feat: add labels to chats (#23594)

## Summary

Adds a general-purpose `map[string]string` label system to chats, stored
as jsonb with a GIN index for efficient containment queries.

This is a standalone foundational feature that will be used by the
upcoming Automations feature for session identity (matching webhook
events to existing chats), replacing the need for bespoke session-key
tables.

## Changes

### Database
- **Migration 000451**: Adds `labels jsonb NOT NULL DEFAULT '{}'` column
to `chats` table with a GIN index (`idx_chats_labels`)
- **`InsertChat`**: Accepts labels on creation via `COALESCE(@labels,
'{}')`
- **`UpdateChatByID`**: Supports partial update —
`COALESCE(sqlc.narg('labels'), labels)` preserves existing labels when
NULL is passed
- **`GetChats`**: New `has_labels` filter using PostgreSQL `@>`
containment operator
- **`GetAuthorizedChats`**: Synced with generated `GetChats` (new column
scan + query param)

### API
- **Create chat** (`POST /chats`): Accepts optional `labels` field,
validated before creation
- **Update chat** (`PATCH /chats/{chat}`): Supports `labels` field for
atomic label replacement
- **List chats** (`GET /chats`): Supports `?label=key:value` query
parameters (multiple are AND-ed)

### SDK
- `Chat`, `CreateChatRequest`, `UpdateChatRequest`, `ListChatsOptions`
all gain `Labels` fields
- `UpdateChatRequest.Labels` is a pointer (`*map[string]string`) so
`nil` means "don't change" vs empty map means "clear all"

### Validation (`coderd/httpapi/labels.go`)
- Max 50 labels per chat
- Key: 1–64 chars, must match `[a-zA-Z0-9][a-zA-Z0-9._/-]*` (supports
namespaced keys like `github.repo`, `automation/pr-number`)
- Value: 1–256 chars
- 13 test cases covering all edge cases

### Chat runtime
- `chatd.CreateOptions` gains `Labels` field, threaded through to
`InsertChat`
- Existing `UpdateChatByID` callers (e.g., quickgen title updates) are
unaffected — NULL labels preserve existing values via COALESCE

codersdk/chats.go

@@ -46,20 +46,21 @@ const (
 
 // Chat represents a chat session with an AI agent.
 type Chat struct {
-	ID                uuid.UUID       `json:"id" format:"uuid"`
-	OwnerID           uuid.UUID       `json:"owner_id" format:"uuid"`
-	WorkspaceID       *uuid.UUID      `json:"workspace_id,omitempty" format:"uuid"`
-	ParentChatID      *uuid.UUID      `json:"parent_chat_id,omitempty" format:"uuid"`
-	RootChatID        *uuid.UUID      `json:"root_chat_id,omitempty" format:"uuid"`
-	LastModelConfigID uuid.UUID       `json:"last_model_config_id" format:"uuid"`
-	Title             string          `json:"title"`
-	Status            ChatStatus      `json:"status"`
-	LastError         *string         `json:"last_error"`
-	DiffStatus        *ChatDiffStatus `json:"diff_status,omitempty"`
-	CreatedAt         time.Time       `json:"created_at" format:"date-time"`
-	UpdatedAt         time.Time       `json:"updated_at" format:"date-time"`
-	Archived          bool            `json:"archived"`
-	MCPServerIDs      []uuid.UUID     `json:"mcp_server_ids" format:"uuid"`
+	ID                uuid.UUID         `json:"id" format:"uuid"`
+	OwnerID           uuid.UUID         `json:"owner_id" format:"uuid"`
+	WorkspaceID       *uuid.UUID        `json:"workspace_id,omitempty" format:"uuid"`
+	ParentChatID      *uuid.UUID        `json:"parent_chat_id,omitempty" format:"uuid"`
+	RootChatID        *uuid.UUID        `json:"root_chat_id,omitempty" format:"uuid"`
+	LastModelConfigID uuid.UUID         `json:"last_model_config_id" format:"uuid"`
+	Title             string            `json:"title"`
+	Status            ChatStatus        `json:"status"`
+	LastError         *string           `json:"last_error"`
+	DiffStatus        *ChatDiffStatus   `json:"diff_status,omitempty"`
+	CreatedAt         time.Time         `json:"created_at" format:"date-time"`
+	UpdatedAt         time.Time         `json:"updated_at" format:"date-time"`
+	Archived          bool              `json:"archived"`
+	MCPServerIDs      []uuid.UUID       `json:"mcp_server_ids" format:"uuid"`
+	Labels            map[string]string `json:"labels"`
 }
 
 // ChatMessage represents a single message in a chat.
@@ -311,16 +312,18 @@ type ChatInputPart struct {
 
 // CreateChatRequest is the request to create a new chat.
 type CreateChatRequest struct {
-	Content       []ChatInputPart `json:"content"`
-	WorkspaceID   *uuid.UUID      `json:"workspace_id,omitempty" format:"uuid"`
-	ModelConfigID *uuid.UUID      `json:"model_config_id,omitempty" format:"uuid"`
-	MCPServerIDs  []uuid.UUID     `json:"mcp_server_ids,omitempty" format:"uuid"`
+	Content       []ChatInputPart   `json:"content"`
+	WorkspaceID   *uuid.UUID        `json:"workspace_id,omitempty" format:"uuid"`
+	ModelConfigID *uuid.UUID        `json:"model_config_id,omitempty" format:"uuid"`
+	MCPServerIDs  []uuid.UUID       `json:"mcp_server_ids,omitempty" format:"uuid"`
+	Labels        map[string]string `json:"labels,omitempty"`
 }
 
 // UpdateChatRequest is the request to update a chat.
 type UpdateChatRequest struct {
-	Title    *string `json:"title,omitempty"`
-	Archived *bool   `json:"archived,omitempty"`
+	Title    *string            `json:"title,omitempty"`
+	Archived *bool              `json:"archived,omitempty"`
+	Labels   *map[string]string `json:"labels,omitempty"`
 }
 
 // CreateChatMessageRequest is the request to add a message to a chat.
@@ -1166,7 +1169,8 @@ type ChatUsageLimitConfigResponse struct {
 
 // ListChatsOptions are optional parameters for ListChats.
 type ListChatsOptions struct {
-	Query string
+	Query  string
+	Labels map[string]string
 	Pagination
 }
 
@@ -1182,6 +1186,15 @@ func (c *ExperimentalClient) ListChats(ctx context.Context, opts *ListChatsOptio
 				r.URL.RawQuery = q.Encode()
 			})
 		}
+		if len(opts.Labels) > 0 {
+			reqOpts = append(reqOpts, func(r *http.Request) {
+				q := r.URL.Query()
+				for k, v := range opts.Labels {
+					q.Add("label", k+":"+v)
+				}
+				r.URL.RawQuery = q.Encode()
+			})
+		}
 	}
 	res, err := c.Request(ctx, http.MethodGet, "/api/experimental/chats", nil, reqOpts...)
 	if err != nil {