feat(agent): emit structured _tool_events progress metadata

Extend the existing on_progress callback to carry structured tool-event
payloads alongside the plain-text hint, so channels can render rich
tool execution state (start/finish/error, arguments, results, file
attachments) rather than only the pre-formatted hint string.

Changes
-------
- AgentLoop._tool_event_start_payload() — builds a version-1 start
  payload from a ToolCallRequest
- AgentLoop._tool_event_result_extras() — extracts files/embeds from a
  tool result dict
- AgentLoop._tool_event_finish_payloads() — maps tool_calls +
  tool_results + tool_events from AgentHookContext into finish payloads
- _LoopHook.before_execute_tools() — passes tool_events=[...] to
  on_progress together with the existing tool_hint flag
- _LoopHook.after_iteration() — emits a second on_progress call with
  the finish payloads once tool results are available
- _bus_progress() — forwards tool_events as _tool_events in OutboundMessage
  metadata so channel implementations can read them
- on_progress type widened to Callable[..., Awaitable[None]] on all
  public entry points; _cli_progress updated to accept and ignore
  tool_events

The contract is additive: callers that only accept (content, *, tool_hint)
continue to work unchanged. Callers that also accept tool_events receive
the structured data.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/agent/test_loop_progress.py

@@ -0,0 +1,125 @@
+"""Tests for structured tool-event progress metadata emitted by AgentLoop."""
+
+from pathlib import Path
+from unittest.mock import AsyncMock, MagicMock
+
+import pytest
+
+from nanobot.agent.loop import AgentLoop
+from nanobot.bus.events import InboundMessage
+from nanobot.bus.queue import MessageBus
+from nanobot.providers.base import LLMResponse, ToolCallRequest
+
+
+def _make_loop(tmp_path: Path) -> AgentLoop:
+    bus = MessageBus()
+    provider = MagicMock()
+    provider.get_default_model.return_value = "test-model"
+    return AgentLoop(bus=bus, provider=provider, workspace=tmp_path, model="test-model")
+
+
+class TestToolEventProgress:
+    """_run_agent_loop emits structured tool_events via on_progress."""
+
+    @pytest.mark.asyncio
+    async def test_start_and_finish_events_emitted(self, tmp_path: Path) -> None:
+        loop = _make_loop(tmp_path)
+        tool_call = ToolCallRequest(id="call1", name="custom_tool", arguments={"path": "foo.txt"})
+        calls = iter([
+            LLMResponse(content="Visible", tool_calls=[tool_call]),
+            LLMResponse(content="Done", tool_calls=[]),
+        ])
+        loop.provider.chat_with_retry = AsyncMock(side_effect=lambda *a, **kw: next(calls))
+        loop.tools.get_definitions = MagicMock(return_value=[])
+        loop.tools.prepare_call = MagicMock(return_value=(None, {"path": "foo.txt"}, None))
+        loop.tools.execute = AsyncMock(return_value="ok")
+
+        progress: list[tuple[str, bool, list[dict] | None]] = []
+
+        async def on_progress(
+            content: str,
+            *,
+            tool_hint: bool = False,
+            tool_events: list[dict] | None = None,
+        ) -> None:
+            progress.append((content, tool_hint, tool_events))
+
+        final_content, _, _, _, _ = await loop._run_agent_loop([], on_progress=on_progress)
+
+        assert final_content == "Done"
+        assert progress == [
+            ("Visible", False, None),
+            (
+                'custom_tool("foo.txt")',
+                True,
+                [{
+                    "version": 1,
+                    "phase": "start",
+                    "call_id": "call1",
+                    "name": "custom_tool",
+                    "arguments": {"path": "foo.txt"},
+                    "result": None,
+                    "error": None,
+                    "files": [],
+                    "embeds": [],
+                }],
+            ),
+            (
+                "",
+                False,
+                [{
+                    "version": 1,
+                    "phase": "end",
+                    "call_id": "call1",
+                    "name": "custom_tool",
+                    "arguments": {"path": "foo.txt"},
+                    "result": "ok",
+                    "error": None,
+                    "files": [],
+                    "embeds": [],
+                }],
+            ),
+        ]
+
+    @pytest.mark.asyncio
+    async def test_bus_progress_forwards_tool_events_to_outbound_metadata(self, tmp_path: Path) -> None:
+        """When run() handles a bus message, _tool_events lands in OutboundMessage metadata."""
+        bus = MessageBus()
+        provider = MagicMock()
+        provider.get_default_model.return_value = "test-model"
+        loop = AgentLoop(bus=bus, provider=provider, workspace=tmp_path, model="test-model")
+
+        tool_call = ToolCallRequest(id="tc1", name="exec", arguments={"command": "ls"})
+        calls = iter([
+            LLMResponse(content="", tool_calls=[tool_call]),
+            LLMResponse(content="Done", tool_calls=[]),
+        ])
+        loop.provider.chat_with_retry = AsyncMock(side_effect=lambda *a, **kw: next(calls))
+        loop.tools.get_definitions = MagicMock(return_value=[])
+        loop.tools.prepare_call = MagicMock(return_value=(None, {"command": "ls"}, None))
+        loop.tools.execute = AsyncMock(return_value="file.txt")
+
+        msg = InboundMessage(channel="telegram", chat_id="chat1", content="run ls")
+        await loop.run(msg)
+
+        # Drain all outbound messages and find the one carrying _tool_events
+        outbound = []
+        while bus.outbound_size() > 0:
+            outbound.append(await bus.consume_outbound())
+
+        tool_event_msgs = [m for m in outbound if m.metadata and m.metadata.get("_tool_events")]
+        assert tool_event_msgs, "expected at least one outbound message with _tool_events"
+
+        start_msgs = [m for m in tool_event_msgs if m.metadata["_tool_events"][0]["phase"] == "start"]
+        finish_msgs = [m for m in tool_event_msgs if m.metadata["_tool_events"][0]["phase"] in ("end", "error")]
+        assert start_msgs, "expected a start-phase tool event"
+        assert finish_msgs, "expected a finish-phase tool event"
+
+        start = start_msgs[0].metadata["_tool_events"][0]
+        assert start["name"] == "exec"
+        assert start["call_id"] == "tc1"
+        assert start["result"] is None
+
+        finish = finish_msgs[0].metadata["_tool_events"][0]
+        assert finish["phase"] == "end"
+        assert finish["result"] == "file.txt"