fix(dashboard): prevent unhandled promise rejections and CodeMirror crash

[cursor]

What changed

Fixes two categories of production Sentry errors in the dashboard:

1. Unhandled promise rejections at mutateAsync call sites

Error signatures: DASHBOARD-282, plus similar patterns in topic/context creation and subscriber deletion.

Root cause: TanStack Query's mutateAsync re-throws errors after the onError callback runs. When the calling code uses await mutateAsync() without a try-catch, the re-thrown error becomes an unhandled promise rejection that Sentry captures.

Fix: Added try-catch blocks at all affected call sites:

• create-subscriber.tsx — subscriber creation (DASHBOARD-282: 23 events, 11 users)
• create-topic-form.tsx — topic creation
• create-context-form.tsx — context creation
• subscriber-row.tsx — subscriber deletion
• subscriber-overview-form.tsx — subscriber deletion from overview

This follows the same pattern already used in upsert-variable-form.tsx and other existing call sites.

2. CodeMirror crash on non-string value

Error signature: DASHBOARD-2M8 — value must be typeof string but got object

Root cause: The Editor component passes its value prop directly to @uiw/react-codemirror, which throws at runtime if the value is not a string. When react-hook-form provides an object value (e.g., from a step control schema with nested types), this crashes the editor.

Fix: Added safe string coercion (typeof value === 'string' ? value : String(value ?? '')) in the Editor component before passing to CodeMirror. This is the single choke point for all CodeMirror usage in the dashboard.

Remaining risk

• Minimal — all changes are defensive error handling at leaf call sites
• No behavioral changes when mutations succeed
• The upsert-variable-form.tsx already uses this exact try-catch pattern successfully

  

[netlify]

✅ Deploy Preview for dashboard-v2-novu-staging ready!

Name	Link
🔨 Latest commit	b335fab
🔍 Latest deploy log	https://app.netlify.com/projects/dashboard-v2-novu-staging/deploys/69d101b544317d0008296f57
😎 Deploy Preview	https://deploy-preview-10576.dashboard-v2.novu-staging.co
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify project configuration.

[github-actions]

Hey there and thank you for opening this pull request! 👋

We require pull request titles to follow specific formatting rules and it looks like your proposed title needs to be adjusted.

Your PR title is: fix(dashboard): prevent unhandled promise rejections and CodeMirror crash

Requirements:

1. Follow the Conventional Commits specification
2. As a team member, include Linear ticket ID at the end: fixes TICKET-ID or include it in your branch name

Expected format: feat(scope): Add fancy new feature fixes NOV-123

Details:

PR title must end with 'fixes TICKET-ID' (e.g., 'fixes NOV-123') or include ticket ID in branch name