feat: add database tables and API routes for agentic chat feature (#17570)

Backend portion of experimental `AgenticChat` feature:
- Adds database tables for chats and chat messages
- Adds functionality to stream messages from LLM providers using
`kylecarbs/aisdk-go`
- Adds API routes with relevant functionality (list, create, update
chats, insert chat message)
- Adds experiment `codersdk.AgenticChat`

---------

Co-authored-by: Kyle Carberry <kyle@carberry.com>

coderd/httpmw/chat_test.go

@@ -0,0 +1,150 @@
+package httpmw_test
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	"github.com/go-chi/chi/v5"
+	"github.com/google/uuid"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/coder/coder/v2/coderd/database"
+	"github.com/coder/coder/v2/coderd/database/dbgen"
+	"github.com/coder/coder/v2/coderd/database/dbmem"
+	"github.com/coder/coder/v2/coderd/database/dbtime"
+	"github.com/coder/coder/v2/coderd/httpmw"
+	"github.com/coder/coder/v2/codersdk"
+)
+
+func TestExtractChat(t *testing.T) {
+	t.Parallel()
+
+	setupAuthentication := func(db database.Store) (*http.Request, database.User) {
+		r := httptest.NewRequest("GET", "/", nil)
+
+		user := dbgen.User(t, db, database.User{
+			ID: uuid.New(),
+		})
+		_, token := dbgen.APIKey(t, db, database.APIKey{
+			UserID: user.ID,
+		})
+		r.Header.Set(codersdk.SessionTokenHeader, token)
+		r = r.WithContext(context.WithValue(r.Context(), chi.RouteCtxKey, chi.NewRouteContext()))
+		return r, user
+	}
+
+	t.Run("None", func(t *testing.T) {
+		t.Parallel()
+		var (
+			db   = dbmem.New()
+			rw   = httptest.NewRecorder()
+			r, _ = setupAuthentication(db)
+			rtr  = chi.NewRouter()
+		)
+		rtr.Use(
+			httpmw.ExtractAPIKeyMW(httpmw.ExtractAPIKeyConfig{
+				DB:              db,
+				RedirectToLogin: false,
+			}),
+			httpmw.ExtractChatParam(db),
+		)
+		rtr.Get("/", nil)
+		rtr.ServeHTTP(rw, r)
+		res := rw.Result()
+		defer res.Body.Close()
+		require.Equal(t, http.StatusBadRequest, res.StatusCode)
+	})
+
+	t.Run("InvalidUUID", func(t *testing.T) {
+		t.Parallel()
+		var (
+			db   = dbmem.New()
+			rw   = httptest.NewRecorder()
+			r, _ = setupAuthentication(db)
+			rtr  = chi.NewRouter()
+		)
+		chi.RouteContext(r.Context()).URLParams.Add("chat", "not-a-uuid")
+		rtr.Use(
+			httpmw.ExtractAPIKeyMW(httpmw.ExtractAPIKeyConfig{
+				DB:              db,
+				RedirectToLogin: false,
+			}),
+			httpmw.ExtractChatParam(db),
+		)
+		rtr.Get("/", nil)
+		rtr.ServeHTTP(rw, r)
+		res := rw.Result()
+		defer res.Body.Close()
+		require.Equal(t, http.StatusBadRequest, res.StatusCode) // Changed from NotFound in org test to BadRequest as per chat.go
+	})
+
+	t.Run("NotFound", func(t *testing.T) {
+		t.Parallel()
+		var (
+			db   = dbmem.New()
+			rw   = httptest.NewRecorder()
+			r, _ = setupAuthentication(db)
+			rtr  = chi.NewRouter()
+		)
+		chi.RouteContext(r.Context()).URLParams.Add("chat", uuid.NewString())
+		rtr.Use(
+			httpmw.ExtractAPIKeyMW(httpmw.ExtractAPIKeyConfig{
+				DB:              db,
+				RedirectToLogin: false,
+			}),
+			httpmw.ExtractChatParam(db),
+		)
+		rtr.Get("/", nil)
+		rtr.ServeHTTP(rw, r)
+		res := rw.Result()
+		defer res.Body.Close()
+		require.Equal(t, http.StatusNotFound, res.StatusCode)
+	})
+
+	t.Run("Success", func(t *testing.T) {
+		t.Parallel()
+		var (
+			db      = dbmem.New()
+			rw      = httptest.NewRecorder()
+			r, user = setupAuthentication(db)
+			rtr     = chi.NewRouter()
+		)
+
+		// Create a test chat
+		testChat := dbgen.Chat(t, db, database.Chat{
+			ID:        uuid.New(),
+			OwnerID:   user.ID,
+			CreatedAt: dbtime.Now(),
+			UpdatedAt: dbtime.Now(),
+			Title:     "Test Chat",
+		})
+
+		rtr.Use(
+			httpmw.ExtractAPIKeyMW(httpmw.ExtractAPIKeyConfig{
+				DB:              db,
+				RedirectToLogin: false,
+			}),
+			httpmw.ExtractChatParam(db),
+		)
+		rtr.Get("/", func(rw http.ResponseWriter, r *http.Request) {
+			chat := httpmw.ChatParam(r)
+			require.NotZero(t, chat)
+			assert.Equal(t, testChat.ID, chat.ID)
+			assert.WithinDuration(t, testChat.CreatedAt, chat.CreatedAt, time.Second)
+			assert.WithinDuration(t, testChat.UpdatedAt, chat.UpdatedAt, time.Second)
+			assert.Equal(t, testChat.Title, chat.Title)
+			rw.WriteHeader(http.StatusOK)
+		})
+
+		// Try by ID
+		chi.RouteContext(r.Context()).URLParams.Add("chat", testChat.ID.String())
+		rtr.ServeHTTP(rw, r)
+		res := rw.Result()
+		defer res.Body.Close()
+		require.Equal(t, http.StatusOK, res.StatusCode, "by id")
+	})
+}