fix(python): preserve security config across Bash.reset() (#463)

## Summary
- `reset()` was creating bare `Bash::builder()`, discarding all config
- Now rebuilds with stored username, hostname, max_commands,
max_loop_iterations
- Prevents silent removal of DoS protections after reset

## Test plan
- [x] `test_reset_preserves_config` — verifies username, hostname, and
limits survive reset
- [x] Rust builds clean, Python lint/format pass

Closes #424

Co-authored-by: Claude <noreply@anthropic.com>

Author: chaliy

crates/bashkit-python/src/lib.rs

@@ -267,15 +267,34 @@ impl PyBash {
         })
     }
 
-    /// Reset interpreter to fresh state.
+    /// Reset interpreter to fresh state, preserving security configuration.
     /// Releases GIL before blocking on tokio to prevent deadlock.
     fn reset(&self, py: Python<'_>) -> PyResult<()> {
         let inner = self.inner.clone();
+        // THREAT[TM-PY-026]: Rebuild with same config to preserve DoS protections.
+        let username = self.username.clone();
+        let hostname = self.hostname.clone();
+        let max_commands = self.max_commands;
+        let max_loop_iterations = self.max_loop_iterations;
 
         py.detach(|| {
             self.rt.block_on(async move {
                 let mut bash = inner.lock().await;
-                let builder = Bash::builder();
+                let mut builder = Bash::builder();
+                if let Some(ref u) = username {
+                    builder = builder.username(u);
+                }
+                if let Some(ref h) = hostname {
+                    builder = builder.hostname(h);
+                }
+                let mut limits = ExecutionLimits::new();
+                if let Some(mc) = max_commands {
+                    limits = limits.max_commands(mc as usize);
+                }
+                if let Some(mli) = max_loop_iterations {
+                    limits = limits.max_loop_iterations(mli as usize);
+                }
+                builder = builder.limits(limits);
                 *bash = builder.build();
                 Ok(())
             })

crates/bashkit-python/tests/test_bashkit.py

@@ -249,6 +249,28 @@ def test_reset():
     assert r.stdout.strip() == "empty"
 
 
+# Issue #424: reset() should preserve security configuration
+def test_reset_preserves_config():
+    bash = Bash(max_commands=5, username="testuser", hostname="testhost")
+    # Verify config works before reset
+    r = bash.execute_sync("whoami")
+    assert r.stdout.strip() == "testuser"
+
+    bash.reset()
+
+    # Config should survive reset
+    r = bash.execute_sync("whoami")
+    assert r.stdout.strip() == "testuser", "username lost after reset"
+
+    r = bash.execute_sync("hostname")
+    assert r.stdout.strip() == "testhost", "hostname lost after reset"
+
+    # Max commands limit should still be enforced
+    # Run enough commands to hit the limit
+    r = bash.execute_sync("echo 1; echo 2; echo 3; echo 4; echo 5; echo 6")
+    assert r.exit_code != 0 or "limit" in r.stderr.lower() or r.stdout.count("\n") <= 5
+
+
 # -- BashTool: LLM metadata ------------------------------------------------