diff --git a/astrbot/core/agent/runners/tool_loop_agent_runner.py b/astrbot/core/agent/runners/tool_loop_agent_runner.py
index 8c91adbbfd..7283e0ff43 100644
--- a/astrbot/core/agent/runners/tool_loop_agent_runner.py
+++ b/astrbot/core/agent/runners/tool_loop_agent_runner.py
@@ -27,7 +27,7 @@
 from astrbot import logger
 from astrbot.core.agent.message import ImageURLPart, TextPart, ThinkPart
 from astrbot.core.agent.tool import FunctionTool, ToolSet
-from astrbot.core.agent.tool_image_cache import tool_image_cache
+from astrbot.core.agent.tool_image_cache import CachedImage, tool_image_cache
 from astrbot.core.exceptions import EmptyModelOutputError
 from astrbot.core.message.components import Json
 from astrbot.core.message.message_event_result import (
@@ -103,6 +103,24 @@ class _ToolExecutionInterrupted(Exception):
     """Raised when a running tool call is interrupted by a stop request."""
 
 
+def _get_image_caption_config(
+    run_context: ContextWrapper[TContext],
+) -> tuple[str, dict]:
+    """Resolve the configured image caption provider id and provider settings."""
+    plugin_context = getattr(run_context.context, "context", None)
+    event = getattr(run_context.context, "event", None)
+    if plugin_context is None:
+        return "", {}
+    try:
+        cfg = plugin_context.get_config(
+            umo=getattr(event, "unified_msg_origin", None)
+        ).get("provider_settings", {})
+    except Exception as exc:  # noqa: BLE001
+        logger.debug("Failed to read provider settings: %s", exc)
+        return "", {}
+    return cfg.get("default_image_caption_provider_id") or "", cfg
+
+
 ToolExecutorResultT = T.TypeVar("ToolExecutorResultT")
 AwaitableResultT = T.TypeVar("AwaitableResultT")
 
@@ -1054,9 +1072,88 @@ async def step(self):
                         logger.debug(
                             f"Appended {len(cached_images)} cached image(s) to context for LLM review"
                         )
+                else:
+                    # The main model cannot view images: fall back to the configured
+                    # image caption provider so the image content is not silently
+                    # dropped. Mirrors astr_main_agent._ensure_img_caption().
+                    caption_parts = await self._caption_cached_tool_images(
+                        cached_images
+                    )
+                    self.run_context.messages.append(
+                        Message(role="user", content=caption_parts)
+                    )
+                    logger.debug(
+                        f"Appended captions for {len(cached_images)} cached image(s) to context for LLM review"
+                    )
 
             self.req.append_tool_calls_result(tool_calls_result)
 
+    async def _caption_cached_tool_images(
+        self, cached_images: list[CachedImage]
+    ) -> list[TextPart]:
+        """主模型不支持图片时，用默认图片转述模型为缓存图片生成一段文字描述，失败或未配置则退化为占位文本。"""
+        img_cap_prov_id, cfg = _get_image_caption_config(self.run_context)
+
+        parts: list[TextPart] = [
+            TextPart(
+                text=(
+                    f"[Image from tool '{cached_img.tool_name}', "
+                    f"path='{cached_img.file_path}']"
+                )
+            )
+            for cached_img in cached_images
+        ]
+
+        # 与 astr_main_agent._ensure_img_caption() 一致：一次调用处理全部图片，
+        # 避免按图逐个调用导致长对话中工具循环被多次串行转述拖慢。
+        caption = await self._request_tool_image_captions(
+            img_cap_prov_id, cfg, cached_images
+        )
+        if caption:
+            parts.append(TextPart(text=f"<image_caption>{caption}</image_caption>"))
+        else:
+            parts.append(
+                TextPart(
+                    text=(
+                        "[Image not visible to the current model]"
+                        if not img_cap_prov_id
+                        else "[Image Captioning Failed]"
+                    )
+                )
+            )
+        return parts
+
+    async def _request_tool_image_captions(
+        self,
+        img_cap_prov_id: str,
+        cfg: dict,
+        cached_images: list[CachedImage],
+    ) -> str | None:
+        if not img_cap_prov_id:
+            return None
+        caption_paths = [
+            cached_img.file_path
+            for cached_img in cached_images
+            if Path(cached_img.file_path).exists()
+        ]
+        if not caption_paths:
+            return None
+        plugin_context = getattr(self.run_context.context, "context", None)
+        if plugin_context is None:
+            return None
+        try:
+            from astrbot.core.astr_main_agent import _request_img_caption
+
+            return await _request_img_caption(
+                img_cap_prov_id,
+                cfg,
+                caption_paths,
+                plugin_context,
+            )
+        except Exception as exc:  # noqa: BLE001
+            logger.error("Failed to caption tool images: %s", exc)
+            return None
+
     async def step_until_done(
         self, max_step: int
     ) -> T.AsyncGenerator[AgentResponse, None]:
diff --git a/tests/test_tool_loop_agent_runner.py b/tests/test_tool_loop_agent_runner.py
index 1e679de4aa..56d60dcd52 100644
--- a/tests/test_tool_loop_agent_runner.py
+++ b/tests/test_tool_loop_agent_runner.py
@@ -142,6 +142,76 @@ async def generator():
         return generator()
 
 
+class MockMultiImageToolExecutor:
+    """模拟一次工具调用返回多张图片的工具执行器。"""
+
+    @classmethod
+    def execute(cls, tool, run_context, **tool_args):
+        async def generator():
+            from mcp.types import CallToolResult, ImageContent
+
+            result = CallToolResult(
+                content=[
+                    ImageContent(
+                        type="image",
+                        data="dGVzdA==",
+                        mimeType="image/png",
+                    ),
+                    ImageContent(
+                        type="image",
+                        data="dGVzdA==",
+                        mimeType="image/png",
+                    ),
+                ]
+            )
+            yield result
+
+        return generator()
+
+
+class MockCaptionProvider(MockProvider):
+    """模拟默认图片转述模型，记录收到的图片路径并返回固定描述。"""
+
+    def __init__(self, caption_text: str = "图片中是一只猫"):
+        super().__init__()
+        self.caption_text = caption_text
+        self.captioned_paths: list[str] = []
+
+    async def text_chat(self, **kwargs) -> LLMResponse:
+        self.call_count += 1
+        self.captioned_paths.extend(kwargs.get("image_urls", []))
+        return LLMResponse(
+            role="assistant",
+            completion_text=self.caption_text,
+            usage=TokenUsage(input_other=10, output=5),
+        )
+
+
+class MockFailingCaptionProvider(MockCaptionProvider):
+    """模拟转述模型调用失败的场景。"""
+
+    async def text_chat(self, **kwargs) -> LLMResponse:
+        raise RuntimeError("caption provider down")
+
+
+class MockImageCaptionContext:
+    """模拟含 default_image_caption_provider_id 配置的 star Context。"""
+
+    def __init__(self, caption_provider: Any, provider_id: str = "cap_prov"):
+        self.caption_provider = caption_provider
+        self.provider_id = provider_id
+
+    def get_config(self, umo=None):
+        return {
+            "provider_settings": {
+                "default_image_caption_provider_id": self.provider_id,
+            }
+        }
+
+    def get_provider_by_id(self, provider_id: str):
+        return self.caption_provider
+
+
 class VaryingUsageProvider(MockProvider):
     """Return distinct token usage values for each tool-loop request."""
 
@@ -906,6 +976,177 @@ def fake_save_image(
     ]
 
 
+def _all_context_texts(contexts: list[Any]) -> list[str]:
+    texts: list[str] = []
+    for msg in contexts:
+        content = msg.get("content")
+        if isinstance(content, str):
+            texts.append(content)
+        elif isinstance(content, list):
+            for part in content:
+                if isinstance(part, dict) and part.get("type") == "text":
+                    texts.append(str(part.get("text", "")))
+    return texts
+
+
+def _tool_image_runner_setup(
+    runner,
+    provider_request,
+    mock_hooks,
+    monkeypatch,
+    tmp_path,
+    caption_context,
+    modalities: list[str] | None = None,
+    tool_executor=MockMixedContentToolExecutor,
+):
+    if modalities is None:
+        modalities = ["tool_use"]
+    from astrbot.core.agent.tool_image_cache import CachedImage, tool_image_cache
+
+    img_path = tmp_path / "tool_img.png"
+    img_path.write_bytes(b"fake-png-bytes")
+
+    def fake_save_image(
+        base64_data, tool_call_id, tool_name, index=0, mime_type="image/png"
+    ):
+        return CachedImage(
+            tool_call_id=tool_call_id,
+            tool_name=tool_name,
+            file_path=str(img_path),
+            mime_type=mime_type,
+        )
+
+    monkeypatch.setattr(tool_image_cache, "save_image", fake_save_image)
+
+    event = MockEvent("test:FriendMessage:tool_caption", "u1")
+    provider = CapturingToolLoopProvider("test_tool")
+    provider.provider_config["modalities"] = modalities
+
+    async def _run():
+        await runner.reset(
+            provider=provider,
+            request=provider_request,
+            run_context=ContextWrapper(
+                context=SimpleNamespace(event=event, context=caption_context)
+            ),
+            tool_executor=tool_executor,
+            agent_hooks=mock_hooks,
+            streaming=False,
+        )
+        async for _ in runner.step_until_done(3):
+            pass
+
+    return provider, img_path, _run
+
+
+@pytest.mark.asyncio
+async def test_tool_image_caption_injected_when_main_model_lacks_image(
+    runner, provider_request, mock_hooks, monkeypatch, tmp_path
+):
+    """主模型不支持图片时，工具返回的图片应经默认转述模型生成文字描述注入上下文。"""
+    caption_provider = MockCaptionProvider(caption_text="图片中是一只猫")
+    provider, img_path, run = _tool_image_runner_setup(
+        runner,
+        provider_request,
+        mock_hooks,
+        monkeypatch,
+        tmp_path,
+        caption_context=MockImageCaptionContext(caption_provider),
+    )
+    await run()
+
+    assert provider.call_count == 2
+    assert caption_provider.captioned_paths == [str(img_path)]
+    second_contexts = provider.received_contexts[1]
+    context_texts = _all_context_texts(second_contexts)
+    assert any(
+        "<image_caption>图片中是一只猫</image_caption>" in t for t in context_texts
+    )
+    tool_msg_index = next(
+        i for i, msg in enumerate(second_contexts) if msg.get("role") == "tool"
+    )
+    caption_msg_index = next(
+        i
+        for i, msg in enumerate(second_contexts)
+        if isinstance(msg.get("content"), list)
+        and any(
+            isinstance(part, dict)
+            and part.get("type") == "text"
+            and "<image_caption>" in str(part.get("text", ""))
+            for part in msg.get("content", [])
+        )
+    )
+    assert caption_msg_index > tool_msg_index
+
+
+@pytest.mark.asyncio
+async def test_tool_multi_image_caption_single_call(
+    runner, provider_request, mock_hooks, monkeypatch, tmp_path
+):
+    """一次工具调用返回多张图片时，只发起一次转述调用，避免长对话中被多次串行转述拖慢。"""
+    caption_provider = MockCaptionProvider(caption_text="两张截图")
+    provider, img_path, run = _tool_image_runner_setup(
+        runner,
+        provider_request,
+        mock_hooks,
+        monkeypatch,
+        tmp_path,
+        caption_context=MockImageCaptionContext(caption_provider),
+        tool_executor=MockMultiImageToolExecutor,
+    )
+    await run()
+
+    assert provider.call_count == 2
+    assert caption_provider.call_count == 1
+    assert caption_provider.captioned_paths == [str(img_path), str(img_path)]
+    second_contexts = provider.received_contexts[1]
+    context_texts = _all_context_texts(second_contexts)
+    assert context_texts.count("<image_caption>两张截图</image_caption>") == 1
+
+
+@pytest.mark.asyncio
+async def test_tool_image_placeholder_when_no_caption_provider(
+    runner, provider_request, mock_hooks, monkeypatch, tmp_path
+):
+    """未配置默认转述模型时，注入占位文本而非静默丢弃图片内容。"""
+    provider, _, run = _tool_image_runner_setup(
+        runner,
+        provider_request,
+        mock_hooks,
+        monkeypatch,
+        tmp_path,
+        caption_context=MockImageCaptionContext(caption_provider=None, provider_id=""),
+    )
+    await run()
+
+    assert provider.call_count == 2
+    second_contexts = provider.received_contexts[1]
+    context_texts = _all_context_texts(second_contexts)
+    assert any("[Image not visible to the current model]" in t for t in context_texts)
+    assert not any("<image_caption>" in t for t in context_texts)
+
+
+@pytest.mark.asyncio
+async def test_tool_image_caption_failure_placeholder(
+    runner, provider_request, mock_hooks, monkeypatch, tmp_path
+):
+    """转述模型调用失败时注入 [Image Captioning Failed]，工具循环不被中断。"""
+    provider, _, run = _tool_image_runner_setup(
+        runner,
+        provider_request,
+        mock_hooks,
+        monkeypatch,
+        tmp_path,
+        caption_context=MockImageCaptionContext(MockFailingCaptionProvider()),
+    )
+    await run()
+
+    assert provider.call_count == 2
+    second_contexts = provider.received_contexts[1]
+    context_texts = _all_context_texts(second_contexts)
+    assert any("[Image Captioning Failed]" in t for t in context_texts)
+
+
 @pytest.mark.asyncio
 async def test_runner_replaces_runtime_image_context_before_provider_call(
     runner, provider_request, mock_hooks