Docs: remove What Is Not Implemented after all release gates pass

Parent: #134 Depends on: #147, #140, #141, #142, #143, #144, #145, #146

Track the final, reviewable change that removes the README What Is Not Implemented section after every implementation and evidence gate is genuinely complete.

This is the terminal documentation issue, not a duplicate implementation umbrella: implementation remains in #134 and its children; the compatibility/evidence matrix remains in #147.

Required implementation gates

• Every declared Home and Bun private-JSC profile reaches zero pending inventoried entries, with unknown revisions rejected explicitly.
• The Objective-C bridge and inspector/debugger profiles are complete for their pinned targets.
• WebAssembly and the selected post-MVP feature profiles are implemented and pass versioned upstream inventories.
• Every relevant PR-249 WebAssembly/JIT shell hook is implemented or explicitly dispositioned with no hidden skips.
• Moving/compacting, multi-age generational GC and parallel mid-script minor collection pass relocation, weak-reference, leak, stress, and TSan gates (#446 and #447 remain).
• The optimizing JIT includes speculation, deoptimization, OSR, stack maps, invalidation, precise-GC integration, and declared architecture coverage.

Final evidence and README gate

• #147 publishes a checked-in compatibility matrix covering exact OS, architecture, ABI, Wasm, GC, and JIT targets.
• Normal, no-GIL, stress, leak, sanitizer/TSan, differential, bridge, inspector, ABI, Wasm, and JIT evidence is green with no unexplained exclusions.
• README benchmark scores are regenerated from the latest committed single-thread, multithread, and JavaScriptCore artifact and clearly separate correctness from speed.
• Unsupported hosts, revisions, or profiles fail clearly instead of exposing partial behavior.
• Remove the section and its table-of-contents entry in one final commit, replacing any still-useful target limitations with links to the versioned compatibility matrix.

Completion rule

Close this issue only after the README no longer needs the warning section because every claim is backed by the exact declared inventories and evidence. No universal-JavaScriptCore claim is implied beyond those named targets.

Current checkpoint

The release matrix is 10/12 green at 9e51e1ff. PR-249 and the optimizing JIT are complete. Only #446 automatic shared compaction evidence and #447 moving nursery remain before the final evidence batch and README removal.

WebAssembly MVP gate progress: #141 and #260 are complete. README.md now removes the upstream MVP inventory/runtime from the missing-surface list and publishes the 16,801/16,801 observable-command score. The remaining WebAssembly README caveat is correctly narrowed to post-MVP profiles and PR-249 WebAssembly/JIT shell hooks; #261 tracks supplemental bit-exact NaN corpus execution. The terminal removal gate remains open for #142/#143 and the private ABI, GC, optimizing-JIT, and compatibility-matrix work.

The complete WebAssembly MVP chain #141/#260/#261 is now closed. README evidence is 18,840/18,840 applicable wg-1.0 commands passing with 0 failures/runner errors, and the missing-surface section contains only post-MVP profiles plus PR-249 WebAssembly/JIT shell hooks. #142 and #143 remain the genuine WebAssembly-side removal gates.

README removal progress: post-MVP WebAssembly is no longer wholly unimplemented. #262, #269, and #270 are complete; the README now names opt-in sign-extension, saturating conversion, and multi-value support while retaining the remaining-profile caveat. Reference types #271, bulk memory #272, structural score #273, and #264-#268 still block removing that caveat entirely.

WebAssembly removal-gate progress: #274 is complete. The runtime now has tagged funcref/externref slots with ordinary and no-GIL precise-GC publication, identity preservation, and exact reclamation after overwrite/drop/unwind. Focused evidence is 145/145 plus a dedicated 3/3 no-GIL filter at e2f01223; README/docs were refreshed in 72bcfad0. The WebAssembly gate remains open for #275, #272, #273 and the later selected profiles.

WebAssembly removal-gate update: d2fca189 adds tagged arbitrary externref tables plus JavaScript externref Table/Global identity and exact GC reclamation; focused evidence is now 151/151 with zero skips/failures/leaks. README/docs are current at 7e9417c9. #275 remains open for reference-valued function-call boundaries and final multi-table/cross-instance evidence.

WebAssembly removal-gate progress: reference types #271/#274/#275 are complete. The runtime now covers feature-gated reference instructions, multiple typed tables and exact explicit indices, arbitrary externref Table/Global identity and reclamation, canonical reference-valued JS/Wasm calls, mixed multi-value references, and cross-instance indirect calls. Focused evidence is 153/153 at d3736891; the strengthened table-index witness is green at 5374e601; README/docs are current at bfb22343. Remaining WebAssembly gates are bulk memory #272, structural score #273, later profiles #264-#267, and matrix #268.

WebAssembly removal-gate progress: bulk memory #272/#276-#278 is complete alongside multi-value and reference types. Focused evidence is 159/159 plus the final cross-instance/precise-GC 3/3 witness; README/docs at 03d46ae9 now list DataCount/passive segments and complete memory/table bulk operations as implemented. The next structural gate is exact profile score #273; later profiles #264-#268 and PR-249 #143 remain open.

WebAssembly Core 2 structural evidence advanced: #263 and #273 are now complete. The committed pinned inventory scores 27,437/27,437 applicable commands across 90/90 official wg-2.0 files, with 581 explicit text-format n/a commands and zero failures/runner errors. README/docs are current through 66a953a, and the July 17 1,540-sample single-thread/multithread/JSC benchmark remains current because these paths do not execute in those workloads. This terminal issue remains open: SIMD/Threads/exceptions-tail-calls/memory64-GC, PR-249 hooks, private ABIs, production GC, optimizing JIT, and final matrix gates are still outstanding.

README status was refreshed in dfff7df3: Threads is no longer described as unimplemented. The section now names only terminal Threads proposal-script/TSan/scaling evidence under #287, while retaining this issue as the evidence-backed gate for eventually removing the entire “What Is Not Implemented” section.

README-removal progress: the WebAssembly Threads proposal-script caveat is now obsolete and was removed in bf258e90. The complete pinned Threads corpus passes 551/551 with zero failures/n/a/runner errors and has a checked-in exact inventory. The broader WebAssembly gate remains open for the other selected post-Core-2 profiles/shell hooks and #287's terminal TSan/scaling evidence; no checkbox is prematurely closed.

README benchmark evidence advanced again on main: the new WebAssembly Threads section links the 105-sample raw/report artifact, presents 1/2/4/8-worker atomic and wait/notify results, preserves the equivalent ordinary-JS and SIMD JSC comparisons, and explicitly records why shared Wasm is N/A in the public system-JSC embedding. The terminal README-removal gate remains open for the broader implementation roadmap and #287 host-wide TSan evidence.

README-gate progress: ff6004d removes the stale “remaining Wasm GC failures” limitation and publishes the terminal GC score (697 / 697 applicable, zero failures). The warning section remains intentionally present and #246 stays open because the broader WebAssembly gate still includes Memory64/multi-memory coverage (#300/#305), alongside the private ABI, shell-hook, moving-GC, and optimizing-JIT gates already listed here.

README progress in c2d6d61b: the status table now publishes the latest combined GC + multi-memory score (1,526/1,526 applicable), and the stale “remaining multi-memory profile coverage” caveat was removed after the independent 829/829 terminal corpus. The README remains compact at 97 lines / 730 words. This tracker correctly stays open for Memory64, private ABI, shell/JIT, moving-generational GC, and final evidence gates.

README progress in b5567501: Memory64 is now published at 13,826/13,826 applicable, combined with terminal multi-memory in one compact status row, and the stale “remaining Memory64 terminal profile coverage” caveat has been removed. README size is 98 lines / 727 words. The section still correctly remains for private ABI, shell/JIT, moving-generational GC, and final evidence gates.

The README deletion gate is now executable in 54f183f. zig build release-compatibility-check requires ## What Is Not Implemented while any #134 gate is open; zig build release-ready currently refuses and names the eight blockers. When all 12 matrix gates become green, the same checker flips the invariant and requires the section to be absent.

README editorial checkpoint: the landing page is currently 77 lines / 491 words, with the latest accepted July 17 single-thread, eight-lane independent, cold-lifecycle, shared-realm no-GIL, and JSC comparison matrix still embedded. The warning section remains intentionally present because the implementation gates above are not yet complete; no ABI implementation prose is being added back to the root README.

The moving/compacting portion of the GC prerequisite is complete and #144 is closed with green terminal evidence. The README warning remains necessary for multi-age/parallel-minor completion (#145/#365), private ABI, WebAssembly Core 3/post-MVP (#366), PR-249, and optimizing-JIT gates; no premature section removal.

README removal-gate update: #366/#142 are complete. The exact terminal Core 3 audit passes 63,964/63,964 applicable commands across 258/258 files, and the ten-profile matrix passes 151,802/151,802 applicable commands with zero failures/runner errors. The WebAssembly/profile checkbox is now complete; PR-249 shell hooks (#143), private ABI (currently 124 pending), multi-age/parallel-minor GC, optimizing JIT, and final release evidence still correctly keep the warning section present. The root README remains concise and its accepted benchmark scores are unchanged.

README removal-gate update: moving/compacting plus multi-age/parallel-minor GC are complete, with the generated README headline linked to 112 raw samples. The warning still correctly remains for private ABI, PR-249 shell hooks, optimizing JIT, platform/final release evidence.

Heap snapshot/profile child #403 is implemented on main through 7983fca: real VM-wide graph serialization, WebKit/V8 formats, stable relocation-safe IDs, external ArrayBuffer accounting, dominator retained sizes, OOM atomicity, both ownership ABIs, and Debug/ReleaseSafe/TSan evidence. The child remains open only for its exact fixing CI gate.

Heap snapshot prerequisite #403 is complete and closed. Its portable PR-249 graph/ownership case is promoted; the shared-collector-only election gate remains explicitly reference-only.

The optimizer and PR-249 implementation gates are now complete, and the exact compatibility matrix is published and CI-gated by 9e51e1ff. This remains open by design: #446 and #447 must complete before the final all-green evidence batch and README warning removal.