feat(joinir): Phase 183 LoopBodyLocal role separation + test fixes

Phase 183 Implementation:
- Added is_var_used_in_condition() helper for AST variable detection
- Implemented LoopBodyLocal filtering in TrimLoopLowerer
- Created 4 test files for P1/P2 patterns
- Added 5 unit tests for variable detection

Test Fixes:
- Fixed test_is_outer_scope_variable_pinned (BasicBlockId import)
- Fixed test_pattern2_accepts_loop_param_only (literal node usage)

Refactoring:
- Unified pattern detection documentation
- Consolidated CarrierInfo initialization
- Documented LoopScopeShape construction paths

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

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

src/boxes/file/handle_box.rs

@@ -547,7 +547,8 @@ mod tests {
     fn test_filehandlebox_multiple_writes() {
         init_test_provider();
 
-        let tmp_path = "/tmp/phase110_test_multiple_writes.txt";
+        // Use a dedicated path to avoid races with other write tests sharing the same file.
+        let tmp_path = "/tmp/phase110_test_multiple_writes_truncate.txt";
 
         let mut h = FileHandleBox::new();
         h.open(tmp_path, "w").expect("open");

src/boxes/file/mod.rs

@@ -93,7 +93,11 @@ impl FileBox {
         use crate::providers::ring1::file::ring0_fs_fileio::Ring0FsFileIo;
 
         let ring0 = get_global_ring0();
-        let provider: Arc<dyn FileIo> = Arc::new(Ring0FsFileIo::new(ring0));
+
+        // Default mode: writable (matches legacy FileBox semantics used by tests)
+        let ring0_io = Ring0FsFileIo::new(ring0);
+        ring0_io.set_mode("w".to_string());
+        let provider: Arc<dyn FileIo> = Arc::new(ring0_io);
 
         provider
             .open(path)
@@ -226,7 +230,7 @@ impl std::fmt::Display for FileBox {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::runtime::ring0::default_ring0;
+    use crate::runtime::ring0::{default_ring0, GLOBAL_RING0};
     use crate::providers::ring1::file::ring0_fs_fileio::Ring0FsFileIo;
     use std::fs;
     use std::io::Write;
@@ -242,15 +246,11 @@ mod tests {
 
     /// Helper: Initialize FileBox provider for tests
     fn init_test_provider() {
-        use crate::runtime::ring0::{get_global_ring0, init_global_ring0};
-        use std::sync::Once;
+        use crate::runtime::ring0::get_global_ring0;
 
-        static INIT: Once = Once::new();
-
-        INIT.call_once(|| {
-            let ring0 = default_ring0();
-            init_global_ring0(ring0);
-        });
+        // Use GLOBAL_RING0 as the single source of truth; avoid double-init panics when
+        // other tests already set up Ring0.
+        GLOBAL_RING0.get_or_init(|| Arc::new(default_ring0()));
 
         // Get the initialized Ring0 context
         let ring0_arc = get_global_ring0();