@@ -26,7 +26,7 @@ Want to take on an issue? Leave a comment and a maintainer may assign it to you
 
 ## Adding New Providers
 
-Built-in providers and models live in the static catalog at `packages/cli/src/provider/catalog.json` (one model per line, in the `Provider.Model` shape). To add or update a built-in model, edit that file; providers that need custom loading also need an entry in `CUSTOM_LOADERS` in `packages/cli/src/provider/provider.ts`.
+Built-in providers and models live in the static catalog at `packages/cli/src/provider/catalog.json` (one model per line, in the `Provider.Model` shape; `api.url` is left out for providers whose SDK knows its own endpoint, and each provider also carries `npm`/`api` defaults for models added through config). To add or update a built-in model, edit that file; providers that need custom loading also need an entry in `CUSTOM_LOADERS` in `packages/cli/src/provider/provider.ts`.
 
 Any other OpenAI-compatible provider does not need a code change: users define it under `provider` in `aictrl.json`.
 
 
@@ -268,7 +268,7 @@ For compatibility with sessions written before usage provenance was persisted, a
 **`context`** (context-window utilization):
 
 - `used` (number) — tokens occupying the model's context window this turn: `input + cache.read + cache.write`.
-- `limit` (number) — the model's total context-window size in tokens, sourced from the provider registry: the built-in model catalog plus `provider` config (`model.limit.context`).
+- `limit` (number) — the model's total context-window size in tokens, sourced from the provider registry: the built-in model catalog plus `provider` config (`model.limit.context`). With `aictrl run --attach`, the attached server's provider registry is used instead.
 - `ratio` (number) — `used / limit` (≥0; may exceed 1 if usage exceeds the model's registered limit). A value approaching or exceeding 1 signals context-exhaustion risk.
 - `null` — emitted when the model's context limit is not known (e.g. unregistered custom endpoint), or usage is missing.
 
 
@@ -1574,8 +1574,11 @@ export namespace ACP {
 
     if (specified) return specified
 
-    throw new Error(
-      'No providers found. Run `aictrl auth login`, set a provider API key, or define a provider under "provider" in aictrl.json.',
+    // Every caller is an ACP request handler that rethrows this as-is, so the client gets
+    // the structured authRequired response and can offer its login flow.
+    throw RequestError.authRequired(
+      undefined,
+      'no providers found. Run `aictrl auth login`, set a provider API key, or define a provider under "provider" in aictrl.json.',
     )
   }
 
 
@@ -738,7 +738,7 @@ export const RunCommand = cmd({
                 // part of the prompt sent to the model and count against the context
                 // window, just billed at the cache-write rate. Excluding them
                 // undercounts utilization on the first turn of a conversation.
-                // limit comes from the provider registry (the built-in catalog plus config).
+                // limit comes from the provider registry (the built-in catalog plus config, or the attached server's).
                 // On lookup failure (or limit===0 for custom models) buildContextWindow returns null.
                 const contextLimit = await (args.attach
                   ? attachedContextLimit(info.providerID, info.modelID, attachedProviders())
 
@@ -17,6 +17,7 @@ export function FormatError(input: unknown) {
       `Providers that are not built in must be defined under "provider" in aictrl.json`,
     ].join("\n")
   }
+  if (Provider.BaseURLMissingError.isInstance(input)) return input.message
   if (Provider.InitError.isInstance(input)) {
     return `Failed to initialize provider "${input.data.providerID}". Check credentials and configuration.`
   }
 
@@ -652,6 +652,19 @@ export namespace Provider {
     })
   export type Info = z.infer<typeof Info>
 
+  // The OpenAI-compatible SDK has no default endpoint. A provider outside the catalog that
+  // config declares without `api` or `options.baseURL` would otherwise fail with an invalid URL.
+  function lacksBaseURL(model: Model, options: Record<string, any>) {
+    if (model.api.npm !== "@ai-sdk/openai-compatible") return false
+    return model.api.url === undefined && options["baseURL"] === undefined
+  }
+
+  function baseURLMissing(providerID: string) {
+    const error = new BaseURLMissingError({ providerID })
+    error.message = `Provider "${providerID}" has no base URL. Set "api" or "options.baseURL" for it under "provider" in aictrl.json.`
+    return error
+  }
+
   const state = Instance.state(async () => {
     using _ = log.time("state")
     const config = await Config.get()
@@ -1061,6 +1074,7 @@ export namespace Provider {
     if (s.models.has(key)) return s.models.get(key)!
 
     const provider = s.providers[model.providerID]
+    if (lacksBaseURL(model, provider.options)) throw baseURLMissing(model.providerID)
     const sdk = await getSDK(model)
 
     try {
@@ -1231,4 +1245,11 @@ export namespace Provider {
   )
 
   export const VertexConfigError = NamedError.create("VertexConfigError", z.object({ reason: z.string() }))
+
+  export const BaseURLMissingError = NamedError.create(
+    "ProviderBaseURLMissingError",
+    z.object({
+      providerID: z.string(),
+    }),
+  )
 }
@@ -1,6 +1,6 @@
 import { describe, expect, test } from "bun:test"
 import { ACP } from "../../src/acp/agent"
-import type { Agent as ACPAgent } from "@agentclientprotocol/sdk"
+import { RequestError, type Agent as ACPAgent } from "@agentclientprotocol/sdk"
 
 /**
  * Type-level test: This line will fail to compile if ACP.Agent
@@ -63,9 +63,10 @@ describe("acp default model", () => {
     } as unknown as Sdk
   }
 
-  test("fails with an actionable error when no provider is configured", async () => {
+  test("asks the client to authenticate when no provider is configured", async () => {
     const error = await ACP.defaultModel({ sdk: sdkWith([]) }, "/tmp").catch((e: Error) => e)
-    expect(error).toBeInstanceOf(Error)
+    expect(error).toBeInstanceOf(RequestError)
+    expect((error as RequestError).code).toBe(RequestError.authRequired().code)
     expect((error as Error).message).toContain("aictrl auth login")
     expect((error as Error).message).toContain('"provider" in aictrl.json')
   })
 
@@ -32,17 +32,23 @@ async function runGuarded(entry: string, args: string[], env: Record<string, str
     new Response(proc.stderr).text(),
     proc.exited,
   ]).finally(() => clearTimeout(timer))
+  // A child killed by the timer never runs the guard's exit hook, so say so instead of failing on a missing report.
+  expect(proc.signalCode, `CLI was killed before exiting\n${stderr}`).toBeNull()
   const report = stderr.match(/FETCH_ATTEMPTS=(.*)/)
   expect(report, stderr).not.toBeNull()
   return { stdout, stderr, exit, attempts: JSON.parse(report![1]) as string[] }
 }
 
 describe("startup makes no network requests (#40)", () => {
-  test.each(Object.entries(entries))("%s build: --version", async (_, entry) => {
-    const result = await runGuarded(entry, ["--version"])
-    expect(result.exit, result.stderr).toBe(0)
-    expect(result.attempts).toEqual([])
-  })
+  test.each(Object.entries(entries))(
+    "%s build: --version",
+    async (_, entry) => {
+      const result = await runGuarded(entry, ["--version"])
+      expect(result.exit, result.stderr).toBe(0)
+      expect(result.attempts).toEqual([])
+    },
+    30_000,
+  )
 
   test("models lists the built-in catalog offline", async () => {
     const result = await runGuarded(entries.full, ["models", "anthropic"], { ANTHROPIC_API_KEY: "test-key" })
 
@@ -169,6 +169,30 @@ describe("provider registry", () => {
     })
   })
 
+  test("a config-only openai-compatible provider without a base URL fails with the config fix", async () => {
+    await using tmp = await tmpdir({
+      config: {
+        provider: {
+          groq: {
+            options: { apiKey: "key" },
+            models: { "llama-3.3-70b-versatile": { limit: { context: 131_072, output: 32_768 } } },
+          },
+        },
+      },
+    })
+    await Instance.provide({
+      directory: tmp.path,
+      fn: async () => {
+        const model = await Provider.getModel("groq", "llama-3.3-70b-versatile")
+        const error = await Provider.getLanguage(model).catch((e) => e)
+        expect(Provider.BaseURLMissingError.isInstance(error)).toBe(true)
+        expect(FormatError(error)).toBe(
+          `Provider "groq" has no base URL. Set "api" or "options.baseURL" for it under "provider" in aictrl.json.`,
+        )
+      },
+    })
+  })
+
   test("an openai-compatible provider defined in config works without the catalog", async () => {
     await using tmp = await tmpdir({
       config: {
Original file line number	Diff line number	Diff line change
`@@ -1574,8 +1574,11 @@ export namespace ACP {`
`1574`	`1574`
`1575`	`1575`	`if (specified) return specified`
`1576`	`1576`
`1577`		`- throw new Error(`
`1578`		- 'No providers found. Run `aictrl auth login`, set a provider API key, or define a provider under "provider" in aictrl.json.',
	`1577`	`+ // Every caller is an ACP request handler that rethrows this as-is, so the client gets`
	`1578`	`+ // the structured authRequired response and can offer its login flow.`
	`1579`	`+ throw RequestError.authRequired(`
	`1580`	`+ undefined,`
	`1581`	+ 'no providers found. Run `aictrl auth login`, set a provider API key, or define a provider under "provider" in aictrl.json.',
`1579`	`1582`	`)`
`1580`	`1583`	`}`
`1581`	`1584`
Original file line number	Diff line number	Diff line change
`@@ -17,6 +17,7 @@ export function FormatError(input: unknown) {`
`17`	`17`	`Providers that are not built in must be defined under "provider" in aictrl.json`,
`18`	`18`	`].join("\n")`
`19`	`19`	`}`
	`20`	`+ if (Provider.BaseURLMissingError.isInstance(input)) return input.message`
`20`	`21`	`if (Provider.InitError.isInstance(input)) {`
`21`	`22`	return `Failed to initialize provider "${input.data.providerID}". Check credentials and configuration.`
`22`	`23`	`}`