feat(mcp): add response rendering helpers

surfsense_mcp/src/surfsense_mcp/core/rendering.py

@@ -0,0 +1,28 @@
+"""Shape tool results into the format the caller asked for.
+
+Tools default to Markdown (readable for the model and the human watching), and
+can return raw JSON when a caller wants to post-process the data. Large payloads
+are clipped so a single call can't blow the context window.
+"""
+
+from __future__ import annotations
+
+import json
+from typing import Any, Literal
+
+ResponseFormat = Literal["markdown", "json"]
+
+DEFAULT_CLIP_CHARS = 20_000
+
+
+def to_json(payload: Any) -> str:
+    """Pretty-print a payload as JSON, tolerating non-serializable values."""
+    return json.dumps(payload, indent=2, ensure_ascii=False, default=str)
+
+
+def clip(text: str, limit: int = DEFAULT_CLIP_CHARS) -> str:
+    """Trim overlong text, leaving a visible marker of how much was dropped."""
+    if len(text) <= limit:
+        return text
+    dropped = len(text) - limit
+    return f"{text[:limit]}\n\n… [{dropped} more characters truncated]"