feat: sandbox toggles in New Session dialog, gated on bwrap availability

Adds sandbox_available param to NewSessionScreen, renders Switch/Select/
Switch widgets for sandbox on/off, filesystem access (rw/ro), and network
toggle. When bwrap is unavailable the switch is disabled and a warning label
is shown. The _policy_from staticmethod maps widget values to SandboxPolicy.
The result tuple gains SandboxPolicy | None as its fifth element. app.py
passes sandbox_available=sandbox.is_available() when opening the dialog and
unpacks the new element to forward sandbox= to create_session.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_tui.py

@@ -292,7 +292,7 @@ async def test_new_session_on_dismiss_sequential_create_then_refresh():
         call_order: list[str] = []
 
         async def fake_create(
-            project_id, harness_name, nickname, model, worktree_branch=None
+            project_id, harness_name, nickname, model, worktree_branch=None, sandbox=None
         ):
             # Brief yield so that, if two separate workers were used, the list
             # worker would be able to start and record "list" before this
@@ -324,7 +324,7 @@ async def test_new_session_on_dismiss_sequential_create_then_refresh():
             await pilot.pause()
 
         # The NewSessionScreen is now on top; dismiss it with a valid result tuple.
-        app.screen.dismiss(("claude", "mynick", None, None))
+        app.screen.dismiss(("claude", "mynick", None, None, None))
         await pilot.pause()
 
         # Wait for the worker spawned by on_dismiss to finish deterministically.
@@ -396,7 +396,7 @@ async def test_new_session_on_dismiss_notifies_on_spawn_failure():
                 await app.workers.wait_for_complete()
                 await pilot.pause()
 
-                app.screen.dismiss(("claude", "mynick", None, None))
+                app.screen.dismiss(("claude", "mynick", None, None, None))
                 await pilot.pause()
                 await app.workers.wait_for_complete()
                 await pilot.pause()
@@ -467,7 +467,7 @@ async def test_new_session_on_dismiss_no_notify_on_success():
                 await app.workers.wait_for_complete()
                 await pilot.pause()
 
-                app.screen.dismiss(("claude", "mynick", None, None))
+                app.screen.dismiss(("claude", "mynick", None, None, None))
                 await pilot.pause()
                 await app.workers.wait_for_complete()
                 await pilot.pause()
@@ -582,7 +582,7 @@ async def test_new_session_enter_in_input_submits_dialog():
         await pilot.press("enter")
         await pilot.pause()
 
-        assert results == [("claude", "mywork", None, None)], f"got {results}"
+        assert results == [("claude", "mywork", None, None, None)], f"got {results}"
 
 
 # ---------------------------------------------------------------------------
@@ -1291,7 +1291,7 @@ async def test_new_session_worktree_unchecked_returns_none_branch():
         app.screen.query_one("#nickname-input", Input).value = "mywork"
         app.screen.query_one("#ok-btn", Button).press()
         await pilot.pause()
-        assert results == [("claude", "mywork", None, None)], f"got {results}"
+        assert results == [("claude", "mywork", None, None, None)], f"got {results}"
 
 
 @pytest.mark.asyncio
@@ -1316,7 +1316,7 @@ async def test_new_session_worktree_checked_uses_typed_branch():
         branch.value = "feature-x"
         app.screen.query_one("#ok-btn", Button).press()
         await pilot.pause()
-        assert results == [("claude", "My Work", None, "feature-x")], f"got {results}"
+        assert results == [("claude", "My Work", None, "feature-x", None)], f"got {results}"
 
 
 @pytest.mark.asyncio
@@ -1338,7 +1338,7 @@ async def test_new_session_worktree_checked_blank_branch_slugifies_nickname():
         app.screen.query_one("#branch-input", Input).value = ""
         app.screen.query_one("#ok-btn", Button).press()
         await pilot.pause()
-        assert results == [("claude", "Cool Feature!", None, "cool-feature")], (
+        assert results == [("claude", "Cool Feature!", None, "cool-feature", None)], (
             f"got {results}"
         )
 
@@ -1504,3 +1504,46 @@ async def test_delete_non_worktree_session_does_not_push_modal():
         verify_db = app._db_factory()
         assert verify_db.get(Session, sess_id) is None
         verify_db.close()
+
+
+# ---------------------------------------------------------------------------
+# Task 6: Sandbox controls in NewSessionScreen
+# ---------------------------------------------------------------------------
+
+
+def test_policy_from_disabled_returns_none():
+    from hqt.tui.screens.new_session import NewSessionScreen
+
+    assert NewSessionScreen._policy_from(False, "rw", True) is None
+
+
+def test_policy_from_enabled_builds_policy():
+    from hqt.sandbox import SandboxPolicy
+    from hqt.tui.screens.new_session import NewSessionScreen
+
+    p = NewSessionScreen._policy_from(True, "ro", False)
+    assert p == SandboxPolicy(fs="ro", net=False)
+
+
+@pytest.mark.asyncio
+async def test_sandbox_switch_disabled_when_unavailable():
+    from hqt.tui.screens.new_session import NewSessionScreen
+    from textual.widgets import Switch
+
+    app = HqtApp()
+    async with app.run_test(size=(120, 40)) as pilot:
+        app.push_screen(NewSessionScreen(["claude"], is_git_repo=False, sandbox_available=False))
+        await pilot.pause()
+        assert app.screen.query_one("#sandbox-switch", Switch).disabled is True
+
+
+@pytest.mark.asyncio
+async def test_sandbox_switch_enabled_when_available():
+    from hqt.tui.screens.new_session import NewSessionScreen
+    from textual.widgets import Switch
+
+    app = HqtApp()
+    async with app.run_test(size=(120, 40)) as pilot:
+        app.push_screen(NewSessionScreen(["claude"], is_git_repo=False, sandbox_available=True))
+        await pilot.pause()
+        assert app.screen.query_one("#sandbox-switch", Switch).disabled is False