feat(channel): deliver generated files on WhatsApp and honor user tool policy

Add save_deliverable_attachment for explicit document outbound, pass channel user_id into tool risk gating so write_file/run_command respect per-user allow_high settings, and document the workflow in channel-file-delivery skill.

Co-authored-by: Cursor <cursoragent@cursor.com>

runtime/tools/public/save_deliverable_attachment_tool.py

@@ -0,0 +1,81 @@
+from __future__ import annotations
+
+import mimetypes
+from pathlib import Path
+from typing import Any
+
+from runtime.tools.base import ToolSpec
+from runtime.tools.path_guard import resolve_workspace_path
+from svc.files.attachment_assets import AttachmentAssetStore
+
+
+def _guess_mime(path: Path, override: str) -> str:
+    if override:
+        return override
+    guessed, _ = mimetypes.guess_type(str(path))
+    return guessed or "application/octet-stream"
+
+
+def save_deliverable_attachment_tool() -> ToolSpec:
+    def _handler(args: dict[str, Any]) -> dict[str, Any]:
+        raw = str(args.get("path") or "").strip().strip('"').strip("'")
+        if not raw:
+            return {"ok": False, "error": "path_required"}
+        display_name = str(args.get("name") or "").strip()
+        mime_override = str(args.get("mime") or "").strip()
+        try:
+            p = resolve_workspace_path(raw)
+        except ValueError as exc:
+            return {"ok": False, "error": str(exc)}
+        if not p.exists() or not p.is_file():
+            return {"ok": False, "error": "file_not_found", "path": str(p)}
+        filename = display_name or p.name
+        mime = _guess_mime(p, mime_override)
+        try:
+            data = p.read_bytes()
+        except Exception as exc:
+            return {"ok": False, "error": "read_failed", "detail": str(exc)}
+        meta = AttachmentAssetStore().save_bytes(data, filename=filename, mime=mime)
+        return {
+            "ok": True,
+            "attachment_id": meta.attachment_id,
+            "name": meta.name,
+            "mime": meta.mime,
+            "bytes": meta.bytes,
+            "deliverable": True,
+        }
+
+    return ToolSpec(
+        name="save_deliverable_attachment",
+        description=(
+            "Register a workspace file for outbound channel delivery (WhatsApp/WeChat). "
+            "Call this after generating a file with write_file or run_command when the user should receive it as an attachment. "
+            "write_file alone does not send files to messaging channels."
+        ),
+        parameters={
+            "type": "object",
+            "properties": {
+                "path": {
+                    "type": "string",
+                    "description": "Workspace file path (relative to workspace root or allowed absolute path).",
+                },
+                "name": {
+                    "type": "string",
+                    "description": "Optional download filename shown to the user.",
+                },
+                "mime": {
+                    "type": "string",
+                    "description": "Optional MIME type override (e.g. application/vnd.openxmlformats-officedocument.spreadsheetml.sheet).",
+                },
+            },
+            "required": ["path"],
+            "additionalProperties": False,
+        },
+        handler=_handler,
+        tags=frozenset({"public", "workspace", "attachment", "channel"}),
+        read_only=False,
+        risk_level="low",
+    )
+
+
+__all__ = ["save_deliverable_attachment_tool"]