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

docs/releases/21.0-full-selfhosting.md

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+# Phase 21.0 — Full Self‑Hosting (Release Notes)
+
+Date: 2025‑11‑06
+Status: COMPLETE
+
+## Summary
+Hakorune can now build Hakorune end‑to‑end under the defined DoD:
+- S1/S2 (deterministic v1 emit): const/compare/threeblock‑collect repeat 3× with identical normalized hash.
+- PRIMARY (no‑fallback): hv1 inline minimal reps (Option‑A/B) are green.
+- S3 (llvmlite + Nyash Kernel): link + run representatives pass with expected return codes.
+
+## What changed
+- v1 → llvmlite harness direct path
+  - tools/ny_mir_builder.sh now feeds v1 JSON straight to the Python harness and links against libnyash_kernel.a.
+- Python LLVM builder fixes
+  - compare: supports `cmp` (Lt/Le/Gt/Ge/Eq/Ne) and normalizes to `<, <=, >, >=, ==, !=`.
+  - ret: synthesizes a small PHI at block head to avoid ret=0 on multi‑pred blocks.
+  - mir_call: accepts both nested and flat shapes.
+- Using/alias (prod)
+  - modules mapping is considered first; missing aliases added for `selfhost.vm.hakorune-vm.str_cast` and `selfhost.vm.helpers.method_alias_policy`.
+  - Duplicate `using` lines cleaned in extern_provider.
+
+## How to verify (quick)
+- One‑shot (S1/S2 + PRIMARY + S3 auto):
+  ```bash
+  bash tools/smokes/v2/profiles/quick/core/phase2100/run_all.sh
+  ```
+- S3 only (auto when LLVM18/llvmlite present):
+  ```bash
+  NYASH_LLVM_S3=1 bash tools/smokes/v2/profiles/quick/core/phase2100/run_all.sh
+  ```
+
+## Environment
+- LLVM 18 (llvm-config-18) + llvmlite (Python 3)
+- For faster runs: prebuild
+  ```bash
+  cargo build --release --features llvm
+  cargo build --release -p nyash-llvm-compiler
+  cargo build --release -p nyash_kernel
+  ```
+
+## Next
+- Optional: broaden reps and harden typeops/extern coverage in follow‑on phases.
+