feat(harness): authority, turn contract, tools, clean_agent_preview

Chat/agent harness work: request-authority model, turn contract, tool
policy/parsing/execution, clean_agent_preview streaming/thinking, ask_user
persistence, session probes, and scheduler.

Source: vendor/photocraft (ad1cff44) harness files, 3-way merged onto
upstream/dev (a8c147b2). Harness core files were independently developed
in both lineages; resolution policy documented in pr_work/C_conflicts.md
(vendor kept where ahead, upstream kept where vendor is behind; full delta
preserved in pr_work/C_upstream_delta.patch).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_turn_contract.py

@@ -328,6 +328,30 @@ def test_conversational_request_wrappers_preserve_explicit_family(message, expec
     assert requested_capabilities(message) == expected
 
 
+@pytest.mark.parametrize("message", [
+    "30-day task + protocol doc",
+    "I wanna work on a project where I test meditation for 30 days. But I test my brain activity before and after so I can compare.",
+    "Protocol doc only",
+    "Make a 30-day meditation plan",
+    "help me build a habit tracker for the project",
+])
+def test_bare_project_task_noun_does_not_inject_task_tools(message):
+    # A project description that merely contains the noun "task" must not offer
+    # the background-task scheduler or let the model auto-create a task.
+    assert "tasks" not in requested_capabilities(message)
+    assert selected_tools_for_request(message) != frozenset({"manage_tasks"})
+
+
+@pytest.mark.parametrize("message", [
+    "Create a task to call the dentist",
+    "List my scheduled tasks",
+    "show me my automations",
+    "what scheduled tasks do i have?",
+])
+def test_explicit_task_management_still_routes_to_tasks(message):
+    assert "tasks" in requested_capabilities(message)
+
+
 @pytest.mark.parametrize("message", [
     "can u also pop the notes panel open for me?",
     "k leave it for now - also pop open the calendar panel",
@@ -4413,3 +4437,12 @@ def test_chinese_video_to_image_artifact_keeps_media_and_workspace_tools():
         "请完整浏览 /workspace/input/video.mp4，为每款零食截图并拼成清单图，"
         "输出到 /workspace/snack_checklist.jpg，交付前打开成品图检查。"
     ) == {"media_inspection", "shell_files"}
+
+
+def test_named_shell_selects_shell_family_even_for_a_bare_command():
+    # An explicitly named shell is a request to use the shell even when the
+    # rest of the message is a bare/typo'd command; admission must match the
+    # always-offered bash tool.
+    assert requested_capabilities("Bash commabd Ls la") == {"shell_files"}
+    assert requested_capabilities("bash ls") == {"shell_files"}
+    assert requested_capabilities("use the terminal to show me the files") == {"shell_files"}