chore/API: speed up edit/test feedback loop for llmapi module (#64437)

Previously, it took ~6 seconds for a single edit/test/debug feedback
loop in the `llmapi` module. After this change, it's now 1-2s.

The reason the feedback loop was slow was that we depended on the
`//cmd/frontend/internal/modelconfig` target, which transitively brings
in `graphqlbackend` and all the migration code, which adds huge overhead
to Go link times. It was relatively easy to untangle this dependency so
I went ahead and removed it to boost my local feedback loop.

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## Test plan
Green CI.

To measure the timing, I ran the tests, made a tiny change and ran the
tests against to measure the total time to build+test.

```
# Before
❯ time go test -timeout 30s github.com/sourcegraph/sourcegraph/cmd/frontend/internal/llmapi
ok  	github.com/sourcegraph/sourcegraph/cmd/frontend/internal/llmapi	2.394s
go test -timeout 30s   4.26s user 4.73s system 166% cpu 5.393 total

# After
❯ time go test -timeout 30s github.com/sourcegraph/sourcegraph/cmd/frontend/internal/llmapi
ok  	github.com/sourcegraph/sourcegraph/cmd/frontend/internal/llmapi	0.862s
go test -timeout 30s   1.20s user 1.21s system 135% cpu 1.774 total
```
<!-- REQUIRED; info at
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-->

## Changelog

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cmd/frontend/internal/httpapi/BUILD.bazel

@@ -58,6 +58,7 @@ go_library(
         "//internal/gitserver/gitdomain",
         "//internal/httpcli",
         "//internal/licensing",
+        "//internal/modelconfig/types",
         "//internal/opencodegraph",
         "//internal/repoupdater",
         "//internal/sams",

cmd/frontend/internal/httpapi/httpapi.go

@@ -39,6 +39,7 @@ import (
 	"github.com/sourcegraph/sourcegraph/internal/encryption/keyring"
 	"github.com/sourcegraph/sourcegraph/internal/env"
 	"github.com/sourcegraph/sourcegraph/internal/gitserver"
+	"github.com/sourcegraph/sourcegraph/internal/modelconfig/types"
 	"github.com/sourcegraph/sourcegraph/internal/sams"
 	"github.com/sourcegraph/sourcegraph/internal/search"
 	"github.com/sourcegraph/sourcegraph/internal/search/searchcontexts"
@@ -322,7 +323,7 @@ func NewHandler(
 	repo.Path("/refresh").Methods("POST").Handler(jsonHandler(serveRepoRefresh(db)))
 
 	llm := m.PathPrefix("/llm/").Subrouter()
-	llmapi.RegisterHandlers(llm, m)
+	llmapi.RegisterHandlers(llm, m, func() (*types.ModelConfiguration, error) { return modelconfig.Get().Get() })
 
 	m.NotFoundHandler = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		log.Printf("API no route: %s %s from %s", r.Method, r.URL, r.Referer())

cmd/frontend/internal/llmapi/BUILD.bazel

@@ -11,7 +11,6 @@ go_library(
     importpath = "github.com/sourcegraph/sourcegraph/cmd/frontend/internal/llmapi",
     visibility = ["//cmd/frontend:__subpackages__"],
     deps = [
-        "//cmd/frontend/internal/modelconfig",
         "//internal/completions/types",
         "//internal/modelconfig/types",
         "//lib/errors",
@@ -31,15 +30,11 @@ go_test(
     data = glob(["golly-recordings/**"]),
     embed = [":llmapi"],
     deps = [
-        "//cmd/frontend/internal/modelconfig",
-        "//internal/conf",
         "//internal/golly",
         "//internal/httpcli",
         "//internal/modelconfig/types",
-        "//schema",
         "@com_github_gorilla_mux//:mux",
         "@com_github_hexops_autogold_v2//:autogold",
         "@com_github_stretchr_testify//assert",
-        "@com_github_stretchr_testify//require",
     ],
 )

cmd/frontend/internal/llmapi/chat_completions_handler.go

@@ -14,7 +14,6 @@ import (
 	"github.com/sourcegraph/log"
 	sglog "github.com/sourcegraph/log"
 
-	"github.com/sourcegraph/sourcegraph/cmd/frontend/internal/modelconfig"
 	"github.com/sourcegraph/sourcegraph/lib/errors"
 
 	completions "github.com/sourcegraph/sourcegraph/internal/completions/types"
@@ -31,8 +30,12 @@ type chatCompletionsHandler struct {
 	// would have an in-house service we can use instead of going via HTTP but using HTTP
 	// simplifies a lof of things (including testing).
 	apiHandler http.Handler
+
+	GetModelConfig GetModelConfigurationFunc
 }
 
+type GetModelConfigurationFunc func() (*types.ModelConfiguration, error)
+
 var _ http.Handler = (*chatCompletionsHandler)(nil)
 
 func (h *chatCompletionsHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
@@ -45,8 +48,7 @@ func (h *chatCompletionsHandler) ServeHTTP(w http.ResponseWriter, r *http.Reques
 
 	decoder := json.NewDecoder(io.NopCloser(bytes.NewBuffer(body)))
 
-	modelConfigSvc := modelconfig.Get()
-	currentModelConfig, err := modelConfigSvc.Get()
+	currentModelConfig, err := h.GetModelConfig()
 	if err != nil {
 		http.Error(w, fmt.Sprintf("modelConfigSvc.Get: %v", err), http.StatusInternalServerError)
 		return

cmd/frontend/internal/llmapi/chat_completions_handler_test.go

@@ -8,28 +8,16 @@ import (
 
 	"github.com/hexops/autogold/v2"
 	"github.com/stretchr/testify/assert"
-	"github.com/stretchr/testify/require"
 
-	"github.com/sourcegraph/sourcegraph/cmd/frontend/internal/modelconfig"
-	"github.com/sourcegraph/sourcegraph/internal/conf"
 	types "github.com/sourcegraph/sourcegraph/internal/modelconfig/types"
-	"github.com/sourcegraph/sourcegraph/schema"
 )
 
-func SetSiteConfig(t *testing.T, siteConfig schema.SiteConfiguration) {
-	conf.Mock(&conf.Unified{SiteConfiguration: siteConfig})
-	if err := modelconfig.ResetMock(); err != nil {
-		require.NoError(t, err)
-	}
-}
-
 func TestChatCompletionsHandler(t *testing.T) {
-	c := newTest(t)
-	chatModels := c.getChatModels()
-	assert.NoError(t, modelconfig.InitMock())
-	assert.NoError(t, modelconfig.ResetMockWithStaticData(&types.ModelConfiguration{
-		Models: chatModels,
-	}))
+	var c *publicrestTest
+	c = newTest(t, func() (*types.ModelConfiguration, error) {
+		chatModels := c.getChatModels()
+		return &types.ModelConfiguration{Models: chatModels}, nil
+	})
 
 	t.Run("/.api/llm/chat/completions (400 stream=true)", func(t *testing.T) {
 		rr := c.chatCompletions(t, `{
@@ -144,7 +132,7 @@ func TestChatCompletionsHandler(t *testing.T) {
 }`).Equal(t, body)
 	})
 
-	for _, model := range chatModels {
+	for _, model := range c.getChatModels() {
 		if model.DisplayName == "starcoder" {
 			// Skip starcoder because it's not a chat model even if it has the "chat" capability
 			// per the /.api/modelconfig/supported-models.json endpoint. Context:

cmd/frontend/internal/llmapi/httpapi.go

@@ -7,8 +7,12 @@ import (
 	sglog "github.com/sourcegraph/log"
 )
 
-func RegisterHandlers(m *mux.Router, apiHandler http.Handler) {
+func RegisterHandlers(m *mux.Router, apiHandler http.Handler, getModelConfigFunc GetModelConfigurationFunc) {
 	logger := sglog.Scoped("llmapi")
 
-	m.Path("/chat/completions").Methods("POST").Handler(&chatCompletionsHandler{logger: logger, apiHandler: apiHandler})
+	m.Path("/chat/completions").Methods("POST").Handler(&chatCompletionsHandler{
+		logger:         logger,
+		apiHandler:     apiHandler,
+		GetModelConfig: getModelConfigFunc,
+	})
 }

cmd/frontend/internal/llmapi/utils_test.go

@@ -25,13 +25,13 @@ type publicrestTest struct {
 	HttpClient  http.Handler
 }
 
-func newTest(t *testing.T) *publicrestTest {
+func newTest(t *testing.T, getModelConfigFunc GetModelConfigurationFunc) *publicrestTest {
 	MockUUID = "mocked-llmapi-uuid"
 	gollyDoer := golly.NewGollyDoer(t, httpcli.TestExternalClient)
 	recordReplayHandler := newRecordReplayHandler(gollyDoer, gollyDoer.DotcomCredentials())
 	apiHandler := mux.NewRouter().PathPrefix("/.api/llm/").Subrouter()
 
-	RegisterHandlers(apiHandler, recordReplayHandler)
+	RegisterHandlers(apiHandler, recordReplayHandler, getModelConfigFunc)
 
 	return &publicrestTest{
 		t:           t,