fix(ai): switch xiaomi default to api billing, add per-region token plan providers

[Phoen1xCode]

Follow-up to #4005 and closes #4082

Summary

Splits the built-in Xiaomi MiMo provider so the default targets the API billing endpoint (the more common case) and prepaid Token Plan users pick a regional endpoint explicitly with its own API key. Follows the MiniMax / Moonshot precedent: each billing surface is its own KnownProvider.

After this PR there are four Xiaomi providers:

Provider id	Endpoint	Env var
xiaomi	https://api.xiaomimimo.com/anthropic	XIAOMI_API_KEY
xiaomi-token-plan-cn	https://token-plan-cn.xiaomimimo.com/anthropic	XIAOMI_TOKEN_PLAN_CN_API_KEY
xiaomi-token-plan-ams	https://token-plan-ams.xiaomimimo.com/anthropic	XIAOMI_TOKEN_PLAN_AMS_API_KEY
xiaomi-token-plan-sgp	https://token-plan-sgp.xiaomimimo.com/anthropic	XIAOMI_TOKEN_PLAN_SGP_API_KEY

Breaking change

Users who set XIAOMI_API_KEY against the previous Token Plan AMS endpoint must migrate to xiaomi-token-plan-ams + XIAOMI_TOKEN_PLAN_AMS_API_KEY. A platform.xiaomimimo.com (API billing) key continues to work with the xiaomi provider and now reaches the right endpoint.

Changes

packages/ai

• src/types.ts — extend KnownProvider with the three Token Plan region ids.
• src/env-api-keys.ts — each Token Plan provider maps to its own env var (XIAOMI_TOKEN_PLAN_{CN,AMS,SGP}_API_KEY).
• scripts/generate-models.ts — replace the single Xiaomi block with a xiaomiVariants loop (mirrors moonshotVariants); regenerate src/models.generated.ts.
• README.md, CHANGELOG.md — document all four providers with per-region env vars; record endpoint flip under ### Breaking Changes.
• Tests — rename existing xiaomi suites to "(API billing)" and add per-region Token Plan suites across all 10 provider test files (stream, abort, empty, context-overflow, image-tool-result, tool-call-without-result, total-tokens, tokens, unicode-surrogate), each gated by the region-specific env var. Add CN / AMS / SGP matrix entries to cross-provider-handoff.

packages/coding-agent

• src/core/provider-display-names.ts — rename xiaomi to "Xiaomi MiMo"; add three Token Plan entries with region suffixes.
• src/core/model-resolver.ts — keep xiaomi default; add the three Token Plan defaults (same model id mimo-v2.5-pro).
• src/cli/args.ts — replace the single shared XIAOMI_TOKEN_PLAN_API_KEY line with three region-specific lines.
• docs/providers.md, README.md — per-region env vars, updated prose and auth.json example.
• CHANGELOG.md — mirror under ### Breaking Changes and ### Added.

Auth

# API billing (keys from platform.xiaomimimo.com)
export XIAOMI_API_KEY=...

# Token Plan — set the key for the region you have a plan in
export XIAOMI_TOKEN_PLAN_CN_API_KEY=...   # China
export XIAOMI_TOKEN_PLAN_AMS_API_KEY=...  # Amsterdam
export XIAOMI_TOKEN_PLAN_SGP_API_KEY=...  # Singapore

Or via ~/.pi/agent/auth.json:

{
  "xiaomi": { "type": "api_key", "key": "..." },
  "xiaomi-token-plan-cn": { "type": "api_key", "key": "..." },
  "xiaomi-token-plan-ams": { "type": "api_key", "key": "..." },
  "xiaomi-token-plan-sgp": { "type": "api_key", "key": "..." }
}

Verification

• npm run check passes
• I login in Xiaomi MiMo and Xiaomi MiMo Token Plan (China) provider and multiple rounds of dialogue were conducted without any problems.

[Copilot]

Pull request overview

This PR splits Xiaomi MiMo into four built-in provider surfaces so the default xiaomi provider targets the API-billing endpoint while Token Plan users choose an explicit regional provider. It updates both packages/ai and packages/coding-agent so provider metadata, auth env vars, docs, and provider-specific test matrices stay aligned with the new Xiaomi provider model.

Changes:

• Added three new known Xiaomi Token Plan providers (cn, ams, sgp) and mapped each to its own endpoint and environment variable.
• Switched the built-in xiaomi provider to Xiaomi's API-billing Anthropic-compatible endpoint and updated coding-agent display/default-model wiring.
• Expanded Xiaomi test coverage across the provider E2E suites and documented the breaking migration in READMEs/changelogs.

Reviewed changes

Copilot reviewed 22 out of 22 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
packages/coding-agent/src/core/provider-display-names.ts	Renames the default Xiaomi label and adds display names for the three regional Token Plan providers.
packages/coding-agent/src/core/model-resolver.ts	Adds default model resolution entries for the new Xiaomi provider IDs.
packages/coding-agent/src/cli/args.ts	Updates CLI help text to show the new Xiaomi env vars.
packages/coding-agent/docs/providers.md	Documents the four Xiaomi providers and their auth.json keys/env vars.
packages/coding-agent/README.md	Updates the built-in provider list to include the new Xiaomi variants.
packages/coding-agent/CHANGELOG.md	Records the Xiaomi endpoint switch as a breaking change and adds the new login-visible providers.
packages/ai/test/unicode-surrogate.test.ts	Adds Unicode handling coverage for the three Token Plan regional providers.
packages/ai/test/total-tokens.test.ts	Adds total-token accounting tests for each regional Xiaomi provider.
packages/ai/test/tool-call-without-result.test.ts	Adds tool-call filtering coverage for the new Xiaomi provider IDs.
packages/ai/test/tokens.test.ts	Renames Xiaomi abort-token suites and marks the known upstream token-usage limitation for all variants.
packages/ai/test/stream.test.ts	Adds stream/tool/thinking/multi-turn E2E coverage for each Xiaomi regional provider.
packages/ai/test/image-tool-result.test.ts	Adds image tool-result coverage and documents the known Xiaomi multimodal limitation for all variants.
packages/ai/test/empty.test.ts	Adds empty-message handling coverage for each Xiaomi Token Plan region.
packages/ai/test/cross-provider-handoff.test.ts	Extends the cross-provider handoff matrix with the three new Xiaomi providers.
packages/ai/test/context-overflow.test.ts	Adds overflow-detection tests for each Xiaomi regional endpoint.
packages/ai/test/abort.test.ts	Adds abort/immediate-abort coverage for each Xiaomi Token Plan region.
packages/ai/src/types.ts	Extends KnownProvider with the three new Xiaomi provider IDs.
packages/ai/src/models.generated.ts	Regenerates model metadata so xiaomi uses API billing and the three Token Plan providers get their own model sets.
packages/ai/src/env-api-keys.ts	Maps each Xiaomi regional provider to its dedicated environment variable.
packages/ai/scripts/generate-models.ts	Reworks Xiaomi model generation into a variant loop for API billing plus regional Token Plan endpoints.
packages/ai/README.md	Updates provider/auth documentation for the new Xiaomi split.
packages/ai/CHANGELOG.md	Records the Xiaomi endpoint flip and the new regional providers.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[mitsuhiko]

Without looking at the rest of the PR: Can you please disable your copilot thing? It's really annoying getting a PR that comes with these reviews.

[Phoen1xCode]

@mitsuhiko Sorry about that - just disabled Copilot auto-review in my settings. The actual changes are ready for your review when you have time.

[badlogic]

awesome, was about to fix this up myself. thanks!