docs: add model refresh health design

docs/plans/2026-03-10-model-refresh-health-design.md

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+---
+title: Model Refresh Health + Toast Feedback
+date: 2026-03-10
+owner: codex
+status: approved
+---
+
+# Goal
+When users click the "模型" refresh action, failed model discovery should mark the account runtime health as `unhealthy` and surface a clear failure toast. Success should show the discovered model names and count.
+
+# Scope
+- Applies to all account types (Session + API Key).
+- Server determines success/failure and error category; UI uses returned payload for toast text.
+
+# Non-goals
+- Changing upstream adapters' auth logic.
+- Altering auto-refresh schedules or background tasks.
+
+# Architecture
+- Update `refreshModelsForAccount(...)` to return structured outcome:
+  - `status`: `success` | `failed`
+  - `modelCount`
+  - `modelsPreview` (first N names)
+  - `errorCode` (e.g. `timeout`, `unauthorized`, `empty_models`, `unknown`)
+  - `errorMessage` (human-readable)
+- On failure: write `runtimeHealth = unhealthy` with a reason derived from `errorCode`.
+- `/api/models/check/:accountId` should return the above outcome.
+- UI toast reads outcome and displays:
+  - Success: `已获取到模型：A、B、C（共 N 个）`
+  - Failure: `模型获取失败（请求超时）` / `模型获取失败，API Key 已无效` / `模型获取失败：<message>`
+
+# Data Flow
+1. User clicks "模型".
+2. UI calls `/api/models/check/:accountId`.
+3. Server refreshes models and returns structured outcome.
+4. UI shows toast based on outcome and reloads list.
+
+# Error Classification
+- `timeout`: error message contains `timeout` / `timed out` / `请求超时`.
+- `unauthorized`: HTTP 401/403 or message contains `invalid`, `unauthorized`, `无权`, `未提供令牌`.
+- `empty_models`: request succeeded but model list empty.
+- `unknown`: fallback for other errors.
+
+# Testing
+- Unit tests for `refreshModelsForAccount`:
+  - Failure updates runtime health to `unhealthy`.
+  - Failure classification maps to the right `errorCode`.
+  - Success returns `modelsPreview` and `modelCount`.
+- UI behavior: verify toast text for success vs. each failure category.