diff --git a/stovepipe/core/messagequeue/BUILD.bazel b/stovepipe/core/messagequeue/BUILD.bazel
index 4920c8eb..f32ddbd0 100644
--- a/stovepipe/core/messagequeue/BUILD.bazel
+++ b/stovepipe/core/messagequeue/BUILD.bazel
@@ -19,7 +19,7 @@ go_library(
 
 go_test(
     name = "go_default_test",
-    srcs = ["process_test.go"],
+    srcs = ["messagequeue_test.go"],
     embed = [":go_default_library"],
     deps = [
         "@com_github_stretchr_testify//assert:go_default_library",
diff --git a/stovepipe/core/messagequeue/README.md b/stovepipe/core/messagequeue/README.md
index 2a4b32a3..15889fe1 100644
--- a/stovepipe/core/messagequeue/README.md
+++ b/stovepipe/core/messagequeue/README.md
@@ -7,5 +7,7 @@ Payloads are defined in proto3 (`proto/`, generated into `protopb/`) and seriali
 ## Stages
 
 - **process** (`TopicKeyProcess`, `ProcessRequest`) — ingest publishes the minted request id here once it accepts a new head; the process controller reloads the `Request` from storage and decides the build strategy. Only the id travels: producer and consumer share the store, so messages stay small and redelivery is idempotent.
+- **build** (`TopicKeyBuild`, `BuildRequest`) — process/analyze publishes the request id here once its build scope (`BuildStrategy`/`BaseURI`) is decided; the build controller reloads the `Request`, triggers the build, and persists the resulting `Build`. Partitioned by request id.
+- **buildsignal** (`TopicKeyBuildSignal`, `BuildSignal`) — build publishes the build id here after triggering; buildsignal re-publishes to itself between polls until the build reaches a terminal status. Partitioned by build id, so each build's poll loop is an independent partition. See [doc/rfc/stovepipe/steps/build.md](../../../doc/rfc/stovepipe/steps/build.md) and [buildsignal.md](../../../doc/rfc/stovepipe/steps/buildsignal.md).
 
 See [doc/rfc/messagequeue-contract.md](../../../doc/rfc/messagequeue-contract.md) for the contract conventions and `api/runway/messagequeue` for the external reference example.
diff --git a/stovepipe/core/messagequeue/messagequeue.go b/stovepipe/core/messagequeue/messagequeue.go
index e88933e1..0beb8f2a 100644
--- a/stovepipe/core/messagequeue/messagequeue.go
+++ b/stovepipe/core/messagequeue/messagequeue.go
@@ -42,9 +42,13 @@ type (
 	// minted request id to validate.
 	ProcessRequest = protopb.ProcessRequest
 
-	// BuildRequest is the payload process publishes to the build stage: the
-	// admitted request id whose persisted strategy and baseline build reloads.
+	// BuildRequest is the payload process/analyze publishes to the build stage:
+	// the request id to build.
 	BuildRequest = protopb.BuildRequest
+
+	// BuildSignal is the payload build publishes to the buildsignal stage, and
+	// buildsignal re-publishes to itself while polling: the build id to poll.
+	BuildSignal = protopb.BuildSignal
 )
 
 // marshalOpts keeps the JSON field names identical to the proto field names
diff --git a/stovepipe/core/messagequeue/process_test.go b/stovepipe/core/messagequeue/messagequeue_test.go
similarity index 88%
rename from stovepipe/core/messagequeue/process_test.go
rename to stovepipe/core/messagequeue/messagequeue_test.go
index 185de8de..9d1635db 100644
--- a/stovepipe/core/messagequeue/process_test.go
+++ b/stovepipe/core/messagequeue/messagequeue_test.go
@@ -44,6 +44,17 @@ func TestBuildRequestRoundTrip(t *testing.T) {
 	assert.True(t, proto.Equal(req, got), "round-tripped BuildRequest should equal the original")
 }
 
+func TestBuildSignalRoundTrip(t *testing.T) {
+	sig := &BuildSignal{Id: "bk-1001"}
+
+	data, err := Marshal(sig)
+	require.NoError(t, err)
+
+	got := &BuildSignal{}
+	require.NoError(t, Unmarshal(data, got))
+	assert.True(t, proto.Equal(sig, got), "round-tripped BuildSignal should equal the original")
+}
+
 // TestWireFormat locks the protojson encoding decision the contract relies on:
 // snake_case field names (UseProtoNames).
 func TestWireFormat(t *testing.T) {
@@ -58,7 +69,7 @@ func TestWireFormat(t *testing.T) {
 // no topic_keys option names an unknown key.
 func TestTopicKeysBindEveryTopicKey(t *testing.T) {
 	bound := map[string]int{}
-	for _, m := range []proto.Message{&ProcessRequest{}, &BuildRequest{}} {
+	for _, m := range []proto.Message{&ProcessRequest{}, &BuildRequest{}, &BuildSignal{}} {
 		keys := TopicKeys(m)
 		require.NotEmpty(t, keys, "message must declare a non-empty topic_keys option")
 		for _, key := range keys {
@@ -69,6 +80,7 @@ func TestTopicKeysBindEveryTopicKey(t *testing.T) {
 	keys := []TopicKey{
 		TopicKeyProcess,
 		TopicKeyBuild,
+		TopicKeyBuildSignal,
 	}
 
 	valid := map[string]bool{}
diff --git a/stovepipe/core/messagequeue/proto/BUILD.bazel b/stovepipe/core/messagequeue/proto/BUILD.bazel
index 95634720..f625ba47 100644
--- a/stovepipe/core/messagequeue/proto/BUILD.bazel
+++ b/stovepipe/core/messagequeue/proto/BUILD.bazel
@@ -1,6 +1,7 @@
 exports_files(
     [
         "build.proto",
+        "buildsignal.proto",
         "process.proto",
     ],
     visibility = ["//tool/proto:__pkg__"],
diff --git a/stovepipe/core/messagequeue/proto/build.proto b/stovepipe/core/messagequeue/proto/build.proto
index 5b607614..b30ce26e 100644
--- a/stovepipe/core/messagequeue/proto/build.proto
+++ b/stovepipe/core/messagequeue/proto/build.proto
@@ -23,12 +23,14 @@ option java_multiple_files = true;
 option java_outer_classname = "BuildProto";
 option java_package = "com.uber.submitqueue.stovepipe.messagequeue";
 
-// BuildRequest is the payload process publishes after admitting a request. Only
-// the request id travels; build reloads the request from storage and uses the
-// strategy and baseline process persisted at admission.
+// BuildRequest is the payload process/analyze publishes to the build stage once
+// the request's build scope (BuildStrategy/BaseURI) has been decided: only the
+// request id travels on the queue. build reloads the full Request from storage
+// by this id (producer and consumer share the store, so the id is enough and
+// redelivery stays idempotent). See doc/rfc/stovepipe/steps/build.md.
 message BuildRequest {
     option (uber.base.messagequeue.topic_keys) = "build";
 
-    // id is the admitted request id to build. Format: "request/<queue>/<counter>".
+    // id is the request id to build. Format: "request/<queue>/<counter>".
     string id = 1;
 }
diff --git a/stovepipe/core/messagequeue/proto/buildsignal.proto b/stovepipe/core/messagequeue/proto/buildsignal.proto
new file mode 100644
index 00000000..3868ad9e
--- /dev/null
+++ b/stovepipe/core/messagequeue/proto/buildsignal.proto
@@ -0,0 +1,37 @@
+// Copyright (c) 2025 Uber Technologies, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+syntax = "proto3";
+
+package uber.stovepipe.messagequeue;
+
+import "api/base/messagequeue/proto/messagequeue.proto";
+
+option go_package = "github.com/uber/submitqueue/stovepipe/core/messagequeue/protopb";
+option java_multiple_files = true;
+option java_outer_classname = "BuildSignalProto";
+option java_package = "com.uber.submitqueue.stovepipe.messagequeue";
+
+// BuildSignal is the payload build publishes to the buildsignal stage, and
+// buildsignal re-publishes to itself while polling: only the build id travels
+// on the queue. buildsignal reloads the full Build from storage by this id
+// (producer and consumer share the store, so the id is enough and redelivery
+// stays idempotent). See doc/rfc/stovepipe/steps/buildsignal.md.
+message BuildSignal {
+    option (uber.base.messagequeue.topic_keys) = "buildsignal";
+
+    // id is the build id to poll: the runner-assigned id minted by
+    // BuildRunner.Trigger (entity.Build.ID / entity.BuildID.ID).
+    string id = 1;
+}
diff --git a/stovepipe/core/messagequeue/protopb/BUILD.bazel b/stovepipe/core/messagequeue/protopb/BUILD.bazel
index 9a16d825..5c59a722 100644
--- a/stovepipe/core/messagequeue/protopb/BUILD.bazel
+++ b/stovepipe/core/messagequeue/protopb/BUILD.bazel
@@ -4,6 +4,7 @@ go_library(
     name = "go_default_library",
     srcs = [
         "build.pb.go",
+        "buildsignal.pb.go",
         "process.pb.go",
     ],
     importpath = "github.com/uber/submitqueue/stovepipe/core/messagequeue/protopb",
diff --git a/stovepipe/core/messagequeue/protopb/build.pb.go b/stovepipe/core/messagequeue/protopb/build.pb.go
index 60025cf8..e8150153 100644
--- a/stovepipe/core/messagequeue/protopb/build.pb.go
+++ b/stovepipe/core/messagequeue/protopb/build.pb.go
@@ -37,12 +37,14 @@ const (
 	_ = protoimpl.EnforceVersion(protoimpl.MaxVersion - 20)
 )
 
-// BuildRequest is the payload process publishes after admitting a request. Only
-// the request id travels; build reloads the request from storage and uses the
-// strategy and baseline process persisted at admission.
+// BuildRequest is the payload process/analyze publishes to the build stage once
+// the request's build scope (BuildStrategy/BaseURI) has been decided: only the
+// request id travels on the queue. build reloads the full Request from storage
+// by this id (producer and consumer share the store, so the id is enough and
+// redelivery stays idempotent). See doc/rfc/stovepipe/steps/build.md.
 type BuildRequest struct {
 	state protoimpl.MessageState `protogen:"open.v1"`
-	// id is the admitted request id to build. Format: "request/<queue>/<counter>".
+	// id is the request id to build. Format: "request/<queue>/<counter>".
 	Id            string `protobuf:"bytes,1,opt,name=id,proto3" json:"id,omitempty"`
 	unknownFields protoimpl.UnknownFields
 	sizeCache     protoimpl.SizeCache
diff --git a/stovepipe/core/messagequeue/protopb/buildsignal.pb.go b/stovepipe/core/messagequeue/protopb/buildsignal.pb.go
new file mode 100644
index 00000000..2e4eff18
--- /dev/null
+++ b/stovepipe/core/messagequeue/protopb/buildsignal.pb.go
@@ -0,0 +1,146 @@
+// Copyright (c) 2025 Uber Technologies, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Code generated by protoc-gen-go. DO NOT EDIT.
+// versions:
+// 	protoc-gen-go v1.36.10
+// 	protoc        v5.29.3
+// source: buildsignal.proto
+
+package protopb
+
+import (
+	reflect "reflect"
+	sync "sync"
+	unsafe "unsafe"
+
+	_ "github.com/uber/submitqueue/api/base/messagequeue/protopb"
+	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
+	protoimpl "google.golang.org/protobuf/runtime/protoimpl"
+)
+
+const (
+	// Verify that this generated code is sufficiently up-to-date.
+	_ = protoimpl.EnforceVersion(20 - protoimpl.MinVersion)
+	// Verify that runtime/protoimpl is sufficiently up-to-date.
+	_ = protoimpl.EnforceVersion(protoimpl.MaxVersion - 20)
+)
+
+// BuildSignal is the payload build publishes to the buildsignal stage, and
+// buildsignal re-publishes to itself while polling: only the build id travels
+// on the queue. buildsignal reloads the full Build from storage by this id
+// (producer and consumer share the store, so the id is enough and redelivery
+// stays idempotent). See doc/rfc/stovepipe/steps/buildsignal.md.
+type BuildSignal struct {
+	state protoimpl.MessageState `protogen:"open.v1"`
+	// id is the build id to poll: the runner-assigned id minted by
+	// BuildRunner.Trigger (entity.Build.ID / entity.BuildID.ID).
+	Id            string `protobuf:"bytes,1,opt,name=id,proto3" json:"id,omitempty"`
+	unknownFields protoimpl.UnknownFields
+	sizeCache     protoimpl.SizeCache
+}
+
+func (x *BuildSignal) Reset() {
+	*x = BuildSignal{}
+	mi := &file_buildsignal_proto_msgTypes[0]
+	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+	ms.StoreMessageInfo(mi)
+}
+
+func (x *BuildSignal) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*BuildSignal) ProtoMessage() {}
+
+func (x *BuildSignal) ProtoReflect() protoreflect.Message {
+	mi := &file_buildsignal_proto_msgTypes[0]
+	if x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use BuildSignal.ProtoReflect.Descriptor instead.
+func (*BuildSignal) Descriptor() ([]byte, []int) {
+	return file_buildsignal_proto_rawDescGZIP(), []int{0}
+}
+
+func (x *BuildSignal) GetId() string {
+	if x != nil {
+		return x.Id
+	}
+	return ""
+}
+
+var File_buildsignal_proto protoreflect.FileDescriptor
+
+const file_buildsignal_proto_rawDesc = "" +
+	"\n" +
+	"\x11buildsignal.proto\x12\x1buber.stovepipe.messagequeue\x1a.api/base/messagequeue/proto/messagequeue.proto\".\n" +
+	"\vBuildSignal\x12\x0e\n" +
+	"\x02id\x18\x01 \x01(\tR\x02id:\x0f\x8a\xb5\x18\vbuildsignalB\x82\x01\n" +
+	"+com.uber.submitqueue.stovepipe.messagequeueB\x10BuildSignalProtoP\x01Z?github.com/uber/submitqueue/stovepipe/core/messagequeue/protopbb\x06proto3"
+
+var (
+	file_buildsignal_proto_rawDescOnce sync.Once
+	file_buildsignal_proto_rawDescData []byte
+)
+
+func file_buildsignal_proto_rawDescGZIP() []byte {
+	file_buildsignal_proto_rawDescOnce.Do(func() {
+		file_buildsignal_proto_rawDescData = protoimpl.X.CompressGZIP(unsafe.Slice(unsafe.StringData(file_buildsignal_proto_rawDesc), len(file_buildsignal_proto_rawDesc)))
+	})
+	return file_buildsignal_proto_rawDescData
+}
+
+var file_buildsignal_proto_msgTypes = make([]protoimpl.MessageInfo, 1)
+var file_buildsignal_proto_goTypes = []any{
+	(*BuildSignal)(nil), // 0: uber.stovepipe.messagequeue.BuildSignal
+}
+var file_buildsignal_proto_depIdxs = []int32{
+	0, // [0:0] is the sub-list for method output_type
+	0, // [0:0] is the sub-list for method input_type
+	0, // [0:0] is the sub-list for extension type_name
+	0, // [0:0] is the sub-list for extension extendee
+	0, // [0:0] is the sub-list for field type_name
+}
+
+func init() { file_buildsignal_proto_init() }
+func file_buildsignal_proto_init() {
+	if File_buildsignal_proto != nil {
+		return
+	}
+	type x struct{}
+	out := protoimpl.TypeBuilder{
+		File: protoimpl.DescBuilder{
+			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
+			RawDescriptor: unsafe.Slice(unsafe.StringData(file_buildsignal_proto_rawDesc), len(file_buildsignal_proto_rawDesc)),
+			NumEnums:      0,
+			NumMessages:   1,
+			NumExtensions: 0,
+			NumServices:   0,
+		},
+		GoTypes:           file_buildsignal_proto_goTypes,
+		DependencyIndexes: file_buildsignal_proto_depIdxs,
+		MessageInfos:      file_buildsignal_proto_msgTypes,
+	}.Build()
+	File_buildsignal_proto = out.File
+	file_buildsignal_proto_goTypes = nil
+	file_buildsignal_proto_depIdxs = nil
+}
diff --git a/stovepipe/core/messagequeue/topics.go b/stovepipe/core/messagequeue/topics.go
index 44876958..cbc12387 100644
--- a/stovepipe/core/messagequeue/topics.go
+++ b/stovepipe/core/messagequeue/topics.go
@@ -28,8 +28,17 @@ const (
 	// controller consumes it, reloads the Request, and decides the build strategy.
 	TopicKeyProcess TopicKey = "process"
 
-	// TopicKeyBuild carries admitted requests from process to build. process
-	// publishes a BuildRequest (the request id) after it persists the strategy
-	// and baseline; build reloads the Request from storage.
+	// TopicKeyBuild carries requests whose build scope has been decided from
+	// process/analyze to the build stage. The producer publishes a BuildRequest
+	// (the request id) here; the build controller consumes it, reloads the
+	// Request, and triggers the build. Partitioned by request id.
 	TopicKeyBuild TopicKey = "build"
+
+	// TopicKeyBuildSignal carries builds to poll from build to the buildsignal
+	// stage, and from buildsignal back to itself between polls. Producers
+	// publish a BuildSignal (the build id) here; the buildsignal controller
+	// consumes it, polls the build runner, and records terminal status.
+	// Partitioned by build id, so each build's poll loop is an independent
+	// partition.
+	TopicKeyBuildSignal TopicKey = "buildsignal"
 )
diff --git a/tool/proto/BUILD.bazel b/tool/proto/BUILD.bazel
index fb86abe2..9e3f55d7 100644
--- a/tool/proto/BUILD.bazel
+++ b/tool/proto/BUILD.bazel
@@ -68,6 +68,7 @@ go_proto_generated_files(
     name = "stovepipe_core_messagequeue",
     srcs = [
         "//stovepipe/core/messagequeue/proto:build.proto",
+        "//stovepipe/core/messagequeue/proto:buildsignal.proto",
         "//stovepipe/core/messagequeue/proto:process.proto",
     ],
     gen_services = False,