Fix hash extraction to handle hash-only instance identifiers

The target_hash extraction logic previously only handled the "ProjectName@hash"
format, causing it to fail when instance_id was a plain hash (fallback format).
This resulted in read_status_file returning the most recent instance instead of
the specific instance, breaking per-instance routing during reconnection.

Changes:
- Update hash extraction to handle both "ProjectName@hash" and hash-only formats
- When instance_id contains '@', extract the part after '@' as before
- When instance_id has no '@', treat the entire string as the hash
- Applied to both Server/ and MCPForUnity/ versions

Addresses CodeRabbit feedback:
- #360 (comment)
- #360 (comment)

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

Co-Authored-By: Claude <[email protected]>

Author: sakurachan

MCPForUnity/UnityMcpServer~/src/unity_connection.py

@@ -263,10 +263,14 @@ def read_status_file(target_hash: str | None = None) -> dict | None:
 
         # Extract hash suffix from instance id (e.g., Project@hash)
         target_hash: str | None = None
-        if self.instance_id and '@' in self.instance_id:
-            maybe_hash = self.instance_id.split('@', 1)[1].strip()
-            if maybe_hash:
-                target_hash = maybe_hash
+        if self.instance_id:
+            if '@' in self.instance_id:
+                maybe_hash = self.instance_id.split('@', 1)[1].strip()
+                if maybe_hash:
+                    target_hash = maybe_hash
+            else:
+                # instance_id is just the hash (fallback format)
+                target_hash = self.instance_id.strip()
 
         # Preflight: if Unity reports reloading, return a structured hint so clients can retry politely
         try:

Server/unity_connection.py

@@ -263,10 +263,14 @@ def read_status_file(target_hash: str | None = None) -> dict | None:
 
         # Extract hash suffix from instance id (e.g., Project@hash)
         target_hash: str | None = None
-        if self.instance_id and '@' in self.instance_id:
-            maybe_hash = self.instance_id.split('@', 1)[1].strip()
-            if maybe_hash:
-                target_hash = maybe_hash
+        if self.instance_id:
+            if '@' in self.instance_id:
+                maybe_hash = self.instance_id.split('@', 1)[1].strip()
+                if maybe_hash:
+                    target_hash = maybe_hash
+            else:
+                # instance_id is just the hash (fallback format)
+                target_hash = self.instance_id.strip()
 
         # Preflight: if Unity reports reloading, return a structured hint so clients can retry politely
         try: