Fix sessionid null error when resuming incremental parsing

When parsing resumes from an offset (mid-file), the "Start Log" line
was already processed in a previous run, leaving current_session_id
as None. Added get_or_create_session() to look up or create a session
when resuming from a non-zero offset.

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

parser/udcparser.py

@@ -230,6 +230,20 @@ class UDCParser:
             return {'fileid': row['fileid'], 'offset': row['lastoffset'], 'size': row['filesize']}
         return {'fileid': None, 'offset': 0, 'size': 0}
 
+    def get_or_create_session(self, filepath: str, machine_number: str) -> int:
+        """Get existing session for this file or create a new one for incremental parsing"""
+        basename = os.path.basename(filepath)
+        # Look for existing session for this file
+        self.cursor.execute(
+            "SELECT sessionid FROM udcsessions WHERE logfilename = %s ORDER BY sessionid DESC LIMIT 1",
+            (basename,)
+        )
+        row = self.cursor.fetchone()
+        if row:
+            return row['sessionid']
+        # No existing session, create one with current timestamp
+        return self.create_session(filepath, machine_number, datetime.now())
+
     def update_file_state(self, filepath: str, machine_number: str, offset: int, filesize: int):
         """Update the file state after parsing"""
         self.cursor.execute(
@@ -565,6 +579,11 @@ class UDCParser:
 
         # Reset state
         self.current_session_id = None
+
+        # If resuming from offset, get or create session immediately
+        # (we may not encounter a "Start Log" line when resuming mid-file)
+        if start_offset > 0:
+            self.current_session_id = self.get_or_create_session(filepath, machine_number)
         self.current_partrun_id = None
         self.current_timestamp = None
         self.current_badge = None