feat(files): update save_file tool description and enforce size limit for base64 payloads

internal/mcpserver/schema.go

@@ -2,6 +2,7 @@ package mcpserver
 
 import (
 	"context"
+	"encoding/json"
 	"fmt"
 	"log/slog"
 	"reflect"
@@ -12,6 +13,8 @@ import (
 	"github.com/modelcontextprotocol/go-sdk/mcp"
 )
 
+const maxLoggedArgBytes = 512
+
 var toolSchemaOptions = &jsonschema.ForOptions{
 	TypeSchemas: map[reflect.Type]*jsonschema.Schema{
 		reflect.TypeFor[uuid.UUID](): {
@@ -37,7 +40,7 @@ func logToolCall[In any, Out any](logger *slog.Logger, toolName string, handler
 		start := time.Now()
 		attrs := []any{slog.String("tool", toolName)}
 		if req != nil && req.Params != nil {
-			attrs = append(attrs, slog.Any("arguments", req.Params.Arguments))
+			attrs = append(attrs, slog.String("arguments", truncateArgs(req.Params.Arguments)))
 		}
 
 		logger.Info("mcp tool started", attrs...)
@@ -56,6 +59,17 @@ func logToolCall[In any, Out any](logger *slog.Logger, toolName string, handler
 	}
 }
 
+func truncateArgs(args any) string {
+	b, err := json.Marshal(args)
+	if err != nil {
+		return "<unserializable>"
+	}
+	if len(b) <= maxLoggedArgBytes {
+		return string(b)
+	}
+	return string(b[:maxLoggedArgBytes]) + fmt.Sprintf("… (%d bytes total)", len(b))
+}
+
 func setToolSchemas[In any, Out any](tool *mcp.Tool) error {
 	if tool.InputSchema == nil {
 		inputSchema, err := jsonschema.For[In](toolSchemaOptions)

internal/mcpserver/server.go

@@ -136,7 +136,7 @@ func New(cfg config.MCPConfig, logger *slog.Logger, toolSet ToolSet) http.Handle
 
 	addTool(server, logger, &mcp.Tool{
 		Name:        "save_file",
-		Description: "Store a base64-encoded file such as an image, document, or audio clip, optionally linking it to a thought.",
+		Description: "Store a file and optionally link it to a thought. Supply either content_base64 (≤10 MB) or content_uri (amcs://files/{id} from a prior POST /files upload). For files larger than 10 MB, upload via POST /files first and pass the returned URI as content_uri.",
 	}, toolSet.Files.Save)
 
 	addTool(server, logger, &mcp.Tool{