refactor(entity): promote Change + ChangeID to shared entity/change (#240)

## Summary

### Why?

`Change` (a code change identified by provider URIs) and the
GitHub/Phabricator `ChangeID` parsers are pure identity-and-parsing
types with no domain semantics and no persisted-as-shared schema. They
are the one cluster genuinely common to every code-change pipeline —
SubmitQueue today, and Stovepipe / Runway / Tango alignment going
forward — so they belong in the shared top-level `entity/` tree rather
than inside `submitqueue/entity/`.

This is deliberately the *only* promotion: facts a domain persists (the
change-provider model embedded in `ChangeRecord`), state machines, and
pipeline types stay domain-local, since sharing them would couple every
domain's storage schema and bend their state machines toward
SubmitQueue's.

### What?

Moves the canonical `Change` struct out of
`submitqueue/entity/request.go` into a new `entity/change` package, and
relocates the parser packages to `entity/change/github` and
`entity/change/phabricator` (preserving git history). No alias shim:
every consumer now references `change.Change` and imports the new path
directly. JSON tags are unchanged, so queue payloads (`Request`,
`LandRequest`, `PushResult`) remain byte-identical across a deploy.

`submitqueue/entity` keeps its full pipeline and facts; `Request`,
`LandRequest`, and `ChangeOutcome` now embed `change.Change`.

## Test Plan

- ✅ `make build`
- ✅ `make test` (51/51 pass)
- ✅ `make fmt` / `make gazelle` (converged, no further changes)
- ✅ `make check-tidy` (go.mod / MODULE.bazel unchanged — internal move,
no new deps)

Author: behinddwalls

entity/change/BUILD.bazel

@@ -0,0 +1,8 @@
+load("@rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "change",
+    srcs = ["change.go"],
+    importpath = "github.com/uber/submitqueue/entity/change",
+    visibility = ["//visibility:public"],
+)

entity/change/change.go

@@ -0,0 +1,32 @@
+// 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.
+
+// Package change holds the shared code-change identity used across SubmitQueue,
+// Stovepipe, and other repo-local domains. A Change names code to act on via
+// provider URIs; the URI parsers live in the github and phabricator subpackages.
+package change
+
+// Change represents a code change identified by URIs from a code change provider (e.g., GitHub Pull Request, Phabricator Diff).
+// The provider is extracted from the URI scheme. The object is immutable after creation.
+type Change struct {
+	// URIs identifies the change(s) to land (RFC 3986 compliant).
+	// The scheme identifies the change provider, and the path contains provider-specific resource identifiers.
+	//
+	// GitHub is supported by default (though other providers can be added):
+	//   Template: "<scheme>://<org>/<repo>/pull/<pr>/<head_commit_sha>"
+	//   Example:  "github://uber/submitqueue/pull/123/c3a4d5e6f7890123456789abcdef0123456789ab"
+	//   Schemes:  "github", "ghe", "ghes". Head commit SHA must be full 40-char lowercase hex.
+	//
+	URIs []string `json:"uris"`
+}

submitqueue/entity/github/BUILD.bazel entity/change/github/BUILD.bazelsubmitqueue/entity/github/BUILD.bazel renamed to entity/change/github/BUILD.bazel

@@ -3,7 +3,7 @@ load("@rules_go//go:def.bzl", "go_library", "go_test")
 go_library(
     name = "github",
     srcs = ["change_id.go"],
-    importpath = "github.com/uber/submitqueue/submitqueue/entity/github",
+    importpath = "github.com/uber/submitqueue/entity/change/github",
     visibility = ["//visibility:public"],
 )
 

submitqueue/entity/github/change_id.go entity/change/github/change_id.gosubmitqueue/entity/github/change_id.go renamed to entity/change/github/change_id.go

@@ -3,7 +3,7 @@ load("@rules_go//go:def.bzl", "go_library", "go_test")
 go_library(
     name = "phabricator",
     srcs = ["change_id.go"],
-    importpath = "github.com/uber/submitqueue/submitqueue/entity/phabricator",
+    importpath = "github.com/uber/submitqueue/entity/change/phabricator",
     visibility = ["//visibility:public"],
 )
 

…mitqueue/entity/github/change_id_test.go entity/change/github/change_id_test.gosubmitqueue/entity/github/change_id_test.go renamed to entity/change/github/change_id_test.go submitqueue/entity/github/change_id_test.go renamed to entity/change/github/change_id_test.go

@@ -54,7 +54,7 @@ var diffPattern = regexp.MustCompile(`^[1-9]\d*$`)
 //     code state, analogous to GitHub's head commit SHA on a pull request.
 type ChangeID struct {
 	// Scheme captures the URI scheme. Always "phab" today; kept as a field so
-	// the parsed form mirrors entity/github.ChangeID and so future variants
+	// the parsed form mirrors entity/change/github.ChangeID and so future variants
 	// (e.g., a separate scheme per Phabricator install) are a non-breaking add.
 	Scheme string
 	// RevisionID is the numeric portion of the Phabricator revision identifier

…bmitqueue/entity/phabricator/BUILD.bazel entity/change/phabricator/BUILD.bazelsubmitqueue/entity/phabricator/BUILD.bazel renamed to entity/change/phabricator/BUILD.bazel submitqueue/entity/phabricator/BUILD.bazel renamed to entity/change/phabricator/BUILD.bazel

@@ -9,6 +9,7 @@ go_library(
     importpath = "github.com/uber/submitqueue/submitqueue/core/changeset",
     visibility = ["//visibility:public"],
     deps = [
+        "//entity/change",
         "//submitqueue/entity",
         "//submitqueue/extension/storage",
     ],
@@ -19,6 +20,7 @@ go_test(
     srcs = ["resolver_test.go"],
     embed = [":changeset"],
     deps = [
+        "//entity/change",
         "//submitqueue/entity",
         "//submitqueue/extension/storage/mock",
         "@com_github_stretchr_testify//assert",

…mitqueue/entity/phabricator/change_id.go entity/change/phabricator/change_id.gosubmitqueue/entity/phabricator/change_id.go renamed to entity/change/phabricator/change_id.go submitqueue/entity/phabricator/change_id.go renamed to entity/change/phabricator/change_id.go

@@ -26,6 +26,7 @@ package changeset
 import (
 	"context"
 
+	"github.com/uber/submitqueue/entity/change"
 	"github.com/uber/submitqueue/submitqueue/entity"
 )
 
@@ -39,7 +40,7 @@ type Resolver interface {
 	// changes (URIs only; no change-store read), in batch.Contains order. A batch
 	// with no requests yields an empty slice. Used by the build (base/head) and
 	// merge stages.
-	ChangesForBatch(ctx context.Context, batch entity.Batch) ([]entity.Change, error)
+	ChangesForBatch(ctx context.Context, batch entity.Batch) ([]change.Change, error)
 
 	// DetailedForBatch resolves a batch into its normalized, batch-level view:
 	// one entity.ChangeInfo per claimed URI (URI plus the provider details read