refactor(command): improve formula commitment and buffer management

Refactor command execution and buffer management.

- `CommitFormula` now defaults to targeting `_Measure` .
- `CommitFormula` no longer automatically clears the buffer; buffer
  clearing is now handled by keymap sequences.
- Added `ClearBufferCmd` to the command registry.
- Updated `AddFormulaCmd` to support optional target category.
- Added `SetBuffer` effect to allow clearing buffers.

Co-Authored-By: fiddlerwoaroof/git-smart-commit (unsloth/gemma-4-26B-A4B-it-GGUF:UD-Q5_K_XL)

src/command/cmd/commit.rs

@@ -34,8 +34,10 @@ mod tests {
         );
     }
 
+    /// Formulas always target _Measure by default, even when no regular
+    /// categories exist. _Measure is a virtual category that always exists.
     #[test]
-    fn commit_formula_without_regular_categories_shows_status() {
+    fn commit_formula_without_regular_categories_targets_measure() {
         let m = Model::new("Empty");
         let layout = make_layout(&m);
         let reg = make_registry();
@@ -46,12 +48,12 @@ mod tests {
         let effects = CommitFormula.execute(&ctx);
         let dbg = effects_debug(&effects);
         assert!(
-            !dbg.contains("AddFormula"),
-            "Should not add formula when only virtual categories exist, got: {dbg}"
+            dbg.contains("AddFormula"),
+            "Should add formula targeting _Measure, got: {dbg}"
         );
         assert!(
-            dbg.contains("Add at least one category first"),
-            "Expected status message, got: {dbg}"
+            dbg.contains("_Measure"),
+            "target_category should be _Measure, got: {dbg}"
         );
     }
 
@@ -220,30 +222,23 @@ impl Cmd for CommitFormula {
     }
     fn execute(&self, ctx: &CmdContext) -> Vec<Box<dyn Effect>> {
         let buf = ctx.buffers.get("formula").cloned().unwrap_or_default();
-        let first_cat = ctx
-            .model
-            .regular_category_names()
-            .into_iter()
-            .next()
-            .map(String::from);
         let mut effects: Vec<Box<dyn Effect>> = Vec::new();
-        if let Some(cat) = first_cat {
-            effects.push(Box::new(effect::AddFormula {
-                raw: buf,
-                target_category: cat,
-            }));
-            effects.push(effect::mark_dirty());
-            effects.push(effect::set_status("Formula added"));
-        } else {
-            effects.push(effect::set_status("Add at least one category first."));
-        }
+        // Default formula target to _Measure (the virtual measure category).
+        // _Measure dynamically includes all formula targets.
+        effects.push(Box::new(effect::AddFormula {
+            raw: buf,
+            target_category: "_Measure".to_string(),
+        }));
+        effects.push(effect::mark_dirty());
+        effects.push(effect::set_status("Formula added"));
         effects.push(effect::change_mode(AppMode::FormulaPanel));
         effects
     }
 }
 
 /// Shared helper: read a buffer, trim it, and if non-empty, produce add + dirty
-/// + status + clear-buffer effects. If empty, return to CategoryPanel.
+/// + status effects. If empty, return to CategoryPanel.
+/// Buffer clearing is handled by the keymap (Enter → [commit, clear-buffer]).
 fn commit_add_from_buffer(
     ctx: &CmdContext,
     buffer_name: &str,
@@ -262,10 +257,6 @@ fn commit_add_from_buffer(
         add,
         effect::mark_dirty(),
         effect::set_status(status_msg(&trimmed)),
-        Box::new(effect::SetBuffer {
-            name: buffer_name.to_string(),
-            value: String::new(),
-        }),
     ]
 }