feat: Add instrumentation decorator and apply to notes tools (Phase 5)

Created @instrument_tool decorator for automatic MCP tool metrics collection.
Applied to all 7 tools in notes.py.

Changes:
- observability/metrics.py:
  * New instrument_tool() decorator for automatic timing and error tracking
  * Compatible with @mcp.tool() and @require_scopes() decorators
  * Records tool_name, duration, and success/error status

- server/notes.py:
  * Applied @instrument_tool to all 7 tool functions
  * nc_notes_create_note, nc_notes_update_note, nc_notes_append_content
  * nc_notes_search_notes, nc_notes_get_note, nc_notes_get_attachment
  * nc_notes_delete_note

These metrics will populate the MCP Tool Calls dashboard panels.

Part of PR #295 - Complete metrics instrumentation (Phase 5)
Remaining: 86 tools across 8 server files

nextcloud_mcp_server/observability/metrics.py

@@ -395,3 +395,49 @@ def update_vector_sync_queue_size(size: int) -> None:
         size: Current queue size
     """
     vector_sync_queue_size.set(size)
+
+
+# =============================================================================
+# Decorator for Automatic Tool Instrumentation
+# =============================================================================
+
+
+def instrument_tool(func):
+    """
+    Decorator to automatically instrument MCP tool functions with metrics.
+
+    Wraps async tool functions to record execution time and success/error status.
+    Compatible with @mcp.tool() and @require_scopes() decorators.
+
+    Usage:
+        @mcp.tool()
+        @require_scopes("notes:write")
+        @instrument_tool
+        async def nc_notes_create_note(...):
+            ...
+
+    Args:
+        func: The async function to instrument
+
+    Returns:
+        Wrapped function with metrics instrumentation
+    """
+    import functools
+    import time
+
+    @functools.wraps(func)
+    async def wrapper(*args, **kwargs):
+        tool_name = func.__name__
+        start_time = time.time()
+        try:
+            result = await func(*args, **kwargs)
+            duration = time.time() - start_time
+            record_tool_call(tool_name, duration, "success")
+            return result
+        except Exception as e:
+            duration = time.time() - start_time
+            record_tool_call(tool_name, duration, "error")
+            record_tool_error(tool_name, type(e).__name__)
+            raise
+
+    return wrapper

nextcloud_mcp_server/server/notes.py

@@ -17,6 +17,7 @@ from nextcloud_mcp_server.models.notes import (
     SearchNotesResponse,
     UpdateNoteResponse,
 )
+from nextcloud_mcp_server.observability.metrics import instrument_tool
 
 logger = logging.getLogger(__name__)
 
@@ -86,6 +87,7 @@ def configure_notes_tools(mcp: FastMCP):
 
     @mcp.tool()
     @require_scopes("notes:write")
+    @instrument_tool
     async def nc_notes_create_note(
         title: str, content: str, category: str, ctx: Context
     ) -> CreateNoteResponse:
@@ -132,6 +134,7 @@ def configure_notes_tools(mcp: FastMCP):
 
     @mcp.tool()
     @require_scopes("notes:write")
+    @instrument_tool
     async def nc_notes_update_note(
         note_id: int,
         etag: str,
@@ -197,6 +200,7 @@ def configure_notes_tools(mcp: FastMCP):
 
     @mcp.tool()
     @require_scopes("notes:write")
+    @instrument_tool
     async def nc_notes_append_content(
         note_id: int, content: str, ctx: Context
     ) -> AppendContentResponse:
@@ -247,6 +251,7 @@ def configure_notes_tools(mcp: FastMCP):
 
     @mcp.tool()
     @require_scopes("notes:read")
+    @instrument_tool
     async def nc_notes_search_notes(query: str, ctx: Context) -> SearchNotesResponse:
         """Search notes by title or content, returning only id, title, and category (requires notes:read scope)."""
         client = await get_client(ctx)
@@ -293,6 +298,7 @@ def configure_notes_tools(mcp: FastMCP):
 
     @mcp.tool()
     @require_scopes("notes:read")
+    @instrument_tool
     async def nc_notes_get_note(note_id: int, ctx: Context) -> Note:
         """Get a specific note by its ID (requires notes:read scope)"""
         client = await get_client(ctx)
@@ -322,6 +328,7 @@ def configure_notes_tools(mcp: FastMCP):
 
     @mcp.tool()
     @require_scopes("notes:read")
+    @instrument_tool
     async def nc_notes_get_attachment(
         note_id: int, attachment_filename: str, ctx: Context
     ) -> dict[str, str]:
@@ -368,6 +375,7 @@ def configure_notes_tools(mcp: FastMCP):
 
     @mcp.tool()
     @require_scopes("notes:write")
+    @instrument_tool
     async def nc_notes_delete_note(note_id: int, ctx: Context) -> DeleteNoteResponse:
         """Delete a note permanently"""
         logger.info("Deleting note %s", note_id)