Function resolve_task 

pub fn resolve_task(
    cli: &Cli,
    explicit: Option<&str>,
    allow_branch: bool,
) -> Result<Option<ResolvedTask>, CliError>

Resolve a task ID from the priority chain: explicit → env → branch. Returns None if nothing is found — callers decide whether that’s an error.

allow_branch should be false for destructive or ambiguous commands (task delete, task link, task unlink, guest share-task, guest unshare-task).