[Sheraff]

Includes the oracle test-suite branch compiler-tests/baseline. That branch adds the oracle (packages/compiler-test-utils) and pins main's bugs as .fails. This PR replaces the compilers and turns the pins green.

Summary

Every TanStack build-time compiler now runs on one shared core built on Yuku. That covers route code splitting and route HMR (router-plugin), all of Start's transforms (server functions, environment separation, <Hydrate>, RSC CSS, import protection) and the route generator. Babel, babel-dead-code-elimination and the Prettier hot path are gone.

On main, Babel took ~90% of compiler time. On 333- and 1,485-route React and Solid apps, builds are 2.1–4.8× faster and dev cold start is 2.1–5.0× faster. Start builds also end with 3–10× less heap.

Each module and environment gets one parse and one plan. Outputs no longer depend on transform or request order, and source maps are exact. The oracle's known-bug pins drop from 874 to 45 (36 of those keep main's behaviour on purpose), and 29 open issues are fixed.

Architecture

Full map: packages/router-utils/src/compiler/README.md.

• Analysis → plan → emit. Each (env, module, text) gets one analysis and one plan. The plan emits the env module plus derived modules (?tsr-split=…, ?tss-hydrate=…, ?tss-serverfn-split, ?tss-serverfn-handler) and facts (import edges, server-fn registry, diagnostics, dependencies).
• Planners are the jobs. Each one adds edits and roots to the shared plan, in a fixed order: start-env → hydrate → rsc-css → route-hmr → route-split → import-edges. APIs are recognised by binding, through an abstract value domain. Cross-module summaries come from raw text, never from the bundler pipeline.
• Emit builds a rewrite tree over the original source ranges, so user code is never re-printed. OutputBuilder writes VLQ maps directly and composes them with input maps.
• Reachability = splitting = dead-code removal, at cluster granularity. Code is removed only when our own edits orphaned it, so user side effects and unread imports stay. One mutation model (who writes each binding, and when) decides what may move. If a split does not settle within its re-planning bound, the route stays unsplit and a warning is emitted.
• Lazy server-fn handlers (when SSR is the provider). The handlers, and what only they reach, move to ?tss-serverfn-handler, which loads on the first call. The defining module runs once.
• Verifier (TSR_COMPILER_VERIFY=1, on in all tests). Every output is re-parsed and checked: no assignment to an import, glue imports resolve, each effect is emitted once, and extracted outputs make no eager env-module reads.
• Caching and hosts. Caching is a plan cache, a dependency ledger and one invalidate(); no Yuku objects are retained. We own the hosts: a native Vite plugin, a Rspack/webpack loader, and Start Rsbuild loaders (with buildInfo replay for the persistent cache). unplugin remains only for the generator and esbuild.

Performance

Measured with benchmarks/compiler-perf at 774eba05a4 against main da2adec76d. Cells marked ² were re-measured at e80188ee7b. Both checkouts run in parallel on mirrored core sets, over 6 paired rounds; values are medians. Times are in ms and heap in MB. Large = 1,485 route files.

large app	build	dev cold → hydrated	compile-all	HMR route edit	dev heap after GC
react-start Vite	30,418 → 9,016	24,801 → 7,401	31,105 → 8,583	65.0 → 41.6	704 → 207
react-start Rsbuild ²	27,484 → 6,143	32,702 → 6,501	–	1,839 → 941	733 → 207
react-router Vite	11,208 → 3,058	11,647 → 2,989	26,984 → 5,026	53.8 → 31.4	113 → 89.7
solid-start Vite	42,999 → 20,019	30,690 → 10,299	43,902 → 19,417	193 → 30.2 ³	618 → 205
solid-router Vite	17,167 → 8,025 ²	14,349 → 4,354	40,273 → 15,426	876 (full reload) → 18.6	107 → 89.7

³ On main, this HMR run aborted in 5 of 6 rounds and full-reloaded 13 edits. This PR had no failures and no reloads.

• tanstack.com (e80188ee7b vs npm main, 6 paired rounds):
  • Build: 18.7 → 12.7 s (−32%).
  • Peak RSS: 3,916 → 3,342 MB (−15%).
  • Dev cold → hydrated: 29.3 → 24.2 s (−17%).
  • First visit of 15 routes, and HMR: parity.
• Corpus (064d29003a, 129 apps, medians of per-app Δ): build −12.1%, dev ready −18.8%, first render −10.5%, peak RSS −1.7%.
• 13 large apps: builds are 2–26% faster in 9 and at parity in 3. kroma (barrel-heavy) builds 2.6% faster (774eba05a4).
• Losses:
  • Build peak RSS: solid-router large +2.5% (+30 MB, e80188ee7b); kroma +3.8% (+64 MB, 774eba05a4).
  • Rsbuild minimal client: +1 / +3 B gzip (raw −22 B; accepted).
  • Server bytes (b25984c166): +308 B raw on Vite *.full, +696 B raw on react-start.rsbuild.full.
  • CodSpeed: +0.8–2.5 KB on 3 memory benchmarks (e80188ee7b).

All 11 cells, HMR, Vue, memory, bytes

Medium = 333 route files. Δ CIs are 95% t intervals of the paired log ratios.

cell	build	dev listen	dev cold → hydrated	compile-all	dev heap after GC	build peak RSS
react-start Vite medium	6,440 → 1,599	613 → 210	6,096 → 2,557	7,333 → 2,066	212 → 89.5	1,226 → 947
react-start Vite large	30,418 → 9,016	1,514 → 311	24,801 → 7,401	31,105 → 8,583	704 → 207	2,570 → 1,468
react-start Rsbuild medium ²	6,728 → 1,942	208 → 158	7,856 → 2,111	–	218 → 84.2	1,063 → 871
react-start Rsbuild large ²	27,484 → 6,143	210 → 159	32,702 → 6,501	–	733 → 207	2,819 → 2,081
react-start-deps Vite medium ¹	6,988 → 1,846	622 → 212	6,709 → 3,126	8,050 → 2,439	236 → 107	1,240 → 1,132
react-router Vite medium	2,742 → 568	585 → 178	3,348 → 1,024	6,525 → 1,282	64.0 → 47.2	751 → 569
react-router Vite large	11,208 → 3,058	1,381 → 278	11,647 → 2,989	26,984 → 5,026	113 → 89.7	1,283 → 1,041
solid-start Vite medium	9,472 → 4,408	623 → 266	7,371 → 3,226	10,719 → 4,561	191 → 92.3	1,334 → 1,121
solid-start Vite large	42,999 → 20,019	1,484 → 357	30,690 → 10,299	43,902 → 19,417	618 → 205	2,799 → 1,975
solid-router Vite medium	4,310 → 1,932	590 → 241	3,814 → 1,543	10,076 → 4,153	63.1 → 54.0	802 → 762
solid-router Vite large	17,167 → 8,025 ²	1,412 → 332	14,349 → 4,354	40,273 → 15,426	107 → 89.7	1,211 → 1,241 ²

¹ react-start plus a generated dependency graph and tanstack.com's manualChunks. Dev SSR fails on both sides here because of a ?url wasm asset in the harness, so <Hydrate> HMR is not measured.

• Speed: every cell is significantly faster. Build −53…−79%, listen −24…−80%, cold start −53…−80%, compile-all −56…−81%.
• HMR (p50): route component −15…−98%, loader −9…−55%, server fn −39…−79%. <Hydrate> is −8…−46% on Vite and −30 / −38% on Rsbuild ². Shared-module edits show no significant slowdown.
• Memory: heap after GC is lower everywhere (Solid Router compile-all n.s.). Peak RSS is lower except for the losses above. 100 edit + revert cycles show no growth (eedc638e42).
• 500-cycle soak (18ef570edc, KB/cycle, PR vs main): react-start Vite −0.7 vs 11.2, react-router Vite 2.3 vs 6.3, react-start Rsbuild 20.9. The soak found five records that grew with deleted files; all are fixed and tested. The remaining growth is upstream (vite#23907, rsbuild#8736).
• Start: import protection keeps a parsed AST per module in dev (hundreds of MB in large apps) #8614: import protection in dev adds +2.4 MB of heap, down from +321 MB.
• [Start] vite build keeps every environment's server-fn compiler alive until the build ends (memory stacks across client → ssr → server) #8794: in Start + Nitro builds, heap is 64.3 MB here, vs 506.5 MB on main and 98.7 MB on main with the issue's fix (fdc48254c8).
• Vue (1 paired round, medium; Vue Start / Vue Router): build 8,665 → 3,917 / 4,162 → 1,588 ms, cold start 10,692 → 3,073 / 5,017 → 1,349 ms. Every HMR edit applies in place, whereas main full-reloads Vue Router route edits.
• Other builds (eedc638e42): webpack build −38%, RSC build −74%.
• Generator without Prettier (498ac9be17): 715 → 94 ms. The react-start build floor drops from 1,629 to 779 ms.
• Client bytes (18 scenarios, b25984c166):
  • 12 are byte-identical.
  • *.full scenarios are −35…−47 B gzip, thanks to shorter server-fn ids.
  • Rsbuild minimal is larger because Rspack renumbers module ids once our loader request changes.
  • react-start.full brotli +92 B is q11 noise.
• Server bytes: Vite scenarios are −12…−419 B raw, except lazy handlers, which add +308 raw / ~+200 gzip per *.full scenario. react-start.rsbuild.full is +696 raw / +326 gzip:
  • +432 because the resolver imports the defining module, which makes __root a second concatenation root;
  • +264 from lazy handlers.
• SSR cold start (a server fn imports a 1.5 MB SDK that GET / never calls; main / eager handlers / this PR): Vite ~88 / ~145 / ~88 ms, Rsbuild ~57 / ~122 / ~57 ms.

Testing

The oracle (packages/compiler-test-utils/oracle) drives real bundlers, dev servers and browsers through public APIs only. Main's bugs are pinned as .fails.

	baseline (main's compilers, 80d1890bed)	this branch
tests	3,594	4,247
known-bug pins (.fails)	874	45
non-pin failures	0	0

• Oracle at b25984c166: all 8 unit and integration targets pass (4,247/4,247). With COMPILER_TESTS_PINS=run, each pin fails for its documented reason.
• CI at e80188ee7b: the Test job passes 881/881 Nx tasks. Compiler Platforms passes on all platforms except Linux arm64, which failed one router-utils unit test, pipeline.test.ts (f), an in-flight dependency-only edit.

Beyond the oracle:

• Real-app corpus: 190 public repos, each built and dev-tested with npm main and with this PR, in a network-restricted sandbox.
• Leak check: a canary in the server-only code of 124 in-repo Start apps.
• Differential fuzzers for compiler output (run against the untransformed source), the route generator, and HMR edit sequences on 5 frameworks.
• Internal verifier, on in all tests.
• Coverage-targeted tests.
• Three independent coherence reviews, each followed by a consolidation pass. Each pass kept client bytes identical and compile time at parity.

Every PR bug these found is fixed, with a regression test. The fuzz differences that remain are pre-existing on main or upstream.

Results

Corpus (b25984c166 vs npm main):

• Builds: 189/190 build on both. The 1 PR-only failure was a type-only import re-emitted as a value import, fixed in 390ca815c3.
• Bytes: client JS 405.01 → 404.72 MB, initial JS 101.42 → 96.92 MB.
• Leaks: 0 server-only canaries in client JS on either side.
• Dev: 158 equal, 18 PR better, 4 PR worse, 6 mixed, 4 both fail.
  • The 4 worse: the type import, a global-boundary reload (main's behaviour), a pre-existing Vite optimizer race, and noise.
• Route-edit HMR median: 159 → 105 ms (71 pairs).
• Bugs it found, all fixed:
  • effectful declarations only split code reads stayed eager (+110 KB initial);
  • extracted-export TDZ cycle;
  • server-only deps kept by function-local chains;
  • lost ASI before (/[;
  • handlers' server-only imports loaded at boot (500s; fixed by lazy handlers);
  • Solid Start fix edit not shown after an error.
• Main sometimes emits fewer chunks; that happens only with two @babel/traverse copies, which break main's DCE.

Leak check (139 builds per side, 5ff36a1816): 0 leaks here. Main leaks in mock mode; that case is pinned.

Fuzzers:

• Compiler (110,000 cases):
  • 0 env-separation differences.
  • 0 PR reference errors, wrong values or duplicated effects.
  • 1 TDZ fixed; unread imports are now kept, as on main.
• Generator (51,000 trees, each generated by main and four times by the PR):
  • 0 crashes or nondeterministic outputs.
  • 2 cases fixed.
• HMR (1,040 sequences):
  • 4 bugs fixed.
  • 322/1,540 steps full-reload, vs 740/1,436 on main.
  • The rest are pre-existing or upstream (solid-refresh#91, Protected Routes Implementation #92).

Coverage: lines 91.1 → 91.5%, branch arms 79.2 → 80.2%. No bug found; 2 unused paths deleted.

Vite 6 / 7 (5ff36a1816): the 13 router-plugin e2e projects pass on Vite 6.0.15, 6.4.5 and 7.3.7. Split Solid and Vue routes update in place, where main full-reloads.

Remaining fail pins (45)

reason	#	expected behaviour still missing
Kept main's behaviour on purpose	20	Route CSS applies only once the route matches. This needs a per-route asset loader (follow-up).
	16	A root route's error/not-found component loads lazily. Root routes are never split: splitting cost SSR CPU on error renders, and the chunk was preloaded anyway.
Bundler limitation	3	On rspack/webpack/rsbuild without sideEffects, an exported component another route's chunk imports loads with that chunk.
	2	On Rsbuild dev, a custom module type (.page as javascript/auto) importing a denied file is reported. Rspack rules select by resource.
	1	On Rsbuild build, an unused exported component with a boundary emits no async chunk.
Upstream	1	On Rsbuild dev, adding a route's first server fn shows on the open page (rspack#16288).
Not supported yet	1	On Vite dev, a Start library's undeclared CommonJS dependency is pre-bundled.
	1	In Vite bundledDev, a factory that becomes a server-fn builder keeps its handler. This needs the full-bundle API.

Behaviour changes

• routeTree.gen.ts formatting changes once. The file is printed in your quoteStyle/semicolons. enableRouteTreeFormatting now defaults to false (true uses Prettier, loaded lazily). Custom templates are inserted as written.
• Server-only server fns: a server fn that only server code calls, or that is only returned as data, is not HTTP-callable in production. Dev still answers it, with a warning.
• serverFns.generateFunctionId receives the stable key (greetUser) as functionName, and default ids are shorter.
• Server-fn handler modules run once, on the first call. A handler stays eager if it writes module state or its module uses top-level await.
• Exported page components are split (?tsr-split=export~Name), together with their augmentations. On one corpus app: −179 KB initial, +2.4 KB total.
• Imports read only by moved code move with that code. Unused imports stay, as on main.
• Stays unsplit, with a warning: route callbacks that read this (Handle route callbacks that reference this during code splitting #8688), and splits that never settle.
• Route HMR after a render error reloads the page in dev, as on main. This applies to any boundary on Solid/Vue, and to the global boundary on React.
• Import protection:
  • per-edge mocks export the target's names;
  • build verdicts come after tree-shaking;
  • onViolation returning false gets the real module;
  • traces follow the bundler graph.
• Route-group layout types match the runtime fullPath: '/', not ''.
• Rsbuild:
  • server-only routes are pruned from the client;
  • manifests list only a route's own chunks;
  • the persistent cache works;
  • spa.enabled dev serves the shell;
  • server.compress is no longer forced;
  • the server env shares async chunks;
  • RSC CSS HMR needs @rspack/core ≥ 2.2.9 (fix: reset MultiCompiler done state on watch restart web-infra-dev/rspack#15865); peer ranges are unchanged.
• Solid Start server envs split like the client. Vue Start dev no longer reloads after dependency optimization.
• Requirements:
  • router-plugin needs Vite ≥ 6;
  • a CommonJS webpack/rspack config needs Node 20.19+ or 22.12+;
  • esbuild + autoCodeSplitting: true throws;
  • @babel/core is no longer transitive, so declare it if a plugin needs it (e.g. React Compiler).
• Removed:
  • Babel-typed experimental hooks: codeSplittingOptions.compilerPlugins, Start compilerTransforms, serverFnProviderModuleDirectives and StartCompilerPlugin;
  • react-start-rsc/plugin/rscCssTransform, replaced by rsc: { loadCssExpression, providerDirective };
  • router-utils' Babel helpers (router-utils gains /compiler);
  • router-generator's format, inferFullPath, checkRouteFullPathUniqueness and writeIfDifferent. onRouteTreeChanged now receives { model }.
• New dev-only subpaths: @tanstack/router-core/hmr and @tanstack/{react,solid,vue}-router/hmr.

16 changesets. Minor bumps: router-utils, router-generator, router-plugin, router-core, start-plugin-core and react-start-rsc. Everything else gets a patch.

Follow-ups

• Server fns sent to the client as data: add an explicit createServerFn({ serializable: true }).
• Fully lazy route CSS (Unnecessary CSS being imported #4396): needs a router-core per-route asset loader.
• Prettier: make it an optional peer.
• Rsbuild __root cache group: unblocked now that the Rspack panic (rspack#16289) is fixed.
• Open issues to handle separately: the Start: the Vite plugin and tsr generate write different routeTree.gen.ts (Start footer added, then stripped) #8437 CLI half, server routes with a .ts extension gets the wrong boilerplate while creating the file. #4462, Vite HMR blank page when editing __root.tsx (Solid SSR) #6331 (solid-refresh#91), [@tanstack/react-start/plugin/rsbuild] tanstackStart() eclipses the client environment's output.assetPrefix, blocking downstream plugins #7827 and ssr: false routes still bundle components in server output #6400.
• Docs: with RSC, a server-fn module's state exists once for server fns and once for server components.
• Ports after merge: the "implementation obsolete" list below.

Upstream issues filed

✅ fixed · ✖ closed without a fix · ○ open

• Yuku: 26 ✅ fixed, 1 ✖ closed. Four of the fixes (Duplicated render after nevigate #288, Routes transitions don't use transitions? #289, How to resolve act(...) errors in components containing Link #291, Update peerDependency react-location to match higher versions #292) land in the next Yuku release. fix: render errorElement when route loader is rejected #290 was closed because the fix is deferred to Yuku's upcoming transformer; we don't need it.

  All 27

  ✅ #202 purity comments · ✅ #203 codegen SIGBUS · ✅ #204 JSX refs for _/$/Unicode · ✅ #229 import X = ns.Y · ✅ #230 decorators after export · ✅ #231 JSXText entities · ✅ #232 false duplicate export · ✅ #237 empty JSX container comments · ✅ #244 WASM stale bytes · ✅ #247 unwrap typing · ✅ #248 copyAst() · ✅ #251 export {} from · ✅ #252 import() specifiers · ✅ #253 big-endian decoding · ✅ #254 JSX attribute mapping · ✅ #255 postfix ++ parens · ✅ #256 for (init;;) no-in · ✅ #257 private method overloads · ✅ #258 import type {} · ✅ #259 super() in computed key · ✅ #260 JSX text after </> · ✅ #287 (a?.b)!.c · ✅ #288 JSXText escaping · ✅ #289 stale JSXText raw · ✖ #290 strip keeps type-only exports · ✅ #291 surrogate-pair spans · ✅ #292 Annex B functions

• Vite:

  • ○ #23719 saves within 50 ms are ignored
  • ○ #23907 the module graph keeps deleted files
  • ○ vite-plugin-vue#866 a removed export breaks HMR accept

• Rolldown:

  • ○ #11054 this.load() returns null in bundled-dev HMR
  • ○ #11223 stale moduleSideEffects in watch mode
  • ○ #11300 bundled-dev MissingFactoryError
  • ✅ #11341 a helper in a dynamic chunk causes an entry cycle (Start SSR bundle calls createServerFn before initialization with pnpm symlinked layout #8139)

• Rspack:

  • ○ #16288 HMR runs a module before its async chunk loads
  • ✅ #16289 splitChunks panic

• Rsbuild:

  • ✅ #8736 the dev FS keeps hot-update files (fix lands in the next release)

• solid-refresh (all ○):

  • #88 rename invalidate loop
  • #89 sticky first registry
  • #90 stale importer after a rename
  • #91 document remount (Vite HMR blank page when editing __root.tsx (Solid SSR) #6331)
  • #92 recursing proxies

• Others:

  • ○ magic-string#368 only \n counts as a line break
  • ○ babel-dead-code-elimination#50 typeof x keeps x
  • ○ webcontainer-core#2173 encodeInto('') returns stale data
  • ✅ tanstack.com#1353 the playground drops Start config

Issues

• Closes Server functions that are stored in a separate file cause middlewares to throw error #7213
• Closes "Server function info not found" when calling a server function that's *only* called on the server #8731
• Closes Start RSC mode: server functions imported only from 'use client' modules are missing from the production manifest ("Server function info not found") #7943
• Closes Start + Rsbuild: server-only routes are not pruned from the client route tree #8545
• Closes Start: symlinked route files skip the client-side server.handlers strip — server code and node-only imports ship in the client bundle #8514
• Closes Empty .ts route file is scaffolded with JSX, breaking all route generation #8480
• Closes Code-splitter breaks every route when the project path contains a single quote/apostrophe (autoCodeSplitting: false does not avoid it) #7754
• Closes router-plugin: object-form loader breaks the code splitter when loader is split #8753
• Closes Code splitter does not support the method shorthand syntax #8623
• Closes router-plugin: split chunk and shared module miss shared bindings when compiled before the route file #8754
• Closes router-plugin: a split route option that is also a shared binding exports an undeclared Split… when two @babel/traverse copies are installed #8715
• Closes Compiler correctness: split-route exports and distinct re-export aliases #8505
• Closes If you pass createServerOnlyFn(...) directly as an argument to createServerFn().handler(), it will generate a broken server function. #8446
• Closes start-plugin-core: the dev server-fn id validator's recovery can never succeed — it transforms under the one flag that skips the compile #8447
• Closes start-compiler-plugin fails to lazy-load dependencies with Vite bundledDev #8407
• Closes start-compiler-plugin: hotUpdate crashes with TypeError under vite experimental.bundledDev #8062
• Closes Start: Ssr doesn't reflect changes with bundledDev: true #7535
• Closes Server-fn transform filter regex rejects whitespace between . and handler/server/client, silently disabling transform after AST-roundtripping pre-plugins #7280
• Closes Bug: Breakpoints fail to attach in VSCode when autoCodeSplitting is enabled #6667
• Closes autoCodeSplitting on Rsbuild breaks source maps #3828
• Closes [Vite plugin][Module Federation] Multiple routers in the same window cause an Invalid Hook Call when the remote uses @tanstack/router-plugin — regression in 1.168.17 #7921
• Closes Route generation does not allow plain template literals anymore after 1.166.31 #7216
• Closes Start: user router.plugins never reach the route generator (start-plugin-core overwrites them) #7768
• Closes Start + Rsbuild: SPA mode dev server SSRs routes and runs loaders on the server #8543
• Closes Start + Rsbuild: plugin forces server.compress: false, overriding user config #8544
• Closes Handle route callbacks that reference this during code splitting #8688
• Closes Start: import protection keeps a parsed AST per module in dev (hundreds of MB in large apps) #8614
• Closes [Start] vite build keeps every environment's server-fn compiler alive until the build ends (memory stacks across client → ssr → server) #8794
• Closes Crash "TypeError: serverFn is not a function" when calling server function with nested server function multiple times #6451

Other issues:

• Start: the Vite plugin and tsr generate write different routeTree.gen.ts (Start footer added, then stripped) #8437, partially addressed: Start's footer follows quoteStyle/semicolons, but tsr generate still writes none.
• Crash "TypeError: serverFn is not a function" when calling server function with nested server function multiple times #6451, a Vite race fixed in Vite 8.2.2 (fix(module-runner): exclude completed modules from in-flight cycle detection (fix #22999) vitejs/vite#23009): main's peer range still allows 8.0–8.2.1. This PR compiles server fns in place, so it avoids the race on any Vite.
• Start: during build, warnings for imports from external modules that are never used #5721, not fixed here: it is already fixed on main.
• Start SSR bundle calls createServerFn before initialization with pnpm symlinked layout #8139, not fixed here: it is rolldown#11341, now fixed upstream. On an older Rolldown, set strictExecutionOrder: true on ssr.

Supersedes #8805, #8504, #8630, #8721, #8780, #8773, #8756, #8755, #8732, #8686, #8682, #8681, #8061, #8541, #8493, #8481, #8459, #8455, #7892, #8515, #7281, #8269, #8628, #8797, #8662, #8296, #8215, #8454, #8276, #8675, #8540, #8523, #8524, #8680, #8684, #8642, #8749, #8801, #7338, #8656, #8798, #8818

Implementation obsolete (still needs a re-port after merge): #8804, #7693, #7766, #7872, #8291, #8293, #8277, #8799, #8800, #6748, #8256, #8057, #7925

How to review

The diff is +164k/−75k lines in 2,000 files. The compiler-tests/baseline branch accounts for +102k/−42k of it, and most of the rest is tests and regenerated route trees. Product code (packages/*/src) is +31k/−23k in 211 files.

1. Core: start with router-utils/src/compiler/README.md, then read identity → source/analysis → units/mutation → rewrite → reach → plan → emit → values/summary/facts → cache/pipeline → verify. Keep tests/helpers.ts and tests/placement.test.ts open alongside.
2. Planners:
   • Router: router-plugin/ARCHITECTURE-CODE-SPLITTING.md, then src/planners/.
   • Start: start-plugin-core/src/planners/ (start-env, hydrate, rsc-css, edges), with src/compiler/, src/server-fns/ and src/import-protection/.
3. Hosts:
   • router-plugin/src/hosts/.
   • Start's src/vite/compiler-plugin.ts.
   • Start's src/rsbuild/ (read COMPILER_ARCHITECTURE.md first).
4. Generator and runtime:
   • router-generator (AGENTS.md, analyze/, model/, print/).
   • router-core/src/hmr.ts and {react,solid,vue}-router/src/hmr.ts.
   • start-client-core/src/createServerFn.ts.
5. Tests: the oracle's README.md, SPEC.md and KNOWN-BUGS.md.

To reproduce the measurements, see:

• packages/compiler-test-utils/oracle/README.md
• benchmarks/compiler-perf/README.md (run.mjs, compare.mjs, soak-analyze.mjs)
• pnpm benchmark:bundle-size:run
• scripts/benchmarks/bundle-size/server.mjs

---

This PR was written with AI assistance: Claude Code agents working under a human architect. Their work was checked against the oracle, e2e, perf and bytes gates above.

🤖 Generated with Claude Code

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[changeset-bot]

🦋 Changeset detected

Latest commit: 78db3da

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 24 packages

Name	Type
@tanstack/router-utils	Minor
@tanstack/router-plugin	Minor
@tanstack/start-plugin-core	Minor
@tanstack/vue-start	Patch
@tanstack/react-start-rsc	Minor
@tanstack/router-generator	Minor
@tanstack/router-cli	Patch
@tanstack/router-core	Minor
@tanstack/react-router	Patch
@tanstack/solid-router	Patch
@tanstack/vue-router	Patch
@tanstack/start-client-core	Patch
@tanstack/react-start	Patch
@tanstack/solid-start	Patch
@tanstack/router-vite-plugin	Patch
@tanstack/react-start-client	Patch
@tanstack/react-start-server	Patch
@tanstack/solid-start-client	Patch
@tanstack/solid-start-server	Patch
@tanstack/start-server-core	Patch
@tanstack/start-storage-context	Patch
@tanstack/vue-start-client	Patch
@tanstack/vue-start-server	Patch
@tanstack/start-static-server-functions	Patch

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Click here if you're a maintainer who wants to add another changeset to this PR