fix: add missing_key error kind for missing chat api_key_id (#25783)

Refs CODAGT-486

- `codersdk/chats.go`: New `ChatErrorKindMissingKey` constant and
`AllChatErrorKinds` entry
- `coderd/x/chatd/chaterror/message.go`: `terminalMessage` and
`retryMessage` cases
- `coderd/x/chatd/model_routing_aibridge.go`: Pre-classify error with
`WithClassification`
- `coderd/x/chatd/model_routing_internal_test.go`: Classification
assertion on production path (CRF-2)
- `chatStatusHelpers.ts`: Frontend title "Chat interrupted"
- `LiveStreamTail.stories.tsx`: Storybook story with `detail` assertion
- `docs/ai-coder/ai-gateway/clients/coder-agents.md`: Troubleshooting
entry
- Tests: classification round-trip, terminal message, metrics kind
enumeration

> Generated with [Coder Agents](https://coder.com/agents) on behalf of
@johnstcn

docs/ai-coder/ai-gateway/clients/coder-agents.md

@@ -164,6 +164,13 @@ key is a valid Coder token.
   one [model](../../agents/models.md#add-a-model) to the provider after
   saving the Base URL. Providers without an enabled model are hidden from
   developers.
+- **"Chat interrupted" error when resuming a conversation.**
+  This occurs when the API key that was used to start a chat turn is no
+  longer available. Common causes: upgrading from a version before
+  `api_key_id` tracking was introduced, or deleting an API key while a
+  chat is active. The error is self-healing: send your message again and
+  the new message will use your current API key. If the error persists
+  after resending, this indicates a bug. Please report it.
 
 ## Known limitations
 

docs/reference/api/chats.md

@@ -292,13 +292,13 @@ Status Code **200**
 
 #### Enumerated Values
 
-| Property      | Value(s)                                                                                                     |
-|---------------|--------------------------------------------------------------------------------------------------------------|
-| `client_type` | `api`, `ui`                                                                                                  |
-| `kind`        | `auth`, `config`, `generic`, `overloaded`, `rate_limit`, `startup_timeout`, `timeout`, `usage_limit`         |
-| `type`        | `context-file`, `file`, `file-reference`, `reasoning`, `skill`, `source`, `text`, `tool-call`, `tool-result` |
-| `plan_mode`   | `plan`                                                                                                       |
-| `status`      | `completed`, `error`, `paused`, `pending`, `requires_action`, `running`, `waiting`                           |
+| Property      | Value(s)                                                                                                            |
+|---------------|---------------------------------------------------------------------------------------------------------------------|
+| `client_type` | `api`, `ui`                                                                                                         |
+| `kind`        | `auth`, `config`, `generic`, `missing_key`, `overloaded`, `rate_limit`, `startup_timeout`, `timeout`, `usage_limit` |
+| `type`        | `context-file`, `file`, `file-reference`, `reasoning`, `skill`, `source`, `text`, `tool-call`, `tool-result`        |
+| `plan_mode`   | `plan`                                                                                                              |
+| `status`      | `completed`, `error`, `paused`, `pending`, `requires_action`, `running`, `waiting`                                  |
 
 To perform this operation, you must be authenticated. [Learn more](authentication.md).
 

docs/reference/api/schemas.md

@@ -2732,9 +2732,9 @@ AuthorizationObject can represent a "set" of objects, such as: all workspaces in
 
 #### Enumerated Values
 
-| Value(s)                                                                                             |
-|------------------------------------------------------------------------------------------------------|
-| `auth`, `config`, `generic`, `overloaded`, `rate_limit`, `startup_timeout`, `timeout`, `usage_limit` |
+| Value(s)                                                                                                            |
+|---------------------------------------------------------------------------------------------------------------------|
+| `auth`, `config`, `generic`, `missing_key`, `overloaded`, `rate_limit`, `startup_timeout`, `timeout`, `usage_limit` |
 
 ## codersdk.ChatFileMetadata