Function write_full_content 

pub fn write_full_content(
    file: ConfigFile,
    content: &str,
    dry_run: bool,
) -> Result<PatchOutcome, ConfigWriteError>

What: Atomically replace the entire content of a config file.

Inputs:

• file: Target ConfigFile.
• content: Full new content.
• dry_run: When true, do not modify disk.

Output:

• PatchOutcome mirroring patch_key semantics.

Errors

• ConfigWriteError::Io when the atomic temp-file write or rename fails.

Details:

• Used by callers that have already produced a fully serialized buffer (e.g. theme pre-commit validation that writes to a temp path, validates, then commits).