Clear remaining low-risk review debt on the release branch

The PR still had a few targeted review threads around contributor pagination,
route-layer passthroughs, dead header fallbacks, and synthetic response ids.
These are small enough to settle directly on the release branch without
broadening the merge scope, and they tighten the repo back toward the
service-owned boundaries this refactor is aiming for.

Constraint: Keep the changes narrow and regression-covered so the release PR stays green while review threads are closed out
Rejected: Leave the minor threads for follow-up after merge | they were isolated enough to fix now and would keep noise on the PR
Confidence: high
Scope-risk: narrow
Directive: When a route shim stops serving any route-local behavior, point callers at the owning service instead of keeping a passthrough around
Tested: Focused vitest for contributor updater, openai responses response bridge, upstream request builder, stats proxy logs, architecture boundaries; typecheck; repo drift check; git diff --check
Not-tested: Full npm test; unresolved review threads that still require larger product decisions

scripts/dev/update-readme-contributors.test.ts

@@ -1,5 +1,6 @@
 import { describe, expect, it } from 'vitest';
 import {
+  parsePaginatedJson,
   normalizeContributors,
   replaceContributorsSection,
   renderContributorsBlock,
@@ -108,4 +109,11 @@ describe('README contributors updater', () => {
     expect(html).toContain('\n  <a href="https://github.com/Babylonehy"');
     expect((html.match(/\n  <a href=/g) || []).length).toBe(2);
   });
+
+  it('parses concatenated paginated gh api arrays without requiring newlines between pages', () => {
+    expect(parsePaginatedJson('[{"login":"a"}][{"login":"b"}]')).toEqual([
+      { login: 'a' },
+      { login: 'b' },
+    ]);
+  });
 });