backend/src/client.py

"""DeerFlowClient — Embedded Python client for DeerFlow agent system.

Provides direct programmatic access to DeerFlow's agent capabilities
without requiring LangGraph Server or Gateway API processes.

Usage:
    from src.client import DeerFlowClient

    client = DeerFlowClient()
    response = client.chat("Analyze this paper for me", thread_id="my-thread")
    print(response)

    # Streaming
    for event in client.stream("hello"):
        print(event)
"""

import asyncio
import json
import logging
import mimetypes
import re
import shutil
import tempfile
import uuid
import zipfile
from collections.abc import Generator
from dataclasses import dataclass, field
from pathlib import Path
from typing import Any

from langchain.agents import create_agent
from langchain_core.messages import AIMessage, HumanMessage, SystemMessage, ToolMessage
from langchain_core.runnables import RunnableConfig

from src.agents.lead_agent.agent import _build_middlewares
from src.agents.lead_agent.prompt import apply_prompt_template
from src.agents.thread_state import ThreadState
from src.config.app_config import get_app_config, reload_app_config
from src.config.extensions_config import ExtensionsConfig, SkillStateConfig, get_extensions_config, reload_extensions_config
from src.config.paths import get_paths
from src.models import create_chat_model

logger = logging.getLogger(__name__)


@dataclass
class StreamEvent:
    """A single event from the streaming agent response.

    Event types align with the LangGraph SSE protocol:
        - ``"values"``: Full state snapshot (title, messages, artifacts).
        - ``"messages-tuple"``: Per-message update (AI text, tool calls, tool results).
        - ``"end"``: Stream finished.

    Attributes:
        type: Event type.
        data: Event payload. Contents vary by type.
    """

    type: str
    data: dict[str, Any] = field(default_factory=dict)


class DeerFlowClient:
    """Embedded Python client for DeerFlow agent system.

    Provides direct programmatic access to DeerFlow's agent capabilities
    without requiring LangGraph Server or Gateway API processes.

    Note:
        Multi-turn conversations require a ``checkpointer``. Without one,
        each ``stream()`` / ``chat()`` call is stateless — ``thread_id``
        is only used for file isolation (uploads / artifacts).

        The system prompt (including date, memory, and skills context) is
        generated when the internal agent is first created and cached until
        the configuration key changes. Call :meth:`reset_agent` to force
        a refresh in long-running processes.

    Example::

        from src.client import DeerFlowClient

        client = DeerFlowClient()

        # Simple one-shot
        print(client.chat("hello"))

        # Streaming
        for event in client.stream("hello"):
            print(event.type, event.data)

        # Configuration queries
        print(client.list_models())
        print(client.list_skills())
    """

    def __init__(
        self,
        config_path: str | None = None,
        checkpointer=None,
        *,
        model_name: str | None = None,
        thinking_enabled: bool = True,
        subagent_enabled: bool = False,
        plan_mode: bool = False,
    ):
        """Initialize the client.

        Loads configuration but defers agent creation to first use.

        Args:
            config_path: Path to config.yaml. Uses default resolution if None.
            checkpointer: LangGraph checkpointer instance for state persistence.
                Required for multi-turn conversations on the same thread_id.
                Without a checkpointer, each call is stateless.
            model_name: Override the default model name from config.
            thinking_enabled: Enable model's extended thinking.
            subagent_enabled: Enable subagent delegation.
            plan_mode: Enable TodoList middleware for plan mode.
        """
        if config_path is not None:
            reload_app_config(config_path)
        self._app_config = get_app_config()

        self._checkpointer = checkpointer
        self._model_name = model_name
        self._thinking_enabled = thinking_enabled
        self._subagent_enabled = subagent_enabled
        self._plan_mode = plan_mode

        # Lazy agent — created on first call, recreated when config changes.
        self._agent = None
        self._agent_config_key: tuple | None = None

    def reset_agent(self) -> None:
        """Force the internal agent to be recreated on the next call.

        Use this after external changes (e.g. memory updates, skill
        installations) that should be reflected in the system prompt
        or tool set.
        """
        self._agent = None
        self._agent_config_key = None

    # ------------------------------------------------------------------
    # Internal helpers
    # ------------------------------------------------------------------

    @staticmethod
    def _atomic_write_json(path: Path, data: dict) -> None:
        """Write JSON to *path* atomically (temp file + replace)."""
        fd = tempfile.NamedTemporaryFile(
            mode="w", dir=path.parent, suffix=".tmp", delete=False,
        )
        try:
            json.dump(data, fd, indent=2)
            fd.close()
            Path(fd.name).replace(path)
        except BaseException:
            fd.close()
            Path(fd.name).unlink(missing_ok=True)
            raise

    def _get_runnable_config(self, thread_id: str, **overrides) -> RunnableConfig:
        """Build a RunnableConfig for agent invocation."""
        configurable = {
            "thread_id": thread_id,
            "model_name": overrides.get("model_name", self._model_name),
            "thinking_enabled": overrides.get("thinking_enabled", self._thinking_enabled),
            "is_plan_mode": overrides.get("plan_mode", self._plan_mode),
            "subagent_enabled": overrides.get("subagent_enabled", self._subagent_enabled),
        }
        return RunnableConfig(
            configurable=configurable,
            recursion_limit=overrides.get("recursion_limit", 100),
        )

    def _ensure_agent(self, config: RunnableConfig):
        """Create (or recreate) the agent when config-dependent params change."""
        cfg = config.get("configurable", {})
        key = (
            cfg.get("model_name"),
            cfg.get("thinking_enabled"),
            cfg.get("is_plan_mode"),
            cfg.get("subagent_enabled"),
        )

        if self._agent is not None and self._agent_config_key == key:
            return

        thinking_enabled = cfg.get("thinking_enabled", True)
        model_name = cfg.get("model_name")
        subagent_enabled = cfg.get("subagent_enabled", False)
        max_concurrent_subagents = cfg.get("max_concurrent_subagents", 3)

        kwargs: dict[str, Any] = {
            "model": create_chat_model(name=model_name, thinking_enabled=thinking_enabled),
            "tools": self._get_tools(model_name=model_name, subagent_enabled=subagent_enabled),
            "middleware": _build_middlewares(config, model_name=model_name),
            "system_prompt": apply_prompt_template(
                subagent_enabled=subagent_enabled,
                max_concurrent_subagents=max_concurrent_subagents,
            ),
            "state_schema": ThreadState,
        }
        if self._checkpointer is not None:
            kwargs["checkpointer"] = self._checkpointer

        self._agent = create_agent(**kwargs)
        self._agent_config_key = key
        logger.info("Agent created: model=%s, thinking=%s", model_name, thinking_enabled)

    @staticmethod
    def _get_tools(*, model_name: str | None, subagent_enabled: bool):
        """Lazy import to avoid circular dependency at module level."""
        from src.tools import get_available_tools

        return get_available_tools(model_name=model_name, subagent_enabled=subagent_enabled)

    @staticmethod
    def _serialize_message(msg) -> dict:
        """Serialize a LangChain message to a plain dict for values events."""
        if isinstance(msg, AIMessage):
            d: dict[str, Any] = {"type": "ai", "content": msg.content, "id": getattr(msg, "id", None)}
            if msg.tool_calls:
                d["tool_calls"] = [{"name": tc["name"], "args": tc["args"], "id": tc.get("id")} for tc in msg.tool_calls]
            return d
        if isinstance(msg, ToolMessage):
            return {
                "type": "tool",
                "content": msg.content if isinstance(msg.content, str) else str(msg.content),
                "name": getattr(msg, "name", None),
                "tool_call_id": getattr(msg, "tool_call_id", None),
                "id": getattr(msg, "id", None),
            }
        if isinstance(msg, HumanMessage):
            return {"type": "human", "content": msg.content, "id": getattr(msg, "id", None)}
        if isinstance(msg, SystemMessage):
            return {"type": "system", "content": msg.content, "id": getattr(msg, "id", None)}
        return {"type": "unknown", "content": str(msg), "id": getattr(msg, "id", None)}

    @staticmethod
    def _extract_text(content) -> str:
        """Extract plain text from AIMessage content (str or list of blocks)."""
        if isinstance(content, str):
            return content
        if isinstance(content, list):
            parts = []
            for block in content:
                if isinstance(block, str):
                    parts.append(block)
                elif isinstance(block, dict) and block.get("type") == "text":
                    parts.append(block["text"])
            return "\n".join(parts) if parts else ""
        return str(content)

    # ------------------------------------------------------------------
    # Public API — conversation
    # ------------------------------------------------------------------

    def stream(
        self,
        message: str,
        *,
        thread_id: str | None = None,
        **kwargs,
    ) -> Generator[StreamEvent, None, None]:
        """Stream a conversation turn, yielding events incrementally.

        Each call sends one user message and yields events until the agent
        finishes its turn. A ``checkpointer`` must be provided at init time
        for multi-turn context to be preserved across calls.

        Event types align with the LangGraph SSE protocol so that
        consumers can switch between HTTP streaming and embedded mode
        without changing their event-handling logic.

        Args:
            message: User message text.
            thread_id: Thread ID for conversation context. Auto-generated if None.
            **kwargs: Override client defaults (model_name, thinking_enabled,
                plan_mode, subagent_enabled, recursion_limit).

        Yields:
            StreamEvent with one of:
            - type="values"          data={"title": str|None, "messages": [...], "artifacts": [...]}
            - type="messages-tuple"  data={"type": "ai", "content": str, "id": str}
            - type="messages-tuple"  data={"type": "ai", "content": "", "id": str, "tool_calls": [...]}
            - type="messages-tuple"  data={"type": "tool", "content": str, "name": str, "tool_call_id": str, "id": str}
            - type="end"             data={}
        """
        if thread_id is None:
            thread_id = str(uuid.uuid4())

        config = self._get_runnable_config(thread_id, **kwargs)
        self._ensure_agent(config)

        state: dict[str, Any] = {"messages": [HumanMessage(content=message)]}
        context = {"thread_id": thread_id}

        seen_ids: set[str] = set()

        for chunk in self._agent.stream(state, config=config, context=context, stream_mode="values"):
            messages = chunk.get("messages", [])

            for msg in messages:
                msg_id = getattr(msg, "id", None)
                if msg_id and msg_id in seen_ids:
                    continue
                if msg_id:
                    seen_ids.add(msg_id)

                if isinstance(msg, AIMessage):
                    if msg.tool_calls:
                        yield StreamEvent(
                            type="messages-tuple",
                            data={
                                "type": "ai",
                                "content": "",
                                "id": msg_id,
                                "tool_calls": [
                                    {"name": tc["name"], "args": tc["args"], "id": tc.get("id")}
                                    for tc in msg.tool_calls
                                ],
                            },
                        )

                    text = self._extract_text(msg.content)
                    if text:
                        yield StreamEvent(
                            type="messages-tuple",
                            data={"type": "ai", "content": text, "id": msg_id},
                        )

                elif isinstance(msg, ToolMessage):
                    yield StreamEvent(
                        type="messages-tuple",
                        data={
                            "type": "tool",
                            "content": msg.content if isinstance(msg.content, str) else str(msg.content),
                            "name": getattr(msg, "name", None),
                            "tool_call_id": getattr(msg, "tool_call_id", None),
                            "id": msg_id,
                        },
                    )

            # Emit a values event for each state snapshot
            yield StreamEvent(
                type="values",
                data={
                    "title": chunk.get("title"),
                    "messages": [self._serialize_message(m) for m in messages],
                    "artifacts": chunk.get("artifacts", []),
                },
            )

        yield StreamEvent(type="end", data={})

    def chat(self, message: str, *, thread_id: str | None = None, **kwargs) -> str:
        """Send a message and return the final text response.

        Convenience wrapper around :meth:`stream` that returns only the
        **last** AI text from ``messages-tuple`` events. If the agent emits
        multiple text segments in one turn, intermediate segments are
        discarded. Use :meth:`stream` directly to capture all events.

        Args:
            message: User message text.
            thread_id: Thread ID for conversation context. Auto-generated if None.
            **kwargs: Override client defaults (same as stream()).

        Returns:
            The last AI message text, or empty string if no response.
        """
        last_text = ""
        for event in self.stream(message, thread_id=thread_id, **kwargs):
            if event.type == "messages-tuple" and event.data.get("type") == "ai":
                content = event.data.get("content", "")
                if content:
                    last_text = content
        return last_text

    # ------------------------------------------------------------------
    # Public API — configuration queries
    # ------------------------------------------------------------------

    def list_models(self) -> dict:
        """List available models from configuration.

        Returns:
            Dict with "models" key containing list of model info dicts,
            matching the Gateway API ``ModelsListResponse`` schema.
        """
        return {
            "models": [
                {
                    "name": model.name,
                    "display_name": getattr(model, "display_name", None),
                    "description": getattr(model, "description", None),
                    "supports_thinking": getattr(model, "supports_thinking", False),
                }
                for model in self._app_config.models
            ]
        }

    def list_skills(self, enabled_only: bool = False) -> dict:
        """List available skills.

        Args:
            enabled_only: If True, only return enabled skills.

        Returns:
            Dict with "skills" key containing list of skill info dicts,
            matching the Gateway API ``SkillsListResponse`` schema.
        """
        from src.skills.loader import load_skills

        return {
            "skills": [
                {
                    "name": s.name,
                    "description": s.description,
                    "license": s.license,
                    "category": s.category,
                    "enabled": s.enabled,
                }
                for s in load_skills(enabled_only=enabled_only)
            ]
        }

    def get_memory(self) -> dict:
        """Get current memory data.

        Returns:
            Memory data dict (see src/agents/memory/updater.py for structure).
        """
        from src.agents.memory.updater import get_memory_data

        return get_memory_data()

    def get_model(self, name: str) -> dict | None:
        """Get a specific model's configuration by name.

        Args:
            name: Model name.

        Returns:
            Model info dict matching the Gateway API ``ModelResponse``
            schema, or None if not found.
        """
        model = self._app_config.get_model_config(name)
        if model is None:
            return None
        return {
            "name": model.name,
            "display_name": getattr(model, "display_name", None),
            "description": getattr(model, "description", None),
            "supports_thinking": getattr(model, "supports_thinking", False),
        }

    # ------------------------------------------------------------------
    # Public API — MCP configuration
    # ------------------------------------------------------------------

    def get_mcp_config(self) -> dict:
        """Get MCP server configurations.

        Returns:
            Dict with "mcp_servers" key mapping server name to config,
            matching the Gateway API ``McpConfigResponse`` schema.
        """
        config = get_extensions_config()
        return {"mcp_servers": {name: server.model_dump() for name, server in config.mcp_servers.items()}}

    def update_mcp_config(self, mcp_servers: dict[str, dict]) -> dict:
        """Update MCP server configurations.

        Writes to extensions_config.json and reloads the cache.

        Args:
            mcp_servers: Dict mapping server name to config dict.
                Each value should contain keys like enabled, type, command, args, env, url, etc.

        Returns:
            Dict with "mcp_servers" key, matching the Gateway API
            ``McpConfigResponse`` schema.

        Raises:
            OSError: If the config file cannot be written.
        """
        config_path = ExtensionsConfig.resolve_config_path()
        if config_path is None:
            raise FileNotFoundError(
                "Cannot locate extensions_config.json. "
                "Set DEER_FLOW_EXTENSIONS_CONFIG_PATH or ensure it exists in the project root."
            )

        current_config = get_extensions_config()

        config_data = {
            "mcpServers": mcp_servers,
            "skills": {name: {"enabled": skill.enabled} for name, skill in current_config.skills.items()},
        }

        self._atomic_write_json(config_path, config_data)

        self._agent = None
        reloaded = reload_extensions_config()
        return {"mcp_servers": {name: server.model_dump() for name, server in reloaded.mcp_servers.items()}}

    # ------------------------------------------------------------------
    # Public API — skills management
    # ------------------------------------------------------------------

    def get_skill(self, name: str) -> dict | None:
        """Get a specific skill by name.

        Args:
            name: Skill name.

        Returns:
            Skill info dict, or None if not found.
        """
        from src.skills.loader import load_skills

        skill = next((s for s in load_skills(enabled_only=False) if s.name == name), None)
        if skill is None:
            return None
        return {
            "name": skill.name,
            "description": skill.description,
            "license": skill.license,
            "category": skill.category,
            "enabled": skill.enabled,
        }

    def update_skill(self, name: str, *, enabled: bool) -> dict:
        """Update a skill's enabled status.

        Args:
            name: Skill name.
            enabled: New enabled status.

        Returns:
            Updated skill info dict.

        Raises:
            ValueError: If the skill is not found.
            OSError: If the config file cannot be written.
        """
        from src.skills.loader import load_skills

        skills = load_skills(enabled_only=False)
        skill = next((s for s in skills if s.name == name), None)
        if skill is None:
            raise ValueError(f"Skill '{name}' not found")

        config_path = ExtensionsConfig.resolve_config_path()
        if config_path is None:
            raise FileNotFoundError(
                "Cannot locate extensions_config.json. "
                "Set DEER_FLOW_EXTENSIONS_CONFIG_PATH or ensure it exists in the project root."
            )

        extensions_config = get_extensions_config()
        extensions_config.skills[name] = SkillStateConfig(enabled=enabled)

        config_data = {
            "mcpServers": {n: s.model_dump() for n, s in extensions_config.mcp_servers.items()},
            "skills": {n: {"enabled": sc.enabled} for n, sc in extensions_config.skills.items()},
        }

        self._atomic_write_json(config_path, config_data)

        self._agent = None
        reload_extensions_config()

        updated = next((s for s in load_skills(enabled_only=False) if s.name == name), None)
        if updated is None:
            raise RuntimeError(f"Skill '{name}' disappeared after update")
        return {
            "name": updated.name,
            "description": updated.description,
            "license": updated.license,
            "category": updated.category,
            "enabled": updated.enabled,
        }

    def install_skill(self, skill_path: str | Path) -> dict:
        """Install a skill from a .skill archive (ZIP).

        Args:
            skill_path: Path to the .skill file.

        Returns:
            Dict with success, skill_name, message.

        Raises:
            FileNotFoundError: If the file does not exist.
            ValueError: If the file is invalid.
        """
        from src.gateway.routers.skills import _validate_skill_frontmatter
        from src.skills.loader import get_skills_root_path

        path = Path(skill_path)
        if not path.exists():
            raise FileNotFoundError(f"Skill file not found: {skill_path}")
        if not path.is_file():
            raise ValueError(f"Path is not a file: {skill_path}")
        if path.suffix != ".skill":
            raise ValueError("File must have .skill extension")
        if not zipfile.is_zipfile(path):
            raise ValueError("File is not a valid ZIP archive")

        skills_root = get_skills_root_path()
        custom_dir = skills_root / "custom"
        custom_dir.mkdir(parents=True, exist_ok=True)

        with tempfile.TemporaryDirectory() as tmp:
            tmp_path = Path(tmp)
            with zipfile.ZipFile(path, "r") as zf:
                total_size = sum(info.file_size for info in zf.infolist())
                if total_size > 100 * 1024 * 1024:
                    raise ValueError("Skill archive too large when extracted (>100MB)")
                for info in zf.infolist():
                    if Path(info.filename).is_absolute() or ".." in Path(info.filename).parts:
                        raise ValueError(f"Unsafe path in archive: {info.filename}")
                zf.extractall(tmp_path)
            for p in tmp_path.rglob("*"):
                if p.is_symlink():
                    p.unlink()

            items = list(tmp_path.iterdir())
            if not items:
                raise ValueError("Skill archive is empty")

            skill_dir = items[0] if len(items) == 1 and items[0].is_dir() else tmp_path

            is_valid, message, skill_name = _validate_skill_frontmatter(skill_dir)
            if not is_valid:
                raise ValueError(f"Invalid skill: {message}")
            if not re.fullmatch(r"[a-zA-Z0-9_-]+", skill_name):
                raise ValueError(f"Invalid skill name: {skill_name}")

            target = custom_dir / skill_name
            if target.exists():
                raise ValueError(f"Skill '{skill_name}' already exists")

            shutil.copytree(skill_dir, target)

        return {"success": True, "skill_name": skill_name, "message": f"Skill '{skill_name}' installed successfully"}

    # ------------------------------------------------------------------
    # Public API — memory management
    # ------------------------------------------------------------------

    def reload_memory(self) -> dict:
        """Reload memory data from file, forcing cache invalidation.

        Returns:
            The reloaded memory data dict.
        """
        from src.agents.memory.updater import reload_memory_data

        return reload_memory_data()

    def get_memory_config(self) -> dict:
        """Get memory system configuration.

        Returns:
            Memory config dict.
        """
        from src.config.memory_config import get_memory_config

        config = get_memory_config()
        return {
            "enabled": config.enabled,
            "storage_path": config.storage_path,
            "debounce_seconds": config.debounce_seconds,
            "max_facts": config.max_facts,
            "fact_confidence_threshold": config.fact_confidence_threshold,
            "injection_enabled": config.injection_enabled,
            "max_injection_tokens": config.max_injection_tokens,
        }

    def get_memory_status(self) -> dict:
        """Get memory status: config + current data.

        Returns:
            Dict with "config" and "data" keys.
        """
        return {
            "config": self.get_memory_config(),
            "data": self.get_memory(),
        }

    # ------------------------------------------------------------------
    # Public API — file uploads
    # ------------------------------------------------------------------

    @staticmethod
    def _get_uploads_dir(thread_id: str) -> Path:
        """Get (and create) the uploads directory for a thread."""
        base = get_paths().sandbox_uploads_dir(thread_id)
        base.mkdir(parents=True, exist_ok=True)
        return base

    def upload_files(self, thread_id: str, files: list[str | Path]) -> dict:
        """Upload local files into a thread's uploads directory.

        For PDF, PPT, Excel, and Word files, they are also converted to Markdown.

        Args:
            thread_id: Target thread ID.
            files: List of local file paths to upload.

        Returns:
            Dict with success, files, message — matching the Gateway API
            ``UploadResponse`` schema.

        Raises:
            FileNotFoundError: If any file does not exist.
        """
        from src.gateway.routers.uploads import CONVERTIBLE_EXTENSIONS, convert_file_to_markdown

        # Validate all files upfront to avoid partial uploads.
        resolved_files = []
        for f in files:
            p = Path(f)
            if not p.exists():
                raise FileNotFoundError(f"File not found: {f}")
            resolved_files.append(p)

        uploads_dir = self._get_uploads_dir(thread_id)
        uploaded_files: list[dict] = []

        for src_path in resolved_files:

            dest = uploads_dir / src_path.name
            shutil.copy2(src_path, dest)

            info: dict[str, Any] = {
                "filename": src_path.name,
                "size": str(dest.stat().st_size),
                "path": str(dest),
                "virtual_path": f"/mnt/user-data/uploads/{src_path.name}",
                "artifact_url": f"/api/threads/{thread_id}/artifacts/mnt/user-data/uploads/{src_path.name}",
            }

            if src_path.suffix.lower() in CONVERTIBLE_EXTENSIONS:
                try:
                    try:
                        asyncio.get_running_loop()
                        import concurrent.futures
                        with concurrent.futures.ThreadPoolExecutor() as pool:
                            md_path = pool.submit(lambda: asyncio.run(convert_file_to_markdown(dest))).result()
                    except RuntimeError:
                        md_path = asyncio.run(convert_file_to_markdown(dest))
                except Exception:
                    logger.warning("Failed to convert %s to markdown", src_path.name, exc_info=True)
                    md_path = None

                if md_path is not None:
                    info["markdown_file"] = md_path.name
                    info["markdown_virtual_path"] = f"/mnt/user-data/uploads/{md_path.name}"
                    info["markdown_artifact_url"] = f"/api/threads/{thread_id}/artifacts/mnt/user-data/uploads/{md_path.name}"

            uploaded_files.append(info)

        return {
            "success": True,
            "files": uploaded_files,
            "message": f"Successfully uploaded {len(uploaded_files)} file(s)",
        }

    def list_uploads(self, thread_id: str) -> dict:
        """List files in a thread's uploads directory.

        Args:
            thread_id: Thread ID.

        Returns:
            Dict with "files" and "count" keys, matching the Gateway API
            ``list_uploaded_files`` response.
        """
        uploads_dir = self._get_uploads_dir(thread_id)
        if not uploads_dir.exists():
            return {"files": [], "count": 0}

        files = []
        for fp in sorted(uploads_dir.iterdir()):
            if fp.is_file():
                stat = fp.stat()
                files.append({
                    "filename": fp.name,
                    "size": str(stat.st_size),
                    "path": str(fp),
                    "virtual_path": f"/mnt/user-data/uploads/{fp.name}",
                    "artifact_url": f"/api/threads/{thread_id}/artifacts/mnt/user-data/uploads/{fp.name}",
                    "extension": fp.suffix,
                    "modified": stat.st_mtime,
                })
        return {"files": files, "count": len(files)}

    def delete_upload(self, thread_id: str, filename: str) -> dict:
        """Delete a file from a thread's uploads directory.

        Args:
            thread_id: Thread ID.
            filename: Filename to delete.

        Returns:
            Dict with success and message, matching the Gateway API
            ``delete_uploaded_file`` response.

        Raises:
            FileNotFoundError: If the file does not exist.
            PermissionError: If path traversal is detected.
        """
        uploads_dir = self._get_uploads_dir(thread_id)
        file_path = (uploads_dir / filename).resolve()

        try:
            file_path.relative_to(uploads_dir.resolve())
        except ValueError as exc:
            raise PermissionError("Access denied: path traversal detected") from exc

        if not file_path.is_file():
            raise FileNotFoundError(f"File not found: {filename}")

        file_path.unlink()
        return {"success": True, "message": f"Deleted {filename}"}

    # ------------------------------------------------------------------
    # Public API — artifacts
    # ------------------------------------------------------------------

    def get_artifact(self, thread_id: str, path: str) -> tuple[bytes, str]:
        """Read an artifact file produced by the agent.

        Args:
            thread_id: Thread ID.
            path: Virtual path (e.g. "mnt/user-data/outputs/file.txt").

        Returns:
            Tuple of (file_bytes, mime_type).

        Raises:
            FileNotFoundError: If the artifact does not exist.
            ValueError: If the path is invalid.
        """
        virtual_prefix = "mnt/user-data"
        clean_path = path.lstrip("/")
        if not clean_path.startswith(virtual_prefix):
            raise ValueError(f"Path must start with /{virtual_prefix}")

        relative = clean_path[len(virtual_prefix):].lstrip("/")
        base_dir = get_paths().sandbox_user_data_dir(thread_id)
        actual = (base_dir / relative).resolve()

        try:
            actual.relative_to(base_dir.resolve())
        except ValueError as exc:
            raise PermissionError("Access denied: path traversal detected") from exc
        if not actual.exists():
            raise FileNotFoundError(f"Artifact not found: {path}")
        if not actual.is_file():
            raise ValueError(f"Path is not a file: {path}")

        mime_type, _ = mimetypes.guess_type(actual)
        return actual.read_bytes(), mime_type or "application/octet-stream"