feat(stovepipe): add storage extension with RequestStore + RequestURIStore (MySQL)

Add the stovepipe `storage` extension and its first backend, so the pipeline can persist validation requests and look them up. Mirrors the SubmitQueue storage conventions (factory `Storage` interface, `ErrNotFound`/`ErrAlreadyExists`/`ErrVersionMismatch` sentinels, metrics-wrapped MySQL ops, optimistic-locking CAS where version arithmetic stays in the caller).

Two stores, one per table:

- `RequestStore` (`request` table) — `Create` (ErrAlreadyExists on duplicate ID), `Get` by ID (ErrNotFound), and `Update`, a pure conditional write that takes the full `Request` plus `oldVersion`/`newVersion` and persists the mutable fields (uri, state) only if the stored version matches (ErrVersionMismatch otherwise).
- `RequestURIStore` (`request_uri` table) — the reverse index from a validated commit to its request, keyed by `(queue, uri)`: `Create` (ErrAlreadyExists on a duplicate `(queue, uri)` — the dedup signal backing the RFC's `(Queue, head URI)` key) and `GetIDByURI` (ErrNotFound). Kept a separate store because it is a separate table; the two are written independently so the contract stays satisfiable by key/value backends.

Includes the MySQL implementation, schema (`request.sql`, `request_uri.sql`), generated mocks, and a docker-compose integration test covering create/get/update-CAS/not-found/duplicate and the URI mapping (including dedup and per-queue isolation).

Author: behinddwalls

stovepipe/extension/storage/BUILD.bazel

@@ -0,0 +1,13 @@
+load("@rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "storage",
+    srcs = [
+        "request_store.go",
+        "request_uri_store.go",
+        "storage.go",
+    ],
+    importpath = "github.com/uber/submitqueue/stovepipe/extension/storage",
+    visibility = ["//visibility:public"],
+    deps = ["//stovepipe/entity"],
+)

stovepipe/extension/storage/mock/BUILD.bazel

@@ -0,0 +1,17 @@
+load("@rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "mock",
+    srcs = [
+        "request_store_mock.go",
+        "request_uri_store_mock.go",
+        "storage_mock.go",
+    ],
+    importpath = "github.com/uber/submitqueue/stovepipe/extension/storage/mock",
+    visibility = ["//visibility:public"],
+    deps = [
+        "//stovepipe/entity",
+        "//stovepipe/extension/storage",
+        "@org_uber_go_mock//gomock",
+    ],
+)

stovepipe/extension/storage/mock/request_store_mock.go

@@ -0,0 +1,19 @@
+load("@rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "mysql",
+    srcs = [
+        "request_store.go",
+        "request_uri_store.go",
+        "storage.go",
+    ],
+    importpath = "github.com/uber/submitqueue/stovepipe/extension/storage/mysql",
+    visibility = ["//visibility:public"],
+    deps = [
+        "//platform/metrics",
+        "//stovepipe/entity",
+        "//stovepipe/extension/storage",
+        "@com_github_go_sql_driver_mysql//:mysql",
+        "@com_github_uber_go_tally//:tally",
+    ],
+)