Fix medium/low severity issues: script splitter, EXPLAIN, keyring, imports

execute_script() semicolon splitter (all drivers)
- Add BaseDriver._split_statements() that tracks single/double-quoted
  strings and -- / /* */ comments so semicolons inside procedure bodies
  are not treated as statement boundaries.
- Replace the naive sql.split(';') in all four drivers with this helper.
- MSSQL execute_script() also pre-splits on GO (case-insensitive, own
  line) so scripts pasted from SSMS work correctly.

MSSQL EXPLAIN
- SET SHOWPLAN_TEXT ON/execute/SET SHOWPLAN_TEXT OFF must be separate
  execute() calls; pyodbc rejects multiple statements in one call.
  Hold self._lock for the entire sequence to keep session state atomic.

Keyring (connections.py)
- Log warnings (with traceback) on load/save failures instead of
  silently returning "".
- save_password() now calls delete_password() when password is empty,
  so clearing a saved password actually removes the old keyring entry
  rather than leaving a stale one behind.

SQLite get_tables() O(N) lock acquisitions
- Run all COUNT(*) queries inside the same `with self._cur() as c:`
  block, reducing N+1 lock acquisitions to 1.

Unused import: remove psycopg2.extras from postgres_driver.py.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/config/connections.py

@@ -8,6 +8,9 @@ from pathlib import Path
 from typing import Optional
 
 from app.models.connection_model import ConnectionProfile
+from app.utils.logger import get_logger
+
+_log = get_logger(__name__)
 
 _CONN_FILE = Path.home() / ".dbclient" / "connections.json"
 
@@ -23,8 +26,15 @@ _SERVICE = "DBClient"
 # ── Keyring helpers ──────────────────────────────────────────────────────────
 
 def save_password(profile_id: str, password: str) -> None:
-    if _KEYRING_OK and password:
+    if not _KEYRING_OK:
+        return
+    if password:
+        try:
             keyring.set_password(_SERVICE, profile_id, password)
+        except Exception:
+            _log.warning("keyring: failed to save password for %s", profile_id, exc_info=True)
+    else:
+        delete_password(profile_id)
 
 
 def load_password(profile_id: str) -> str:
@@ -32,6 +42,7 @@ def load_password(profile_id: str) -> str:
         try:
             return keyring.get_password(_SERVICE, profile_id) or ""
         except Exception:
+            _log.warning("keyring: failed to load password for %s", profile_id, exc_info=True)
             return ""
     return ""
 
@@ -41,7 +52,7 @@ def delete_password(profile_id: str) -> None:
         try:
             keyring.delete_password(_SERVICE, profile_id)
         except Exception:
-            pass
+            pass  # Already absent is fine
 
 
 # ── Profile CRUD ─────────────────────────────────────────────────────────────

app/drivers/base.py

@@ -197,6 +197,52 @@ class BaseDriver(ABC):
         """Rename a column via ALTER TABLE."""
         pass
 
+    @staticmethod
+    def _split_statements(sql: str) -> list:
+        """Split SQL text on unquoted semicolons, preserving quoted strings and comments."""
+        stmts, buf = [], []
+        i, n = 0, len(sql)
+        while i < n:
+            ch = sql[i]
+            if ch == '-' and i + 1 < n and sql[i + 1] == '-':
+                end = sql.find('\n', i)
+                end = end + 1 if end != -1 else n
+                buf.append(sql[i:end])
+                i = end
+            elif ch == '/' and i + 1 < n and sql[i + 1] == '*':
+                end = sql.find('*/', i + 2)
+                end = end + 2 if end != -1 else n
+                buf.append(sql[i:end])
+                i = end
+            elif ch in ("'", '"'):
+                q, j = ch, i + 1
+                while j < n:
+                    if sql[j] == '\\':
+                        j += 2
+                    elif sql[j] == q:
+                        j += 1
+                        if j < n and sql[j] == q:
+                            j += 1
+                            continue
+                        break
+                    else:
+                        j += 1
+                buf.append(sql[i:j])
+                i = j
+            elif ch == ';':
+                stmt = ''.join(buf).strip()
+                if stmt:
+                    stmts.append(stmt)
+                buf = []
+                i += 1
+            else:
+                buf.append(ch)
+                i += 1
+        stmt = ''.join(buf).strip()
+        if stmt:
+            stmts.append(stmt)
+        return stmts
+
     @property
     def is_connected(self) -> bool:
         return self._connection is not None

app/drivers/mssql_driver.py

@@ -233,9 +233,11 @@ class MSSQLDriver(BaseDriver):
             return [], [], c.rowcount
 
     def execute_script(self, sql: str) -> list:
+        import re
         results = []
-        stmts = [s.strip() for s in sql.split(';') if s.strip()]
-        for stmt in stmts:
+        batches = re.split(r'^\s*GO\s*$', sql, flags=re.IGNORECASE | re.MULTILINE)
+        for batch in batches:
+            for stmt in self._split_statements(batch):
                 try:
                     with self._cur() as c:
                         c.execute(stmt)
@@ -305,9 +307,20 @@ class MSSQLDriver(BaseDriver):
     # ── Server tools ──────────────────────────────────────────────────────────
 
     def explain_query(self, sql: str) -> tuple:
-        with self._cur() as c:
-            c.execute(f"SET SHOWPLAN_TEXT ON; {sql}; SET SHOWPLAN_TEXT OFF")
-            return ["Plan"], c.fetchall()
+        with self._lock:
+            cur = self._connection.cursor()
+            try:
+                cur.execute("SET SHOWPLAN_TEXT ON")
+                cur.execute(sql)
+                cols = [d[0] for d in cur.description] if cur.description else ["Plan"]
+                rows = cur.fetchall()
+                cur.execute("SET SHOWPLAN_TEXT OFF")
+            finally:
+                try:
+                    cur.close()
+                except Exception:
+                    pass
+        return cols, rows
 
     def get_process_list(self) -> tuple:
         with self._cur() as c:

app/drivers/mysql_driver.py

@@ -254,9 +254,8 @@ class MySQLDriver(BaseDriver):
 
     def execute_script(self, sql: str) -> list:
         results = []
-        stmts = [s.strip() for s in sql.split(';') if s.strip()]
         with self._cur() as c:
-            for stmt in stmts:
+            for stmt in self._split_statements(sql):
                 try:
                     c.execute(stmt)
                     if c.description:

app/drivers/postgres_driver.py

@@ -1,6 +1,5 @@
 """PostgreSQL driver implementation using psycopg2."""
 import psycopg2
-import psycopg2.extras
 from contextlib import contextmanager
 from typing import Optional
 from app.drivers.base import (
@@ -230,9 +229,8 @@ class PostgreSQLDriver(BaseDriver):
 
     def execute_script(self, sql: str) -> list:
         results = []
-        stmts = [s.strip() for s in sql.split(';') if s.strip()]
         with self._cur() as c:
-            for stmt in stmts:
+            for stmt in self._split_statements(sql):
                 try:
                     c.execute(stmt)
                     if c.description:

app/drivers/sqlite_driver.py

@@ -72,9 +72,8 @@ class SQLiteDriver(BaseDriver):
             tables = []
             for name in names:
                 try:
-                with self._cur() as rc:
-                    rc.execute(f'SELECT COUNT(*) FROM "{name}"')
-                    row_count = rc.fetchone()[0]
+                    c.execute(f'SELECT COUNT(*) FROM "{name}"')
+                    row_count = c.fetchone()[0]
                 except Exception:
                     row_count = 0
                 tables.append(TableInfo(name=name, schema="main", row_count=row_count))
@@ -164,8 +163,7 @@ class SQLiteDriver(BaseDriver):
 
     def execute_script(self, sql: str) -> list:
         results = []
-        stmts = [s.strip() for s in sql.split(';') if s.strip()]
-        for stmt in stmts:
+        for stmt in self._split_statements(sql):
             try:
                 with self._cur() as c:
                     c.execute(stmt)