fix(grain): save before deploying workflow

[aadamgough]

Summary

createWebhookPreprocessing was throwing a 403 if I tried to save the grain trigger before deploying workflow. Grain sends a POST request to the actualy url for verification. This fix allows you to save the webhook before deploying the workflow without getting an error.

Type of Change

• Bug fix

Testing

Tested Manually

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)

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1 Skipped Deployment

Project	Deployment	Review	Updated (UTC)
docs	Skipped		Jan 4, 2026 7:45pm

[greptile-apps]

Greptile Summary

This PR fixes a bug where saving a Grain webhook trigger before deploying the workflow would fail with a 403 error. The fix adds a verification request detector for Grain webhooks that intercepts the provider's reachability check (empty POST requests with no type field) and returns 200 OK, bypassing the deployment status check that was causing the failure. The implementation is correct and properly positioned in the request flow after authentication but before preprocessing checks.

Confidence Score: 5/5

• This PR is safe to merge with no risks - a straightforward bug fix that correctly handles Grain webhook verification requests.
• The change is minimal, focused, and logically sound. It adds a specific check for Grain verification requests (empty POST with no type field) before preprocessing, which is the correct approach to prevent 403 errors during webhook setup. The detection logic matches Grain's known verification pattern, and the placement in the request flow (after auth, before preprocessing) is appropriate. No new vulnerabilities or edge cases are introduced.
• No files require special attention

Important Files Changed

Filename

Overview

apps/sim/app/api/webhooks/trigger/[path]/route.ts

Added Grain webhook verification request detection. The new code intercepts empty POST requests from Grain's reachability test and returns 200 OK before hitting the deployment check, allowing users to save webhook triggers before deploying workflows. Logic is sound: detects Grain provider with empty/minimal body and no type field, which matches Grain's verification pattern. Placed strategically after auth verification but before preprocessing to avoid 403 errors during webhook setup. No security or functionality issues introduced.

Sequence Diagram

sequenceDiagram
    participant User
    participant Grain as Grain Service
    participant Webhook as Webhook Handler
    participant Auth as Auth Verify
    participant Grain_Check as Grain Check
    participant Preprocess as Preprocessing
    participant Deploy as Deployment Check

    User->>Grain: Configure webhook trigger
    Grain->>Webhook: POST (verification with empty/minimal body)
    Webhook->>Auth: Verify provider auth
    Auth-->>Webhook: ✓ Auth passed
    Webhook->>Grain_Check: Check if Grain verification
    Grain_Check-->>Webhook: ✓ Is Grain verification
    Webhook-->>Grain: 200 OK (webhook verified)
    Webhook-->>User: Success (before deployment needed)
    
    Note over Webhook: Without fix:<br/>Would continue to Preprocess<br/>→ Deploy Check (403)<br/>→ Error

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