chore(shell): fix ruff F401/F841 + apply ruff format

Pre-existing ruff errors surfaced during Wave 4 QC:
- F401: drop unused `TerminalSession` import (only `TerminalSessionManager` is used)
- F841: drop unused `start = time.monotonic()` local in `_execute_standalone`

`ruff format` then reformatted a few long lines in the same file
(frozenset literal, curl exfiltration regex, pipe operators, session.env
call). No behavior change — formatting only.

Why now: shell.py was already touched by U1 (widen
`bash_command_filter`). Leaving known ruff failures in a file this PR
modifies would make future CI gates noisy.

src/agentkit/tools/shell.py

@@ -18,7 +18,7 @@ from typing import Any, Callable, Awaitable
 
 from agentkit.tools.base import Tool
 from agentkit.tools.output_parser import OutputParser, ParsedOutput
-from agentkit.tools.terminal_session import TerminalSession, TerminalSessionManager
+from agentkit.tools.terminal_session import TerminalSessionManager
 from agentkit.tools.pty_session import PTYSession
 
 logger = logging.getLogger(__name__)
@@ -159,10 +159,22 @@ _SAFE_COMMAND_PREFIXES: tuple[str, ...] = (
 # 危险命令检测 — 基于精确 token 匹配，避免子串误判
 
 # 总是危险的二进制命令（无论参数）
-_DANGEROUS_BINARIES: frozenset[str] = frozenset({
-    "rm", "rmdir", "mkfs", "dd", "format", "shutdown", "reboot",
-    "halt", "killall", "chown", "fdisk", "parted",
-})
+_DANGEROUS_BINARIES: frozenset[str] = frozenset(
+    {
+        "rm",
+        "rmdir",
+        "mkfs",
+        "dd",
+        "format",
+        "shutdown",
+        "reboot",
+        "halt",
+        "killall",
+        "chown",
+        "fdisk",
+        "parted",
+    }
+)
 
 # 需要特定参数才危险的二进制命令：binary → 危险 flag/子命令集合
 _DANGEROUS_BINARY_FLAGS: dict[str, set[str]] = {
@@ -183,13 +195,16 @@ _DANGEROUS_ARG_PATTERNS: list[re.Pattern[str]] = [
     re.compile(r"drop\s+database", re.IGNORECASE),
     re.compile(r"truncate\s+table", re.IGNORECASE),
     # curl/wget data exfiltration: POST/PUT/upload flags
-    re.compile(r"\bcurl\b.*(-X\s*(POST|PUT|PATCH|DELETE)|--data|--data-binary|--data-raw|--data-urlencode|-d\s|--post\d)", re.IGNORECASE),
+    re.compile(
+        r"\bcurl\b.*(-X\s*(POST|PUT|PATCH|DELETE)|--data|--data-binary|--data-raw|--data-urlencode|-d\s|--post\d)",
+        re.IGNORECASE,
+    ),
     re.compile(r"\bwget\b.*(--post-data|--post-file)", re.IGNORECASE),
 ]
 
 
-_SHELL_PIPE_OPERATORS = re.compile(r'\|')
-_SHELL_CHAIN_OPERATORS = re.compile(r'[;&]|\|\||&&|\$\(|\$\{|`|\$<|>|<|\n')
+_SHELL_PIPE_OPERATORS = re.compile(r"\|")
+_SHELL_CHAIN_OPERATORS = re.compile(r"[;&]|\|\||&&|\$\(|\$\{|`|\$<|>|<|\n")
 
 
 class ShellTool(Tool):
@@ -360,6 +375,7 @@ class ShellTool(Tool):
         # Ensure non-empty output for successful commands (all execution modes)
         if result.exit_code == 0 and not output.strip():
             from agentkit.core.fallback import SHELL_NO_OUTPUT
+
             output = SHELL_NO_OUTPUT
 
         return {
@@ -383,7 +399,6 @@ class ShellTool(Tool):
         if interactive:
             return await self._execute_with_pty(command, timeout, working_dir)
 
-        start = time.monotonic()
         try:
             proc = await asyncio.create_subprocess_shell(
                 command,
@@ -430,9 +445,7 @@ class ShellTool(Tool):
         )
 
         if interactive:
-            return await self._execute_with_pty(
-                command, timeout, session.cwd, session.env
-            )
+            return await self._execute_with_pty(command, timeout, session.cwd, session.env)
 
         return await session.execute(command, timeout=timeout)
 
@@ -482,7 +495,7 @@ class ShellTool(Tool):
 
         # Handle pipe commands: split and check each sub-command
         if _SHELL_PIPE_OPERATORS.search(command_stripped):
-            parts = command_stripped.split('|')
+            parts = command_stripped.split("|")
             for part in parts:
                 part = part.strip()
                 if not part: