feat(phase21.5): MirBuilder optimization prep + crate EXE infrastructure

Phase 21.5 optimization readiness - C-level performance target:
- MirBuilder: JsonFrag purify toggle (HAKO_MIR_BUILDER_JSONFRAG_PURIFY=1)
- Normalizer: extended f64 canonicalization + dedupe improvements
- loop_opts_adapter: JsonFrag path refinement for crate EXE compatibility

Infrastructure improvements:
- provider_registry: add diagnostics + ring-1 providers (array/console/map/path)
- mir_interpreter: add normalization/purify feature gates
- tools/selfhost_exe_stageb.sh: new end-to-end Stage-B→crate EXE pipeline
- tools/perf/microbench.sh: performance measurement tooling

Smoke tests (phase2100):
- Extend timeout 15s→120s for heavy crate EXE builds
- Add stageb_loop_jsonfrag_crate_exe_canary_vm.sh (target test)
- Add s3_backend_selector_crate_exe_vm_parity_return42_canary_vm.sh

Documentation:
- ENV_VARS.md: add Phase 21.5 optimization toggles
- README updates: clarify crate backend strategy
- phase215-optimization.md: new optimization roadmap

This commit sets the stage for Phase 21.5 critical optimization:
achieving C-level performance to decide hakorune's future viability.

tools/smokes/v2/README.md

@@ -1,29 +1,24 @@
-Smokes v2 — Quick vs Optional
+Smokes v2 — Minimal Runner and Policy
 
-Purpose
-- Keep an always‑on, fast “quick” subset to sanity‑check core paths every time.
-- Keep broader/experimental/host‑dependent reps as optional, SKIP‑guarded.
+Policy
+- Use [SKIP:<reason>] prefix for environment/host dependent skips.
+  - Examples: [SKIP] hakorune not built, [SKIP:env] plugin path missing
+  - Keep reasons short and stable to allow grep-based canaries.
+- Prefer JSON-only output in CI: set `NYASH_JSON_ONLY=1` to avoid noisy logs.
+- Diagnostics lines like `[provider/select:*]` are filtered by default in `lib/test_runner.sh`.
 
-Always‑on (quick)
-- Runner: `tools/smokes/v2/run_quick.sh`
-- Includes:
-  - Core crate/native reps (phase2100/run_all.sh) — SKIP when unavailable
-  - Stage‑B Program(JSON) shape (phase2160: stageb_* canaries)
-  - loop_scan minimal canaries (!=' + else Break/Continue)
+Helpers
+- `tools/smokes/v2/lib/mir_canary.sh` provides:
+  - `extract_mir_from_output` — between [MIR_BEGIN]/[MIR_END]
+  - `assert_has_tokens`, `assert_skip_tag`, `assert_order`, `assert_token_count`
+- `tools/lib/canary.sh` provides minimal, harness-agnostic aliases:
+  - `extract_mir_between_tags` — same as `extract_mir_from_output`
+  - `require_tokens token...` — fail if any token missing
 
-Optional (per‑phase)
-- Richer/experimental reps remain under `profiles/quick/core/phase*/run_all.sh` and individual canaries.
-- Examples:
-  - registry_* tag observation canaries (structure only)
-  - program_to_mir_exe_* (host/tooling dependent, SKIP‑guarded)
-
-Conventions
-- 3‑state outcomes: PASS / SKIP / FAIL（FAIL should be rare and intentional）
-- SKIP guards are preferred over brittle environment assumptions.
-- Add light canaries first; escalate to run_all only when stable and fast.
-
-Usage
-- Run quick set: `bash tools/smokes/v2/run_quick.sh`
-- Run a phase: `bash tools/smokes/v2/profiles/quick/core/<phase>/run_all.sh`
-- Run a single canary: `bash tools/smokes/v2/profiles/quick/core/<phase>/<name>_canary_vm.sh`
+Notes
+- Avoid running heavy integration smokes in CI by default. Use `--profile quick`.
+- When a test depends on external tools (e.g., LLVM), prefer `[SKIP:<reason>]` over failure.
 
+Quick tips
+- EXE-heavy cases (e.g., `phase2100/*`) may take longer. When running quick with these tests, pass a larger timeout like `--timeout 120`.
+- Smokes v2 auto-cleans temporary crate EXE objects created under `/tmp` (pattern: `ny_crate_backend_exe_*.o`) after the run.