Next.js v15.2.1 — Release Notes & Engineering Impact

### Core Changes - Unify Link and Form prefetching: #76184 - Turbopack: Ensure server actions sourcemaps tests pass: #76157 - [dev-overlay] control dark theme in one place: #76528 - [dev-overlay] change css var for terminal: #76590 - [dev-overlay] Discriminate stack frame settled typed: #76517 - Remove obsolete `sourcePackage` references: #76550 - refactor: remove unused variable in externals handling: #76599 - fix: Add popular embedding libraries to serverExternalPackages: #76574 - [Segment Cache] Implement hash-only navigations: #76179 - Webpack: abstract away getting compilation spans: #76579 - report compiler duration for webpack and improve numbers: #76665 - [dev-overlay] fix dark theme missing close bracket: #76672 - Remove `revalidate` property from incremental cache `ctx` for `FETCH` kind: #76500 - [dev-overlay] fix: env name label style was out of sync with error type label: #76668 - Turbopack: avoid celling source maps before minify: #76626 - refactor(CI): Merge all four bundler test manifest scripts into one: #76652 - [metadata] fix duplicate metadata for parallel routes: #76669 - [Segment Cache] Omit from bundle if flag disabled: #76622 - [Segment Cache] Support output: "export" mode: #75671 - [Segment Cache] Refresh on same-page navigation: #76223 - [metadata] re-enable streaming metadata with PPR: #76119 - [Segment Cache] Search param fallback handling: #75990 - [Segment Cache] Fix: canonicalURL omits origin: #76444 - fix metadata basePath for manifest: #76681 - Propagate expire time to `cache-control` header and prerender manifest: #76207 - Show revalidate/expire columns in build output: #76343 - Gate alternate bundler behind canary only: #76634 - [dynamicIO] routes with dynamic segments should be able to be static in dev: #76691 - [repo] upgrade ts `5.8.2`: #76709 - [metadata]: ensure metadata boundary is only rendered once on client nav: #76692 - [metadata] clean up redudant options: #76712 - Fix uniqueness detection for `generateStaticParams`: #76713 - Upgrade React from `22e39ea7-20250225` to `d55cc79b-20250228`: #76680 - [Turbopack] Compute module batches and use them for chunking: #76133 - [Dev Tools] Improve keyboard interactions for menu & overlays: #76754 - Keep server code out of browser chunks: #76660 - Turbopack: inline minify into code generation and make it a plain function instead of a turbo tasks function: #76628 - fix edge runtime asset fetch in pages api: #76750 - Update use-cache-unknown-cache-kind.test.ts snapshot for alternate bundler: #76682 ### Example Changes - docs: fix reading `params` code blocks: #76705 ### Misc Changes - fix(rustdoc): Fix rustdoc warnings, block on rustdoc failures in CI: #76448 - Update more global turbo CLI usage: #76576 - docs: Node.js runtime support for Middleware: #76556 - build: Update `swc_core` to `v16.0.0`: #76414 - Turbopack: prevent panic in swc issue emitter: #76595 - Unflake `parallel-routes-revalidation` test: #76600 - Fix `octokit.rest.issues.addLabels` call: #76601 - [test] Use new Redbox matchers in app/ error-recovery: #76552 - [test] Use new Redbox matchers in pages/ ReactRefreshLogBox-app-doc: #76551 - Run nightly bundler integration tests also with React 18: #76606 - 15.2: Add version history for `devIndicators` and note on deprecated options: #76611 - 15.2 docs: document missing `htmlLimitedBots` option: #76616 - Update bundler production test manifest: #76584 - Update bundler development test manifest: #76585 - Fix test after CI switched to pnpm 10: #76615 - chore(cna): fix theme extend for tailwind v4: #76583 - [test] Use new Redbox matchers in app/ ReactRefreshLogBoxMisc: #76563 - Don’t use native built-ins for additional bundler: #76577 - Revert "Run nightly bundler integration tests also with React 18": #76640 - Update bundler production test manifest: #76643 - Update bundler development test manifest: #76644 - Turbopack: dedupe middleware-manifest entries: #76621 - Turbopack: Improve edge tests: #76607 - Turbopack: add test test for css order: #76675 - Turbopack: fix order of chunk items in cycles: #76676 - [ci] Fix `test-turbopack-integration` not having any shards : #76355 - Update Turbopack development test manifest: #76658 - Update Turbopack production test manifest: #76659 - fix(CI): Upload to areweturboyet immediately after a manifest is updated, not only on a fixed cron schedule: #76688 - Update test snapshots for alternative bundler [4/n]: #76578 - fix(turbopack): Fix analysis of private properties: #76654 - Turbopack: Simplify emitDecoratorMetadata test: #76678 - [test] Use new Redbox matchers in pages/ ReactRefreshRegression: #76743 - [test] Remove `describeVariants` helper: #76631 - [test] Fix flaky error-recovery test: #76753 - [test] Use new Redbox matchers in app/ dynamic-error: #76744 - [test] Use new Redbox matchers in app/ rsc-runtime-errors: #76745 - Turbopack: avoid panic in module batches: #76757 - Revert "test: temporarily disable after deploy test": #74990 - `toDisplayRedbox()`: replace all occurrences of testDir: #76618 - Fix: missing close brace in demo code: #76549 - Disable flaky Turbopack tests: #76760 - feat(CI): Revalidate vercel data cache on areweturboyet after uploading data to KV store: #76693 - chore(github): move top prs and feature requests to different Slack channel: #76764 - Fix flaky Bun test: #76763 ### Credits Huge thanks to @acdlite, @bgw, @ijjk, @molebox, @kdy1, @timneutkens, @devjiwonchoi, @mischnic, @unstubbable, @eps1lon, @huozhi, @philipithomas, @delbaoliveira, @samcx, @wbinnssmith, @sokra, @gnoff, @leerob, @ztanner, @raunofreiberg, @lubieowoce, and @LihaoWang for helping!