fix(parser): Stage-1 CLI infinite loop - MirBuilder-friendly refactoring (Part 1/3)

**Problem**: Stage-1 CLI hits VM step budget (infinite loops) in multiple functions
- ParserBox.parse_program2: bb2853→bb2854 loop
- StringHelpers.skip_ws: bb488→bb491 loop

**Root Cause**: MirBuilder bug with `loop(cont==1)` + nested `if-else` pattern
- PHI instructions with self-references
- Loop exit blocks jumping back to header instead of continuation

**Solution**: Refactor to MirBuilder-friendly pattern
```hako
// Before (causes infinite loop):
loop(cont == 1) {
  if guard > max { return j } else { guard++ }
  if condition { action } else { cont = 0 }
}

// After (MirBuilder-friendly):
loop(j < n) {
  if condition { j++; continue }
  break
}
```

**Changes**:
1. parser_box.hako: parse_program2 main loop refactored
   - 7 sections: ws→EOF/guard→parse_stmt2→progress guard→trace→semicolons→emit
   - Unconditional parse_stmt2 execution (no nested if-else)
   - Explicit `break` for loop exits

2. string_helpers.hako: StringHelpers.skip_ws simplified
   - Removed `cont` flag and guard counter
   - Direct `loop(j < n)` with `continue/break`

3. vm.rs, vm_fallback.rs: RUST_MIR_DUMP_PATH support
   - Enables offline MIR analysis for debugging

**Progress**:
- ✅ parse_program2: infinite loop fixed
- ✅ StringHelpers.skip_ws: infinite loop fixed
- ⏳ ParserIdentScanBox.scan_ident: next target (bb985 loop)

**Testing**:
- MIR dumps generated successfully (116K+ lines)
- ws_init loop completes
- parse_program2 progresses further
- Still hits infinite loop in scan_ident (Part 2 needed)

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

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

lang/src/compiler/parser/parser_box.hako

@@ -351,17 +351,20 @@ box ParserBox {
     }
 
     loop(cont_prog == 1) {
-      // ✅ TRACE: main_prog loop progress (Task先生推奨トレースポイント)
+      // ===== 1) WS SKIP (inline, simple structure) =====
-      local _loop_info = ""
+      loop(i < n) {
-      if trace == 1 && (guard_prog < 5 || (guard_prog % 10) == 0) {
+        local ch_ws = src.substring(i, i + 1)
-        _loop_info = "[parse_program2:main] count=" + ("" + guard_prog) +
+        if ch_ws == " " || ch_ws == "\n" || ch_ws == "\r" || ch_ws == "\t" {
-                     " i=" + ("" + i) + " n=" + ("" + n)
+          i = i + 1
-        if i < n {
+          continue
-          local _end = i + 40
-          if _end > n { _end = n }
-          _loop_info = _loop_info + " ctx=\"" + src.substring(i, _end) + "\""
         }
-        print(_loop_info)
+        break
+      }
+
+      // ===== 2) EOF/GUARD CHECK (early exit) =====
+      if i >= n {
+        cont_prog = 0
+        break
       }
 
       if max_prog > 0 {
@@ -371,117 +374,78 @@ box ParserBox {
             print("[parser/program2:guard] max iteration reached at pos=" + ("" + i))
           }
           cont_prog = 0
+          break
         }
       }
-      // Fail-fast: EOF まで進んでいれば即座にループを抜ける（無限走行防止）。
+
-      if i >= n {
+      // ===== 3) PARSE_STMT2 + GPOS_GET (unconditional execution) =====
-        cont_prog = 0
+      local start_i = i
-        break
+      local s = me.parse_stmt2(src, i)
+      i = me.gpos_get()
+
+      // ===== 4) PROGRESS GUARD (ensure i always advances) =====
+      if i <= start_i {
+        if trace == 1 {
+          print("[parser/trace:program2] progress-guard bump i from " + ("" + start_i) + " to " + ("" + (start_i + 1)))
+        }
+        i = start_i + 1
+        if i > n { i = n }
+        me.gpos_set(i)
       }
+
+      // ===== 5) TRACE (simplified, at end) =====
       if trace == 1 {
-        local kind = "Stmt"
+        print("[parser/trace:program2] i=" + ("" + i) + " stmt_len=" + ("" + s.length()) + " guard=" + ("" + guard_prog))
-        if i >= n {
+      }
-          kind = "EOF"
+
+      // ===== 6) CONSUME OPTIONAL SEMICOLONS =====
+      local done_semi = 0
+      local guard_semi = 0
+      local max_semi = 100000
+
+      loop(done_semi == 0) {
+        if guard_semi > max_semi {
+          done_semi = 1
         } else {
-          if me.starts_with(src, i, "static box") == 1 { kind = "StaticBox" }
+          guard_semi = guard_semi + 1
-          else {
-            if me.starts_with(src, i, "box ") == 1 { kind = "BoxDecl" }
-            else {
-              if me.starts_with(src, i, "method ") == 1 { kind = "Method" }
-            }
-          }
-        }
-        print("[parser/trace:program2] pos=" + ("" + i) + " kind=" + kind + " stage3=" + ("" + me.stage3))
-        // Dev-only: small preview of remaining source to debug top-level progress
-        {
-          local head = ""
-          if i < n {
-            local end = i + 40
-            if end > n { end = n }
-            head = src.substring(i, end)
-          }
-          print("[parser/trace:program2] head=\"" + head + "\"")
-        }
-      }
-      // Inline skip_ws instead of calling me.skip_ws(src, i)
-      if i < n {
-        local ws_cont_1 = 1
-        loop(ws_cont_1 == 1) {
-          if i < n {
-            local ch1 = src.substring(i, i + 1)
-            if ch1 == " " || ch1 == "\n" || ch1 == "\r" || ch1 == "\t" { i = i + 1 }
-            else { ws_cont_1 = 0 }
-          } else { ws_cont_1 = 0 }
-        }
-      }
-
-      if i >= src.length() {
-        cont_prog = 0
-      } else {
-        local start_i = i
-        if trace == 1 {
-          print("[parser/trace:program2] before_stmt i=" + ("" + i))
-        }
-        local s = me.parse_stmt2(src, i)
-        i = me.gpos_get()
-        if trace == 1 {
-          print("[parser/trace:program2] after_stmt i=" + ("" + i) + " stmt_len=" + ("" + s.length()))
         }
 
-        // Progress guard
+        local before_semi = i
-        if i <= start_i {
-          if trace == 1 {
-            print("[parser/trace:program2] progress-guard bump i from " + ("" + start_i) + " to " + ("" + (start_i + 1)))
-          }
-          if i < src.length() { i = i + 1 }
-          else { i = src.length() }
-          me.gpos_set(i)
-        }
 
-        // consume optional semicolons
+        // Inline ws skip
-        local done2 = 0
+        loop(i < n) {
-        local guard2 = 0
+          local ch_semi = src.substring(i, i + 1)
-        local max2 = 100000
+          if ch_semi == " " || ch_semi == "\n" || ch_semi == "\r" || ch_semi == "\t" {
-
-        loop(done2 == 0) {
-          if guard2 > max2 { done2 = 1 }
-          else { guard2 = guard2 + 1 }
-
-          local before2 = i
-          // Inline skip_ws instead of calling me.skip_ws(src, i)
-          if i < n {
-            local ws_cont_2 = 1
-            loop(ws_cont_2 == 1) {
-              if i < n {
-                local ch2 = src.substring(i, i + 1)
-                if ch2 == " " || ch2 == "\n" || ch2 == "\r" || ch2 == "\t" { i = i + 1 }
-                else { ws_cont_2 = 0 }
-              } else { ws_cont_2 = 0 }
-            }
-          }
-
-          if i < src.length() && src.substring(i, i+1) == ";" {
             i = i + 1
-          } else {
+            continue
-            done2 = 1
           }
-
+          break
-          if i == before2 { done2 = 1 }
         }
 
-        if s.length() > 0 {
+        if i < n && src.substring(i, i+1) == ";" {
-          if first == 1 {
+          i = i + 1
-            if trace == 1 {
+        } else {
-              print("[parser/trace:program2] emit-first stmt_len=" + ("" + s.length()))
+          done_semi = 1
-            }
+        }
-            body = body + s
+
-            first = 0
+        if i == before_semi {
-          } else {
+          done_semi = 1
-            if trace == 1 {
+        }
-              print("[parser/trace:program2] emit stmt_len=" + ("" + s.length()))
+      }
-            }
+
-            body = body + "," + s
+      // ===== 7) EMIT STATEMENT =====
+      if s.length() > 0 {
+        if first == 1 {
+          if trace == 1 {
+            print("[parser/trace:program2] emit-first stmt_len=" + ("" + s.length()))
           }
+          body = body + s
+          first = 0
+        } else {
+          if trace == 1 {
+            print("[parser/trace:program2] emit stmt_len=" + ("" + s.length()))
+          }
+          body = body + "," + s
         }
       }
     }

lang/src/shared/common/string_helpers.hako

@@ -172,14 +172,13 @@ static box StringHelpers {
     local s = "" + src
     local n = s.length()
     local j = i
-    local cont = 1
+    // Simplified loop structure for MirBuilder compatibility
-    local guard = 0
+    loop(j < n) {
-    local max = 100000
+      if me.is_space(s.substring(j, j+1)) {
-    loop(cont == 1) {
+        j = j + 1
-      if guard > max { return j } else { guard = guard + 1 }
+        continue
-      if j < n {
+      }
-        if me.is_space(s.substring(j, j+1)) { j = j + 1 } else { cont = 0 }
+      break
-      } else { cont = 0 }
     }
     return j
   }

src/runner/modes/vm.rs

@@ -431,6 +431,15 @@ impl NyashRunner {
         }
 
         // Optional: dump MIR for diagnostics
+        // Phase 25.1: File dump for offline analysis (ParserBox等)
+        if let Ok(path) = std::env::var("RUST_MIR_DUMP_PATH") {
+            if let Ok(mut f) = std::fs::File::create(&path) {
+                let p = crate::mir::MirPrinter::new();
+                let _ = std::io::Write::write_all(&mut f, p.print_module(&module_vm).as_bytes());
+                eprintln!("[vm] MIR dumped to: {}", path);
+            }
+        }
+        // Existing: NYASH_VM_DUMP_MIR dumps to stderr
         if crate::config::env::env_bool("NYASH_VM_DUMP_MIR") {
             let p = crate::mir::MirPrinter::new();
             eprintln!("{}", p.print_module(&module_vm));

src/runner/modes/vm_fallback.rs

@@ -294,6 +294,15 @@ impl NyashRunner {
         }
 
         // Optional: dump MIR for diagnostics (parity with vm path)
+        // Phase 25.1: File dump for offline analysis (ParserBox等)
+        if let Ok(path) = std::env::var("RUST_MIR_DUMP_PATH") {
+            if let Ok(mut f) = std::fs::File::create(&path) {
+                let p = crate::mir::MirPrinter::new();
+                let _ = std::io::Write::write_all(&mut f, p.print_module(&module_vm).as_bytes());
+                eprintln!("[vm-fallback] MIR dumped to: {}", path);
+            }
+        }
+        // Existing: NYASH_VM_DUMP_MIR dumps to stderr
         if crate::config::env::env_bool("NYASH_VM_DUMP_MIR") {
             let p = crate::mir::MirPrinter::new();
             eprintln!("{}", p.print_module(&module_vm));