Use preset path directly if it exists

[xarantolus]

I usually run just config load <filename> , which is nice because it works with shell completions. This makes that actually work, and falls back to the preset basename if no file with that name exists.

[Copilot]

Pull request overview

This PR updates the xtask config load flow to accept a direct preset file path when it exists, while retaining the previous behavior of loading a named preset from presets/ when no file is found.

Changes:

• Treat the preset argument as a file path if it points to an existing file.
• Fallback to presets/<preset_name>.toml when the provided path doesn’t exist.

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[Copilot]

Fallback path construction uses the entire preset_name string in format!("{preset_name}.toml"). If the user passes a filename that already ends with .toml (common with shell completion) or includes path components (e.g. presets/foo.toml), the fallback becomes presets/foo.toml.toml / presets/presets/foo.toml.toml and will never match the intended preset. Consider deriving the preset key from Path::new(preset_name).file_stem() (and/or file_name()) before appending .toml for the presets/ lookup.

Suggested change

	PathBuf::from("presets").join(format!("{preset_name}.toml"))
	{
	// Derive a preset key (file stem) to avoid double `.toml` or duplicated path segments.
	let preset_stem = Path::new(preset_name)
	.file_stem()
	.and_then(|s| s.to_str())
	.unwrap_or(preset_name);
	PathBuf::from("presets").join(format!("{preset_stem}.toml"))
	}

[Copilot]

pb.is_file() (and the fallback PathBuf::from("presets")...) resolve paths relative to the process working directory, not the current_dir/--root passed into this function. Since just config invokes the xtask with --root {{justfile_directory()}}, running just from a different directory can cause existing preset paths to be missed and the wrong fallback path to be used. Consider resolving relative preset_names (and the presets/ directory) against current_dir to make --root consistently control where presets are found.

Suggested change

	let pb = PathBuf::from(preset_name);
	let preset_path = if pb.is_file() {
	pb
	} else {
	PathBuf::from("presets").join(format!("{preset_name}.toml"))
	};
	// Resolve the preset path relative to `current_dir` (the `--root`), unless `preset_name` is absolute.
	let candidate = if Path::new(preset_name).is_absolute() {
	PathBuf::from(preset_name)
	} else {
	current_dir.join(preset_name)
	};
	let preset_path = if candidate.is_file() {
	candidate
	} else {
	current_dir
	.join("presets")
	.join(format!("{preset_name}.toml"))
	};

[Copilot]

The Load.preset CLI help text still says the argument "must correspond to a file in the presets/ directory without the .toml extension", but this function now accepts direct file paths as well. Update the clap docstring (and any related docs) so users discover the new behavior and don't get misled about what values are valid.

[github-actions]

LCOV of commit fe0ba87 during Osiris CI #395

Total coverage: 14.04%

lcov: WARNING: lcov: WARNING: RC option 'lcov_branch_coverage' is deprecated.  Consider using 'branch_coverage. instead.  (Backward-compatible support will be removed in the future
Summary coverage rate:
  lines......: 14.0% (232 of 1653 lines)
  functions..: 16.7% (39 of 233 functions)
  branches...: no data found

Files changed coverage rate: n/a