feat(ai): add Xiaomi MiMo provider (#4005)

* fix(ai): include minimax-cn in cross-provider-handoff matrix

* feat(ai): add Xiaomi MiMo provider

Adds Xiaomi MiMo as an openai-completions-compatible provider.

- packages/ai: register provider in types/KnownProvider, env-api-keys (XIAOMI_API_KEY), generate-models, models.generated.ts, overflow util, README, CHANGELOG
- packages/ai/test: extend stream, tokens, abort, empty, context-overflow, overflow, image-tool-result, tool-call-without-result, total-tokens, unicode-surrogate, cross-provider-handoff matrices with Xiaomi
- packages/coding-agent: default model (mimo-v2.5-pro), display name (Xiaomi MiMo), CLI env var docs, README, docs/providers.md

closes #3912

---------

Co-authored-by: Mario Zechner <badlogicgames@gmail.com>

packages/coding-agent/src/cli/args.ts

@@ -320,6 +320,7 @@ ${chalk.bold("Environment Variables:")}
   CLOUDFLARE_API_KEY               - Cloudflare API token (Workers AI and AI Gateway)
   CLOUDFLARE_ACCOUNT_ID            - Cloudflare account id (required for both)
   CLOUDFLARE_GATEWAY_ID            - Cloudflare AI Gateway slug (required for AI Gateway)
+  XIAOMI_API_KEY                   - Xiaomi MiMo API key
   AWS_PROFILE                      - AWS profile for Amazon Bedrock
   AWS_ACCESS_KEY_ID                - AWS access key for Amazon Bedrock
   AWS_SECRET_ACCESS_KEY            - AWS secret key for Amazon Bedrock

packages/coding-agent/src/core/model-resolver.ts

@@ -39,6 +39,7 @@ export const defaultModelPerProvider: Record<KnownProvider, string> = {
 	"kimi-coding": "kimi-for-coding",
 	"cloudflare-workers-ai": "@cf/moonshotai/kimi-k2.6",
 	"cloudflare-ai-gateway": "workers-ai/@cf/moonshotai/kimi-k2.6",
+	xiaomi: "mimo-v2.5-pro",
 };
 
 export interface ScopedModel {

packages/coding-agent/src/core/provider-display-names.ts

@@ -24,4 +24,5 @@ export const BUILT_IN_PROVIDER_DISPLAY_NAMES: Record<string, string> = {
 	"vercel-ai-gateway": "Vercel AI Gateway",
 	xai: "xAI",
 	zai: "ZAI",
+	xiaomi: "Xiaomi MiMo",
 };