Optimize _prompt_custom_directory

The optimized code achieves a **364% speedup** (101ms → 21.7ms) through two targeted optimizations:

## 1. Theme Instance Caching (Primary Optimization)
The original code recreated a `CodeflashTheme()` instance on every call to `_get_theme()`. Line profiler shows this function was called 360 times, spending **88.2% of execution time** (133.4ms) just instantiating theme objects.

The optimization introduces a module-level cache (`_cached_theme`) that stores the theme after first creation. This reduces `_get_theme()` total time from **151.2ms to 17.4ms** (88.5% reduction), as subsequent calls simply return the cached instance instead of re-instantiating.

**Test Impact**: Basic path validation tests show **900-1000% speedup** (265μs → 25μs), stress tests with 50-100 invalid retries show **281-300% speedup** (16ms → 4.2ms), and deeply nested paths improve by **300-500%**. The caching is most effective in scenarios with multiple validation attempts, which is common when users enter incorrect paths.

## 2. Faster Absolute Path Check
The original code used `Path(path).is_absolute()` which instantiates a `Path` object just to check if a path is absolute. Line profiler shows this consumed **55.4%** of `validate_relative_directory_path()` time (4.28ms).

The optimization replaces this with `os.path.isabs(path)`, a lightweight string-based check that avoids object instantiation. This reduces the absolute path check from **4.28ms to 0.68ms** (84% reduction).

## Why This Works
- **Lazy initialization + caching** is a classic pattern for expensive object creation that's needed repeatedly
- `os.path.isabs()` is functionally equivalent to `Path().is_absolute()` for validation purposes but avoids the overhead of pathlib's object model
- The `CodeflashTheme` initialization likely involves terminal capability detection and color setup, making it expensive to repeat

## Context Considerations
While function references aren't available, the fact that `_get_theme()` was called 360 times in the test suite suggests this function is in a validation loop where users may enter multiple invalid paths before succeeding. The optimization particularly benefits workflows with:
- Multiple path validation attempts (common in CLI prompts)
- Batch operations validating many paths
- Integration tests that exercise the prompt repeatedly

The test results confirm this: single-path tests show 9-10x speedup, while tests with 50-100 retries show 3-4x speedup, demonstrating scalability benefits for both quick validations and extended retry scenarios.

Author: codeflash-ai[bot]

codeflash/cli_cmds/init_java.py

@@ -26,6 +26,8 @@
 from codeflash.code_utils.shell_utils import get_shell_rc_path, is_powershell
 from codeflash.telemetry.posthog_cf import ph
 
+_cached_theme = None
+
 
 class JavaBuildTool(Enum):
     """Java build tools."""
@@ -57,9 +59,11 @@ class JavaSetupInfo:
 
 def _get_theme():
     """Get the CodeflashTheme - imported lazily to avoid circular imports."""
-    from codeflash.cli_cmds.cmd_init import CodeflashTheme
-
-    return CodeflashTheme()
+    global _cached_theme
+    if _cached_theme is None:
+        from codeflash.cli_cmds.cmd_init import CodeflashTheme
+        _cached_theme = CodeflashTheme()
+    return _cached_theme
 
 
 def detect_java_build_tool(project_root: Path) -> JavaBuildTool:

codeflash/code_utils/code_utils.py

@@ -472,7 +472,8 @@ def validate_relative_directory_path(path: str) -> tuple[bool, str]:
 
     # Check for absolute paths, invalid characters, and validate path format
     error_msg = ""
-    if Path(path).is_absolute():
+    # Use os.path.isabs() which is faster than Path().is_absolute()
+    if os.path.isabs(path):
         error_msg = "Path must be relative, not absolute"
     elif os.name == "nt":  # Windows
         if any(char in _INVALID_CHARS_NT for char in path):