diff --git a/src/openharness/prompts/context.py b/src/openharness/prompts/context.py
index effedba..2b73a33 100644
--- a/src/openharness/prompts/context.py
+++ b/src/openharness/prompts/context.py
@@ -16,6 +16,7 @@ from openharness.memory import load_memory_prompt
 from openharness.memory.relevance import format_relevant_memories, select_relevant_memories
 from openharness.memory.usage import mark_memory_used
 from openharness.personalization.rules import load_local_rules
+from openharness.permissions.modes import PermissionMode
 from openharness.prompts.claudemd import load_claude_md_prompt
 from openharness.prompts.system_prompt import build_system_prompt
 from openharness.skills.loader import load_skill_registry
@@ -76,6 +77,28 @@ def _build_delegation_section() -> str:
     )
 
 
+def _build_permission_mode_section(settings: Settings) -> str:
+    """Build current permission-mode guidance for the model."""
+    mode = settings.permission.mode
+    if mode == PermissionMode.PLAN:
+        guidance = (
+            "Plan mode is enabled. Treat this session as read-only planning and analysis. "
+            "Do not call mutating tools such as file writes, edits, package installs, "
+            "state-changing shell commands, or task-spawning actions unless the user exits plan mode."
+        )
+    elif mode == PermissionMode.FULL_AUTO:
+        guidance = (
+            "Full-auto permission mode is enabled. You may use mutating tools when they are necessary "
+            "for the user's request, while still keeping changes scoped and intentional."
+        )
+    else:
+        guidance = (
+            "Default permission mode is enabled. Read-only tools can run directly; mutating tools "
+            "may require explicit user approval."
+        )
+    return f"# Current Permission Mode\n{guidance}"
+
+
 def build_runtime_system_prompt(
     settings: Settings,
     *,
@@ -94,6 +117,8 @@ def build_runtime_system_prompt(
     if not is_coordinator_mode() and settings.system_prompt is None:
         sections[0] = build_system_prompt(cwd=str(cwd))
 
+    sections.append(_build_permission_mode_section(settings))
+
     if settings.fast_mode:
         sections.append(
             "# Session Mode\nFast mode is enabled. Prefer concise replies, minimal tool use, and quicker progress over exhaustive exploration."
diff --git a/src/openharness/ui/runtime.py b/src/openharness/ui/runtime.py
index 1ceff3b..feda659 100644
--- a/src/openharness/ui/runtime.py
+++ b/src/openharness/ui/runtime.py
@@ -601,6 +601,17 @@ def refresh_runtime_client(bundle: RuntimeBundle) -> None:
             default_model=settings.model,
         )
     bundle.engine.set_model(settings.model)
+    bundle.engine.set_effort(settings.effort)
+    bundle.engine.set_permission_checker(PermissionChecker(settings.permission))
+    system_prompt = build_runtime_system_prompt(
+        settings,
+        cwd=bundle.cwd,
+        latest_user_prompt=_last_user_text(bundle.engine.messages),
+        extra_skill_dirs=bundle.extra_skill_dirs,
+        extra_plugin_roots=bundle.extra_plugin_roots,
+        include_project_memory=bundle.include_project_memory,
+    )
+    bundle.engine.set_system_prompt(system_prompt)
     sync_app_state(bundle)
 
 
diff --git a/tests/test_prompts/test_claudemd.py b/tests/test_prompts/test_claudemd.py
index d804e92..975e4f9 100644
--- a/tests/test_prompts/test_claudemd.py
+++ b/tests/test_prompts/test_claudemd.py
@@ -58,6 +58,23 @@ def test_build_runtime_system_prompt_combines_sections(tmp_path: Path, monkeypat
     assert "Memory" in prompt
 
 
+def test_build_runtime_system_prompt_includes_plan_mode_guidance(tmp_path: Path, monkeypatch):
+    monkeypatch.setenv("OPENHARNESS_DATA_DIR", str(tmp_path / "data"))
+    repo = tmp_path / "repo"
+    repo.mkdir()
+
+    prompt = build_runtime_system_prompt(
+        Settings(permission={"mode": "plan"}),
+        cwd=repo,
+        latest_user_prompt="inspect only",
+    )
+
+    assert "Current Permission Mode" in prompt
+    assert "Plan mode is enabled" in prompt
+    assert "read-only planning and analysis" in prompt
+    assert "Do not call mutating tools" in prompt
+
+
 def test_build_runtime_system_prompt_includes_project_context_and_fast_mode(tmp_path: Path, monkeypatch):
     monkeypatch.setenv("OPENHARNESS_DATA_DIR", str(tmp_path / "data"))
     repo = tmp_path / "repo"
diff --git a/tests/test_ui/test_runtime_plan_mode.py b/tests/test_ui/test_runtime_plan_mode.py
new file mode 100644
index 0000000..e80ed9b
--- /dev/null
+++ b/tests/test_ui/test_runtime_plan_mode.py
@@ -0,0 +1,49 @@
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+
+from openharness.ui.runtime import build_runtime, close_runtime, handle_line
+
+
+class _StaticApiClient:
+    async def stream_message(self, request):
+        del request
+        if False:
+            yield None
+
+
+@pytest.mark.asyncio
+async def test_plan_command_refreshes_engine_system_prompt(tmp_path: Path, monkeypatch):
+    monkeypatch.setenv("OPENHARNESS_CONFIG_DIR", str(tmp_path / "config"))
+    monkeypatch.setenv("OPENHARNESS_DATA_DIR", str(tmp_path / "data"))
+    monkeypatch.setenv("OPENHARNESS_LOGS_DIR", str(tmp_path / "logs"))
+
+    bundle = await build_runtime(cwd=str(tmp_path), api_client=_StaticApiClient())
+    try:
+        assert "Plan mode is enabled" not in bundle.engine.system_prompt
+
+        async def print_system(text: str) -> None:
+            del text
+
+        async def render_event(event) -> None:
+            del event
+
+        async def clear_output() -> None:
+            pass
+
+        should_continue = await handle_line(
+            bundle,
+            "/plan on",
+            print_system=print_system,
+            render_event=render_event,
+            clear_output=clear_output,
+        )
+
+        assert should_continue is True
+        assert bundle.app_state.get().permission_mode == "plan"
+        assert "Plan mode is enabled" in bundle.engine.system_prompt
+        assert "Do not call mutating tools" in bundle.engine.system_prompt
+    finally:
+        await close_runtime(bundle)