[karthik] fix: resolve debugger filepath-not-found on Linux

[Karthik-MP]

What

Fixes Filepath not found: <lowercase-path> spam on Linux startup, and the debugger failing to index any mixed-case file (e.g. Apps.py, Directory.py).

Closes #58.

Root cause

Two .lower() calls interacted to silently break the debugger on Linux:

debugger/debugger_backend/Directory.py:44

# Before
child_abspath = os.path.join(root_dir, child.path).lower()
if os.path.isfile(child_abspath):   # Always False on Linux for mixed-case names
    ordered_abspaths.append(...)    # Never reached → file not indexed

os.path.isfile("apps.py") returns False on Linux when the real file is Apps.py. Files are silently dropped from the index.

debugger/debugger_backend/Debugleton.py:78

# Before
filepath = filepath.lower()
filepath_id = self.abspaths.index(filepath)  # No match → "Filepath not found"

macOS HFS+/APFS is case-insensitive so both sides match regardless — the bug is invisible there.

Fix

Store real filesystem paths always. On darwin only, lowercase both the stored list and the lookup at compare time.

# Directory.py — remove .lower() before existence check
child_abspath = os.path.join(root_dir, child.path)

# Debugleton.py — platform-aware comparison
if sys.platform == "darwin":
    abspaths = [p.lower() for p in self.abspaths]
    filepath_id = abspaths.index(filepath.lower())
else:
    filepath_id = self.abspaths.index(filepath)

Test

Run bash backend/run.sh on Linux — no more Filepath not found lines on startup.

[Karthik-MP]

Fix summary

Stop lowercasing filesystem paths. Store and compare real (original-case) paths everywhere; only fold case on macOS, where the filesystem is case-insensitive.

Directory.py — store the real path so os.path.isfile succeeds for mixed-case files on Linux:

child_abspath = os.path.join(root_dir, child.path)

Debugleton.py — case-fold both sides only on macOS:

if sys.platform == "darwin":
    abspaths = [p.lower() for p in self.abspaths]
    filepath_id = abspaths.index(filepath.lower())
else:
    filepath_id = self.abspaths.index(filepath)

The caller (debug.py) passes os.path.abspath(code.co_filename), the real absolute path. On Linux it now matches the real-case index exactly; on macOS both sides are lowercased so case drift still matches.

Behavior matrix

Platform	Filesystem	Index step	Lookup step
Linux	case-sensitive	real path, isfile ok	exact match
macOS	case-insensitive	real path, isfile ok	lowercase both sides

Verification

• os.path.isfile("/tmp/ctest/apps.py") -> False (old, buggy path)
• os.path.isfile("/tmp/ctest/Apps.py") -> True (new, real path)
• Lookup logic tested both branches: Linux matches real case and rejects wrong case; darwin matches regardless of case.

Note

debugger/build/lib/... is a tracked setuptools build artifact that still holds the pre-fix code. It is not on the runtime import path (runtime imports debugger_backend, not build.lib.debugger_backend), so it does not affect behavior. Suggest a follow-up to git rm -r debugger/build and gitignore it.