release: v21.0.0 – Full Self‑Hosting (S1/S2/S3 complete)

- DoD met: S1/S2 determinism (const/compare/threeblock-collect), PRIMARY hv1 inline no-fallback, S3 (llvmlite+kernel) reps green
- Harness: v1→llvmlite direct, EXE links to libnyash_kernel.a
- Python LLVM builder fixes: cmp normalization, ret PHI synthesis, mir_call flat shape
- Using/alias polish (prod): modules-first; missing aliases added; duplicate using cleaned
- Docs: phase-21.0 COMPLETE; CurrentTask closed; release notes added

CHANGELOG.md

@@ -26,3 +26,13 @@ Notes
 - docs: Added ARCHITECTURE.md, LOWERING_LLVM.md, EXTERNCALL.md, PLUGIN_ABI.md.
 - nyrt: resolved plugin module duplication; build green.
 - builder: suppressed StringBox birth (constructed in LLVM path).
+## 2025‑11‑06 — Phase 21.0 (Full Self‑Hosting)
+- Full Self‑Hosting achieved (DoD met):
+  - S1/S2 determinism: v1 emit for const/compare/threeblock‑collect repeats 3× with identical normalized hash.
+  - PRIMARY no‑fallback (hv1 inline): selfhost_v1 minimal Option‑A/B reps PASS (rc=42).
+  - S3 (llvmlite + Nyash Kernel link + run): ternary collect (rc=44) / map set→size (rc=1) PASS. Auto‑runs when LLVM18/llvmlite is present.
+- Harness/root changes:
+  - ny_mir_builder.sh routes v1 JSON directly to llvmlite harness; EXE links against libnyash_kernel.a.
+  - Python LLVM builder fixes: cmp field normalization (Lt/Le/… → < <= …), ret PHI synthesis (avoid ret=0), flat mir_call shape acceptance.
+- Using/alias polish (prod): modules mapping preferred; missing module aliases added (StrCast / MethodAliasPolicy). Duplicate using in VM extern_provider cleaned.
+- Docs: phase‑21.0 marked COMPLETE (Quick Verify updated). CURRENT_TASK closed.