Handle per-step errors and returning error data (#411)

## Summary
<!-- Succinctly describe your change, providing context, what you've
changed, and why. -->

Adds handling and returning of per-step errors instead of the current
error flow of intentionlly throwing to trigger a `500 Internal Server
Error`.

## Checklist
<!-- Tick these items off as you progress. -->
<!-- If an item isn't applicable, ideally please strikeout the item by
wrapping it in "~~"" and suffix it with "N/A My reason for skipping
this." -->
<!-- e.g. "- [ ] ~~Added tests~~ N/A Only touches docs" -->

- [x] Added a [docs PR](https://github.com/inngest/website) that
references this PR
- [x] Added unit/integration tests
- [x] Added changesets if applicable
- [x] inngest/inngest#843 must be shipped and upstreamed to Cloud before
we merge
- [x] Ensure error serialization always creates a `StepError` for step
errors

## Related

- Relies on inngest/inngest#1058
- inngest/website#655

.changeset/fair-seahorses-push.md

@@ -0,0 +1,5 @@
+---
+"inngest": minor
+---
+
+Add handling of per-step errors and returning step names during error cases to better display issues in the UI

packages/inngest/scripts/integrationTestRunner.ts

@@ -164,6 +164,10 @@ async function startDevServer(
       devServerPort.toString(),
       "--no-discovery",
       "--no-poll",
+      "--retry-interval",
+      "1",
+      "--log-level",
+      "trace",
       "--sdk-url",
       `http://localhost:${exampleServerPort}/api/inngest`,
     ],

packages/inngest/src/components/InngestCommHandler.ts

@@ -737,14 +737,7 @@ export class InngestCommHandler<
          * `null`, as this is appropriately serializable by JSON.
          */
         const opDataUndefinedToNull = (op: OutgoingOp) => {
-          const opData = z.object({ data: z.any() }).safeParse(op.data);
-
-          if (opData.success) {
-            (op.data as { data: unknown }).data = undefinedToNull(
-              opData.data.data
-            );
-          }
-
+          op.data = undefinedToNull(op.data);
           return op;
         };
 
@@ -791,7 +784,17 @@ export class InngestCommHandler<
 
             return {
               status: 206,
-              headers: { "Content-Type": "application/json" },
+              headers: {
+                "Content-Type": "application/json",
+                ...(typeof result.retriable !== "undefined"
+                  ? {
+                      [headerKeys.NoRetry]: result.retriable ? "false" : "true",
+                      ...(typeof result.retriable === "string"
+                        ? { [headerKeys.RetryAfter]: result.retriable }
+                        : {}),
+                    }
+                  : {}),
+              },
               body: stringify([step]),
               version,
             };