Core Changes

• chore: warn when running tests against stale build: #88001
• Redesign default error pages with cleaner, more user-friendly UI: #87988
• dx: avoid next-env.d.ts change in dev: #88103
• prevent browser cache from using stale RSC responses from previous builds: #86554

Misc Changes

• chore: add Claude Code configuration: #87943
• test: reduce flakiness in opentelemetry test for prod mode: #88102
• Rename CLAUDE.md to AGENTS.md with symlink: #88105

Credits

Huge thanks to @feedthejim, @huozhi, and @ztanner for helping!