feat(phase21.5/22.1): MirBuilder JsonFrag refactor + FileBox ring-1 + registry tests

Phase 21.5 (AOT/LLVM Optimization Prep)
- FileBox ring-1 (core-ro) provider: priority=-100, always available, no panic path
  - src/runner/modes/common_util/provider_registry.rs: CoreRoFileProviderFactory
  - Auto-registers at startup, eliminates fallback panic structurally
- StringBox fast path prototypes (length/size optimization)
- Performance benchmarks (C/Python/Hako comparison baseline)

Phase 22.1 (JsonFrag Unification)
- JsonFrag.last_index_of_from() for backward search (VM fallback)
- Replace hand-written lastIndexOf in lower_loop_sum_bc_box.hako
- SentinelExtractorBox for Break/Continue pattern extraction

MirBuilder Refactor (Box → JsonFrag Migration)
- 20+ lower_*_box.hako: Box-heavy → JsonFrag text assembly
- MirBuilderMinBox: lightweight using set for dev env
- Registry-only fast path with [registry:*] tag observation
- pattern_util_box.hako: enhanced pattern matching

Dev Environment & Testing
- Dev toggles: SMOKES_DEV_PREINCLUDE=1 (point-enable), HAKO_MIR_BUILDER_SKIP_LOOPS=1
- phase2160: registry opt-in tests (array/map get/set/push/len) - content verification
- phase2034: rc-dependent → token grep (grep -F based validation)
- run_quick.sh: fast smoke testing harness
- ENV documentation: docs/ENV_VARS.md

Test Results
✅ quick phase2034: ALL GREEN (MirBuilder internal patterns)
✅ registry phase2160: ALL GREEN (array/map get/set/push/len)
✅ rc-dependent tests → content token verification complete
✅ PREINCLUDE policy: default OFF, point-enable only where needed

Technical Notes
- No INCLUDE by default (maintain minimalism)
- FAIL_FAST=0 in Bring-up contexts only (explicit dev toggles)
- Tag-based route observation ([mirbuilder/min:*], [registry:*])
- MIR structure validation (not just rc parity)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/using/ssot_bridge.rs

@@ -68,20 +68,32 @@ fn call_hako_box(name: &str, ctx: &SsotCtx) -> Option<String> {
         nn
     ));
 
-    // Write to a temp file
-    // Write ephemeral file; any failure → None (delegate to legacy)
-    let mut tf = tempfile::Builder::new()
+    // Write to a temp file (Fail-Fast aware)
+    let mut tf = match tempfile::Builder::new()
         .prefix("ny_ssot_")
         .suffix(".hako")
-        .tempfile()
-        .ok()?;
+        .tempfile() {
+        Ok(f) => f,
+        Err(e) => {
+            if crate::config::env::fail_fast() {
+                eprintln!("[failfast/ssot/tempfile] {}", e);
+                panic!("Fail-Fast: SSOT tempfile creation failed");
+            }
+            return None;
+        }
+    };
     let _ = write!(tf, "{}", code);
     let path = tf.path().to_path_buf();
-    // Resolve nyash binary; fallback to current exe or default path on failure
-    let bin = std::env::var("NYASH_BIN").ok().unwrap_or_else(|| {
-        if let Ok(p) = std::env::current_exe() { p.to_string_lossy().to_string() }
-        else { "target/release/nyash".to_string() }
-    });
+    // Resolve nyash binary; Fail-Fast aware fallback
+    let bin = if let Ok(b) = std::env::var("NYASH_BIN") { b } else {
+        if let Ok(p) = std::env::current_exe() { p.to_string_lossy().to_string() } else {
+            if crate::config::env::fail_fast() {
+                eprintln!("[failfast/ssot/nyash-bin] unable to resolve NYASH_BIN/current_exe");
+                panic!("Fail-Fast: cannot resolve nyash binary for SSOT child");
+            }
+            "target/release/nyash".to_string()
+        }
+    };
 
     // Stage‑3 + tolerance (matches smokes wrappers)
     let mut cmd = Command::new(bin);
@@ -99,9 +111,30 @@ fn call_hako_box(name: &str, ctx: &SsotCtx) -> Option<String> {
         .env("HAKO_USING_SSOT_HAKO", "0")
         .env("HAKO_USING_SSOT_RELATIVE", "0")
         .env("HAKO_USING_SSOT_INVOKING", "1");
-    // Any spawn/IO error → None (fail-safe to legacy)
-    let out = cmd.output().ok()?;
-    if !out.status.success() { return None; }
+    // Any spawn/IO error → Fail-Fast or None
+    let out = match cmd.output() {
+        Ok(o) => o,
+        Err(e) => {
+            if crate::config::env::fail_fast() {
+                eprintln!("[failfast/ssot/hako-spawn] {}", e);
+                panic!("Fail-Fast: SSOT child spawn failed");
+            }
+            return None;
+        }
+    };
+    if !out.status.success() {
+        if crate::config::env::fail_fast() {
+            eprintln!("[failfast/ssot/hako-exit] status={}", out.status);
+            panic!("Fail-Fast: SSOT child exited with error");
+        }
+        return None;
+    }
     let s = String::from_utf8_lossy(&out.stdout).trim().to_string();
-    if s.is_empty() { None } else { Some(s) }
+    if s.is_empty() {
+        if crate::config::env::fail_fast() {
+            eprintln!("[failfast/ssot/hako-empty]");
+            panic!("Fail-Fast: SSOT child produced empty output");
+        }
+        None
+    } else { Some(s) }
 }