refactor(tooling): organize build, CI, and test owners (#38130)

* refactor(tooling): organize test runtime and maintenance owners

* test(tooling): preserve relocated runtime fixture dependency edges

* refactor(tooling): preserve xterm routing owner checks

* ci(tooling): include routing owner in sparse checkout

* test(tooling): preserve copied workflow dependency closures

* fix(tooling): normalize hashed JSON assets in release parity

* fix(tooling): distinguish asset aliases from literal references

* fix(tooling): frame normalized asset reference payloads

* fix(tooling): normalize decoded JSON asset references

* refactor(tooling): organize build, CI and release owners

* fix(tooling): align moved generator and workflow path contracts

* fix(tooling): update generated plugin bundle owner banners

* test(tooling): create relocated mobile verifier fixture directories

* test(tooling): copy headless detector dependency closure

* test(tooling): align native batch policy fixtures with owner path

* fix(tooling): link moved reliability command to historical evidence

* fix(tooling): preserve nested sandbox owners and canonical guide source

* fix(tooling): target release version owners in checkout fixture

config/scripts/git/pr-diff-base/git-pull-request-diff-base.mjs

@@ -0,0 +1,33 @@
+import { execFileSync } from 'node:child_process'
+import process from 'node:process'
+import { pathToFileURL } from 'node:url'
+
+export function selectPullRequestDiffBase(requestedBase, headParents, eventName) {
+  if (eventName === 'pull_request' && headParents.length >= 2) {
+    return headParents[0]
+  }
+  return requestedBase
+}
+
+export function resolvePullRequestDiffBase(
+  root,
+  requestedBase,
+  eventName = process.env.GITHUB_EVENT_NAME
+) {
+  const [, ...headParents] = execFileSync('git', ['rev-list', '--parents', '-n', '1', 'HEAD'], {
+    cwd: root,
+    encoding: 'utf8'
+  })
+    .trim()
+    .split(/\s+/)
+  return selectPullRequestDiffBase(requestedBase, headParents, eventName)
+}
+
+// Print shared gate’s resolved base so workflow shell gates can use merge-ref HEAD^1 instead of requiring full history for payload merge-base.
+if (process.argv[1] && import.meta.url === pathToFileURL(process.argv[1]).href) {
+  const resolved = resolvePullRequestDiffBase(process.cwd(), process.argv[2])
+  if (!resolved) {
+    throw new Error('No diff base: pass the pull request base SHA, or run on a merge ref.')
+  }
+  process.stdout.write(`${resolved}\n`)
+}