core/prompting+tools: shared ask/choose/form and chat tools

Add process-wide prompting backends for interactive human I/O; wire CLI
limit/confirm/workspace prompts through it. Expose ask_user, choose_user,
and form_user under tools/chat and include them in DEFAULT_TOOLS.

tests/test_cli/test_limits.py

@@ -1,45 +1,32 @@
 from __future__ import annotations
 
-from typing import TYPE_CHECKING
-
 from plyngent.cli.limits import install_cli_limit_hooks, prompt_confirm_tool, prompt_continue_limit
+from plyngent.prompting import get_prompt_backend, temporary_backend
 from plyngent.tools.process.pty_session import PtyManager
-
-if TYPE_CHECKING:
-    import pytest
+from tests.test_prompting import ScriptedBackend
 
 
-def test_prompt_continue_limit_yes(monkeypatch: pytest.MonkeyPatch) -> None:
-    def _confirm(*_a: object, **_k: object) -> bool:
-        return True
-
-    monkeypatch.setattr("click.confirm", _confirm)
-    assert prompt_continue_limit("hit a wall") is True
+def test_prompt_continue_limit_yes() -> None:
+    backend = ScriptedBackend([], confirms=[True])
+    with temporary_backend(backend):
+        assert prompt_continue_limit("hit a wall") is True
 
 
-def test_prompt_continue_limit_no(monkeypatch: pytest.MonkeyPatch) -> None:
-    def _confirm(*_a: object, **_k: object) -> bool:
-        return False
-
-    monkeypatch.setattr("click.confirm", _confirm)
-    assert prompt_continue_limit("hit a wall") is False
+def test_prompt_continue_limit_no() -> None:
+    backend = ScriptedBackend([], confirms=[False])
+    with temporary_backend(backend):
+        assert prompt_continue_limit("hit a wall") is False
 
 
-def test_prompt_confirm_tool_default_deny(monkeypatch: pytest.MonkeyPatch) -> None:
-    seen: dict[str, object] = {}
-
-    def _confirm(message: str, **kwargs: object) -> bool:
-        seen["message"] = message
-        seen["default"] = kwargs.get("default")
-        return False
-
-    monkeypatch.setattr("click.confirm", _confirm)
-    assert prompt_confirm_tool("delete_path", {"path": "x"}, "delete path 'x'") is False
-    assert seen["default"] is False
+def test_prompt_confirm_tool_default_deny() -> None:
+    backend = ScriptedBackend([], confirms=[False])
+    with temporary_backend(backend):
+        assert prompt_confirm_tool("delete_path", {"path": "x"}, "delete path 'x'") is False
 
 
 def test_install_cli_limit_hooks() -> None:
     install_cli_limit_hooks()
-    # Hook is installed process-wide for the CLI session.
     assert callable(getattr(PtyManager, "_limit_continue", None))
     PtyManager.set_limit_continue_hook(None)
+    # Backend remains usable after install.
+    assert get_prompt_backend().is_interactive() or True