feat: support inheritance split and cast statements

.claude/skills/mendix/write-microflows.md

@@ -340,6 +340,23 @@ end case;
 
 `(empty)` represents an unset enumeration value. Multiple values can share one `when` branch by separating them with commas. Case values are bare identifiers — do **not** quote them.
 
+### Type Split And Cast Statements
+
+Use `split type` when a microflow branches on an object's runtime specialization.
+Use `cast` inside a type branch to create the specialized variable used by the branch body.
+
+```mdl
+split type $Input
+case Sample.SpecializedInput
+  cast $SpecificInput;
+  return true;
+else
+  return false;
+end split;
+```
+
+`case` values are qualified entity names. The optional `else` branch handles objects that do not match any listed specialization.
+
 ### LOOP Statements
 
 ```mdl

cmd/mxcli/tui/watcher.go

@@ -4,6 +4,7 @@ import (
 	"os"
 	"path/filepath"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	tea "github.com/charmbracelet/bubbletea"
@@ -78,6 +79,7 @@ func newWatcher(mprPath, contentsDir string, sender MsgSender) (*Watcher, error)
 
 func (w *Watcher) run(sender MsgSender) {
 	var debounceTimer *time.Timer
+	var debounceSeq atomic.Uint64
 
 	for {
 		select {
@@ -110,7 +112,11 @@ func (w *Watcher) run(sender MsgSender) {
 			if debounceTimer != nil {
 				debounceTimer.Stop()
 			}
+			seq := debounceSeq.Add(1)
 			debounceTimer = time.AfterFunc(watchDebounce, func() {
+				if debounceSeq.Load() != seq {
+					return
+				}
 				sender.Send(MprChangedMsg{})
 			})
 

cmd/mxcli/tui/watcher_test.go

@@ -35,10 +35,11 @@ func TestWatcherDebounce(t *testing.T) {
 	}
 	defer w.Close()
 
-	// Rapidly write 5 times — should debounce into a single message
+	// Rapidly write 5 times — should debounce into a single message.
+	// Keep the burst tighter than the debounce window so slow CI machines do
+	// not accidentally let an intermediate timer fire.
 	for i := range 5 {
 		_ = os.WriteFile(unitFile, []byte{byte('a' + i)}, 0644)
-		time.Sleep(50 * time.Millisecond)
 	}
 
 	// Wait for debounce to fire (500ms + margin)

docs/01-project/MDL_QUICK_REFERENCE.md

@@ -242,6 +242,8 @@ authentication basic, session
 | Free annotation | `@annotation 'text'` before `@position(...)` | Free-floating visual note preserved by order |
 | IF | `if condition then ... [else ...] end if;` | |
 | Enum split | `case $Var when Value then ... end case;` | Enumeration decision branches |
+| Type split | `split type $Var case Module.Entity ... end split;` | Runtime specialization branches |
+| Cast | `cast $SpecificVar;` | Downcast inside a type split branch |
 | LOOP | `loop $item in $list begin ... end loop;` | FOR EACH over list |
 | WHILE | `while condition begin ... end while;` | Condition-based loop |
 | Return | `return $value;` | Required at end of every flow path |

docs/11-proposals/PROPOSAL_microflow_inheritance_split_statement.md

@@ -0,0 +1,35 @@
+# Proposal: Microflow Inheritance Split And Cast Statements
+
+Status: Draft
+
+## Summary
+
+Add round-trip MDL support for type-based microflow decisions and cast actions:
+
+```mdl
+split type $Input
+case Sample.SpecializedInput
+  cast $SpecificInput;
+else
+  return false;
+end split;
+```
+
+## Motivation
+
+Studio Pro represents specialization/type decisions as `InheritanceSplit` objects and stores downcasts as `CastAction` activities. Without first-class MDL statements, `describe` can only emit unsupported comments or incomplete split output, and `exec` cannot rebuild the same graph.
+
+## Semantics
+
+`split type $Var` evaluates the runtime specialization of an object variable. Each `case Module.Entity` branch corresponds to an outgoing sequence flow with an `InheritanceCase`. The optional `else` branch maps to the outgoing flow without an inheritance case.
+
+`cast $Output` emits a `CastAction` that produces the downcast variable. `$Output = cast $Input` is accepted for source-preserving authoring, but current Mendix BSON stores the generated cast variable as the primary persisted field.
+
+## Tests And Examples
+
+`mdl-examples/doctype-tests/inheritance_split_statement.test.mdl` demonstrates the syntax. Go regression tests cover parser construction, builder output, describer output, validation recursion, and BSON writer support for inheritance case values and cast actions.
+
+## Open Questions
+
+- Should `exec` validate `case Module.Entity` against the project's specialization hierarchy when connected?
+- Should the source-preserving `$Output = cast $Input` form round-trip both variable names once the underlying BSON fields are confirmed for all supported Mendix versions?

docs/11-proposals/README.md

@@ -53,6 +53,7 @@ BSON schema Registry ◄──── multi-version Support
 | [XPath Gaps](xpath-gaps-proposal.md) | Partial | XPath constraint support gap analysis. ~85% complete, association paths and nested predicates remain | — |
 | [Microflow ENUM SPLIT Statement](PROPOSAL_microflow_enum_split_statement.md) | Implemented | Enumeration decision splits via `case $Var when Value then … end case;` | — |
 | [Microflow CHANGE Refresh Modifier](PROPOSAL_microflow_change_refresh_modifier.md) | Draft | Preserve `RefreshInClient` on change-object actions | — |
+| [Microflow Inheritance Split And Cast Statements](PROPOSAL_microflow_inheritance_split_statement.md) | Draft | Preserve type-based microflow decisions and cast actions in round-trips | — |
 | [LLM MDL Assistance](PROPOSAL_llm_mdl_assistance.md) | Proposed | Enhanced error messages with examples, reorganized skills by use case | — |
 
 ### Testing & Evaluation