feat(example): per-queue extension wiring; retire buildrunner/noop

## Summary

### Why?

Demonstrate SubmitQueue's core premise — per-queue pluggable extensions —
in the example orchestrator, rather than wiring one implementation for
every queue, and make the fakes drivable end-to-end. Also document where
factory implementations and queue routing belong.

Stacked on the fakes PR, which adds the extension/*/fake packages this PR
wires in.

### What?

- Queue-major registry in example main.go: queueExtensions (one queue's
  full impl set) + queueRegistry (queue -> profile, with a default). Six
  thin Factory adapters resolve impls by Config.QueueName — all routing
  lives here in the wiring layer.
- Per-queue profiles: test-queue (heuristic over lines changed),
  e2e-test-queue (composite scorer, no-conflict), plus a new
  e2e-conflict-error-queue that always fails conflict analysis. Edge
  integrations + build runner share a baseline; scorer/analyzer are wrapped
  by the decorator fakes (score-error marker / failing predicate).
- Retire buildrunner/noop (subsumed by buildrunner/fake); switch the build
  controller unit test to buildfake.
- queues.yaml: register e2e-conflict-error-queue.
- CLAUDE.md: extensions hold contracts + impls only — factory
  implementations and routing live in the wiring layer; plus a TODO to
  evaluate promoting the registry into submitqueue/core later.

## Test Plan

- ✅ `make test` — 44/44 unit tests
- ✅ `make e2e-test` — 1/1
- ✅ `make integration-test` — 7/7
- ✅ `make check-gazelle` / `make check-tidy` — clean
- ✅ Live stack (`make local-submitqueue-start`): Ping OK; gateway rejects
  unknown queues; validated end-to-end — scorer passthrough (test-queue),
  scorer error (`?sq-fake=score-error` -> "fake: marked score error"), and
  conflict error (e2e-conflict-error-queue -> "fake: injected analyze
  error").

Author: behinddwalls

CLAUDE.md

@@ -116,6 +116,8 @@ Vendor-agnostic, pluggable interfaces with implementations in subdirectories:
 2. Implementations at `extension/{ext}/{impl}/`
 3. Factory interface for dependency injection and lifecycle management
 
+**Extensions hold contracts and impls only — never factory implementations or routing.** An `extension/{ext}` package owns the behavioral interface, its `Config`, the `Factory` *interface*, and impl constructors `New(...)` that return the interface. It must NOT contain `Factory` *implementations* (no `NewFactory()` constructors or factory structs) and no queue-selection/routing logic. The reason: an impl package (e.g. `scorer/heuristic`) cannot know the queue topology or the other impls, so any "which impl for which queue" decision baked there is wrong by construction. A `Factory` whose `For(cfg)` ignores `cfg.QueueName` is just an impl→Factory adapter — that adapting, and all per-queue routing, belongs in the **wiring/integrator layer** (e.g. `example/{domain}/{service}/server/main.go`), which is the one place that knows the queue set. There, adapt `New(...)` impls to the `Factory` contract and route on `Config.QueueName`. Keep this seam strict: if you're about to add a `NewFactory()` or a `map[queue]impl` under `extension/`, it belongs in the wiring layer instead.
+
 **Design interfaces for the technology *space*, not the implementation in front of you.** The interface is a contract every backend will have to satisfy — SQL, key-value (DynamoDB, Bigtable), document, message queue, search, RPC, in-memory, mocks. If the contract assumes a capability that some plausible backend can't provide cheaply, you've baked the current impl's strengths into the API.
 
 Common over-constraints to avoid:

example/submitqueue/gateway/server/queues.yaml

@@ -7,3 +7,7 @@ queues:
   - name: test-queue
   - name: e2e-test-queue
   - name: e2e-cancel-queue
+  # Routes to an analyzer that always errors (conflictfake.FailAlways) so e2e can
+  # exercise the conflict-analysis error path. See newQueueRegistry in the
+  # orchestrator example server.
+  - name: e2e-conflict-error-queue

example/submitqueue/orchestrator/server/BUILD.bazel

@@ -21,16 +21,23 @@ go_library(
         "//submitqueue/core/consumer",
         "//submitqueue/entity",
         "//submitqueue/extension/buildrunner",
-        "//submitqueue/extension/buildrunner/noop",
+        "//submitqueue/extension/buildrunner/fake",
         "//submitqueue/extension/changeprovider",
+        "//submitqueue/extension/changeprovider/fake",
         "//submitqueue/extension/changeprovider/github",
         "//submitqueue/extension/conflict",
         "//submitqueue/extension/conflict/all",
+        "//submitqueue/extension/conflict/fake",
+        "//submitqueue/extension/conflict/none",
         "//submitqueue/extension/mergechecker",
+        "//submitqueue/extension/mergechecker/fake",
         "//submitqueue/extension/mergechecker/github",
         "//submitqueue/extension/pusher",
+        "//submitqueue/extension/pusher/fake",
         "//submitqueue/extension/pusher/git",
         "//submitqueue/extension/scorer",
+        "//submitqueue/extension/scorer/composite",
+        "//submitqueue/extension/scorer/fake",
         "//submitqueue/extension/scorer/heuristic",
         "//submitqueue/extension/storage",
         "//submitqueue/extension/storage/mysql",

example/submitqueue/orchestrator/server/main.go

@@ -28,8 +28,8 @@ go_test(
         "//submitqueue/core/consumer",
         "//submitqueue/entity",
         "//submitqueue/extension/buildrunner",
+        "//submitqueue/extension/buildrunner/fake",
         "//submitqueue/extension/buildrunner/mock",
-        "//submitqueue/extension/buildrunner/noop",
         "//submitqueue/extension/storage",
         "//submitqueue/extension/storage/mock",
         "@com_github_stretchr_testify//assert",

submitqueue/extension/buildrunner/noop/BUILD.bazel

@@ -28,8 +28,8 @@ import (
 	"github.com/uber/submitqueue/submitqueue/core/consumer"
 	"github.com/uber/submitqueue/submitqueue/entity"
 	"github.com/uber/submitqueue/submitqueue/extension/buildrunner"
+	buildfake "github.com/uber/submitqueue/submitqueue/extension/buildrunner/fake"
 	buildrunnermock "github.com/uber/submitqueue/submitqueue/extension/buildrunner/mock"
-	buildnoop "github.com/uber/submitqueue/submitqueue/extension/buildrunner/noop"
 	"github.com/uber/submitqueue/submitqueue/extension/storage"
 	storagemock "github.com/uber/submitqueue/submitqueue/extension/storage/mock"
 	"go.uber.org/mock/gomock"
@@ -74,7 +74,7 @@ func newMockStorage(ctrl *gomock.Controller, batch entity.Batch) *storagemock.Mo
 }
 
 // newTestController creates a controller with test dependencies. br is the
-// build runner to inject; pass buildnoop.New() for the pass-through default.
+// build runner to inject; pass buildfake.New() for the pass-through default.
 // staticBuildRunnerFactory is a test factory that returns a fixed BuildRunner
 // for any entityqueue.
 type staticBuildRunnerFactory struct{ r buildrunner.BuildRunner }
@@ -111,7 +111,7 @@ func TestNewController(t *testing.T) {
 	ctrl := gomock.NewController(t)
 	batch := testBatch()
 	store := newMockStorage(ctrl, batch)
-	controller := newTestController(t, ctrl, store, buildnoop.New(), nil)
+	controller := newTestController(t, ctrl, store, buildfake.New(), nil)
 
 	require.NotNil(t, controller)
 	assert.Equal(t, consumer.TopicKeyBuild, controller.TopicKey())
@@ -124,7 +124,7 @@ func TestController_Process_Success(t *testing.T) {
 
 	batch := testBatch()
 	store := newMockStorage(ctrl, batch)
-	controller := newTestController(t, ctrl, store, buildnoop.New(), nil)
+	controller := newTestController(t, ctrl, store, buildfake.New(), nil)
 
 	msg := entityqueue.NewMessage(batch.ID, batchIDPayload(t, batch.ID), batch.Queue, nil)
 	delivery := queuemock.NewMockDelivery(ctrl)
@@ -315,7 +315,7 @@ func TestController_Process_StorageFailure(t *testing.T) {
 	store.EXPECT().GetRequestStore().Return(storagemock.NewMockRequestStore(ctrl)).AnyTimes()
 	store.EXPECT().GetBuildStore().Return(storagemock.NewMockBuildStore(ctrl)).AnyTimes()
 
-	controller := newTestController(t, ctrl, store, buildnoop.New(), nil)
+	controller := newTestController(t, ctrl, store, buildfake.New(), nil)
 
 	msg := entityqueue.NewMessage("test-queue/batch/1", batchIDPayload(t, "test-queue/batch/1"), "test-queue", nil)
 	delivery := queuemock.NewMockDelivery(ctrl)
@@ -332,7 +332,7 @@ func TestController_Process_PublishFailure(t *testing.T) {
 
 	batch := testBatch()
 	store := newMockStorage(ctrl, batch)
-	controller := newTestController(t, ctrl, store, buildnoop.New(), fmt.Errorf("publish failed"))
+	controller := newTestController(t, ctrl, store, buildfake.New(), fmt.Errorf("publish failed"))
 
 	msg := entityqueue.NewMessage(batch.ID, batchIDPayload(t, batch.ID), batch.Queue, nil)
 	delivery := queuemock.NewMockDelivery(ctrl)
@@ -347,7 +347,7 @@ func TestController_InterfaceImplementation(t *testing.T) {
 	ctrl := gomock.NewController(t)
 	batch := testBatch()
 	store := newMockStorage(ctrl, batch)
-	controller := newTestController(t, ctrl, store, buildnoop.New(), nil)
+	controller := newTestController(t, ctrl, store, buildfake.New(), nil)
 
 	var _ consumer.Controller = controller
 }