@@ -4,7 +4,7 @@ Deciding which service of a multi-service domain an extension belongs to, and mo
 
 ## Status
 
-Implemented for SubmitQueue storage and for the core packages that served one service. `submitqueue/gateway/extension/storage` and `submitqueue/orchestrator/extension/storage` each declare a `Factory`, a `Storage` aggregate, and a MySQL schema. The fifteen store contracts, their mocks, and the error vocabulary remain at `submitqueue/extension/storage`. There is no `submitqueue/extension/storage/mysql` package. `submitqueue/extension/storage/BUILD.bazel` filegroups the two service schemas for deployments that colocate them.
+Implemented for SubmitQueue storage and for the core packages that served one service. `submitqueue/gateway/extension/storage` and `submitqueue/orchestrator/extension/storage` each declare a `Factory`, a `Storage` aggregate, and a MySQL schema. The thirteen store contracts, their mocks, and the error vocabulary remain at `submitqueue/extension/storage`. There is no `submitqueue/extension/storage/mysql` package. `submitqueue/extension/storage/BUILD.bazel` filegroups the two service schemas for deployments that colocate them.
 
 `submitqueue/core/batch` and `submitqueue/core/request` are not on disk. Batch helpers live in `submitqueue/orchestrator/core/batch`. Request-log publish and terminate live in `submitqueue/orchestrator/core/request`. The gateway materializer lives in `submitqueue/gateway/core/request`. `submitqueue/core` holds `changeset`, `messagequeue`, and `topickey`. `changeset` still declares `Stores` and `Resolve`, because `buildrunner`, `conflict`, and `speculation` are still domain-level packages that depend on it. Stovepipe keeps `stovepipe/extension/storage/mysql` because that domain is the service; that package is not a leftover SubmitQueue backend.
 
@@ -26,7 +26,7 @@ Separating the services onto their own databases already worked — the orchestr
 2. An extension shared between a domain's services stays wholly at `{domain}/extension/{ext}/` — including one used by a single service today but expected in both. `submitqueue/extension/queueconfig/` is gateway-only now and stays where it is on that basis. A single-service domain is unaffected: its domain root is its service root, so nothing moves.
 3. Storage is the extension this split applied to. `changeprovider`, `validator`, `conflict`, `buildrunner` and `speculation` are orchestrator-only and would qualify under Decision 1, but none has a schema and none was the reason for this change; they stay at `{domain}/extension/` until a later RFC takes them. The trigger for moving storage was a schema that a separate-database deployment must not over-provision.
 4. SubmitQueue's storage aggregate splits in two: `submitqueue/gateway/extension/storage/` declares a `Factory` and a four-accessor `Storage`, `submitqueue/orchestrator/extension/storage/` a `Factory` and a nine-accessor `Storage`. Neither can resolve the other's stores.
-5. `submitqueue/extension/storage/` keeps the fifteen store contracts, their mocks, the error vocabulary, `Config`, and the package README, which documents the contracts. Its import path does not change, so callers that name only a contract or an error are untouched.
+5. `submitqueue/extension/storage/` keeps the thirteen store contracts, their mocks, the error vocabulary, `Config`, and the package README, which documents the contracts. Its import path does not change, so callers that name only a contract or an error are untouched.
 6. The contract package is not promoted to `platform/`. It is not cross-domain — `stovepipe/extension/storage/storage.go` already declares its own verbatim copy of the same symbols, so a per-domain error vocabulary is the existing pattern rather than something this RFC introduces.
 7. Each half owns its own MySQL schema directory, so the tables a service creates are the tables it reads. A union target over both stays available for deployments that colocate the services — the end-to-end tests and the local compose stack take it and name no service directory. Split schemas are the opt-in, not the default.
 
@@ -60,11 +60,11 @@ Every store, verified against actual usage rather than intent.
 ```
 submitqueue/
 ├── extension/storage/                  # contracts, shared
-│   ├── {15 stores}_store.go            # BatchStore, RequestLogStore, …
+│   ├── {13 stores}_store.go            # BatchStore, RequestLogStore, …
 │   ├── storage.go                      # ErrNotFound, ErrAlreadyExists, ErrVersionMismatch,
 │   │                                   # IsNotFound, WrapNotFound, Config
 │   ├── README.md
-│   └── mock/                           # the 15 store mocks
+│   └── mock/                           # the 13 store mocks
 ├── gateway/extension/storage/
 │   ├── storage.go                      # Factory + Storage, 4 accessors
 │   ├── mock/                           # the aggregate's mock
 
@@ -25,8 +25,6 @@ go_library(
         "request_summary.go",
         "speculation.go",
         "subject.go",
-        "target_label.go",
-        "target_signature.go",
     ],
     importpath = "github.com/uber/submitqueue/submitqueue/entity",
     visibility = ["//visibility:public"],
 
@@ -0,0 +1,14 @@
+load("@rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "go_default_library",
+    srcs = [
+        "mock_store.go",
+        "store.go",
+        "target_label.go",
+        "target_signature.go",
+    ],
+    importpath = "github.com/uber/submitqueue/submitqueue/extension/conflict/tango",
+    visibility = ["//visibility:public"],
+    deps = ["@org_uber_go_mock//gomock:go_default_library"],
+)
@@ -0,0 +1,60 @@
+// Copyright (c) 2026 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.
+
+package tango
+
+//go:generate mockgen -source=store.go -destination=mock_store.go -package=tango
+
+import "context"
+
+// SignatureReader reads the target signature of a batch. It is the read-only
+// view of SignatureStore for consumers that must not write.
+type SignatureReader interface {
+	// Get returns the signature of batchID in the bound queue. The bool is
+	// false when no signature has been created for the batch.
+	Get(ctx context.Context, batchID string) (TargetSignature, bool, error)
+}
+
+// SignatureStore persists target signatures. A signature is immutable: it is
+// created once under (Queue, BatchID) and never updated. Reads and writes are
+// per-batch point operations, so any backend can implement it.
+type SignatureStore interface {
+	SignatureReader
+
+	// Create persists signature in one write. Returns an already-exists error
+	// if the bound queue already holds a signature for signature.BatchID, so the
+	// first signature written stays and the caller can read it back with Get.
+	Create(ctx context.Context, signature TargetSignature) error
+}
+
+// DictionaryReader reads the label recorded for a target ID. It is the
+// read-only view of DictionaryStore.
+type DictionaryReader interface {
+	// Get returns the label recorded for id in the bound queue. The bool is
+	// false when none has been recorded.
+	Get(ctx context.Context, id uint64) (TargetLabel, bool, error)
+}
+
+// DictionaryStore persists the target dictionary: one TargetLabel for each
+// 64-bit target ID. A record is immutable: it is created once under
+// (Queue, ID) and never updated. Two labels can share an ID, so the first label
+// recorded stays and the caller can read it back with Get to detect a collision.
+type DictionaryStore interface {
+	DictionaryReader
+
+	// Create persists label in one write. Returns an already-exists error if
+	// the bound queue holds a label for label.ID, whether or not it is the same
+	// label, so repeating a write is harmless.
+	Create(ctx context.Context, label TargetLabel) error
+}
@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package entity
+package tango
 
 // TargetLabel is one build target label and the 64-bit ID it hashes to. The
 // whole record is immutable: (Queue, ID) is its identity and there is no update
 
@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package entity
+package tango
 
 // TargetSignature is the set of build targets a batch changes, as 64-bit IDs.
 // The whole record is immutable: (Queue, BatchID) is its identity and there is
 
@@ -17,8 +17,6 @@ go_library(
         "request_uri_store.go",
         "speculation_path_set_store.go",
         "storage.go",
-        "target_dictionary_store.go",
-        "target_signature_store.go",
     ],
     importpath = "github.com/uber/submitqueue/submitqueue/extension/storage",
     visibility = ["//visibility:public"],
 
@@ -16,8 +16,6 @@ go_library(
         "request_summary_store_mock.go",
         "request_uri_store_mock.go",
         "speculation_path_set_store_mock.go",
-        "target_dictionary_store_mock.go",
-        "target_signature_store_mock.go",
     ],
     importpath = "github.com/uber/submitqueue/submitqueue/extension/storage/mock",
     visibility = ["//visibility:public"],