feat(joinir): Phase 248 - Normalized JoinIR infrastructure

Major refactoring of JoinIR normalization pipeline:

Key changes:
- Structured→Normalized→MIR(direct) pipeline established
- ShapeGuard enhanced with Pattern2 loop validation
- dev_env.rs: New development fixtures and env control
- fixtures.rs: jsonparser_parse_number_real fixture
- normalized_bridge/direct.rs: Direct MIR generation from Normalized
- pattern2_step_schedule.rs: Extracted step scheduling logic

Files changed:
- normalized.rs: Enhanced NormalizedJoinModule with DevEnv support
- shape_guard.rs: Pattern2-specific validation (+300 lines)
- normalized_bridge.rs: Unified bridge with direct path
- loop_with_break_minimal.rs: Integrated step scheduling
- Deleted: step_schedule.rs (moved to pattern2_step_schedule.rs)

New files:
- param_guess.rs: Loop parameter inference
- pattern2_step_schedule.rs: Step scheduling for Pattern2
- phase43-norm-canon-p2-mid.md: Design doc

Tests: 937/937 PASS (+6 from baseline 931)

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/mir/join_ir/frontend/ast_lowerer/mod.rs

@@ -52,24 +52,25 @@ enum FunctionRoute {
 }
 
 fn resolve_function_route(func_name: &str) -> Result<FunctionRoute, String> {
-    const IF_RETURN_NAMES: &[&str] = &["test", "local", "_read_value_from_pair"];
-    const LOOP_NAMES: &[&str] = &[
-        "simple",
-        "filter",
-        "print_tokens",
-        "map",
-        "reduce",
-        "fold",
-        "jsonparser_skip_ws_mini",
-        "jsonparser_atoi_mini",
+    const TABLE: &[(&str, FunctionRoute)] = &[
+        ("test", FunctionRoute::IfReturn),
+        ("local", FunctionRoute::IfReturn),
+        ("_read_value_from_pair", FunctionRoute::IfReturn),
+        ("simple", FunctionRoute::LoopFrontend),
+        ("filter", FunctionRoute::LoopFrontend),
+        ("print_tokens", FunctionRoute::LoopFrontend),
+        ("map", FunctionRoute::LoopFrontend),
+        ("reduce", FunctionRoute::LoopFrontend),
+        ("fold", FunctionRoute::LoopFrontend),
+        ("jsonparser_skip_ws_mini", FunctionRoute::LoopFrontend),
+        ("jsonparser_skip_ws_real", FunctionRoute::LoopFrontend),
+        ("jsonparser_atoi_mini", FunctionRoute::LoopFrontend),
+        ("jsonparser_atoi_real", FunctionRoute::LoopFrontend),
+        ("jsonparser_parse_number_real", FunctionRoute::LoopFrontend),
     ];
 
-    if IF_RETURN_NAMES.contains(&func_name) {
-        return Ok(FunctionRoute::IfReturn);
-    }
-
-    if LOOP_NAMES.contains(&func_name) {
-        return Ok(FunctionRoute::LoopFrontend);
+    if let Some((_, route)) = TABLE.iter().find(|(name, _)| *name == func_name) {
+        return Ok(*route);
     }
 
     if func_name == "parse_loop" {