fix: expanduser in project_root, remove redundant cwd, add tests

- get_myclaude_project_root() now expands ~ in MYCLAUDE_PROJECT_ROOT
  (was resolving to ./~/path instead of $HOME/path)
- Extract hardcoded 16/8 depth limits as _MAX_WALK_DEPTH / _MAX_SOURCE_DEPTH
- Remove redundant cwd= from _run_pip_editable (already specified via -e)
- Add test_cwd_invalid_directory and test_env_var_expands_tilde
- Remove incorrect test_extra_args_forwarded (click.Group does not
  support forwarding arbitrary args; ctx.args is always empty)

bin/commands/update.py

@@ -23,7 +23,7 @@ def _run_make_install(root: Path) -> int:
 
 def _run_pip_editable(root: Path) -> int:
     cmd = [sys.executable, "-m", "pip", "install", "-e", str(root)]
-    return subprocess.run(cmd, cwd=str(root), check=False).returncode
+    return subprocess.run(cmd, check=False).returncode
 
 
 @click.command("update")

bin/project_root.py

@@ -3,6 +3,9 @@
 import os
 from pathlib import Path
 
+_MAX_WALK_DEPTH = 16
+_MAX_SOURCE_DEPTH = 8
+
 
 def _pyproject_names_myclaude(path: Path) -> bool:
     try:
@@ -14,7 +17,7 @@ def _pyproject_names_myclaude(path: Path) -> bool:
 
 def _walk_up_for_pyproject(start: Path) -> Path | None:
     p = start.resolve()
-    for _ in range(16):
+    for _ in range(_MAX_WALK_DEPTH):
         candidate = p / "pyproject.toml"
         if candidate.is_file() and _pyproject_names_myclaude(candidate):
             return p
@@ -33,7 +36,7 @@ def get_myclaude_project_root() -> Path:
     """
     env_root = os.environ.get("MYCLAUDE_PROJECT_ROOT")
     if env_root:
-        return Path(env_root).resolve()
+        return Path(env_root).expanduser().resolve()
 
     try:
         cwd = Path.cwd()
@@ -45,7 +48,7 @@ def get_myclaude_project_root() -> Path:
             return found
 
     here = Path(__file__).resolve().parent
-    for _ in range(8):
+    for _ in range(_MAX_SOURCE_DEPTH):
         pyproject = here / "pyproject.toml"
         if pyproject.is_file() and _pyproject_names_myclaude(pyproject):
             return here