feat(selfhost): Phase 151 - ConsoleBox Selfhost Support

- Identify ConsoleBox registration issue: plugins registered but PluginBoxFactory can't find them
- Root cause: timing/initialization order between BoxFactoryRegistry and UnifiedBoxRegistry
- Solution: Add ConsoleBox builtin fallback for selfhost Stage-3 pipeline
- Implementation: Plugin-preferred, builtin as fallback
- Test results: 2/2 PASS (esc_dirname_smoke.hako, string_ops_basic.hako)

Modified files:
- src/box_factory/builtin_impls/console_box.rs (new, 35 lines)
- src/box_factory/builtin_impls/mod.rs (add console_box module)
- src/box_factory/builtin.rs (add ConsoleBox creation and box_types)
- CURRENT_TASK.md (Phase 151 completion)
- docs/development/current/main/phase151_consolebox_selfhost_support.md (implementation summary)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/box_factory/builtin.rs

@@ -48,8 +48,10 @@ impl BoxFactory for BuiltinBoxFactory {
             "ArrayBox" => builtin_impls::array_box::create(args),
             "MapBox" => builtin_impls::map_box::create(args),
 
-            // Phase 125: ✅ DELETED - ConsoleBox is now plugin-only!
-            // See: plugins/nyash-console-plugin for current implementation
+            // Phase 125: Plugin-preferred, but builtin fallback for selfhost
+            // Primary: plugins/nyash-console-plugin
+            // Fallback: builtin implementation (Phase 151 selfhost support)
+            "ConsoleBox" => builtin_impls::console_box::create(args),
 
             // Phase 15.5: Fallback support (auto/core-ro modes)
             "FileBox" => builtin_impls::file_box::create(args),
@@ -76,7 +78,8 @@ impl BoxFactory for BuiltinBoxFactory {
             // Collections/common
             "ArrayBox",
             "MapBox",
-            // ConsoleBox: Phase 125 - Plugin-only (nyash-console-plugin)
+            // Phase 151: ConsoleBox builtin fallback for selfhost support
+            "ConsoleBox",
             // Fallback support
             "FileBox",
             "FileHandleBox", // Phase 113

src/box_factory/builtin_impls/console_box.rs

@@ -0,0 +1,33 @@
+/*!
+ * Builtin ConsoleBox Implementation (Phase 151: Selfhost Support Fallback)
+ *
+ * ⚠️ PLUGIN-PREFERRED: nyash-console-plugin is the primary implementation
+ * 🎯 Phase 151: Builtin fallback added to support selfhost Stage-3 pipeline
+ *
+ * Context: When running through selfhost compiler, plugins may not be properly
+ * initialized, so we provide a builtin fallback to ensure ConsoleBox is available.
+ */
+
+use crate::box_factory::RuntimeError;
+use crate::box_trait::NyashBox;
+use crate::boxes::ConsoleBox;
+
+/// Create builtin ConsoleBox instance
+///
+/// Primary: nyash-console-plugin
+/// Fallback: This builtin implementation (selfhost support)
+pub fn create(_args: &[Box<dyn NyashBox>]) -> Result<Box<dyn NyashBox>, RuntimeError> {
+    // Phase 151: Quiet fallback (no deprecation warning - this is intentional selfhost support)
+    Ok(Box::new(ConsoleBox::new()))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_builtin_console_box_creation() {
+        let result = create(&[]).unwrap();
+        assert!(result.as_any().downcast_ref::<ConsoleBox>().is_some());
+    }
+}

src/box_factory/builtin_impls/mod.rs

@@ -17,7 +17,7 @@
 // Phase 2.1-2.6: Delete these modules one by one
 pub mod array_box; // DELETE: Phase 2.4 (plugin check)
 pub mod bool_box; // DELETE: Phase 2.3 (plugin needed)
-// Phase 125: console_box ✅ DELETED - Plugin-only (nyash-console-plugin)
+pub mod console_box; // Phase 151: Builtin fallback for selfhost support (plugin-preferred)
 pub mod integer_box; // DELETE: Phase 2.2 (plugin ready)
 pub mod map_box; // DELETE: Phase 2.5 (plugin check)
 pub mod string_box; // DELETE: Phase 2.1 (plugin ready)