&
+      lastRequestHeaders.authorization.startsWith("Bearer "),
+    "compat call should send a bearer Authorization header",
+  )
+
   console.log("[pi-local] verify overflow normalization and compaction recovery")
   overflowMode = true
   overflowRequestCount = 0