🔍 Research: GPT-5-Codex capabilities and GitHub PR integration

## Summary
Investigated OpenAI's new GPT-5-Codex model and Codex GitHub PR review integration capabilities.

## GPT-5-Codex Analysis

### Benchmark Performance (Good)
- SWE-bench Verified: 74.5% (vs GPT-5's 72.8%)
- Refactoring tasks: 51.3% (vs GPT-5's 33.9%)
- Code review: Higher developer ratings

### Real-World Issues (Concerning)
- Users report degraded coding performance
- Scripts that previously worked now fail
- Less consistent than GPT-4.5
- Longer response times (minutes vs instant)
- "Creatively and emotionally flat"
- Basic errors (e.g., counting letters incorrectly)

### Key Finding
Classic case of "optimizing for benchmarks vs real usability" - scores well on tests but performs poorly in practice.

## Codex GitHub PR Integration

### Setup Process
1. Enable MFA and connect GitHub account
2. Authorize Codex GitHub app for repos
3. Enable "Code review" in repository settings

### Usage Methods
- **Manual**: Comment '@codex review' in PR
- **Automatic**: Triggers when PR moves from draft to ready

### Current Limitations
- One-way communication (doesn't respond to review comments)
- Prefers creating new PRs over updating existing ones
- Better for single-pass reviews than iterative feedback

## 'codex resume' Feature
New session management capability:
- Resume previous codex exec sessions
- Useful for continuing long tasks across days
- Maintains context from interrupted work

🐱 The investigation reveals that while GPT-5-Codex shows benchmark improvements, practical developer experience has declined - a reminder that metrics don't always reflect real-world utility\!

src/llvm_py/instructions/newbox.py

@@ -29,9 +29,22 @@ def lower_newbox(
         vmap: Value map
         resolver: Optional resolver for type handling
     """
-    # Use NyRT shim: nyash.env.box.new(type_name: i8*) -> i64
+    # Use NyRT shim: prefer birth_h for core boxes, otherwise env.box.new_i64x
     i64 = ir.IntType(64)
     i8p = ir.IntType(8).as_pointer()
+    # Core fast paths
+    if box_type in ("ArrayBox", "MapBox"):
+        birth_name = "nyash.array.birth_h" if box_type == "ArrayBox" else "nyash.map.birth_h"
+        birth = None
+        for f in module.functions:
+            if f.name == birth_name:
+                birth = f
+                break
+        if not birth:
+            birth = ir.Function(module, ir.FunctionType(i64, []), name=birth_name)
+        handle = builder.call(birth, [], name=f"birth_{box_type}")
+        vmap[dst_vid] = handle
+        return
     # Prefer variadic shim: nyash.env.box.new_i64x(type_name, argc, a1, a2, a3, a4)
     new_i64x = None
     for f in module.functions: