thread spans through (#274)

## Why

<!-- Describe what you are trying to accomplish with this pull request
-->

- being able to add things to the proc span directly from a handler is
nice

## What changed

<!-- Describe the changes you made in this pull request or pointers for
the reviewer -->

## Versioning

- [ ] Breaking protocol change
- [ ] Breaking ts/js API change

<!-- Kind reminder to add tests and updated documentation if needed -->

router/context.ts

@@ -1,3 +1,4 @@
+import { Span } from '@opentelemetry/api';
 import { TransportClientId } from '../transport/message';
 import { SessionId } from '../transport/sessionStateMachine/common';
 
@@ -50,6 +51,11 @@ export type ProcedureHandlerContext<State> = ServiceContext & {
    * State for this service as defined by the service definition.
    */
   state: State;
+  /**
+   * The span for this procedure call. You can use this to add attributes, events, and
+   * links to the span.
+   */
+  span: Span;
   /**
    * Metadata parsed on the server. See {@link ParsedMetadata}
    */

router/server.ts

@@ -539,19 +539,22 @@ class RiverServer<Services extends AnyServiceSchemaMap>
       closeReadable();
     }
 
-    const handlerContext: ProcedureHandlerContext<object> = {
+    const handlerContextWithSpan: (
+      span: Span,
+    ) => ProcedureHandlerContext<object> = (span) => ({
       ...serviceContext,
       from: from,
       sessionId,
       metadata: sessionMetadata,
+      span,
       cancel: () => {
         onServerCancel({
           code: CANCEL_CODE,
           message: 'cancelled by server procedure handler',
         });
       },
       signal: finishedController.signal,
-    };
+    });
 
     switch (procedure.type) {
       case 'rpc':
@@ -564,7 +567,7 @@ class RiverServer<Services extends AnyServiceSchemaMap>
           async (span): ProcHandlerReturn => {
             try {
               const responsePayload = await procedure.handler({
-                ctx: handlerContext,
+                ctx: handlerContextWithSpan(span),
                 reqInit: initPayload,
               });
 
@@ -592,7 +595,7 @@ class RiverServer<Services extends AnyServiceSchemaMap>
           async (span): ProcHandlerReturn => {
             try {
               await procedure.handler({
-                ctx: handlerContext,
+                ctx: handlerContextWithSpan(span),
                 reqInit: initPayload,
                 reqReadable,
                 resWritable,
@@ -616,7 +619,7 @@ class RiverServer<Services extends AnyServiceSchemaMap>
           async (span): ProcHandlerReturn => {
             try {
               await procedure.handler({
-                ctx: handlerContext,
+                ctx: handlerContextWithSpan(span),
                 reqInit: initPayload,
                 resWritable: resWritable,
               });
@@ -638,7 +641,7 @@ class RiverServer<Services extends AnyServiceSchemaMap>
           async (span): ProcHandlerReturn => {
             try {
               const responsePayload = await procedure.handler({
-                ctx: handlerContext,
+                ctx: handlerContextWithSpan(span),
                 reqInit: initPayload,
                 reqReadable: reqReadable,
               });