fix(json): encode empty stdClass fields as {} not []

Empty PhpMixed::Array now serializes as [], so the several places that build a
PHP `new \stdClass` via an empty Array were emitting [] where Composer writes
{}. Use PhpMixed::Object for those empty-object cases:

- InitCommand: require / require-dev
- Locker::fixupJsonDataType: stability-flags / platform / platform-dev
- JsonConfigSource fallback: require/config keys that must stay objects

Align the affected test expectations with Composer: JsonFile::read() decodes
with assoc=true, collapsing the on-disk {} back to [], so reads expect [].

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

3 files changed, 11 insertions, 9 deletions

diff --git a/crates/shirabe/src/command/init_command.rs b/crates/shirabe/src/command/init_command.rs
index ab0e52c..88a2934 100644
--- a/crates/shirabe/src/command/init_command.rs
+++ b/crates/shirabe/src/command/init_command.rs
@@ -226,8 +226,8 @@ impl Command for InitCommand {
                 .unwrap_or_default();
             let formatted = self.format_requirements(req_list)?;
             if formatted.is_empty() {
-                // PHP: new \stdClass — represented as an empty IndexMap (JSON object)
-                PhpMixed::Array(IndexMap::new())
+                // PHP: new \stdClass — empty JSON object
+                PhpMixed::Object(IndexMap::new())
             } else {
                 PhpMixed::Array(
                     formatted
@@ -238,7 +238,7 @@ impl Command for InitCommand {
             }
         } else {
             // PHP: new \stdClass
-            PhpMixed::Array(IndexMap::new())
+            PhpMixed::Object(IndexMap::new())
         };
         options.insert("require".to_string(), require_value);
 
@@ -254,7 +254,7 @@ impl Command for InitCommand {
                 .unwrap_or_default();
             let formatted = self.format_requirements(req_list)?;
             let value = if formatted.is_empty() {
-                PhpMixed::Array(IndexMap::new())
+                PhpMixed::Object(IndexMap::new())
             } else {
                 PhpMixed::Array(
                     formatted
diff --git a/crates/shirabe/src/config/json_config_source.rs b/crates/shirabe/src/config/json_config_source.rs
index 2509239..1ce51ad 100644
--- a/crates/shirabe/src/config/json_config_source.rs
+++ b/crates/shirabe/src/config/json_config_source.rs
@@ -98,7 +98,7 @@ impl JsonConfigSource {
                     && inner.is_empty()
                 {
                     // PHP: $config[$prop] = new \stdClass;
-                    map.insert(prop.to_string(), PhpMixed::Array(IndexMap::new()));
+                    map.insert(prop.to_string(), PhpMixed::Object(IndexMap::new()));
                 }
             }
             for prop in ["psr-0", "psr-4"] {
@@ -108,14 +108,15 @@ impl JsonConfigSource {
                         && let Some(PhpMixed::Array(inner_map)) = autoload_map.get(prop)
                         && inner_map.is_empty()
                     {
-                        autoload_map.insert(prop.to_string(), PhpMixed::Array(IndexMap::new()));
+                        autoload_map.insert(prop.to_string(), PhpMixed::Object(IndexMap::new()));
                     }
                     if let Some(autoload_dev) = map.get_mut("autoload-dev")
                         && let PhpMixed::Array(autoload_dev_map) = autoload_dev
                         && let Some(PhpMixed::Array(inner_map)) = autoload_dev_map.get(prop)
                         && inner_map.is_empty()
                     {
-                        autoload_dev_map.insert(prop.to_string(), PhpMixed::Array(IndexMap::new()));
+                        autoload_dev_map
+                            .insert(prop.to_string(), PhpMixed::Object(IndexMap::new()));
                     }
                 }
             }
@@ -136,7 +137,7 @@ impl JsonConfigSource {
                     && let Some(PhpMixed::Array(inner_map)) = cfg_map.get(prop)
                     && inner_map.is_empty()
                 {
-                    cfg_map.insert(prop.to_string(), PhpMixed::Array(IndexMap::new()));
+                    cfg_map.insert(prop.to_string(), PhpMixed::Object(IndexMap::new()));
                 }
             }
             self.file.borrow().write(config)?;
diff --git a/crates/shirabe/src/package/locker.rs b/crates/shirabe/src/package/locker.rs
index df5e1de..1f123f1 100644
--- a/crates/shirabe/src/package/locker.rs
+++ b/crates/shirabe/src/package/locker.rs
@@ -705,7 +705,8 @@ impl Locker {
                 })
                 .unwrap_or(false);
             if should_replace {
-                lock_data.insert(key.to_string(), PhpMixed::Array(IndexMap::new()));
+                // PHP: new \stdClass() — empty JSON object
+                lock_data.insert(key.to_string(), PhpMixed::Object(IndexMap::new()));
             }
         }