Add --only flag to commit to skip unassigned files

Add an -o/--only option to the commit command so only files assigned to 
the target stack are committed and unassigned files are excluded when 
requested. 

This was needed to provide finer control over commits (commit only 
assigned files) instead of always including unassigned files.

Changes:
- CLI: add --only (-o) boolean flag to commit args.
- Commit logic: respect the only flag and skip adding unassigned files when true.
- Main wiring: pass the only flag from CLI into commit handler.

Author: schacon

crates/but/src/args.rs

@@ -64,6 +64,9 @@ pub enum Subcommands {
         /// Stack ID or name to commit to (if multiple stacks exist)
         #[clap(short = 's', long = "stack")]
         stack: Option<String>,
+        /// Only commit assigned files, not unassigned files
+        #[clap(short = 'o', long = "only")]
+        only: bool,
     },
     /// Insert a blank commit before the specified commit, or at the top of a stack.
     New {

crates/but/src/commit/mod.rs

@@ -19,6 +19,7 @@ pub(crate) fn commit(
     _json: bool,
     message: Option<&str>,
     stack_hint: Option<&str>,
+    only: bool,
 ) -> anyhow::Result<()> {
     let project = Project::from_path(repo_path)?;
     let mut ctx = CommandContext::open(&project, AppSettings::load_from_default_path_creating()?)?;
@@ -78,10 +79,12 @@ pub(crate) fn commit(
     // Get files to commit: unassigned files + files assigned to target stack
     let mut files_to_commit = Vec::new();
 
-    // Add unassigned files
-    let unassigned =
-        crate::status::assignment::filter_by_stack_id(assignments_by_file.values(), &None);
-    files_to_commit.extend(unassigned);
+    if !only {
+        // Add unassigned files (unless --only flag is used)
+        let unassigned =
+            crate::status::assignment::filter_by_stack_id(assignments_by_file.values(), &None);
+        files_to_commit.extend(unassigned);
+    }
 
     // Add files assigned to target stack
     let stack_assigned = crate::status::assignment::filter_by_stack_id(

crates/but/src/main.rs

@@ -130,12 +130,13 @@ async fn main() -> Result<()> {
             metrics_if_configured(app_settings, CommandName::Restore, props(start, &result)).ok();
             result
         }
-        Subcommands::Commit { message, stack } => {
+        Subcommands::Commit { message, stack, only } => {
             let result = commit::commit(
                 &args.current_dir,
                 args.json,
                 message.as_deref(),
                 stack.as_deref(),
+                *only,
             );
             metrics_if_configured(app_settings, CommandName::Commit, props(start, &result)).ok();
             result