feat(executor): opt-in per-block retry for transient failures by waleedlatif1 · Pull Request #6298 · simstudioai/sim

waleedlatif1 · 2026-08-05T22:39:20Z

Summary

Adds a per-block retry setting (maxAttempts, waitMs) that replays the block handler when a failure looks transient. Off by default.
Universal by construction: the retry wraps the single handler invocation in block-executor.ts, so every block type is covered without touching any block definition — the same seam the error port uses.
Follows n8n's model (retryOnFail is opt-in per node) rather than Temporal's (retry-by-default), because Temporal can assume idempotent activities and we can't: replaying "post message" or "create ticket" after an ambiguous transport failure duplicates a real side effect. The builder decides.

Design notes

Only the handler call is retried. For a streaming block the handler returns before any token is drained, so a replay can't duplicate output the client already saw; a failure during the drain falls through untouched. Redaction/compaction are deterministic and would fail identically, so they're outside the loop.
Classification is structural, not string-matching: TimeoutError, socket-level codes, and transient HTTP statuses (408/429/502/503/504). A 4xx other than 408/429 is refused because it'll be rejected identically on replay. The one message-based check is Bun's dropped-connection string, which carries no code — isolated to a single named constant.
Cause chain is walked — providers rewrap transport failures and ProviderError overwrites name, so the classification survives only on cause. Bounded against cyclic causes.
Aborts never retry, including an abort wrapping a retryable cause (a block timeout that already spent its budget).
HITL and loop/parallel sentinels are structurally ineligible — a pause is signalled by throwing, and replaying it would re-arm rather than resume.
Cancellation mid-backoff stops the loop.
Composes with the error port: the port sees the failure only once the budget is spent, exactly as it does for a non-retrying block.
blockLog.attempts is set only when a block actually retried.

Type of Change

New feature

Testing

21 new tests across block-retry.test.ts (eligibility + classification) and block-executor.retry.test.ts (loop behaviour, ceiling, cancellation, error-port composition). Every guard was verified fail-detectable by breaking it and watching the test go red — that process caught one vacuous test of my own (a bare AbortError is unretryable anyway, so the guard needed an abort wrapping a retryable cause to be exercised).

Executor + serializer suites: 1612 passing. The one failure in executor/handlers/pi/cloud-review-tools.test.ts is pre-existing — verified by stashing this branch and reproducing it on clean origin/staging. Typecheck, lint, and check:api-validation clean.

Follow-up

No UI yet — this is the executor/serializer plumbing, so the setting is only reachable via the API/serialized workflow. A shared control alongside the existing block-level toggles is the natural next step.

Checklist

Code follows project style guidelines
Self-reviewed my changes
Tests added/updated and passing
No new warnings introduced
I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

vercel · 2026-08-05T22:39:26Z

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cursor · 2026-08-05T22:39:31Z

PR Summary

Medium Risk
Changes core block execution and can duplicate non-idempotent side effects if retry is enabled; mitigated by opt-in config and structural transient-only classification, but still touches every block type’s handler path.

Overview
Adds opt-in per-block retry (maxAttempts, optional waitMs) on workflow blocks, serialized through the serializer and typed in @sim/workflow-types. Off by default so builders only enable it when the operation is idempotent.

BlockExecutor routes handler execution through runHandlerWithRetry, which replays only the handler call—not streaming drain, redaction, or compaction. Backoff uses backoffWithJitter; run cancellation and abortSignal stop further attempts during backoff.

block-retry.ts centralizes policy resolution (clamped bounds, exclusions for HITL and loop/parallel sentinels) and transient error detection (timeouts, socket codes, 408/429/502/503/504, Bun socket message, cause-chain walk with abort/child-workflow guards). After retries are exhausted, behavior matches a non-retrying block, including error port handling. blockLog.attempts is recorded when a block actually retried.

^{Reviewed by Cursor Bugbot for commit 693340f. Configure here.}

cursor

Cursor Bugbot has reviewed your changes using high effort and found 3 potential issues.

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^{Reviewed by Cursor Bugbot for commit 693340f. Configure here.}

cursor · 2026-08-05T22:44:49Z

  data?: BlockData
  layout?: BlockLayoutState
  locked?: boolean
+  retry?: BlockRetryConfig


API schema strips retry config

High Severity

retry was added to BlockState and the serializer, but workflowBlockStateSchema still omits it. Zod strips unknown keys on PUT/GET /api/workflows/[id]/state and import, so the opt-in setting cannot persist through the API path this PR relies on until UI exists.

^{Reviewed by Cursor Bugbot for commit 693340f. Configure here.}

cursor · 2026-08-05T22:44:49Z

+    if (candidate.code && RETRYABLE_ERROR_CODES.has(candidate.code)) return true
+    if (typeof candidate.status === 'number' && RETRYABLE_HTTP_STATUSES.has(candidate.status)) {
+      return true
+    }


HTTP status classification misses errors

High Severity

isRetryableBlockError only reads status, but generic tool failures attach Sim-owned codes as statusCode and leave upstream statuses on output. Most integration blocks therefore never retry on 408/429/502/503/504 despite opting in.

^{Reviewed by Cursor Bugbot for commit 693340f. Configure here.}

cursor · 2026-08-05T22:44:49Z

+          delayMs,
+          error: normalizeError(error),
+        })
+        await sleep(delayMs)


Cancel ignored after backoff sleep

Medium Severity

Abort is checked only before sleep, and sleep is not abort-aware. A run cancelled during backoff still starts another handler attempt afterward, contrary to the mid-backoff cancellation guarantee.

^{Reviewed by Cursor Bugbot for commit 693340f. Configure here.}

greptile-apps · 2026-08-05T22:47:32Z

Greptile Summary

Adds opt-in transient-error retries around block-handler invocation, including retry policy types, serialization, error classification, attempt logging, and executor tests.

Resolves bounded per-block retry policies and excludes HITL, sentinel, abort, and child-workflow failures.
Retries classified transport and transient HTTP failures with jittered backoff.
Adds retry configuration to workflow and serialized block contracts.

Confidence Score: 4/5

The cancellation and persistence failures should be fixed before merging because retries can run after cancellation and configured policies can silently disappear.

The retry loop does not recheck cancellation after its timer, while the newly supported retry field is omitted from deserialization and normalized workflow persistence.

Files Needing Attention: apps/sim/executor/execution/block-executor.ts, apps/sim/serializer/index.ts, and the normalized workflow persistence mappings

Important Files Changed

Filename	Overview
apps/sim/executor/execution/block-executor.ts	Adds the retry loop around handler invocation, but cancellation during backoff can still permit another attempt.
apps/sim/executor/execution/block-retry.ts	Implements bounded policy resolution and structural transient-error classification with explicit ineligible cases.
apps/sim/serializer/index.ts	Emits retry configuration during serialization, but the reverse and persistence round trips do not preserve it.
packages/workflow-types/src/workflow.ts	Defines the shared retry policy and bounds, while exposing a field that is not yet carried through normalized persistence.
apps/sim/executor/execution/block-executor.retry.test.ts	Covers retry behavior and synchronous cancellation, but not cancellation arriving during backoff.
apps/sim/executor/execution/block-retry.test.ts	Thoroughly covers policy bounds, ineligible block types, transient classification, aborts, and cyclic causes.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
  A[Invoke block handler] -->|Success| B[Post-process output]
  A -->|Failure| C{Retry enabled and transient?}
  C -->|No| D[Error port or throw]
  C -->|Yes| E[Backoff sleep]
  E --> F{Execution cancelled?}
  F -->|Yes| G[Stop retrying]
  F -->|No| A

_{Reviews (1): Last reviewed commit: "feat(executor): opt-in per-block retry f..." | Re-trigger Greptile}

greptile-apps · 2026-08-05T22:47:35Z

+          delayMs,
+          error: normalizeError(error),
+        })
+        await sleep(delayMs)


Cancellation bypasses retry backoff

When an execution is cancelled during the backoff sleep, the loop starts the next handler attempt without rechecking the signal, causing a side-effecting block to run again after the execution was stopped.

Suggested change

await sleep(delayMs)

await sleep(delayMs)

if (ctx.abortSignal?.aborted === true) throw error

Knowledge Base Used: Workflow Executor

greptile-apps · 2026-08-05T22:47:35Z

@@ -327,6 +327,7 @@ export class Serializer {
        color: blockConfig.bgColor,


Retry policy is not persisted

When a retry-enabled workflow is deserialized or saved and reloaded through normalized persistence, the reverse serializer and persistence mappings omit retry, causing the configured policy to disappear and later executions to invoke the block only once.

Knowledge Base Used: Workspace Frontend (Workflow Editor UI)

…, read statusCode

feat(executor): opt-in per-block retry for transient failures

693340f

cursor Bot reviewed Aug 5, 2026

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greptile-apps Bot reviewed Aug 5, 2026

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fix(executor): honor cancellation after backoff, persist retry policy…

7068722

…, read statusCode

waleedlatif1 marked this pull request as draft August 5, 2026 22:58

vercel Bot deployed to Preview August 5, 2026 23:02 View deployment

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feat(executor): opt-in per-block retry for transient failures - #6298

feat(executor): opt-in per-block retry for transient failures#6298
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	await sleep(delayMs)
	await sleep(delayMs)
	if (ctx.abortSignal?.aborted === true) throw error

		@@ -327,6 +327,7 @@ export class Serializer {
		color: blockConfig.bgColor,

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waleedlatif1 commented Aug 5, 2026

Summary

Design notes

Type of Change

Testing

Follow-up

Checklist

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PR Summary

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API schema strips retry config

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HTTP status classification misses errors

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Cancel ignored after backoff sleep

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Greptile Summary

Confidence Score: 4/5

Important Files Changed

Flowchart

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