fix: guard span name to always be a non-empty string

packages/opencode-plugin/src/index.ts

@@ -173,7 +173,7 @@ const plugin: Plugin = async ({ project, directory, worktree }) => {
       state.endToolCall(
         input.callID,
         truncate(output.output ?? "", config.maxOutputLength),
-        output.title ?? input.tool,
+        output.title ?? input.tool ?? "unknown-tool",
         output.metadata as unknown,
       );
     },

packages/opencode-plugin/src/state.ts

@@ -99,7 +99,7 @@ export class SessionState {
     const toolMeta = extractToolMetadata(call.tool, call.args);
 
     trace.addSpan({
-      name: title,
+      name: title || call.tool || "unknown-tool",
       type: SpanType.TOOL_CALL,
       parentSpanId: rootSpanId,
       input: safeJsonValue(call.args),