fix(file): zero byte codegen file format + zoomable preview wrapper + mermaid errors loopback

[icecrasher321]

Summary

Zero byte file on creation showed failed fetch 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	Actions	Updated (UTC)
docs	Skipped		May 2, 2026 7:52am

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PR Summary

Medium Risk
Touches file preview/rendering paths (PDF streaming buffers, image/SVG/Mermaid viewers) and expands server-side compiled-check behavior to new file types, which could impact user-visible preview reliability and agent workflows if regressions slip in.

Overview
Improves file preview robustness and adds shared zoom/pan UI. PDF streaming previews now treat zero-length buffers as loading, and image/SVG previews are refactored to use a new reusable ZoomablePreview component.

Expands Mermaid support end-to-end. The compiled-check endpoint and workspace VFS files/by-id/{id}/compiled-check now accept .mmd/.mermaid files by validating Mermaid syntax via new validateMermaidSource, and the Mermaid renderer is updated to better handle streaming content (debounced rendering, source fallback on invalid diagrams) with optional zoom-to-fit for full-file previews.

Fixes streaming content propagation in embedded file views. Embedded file previews now pass through pending (including empty) previewText to avoid “failed fetch” behavior when newly created/generated content starts as zero bytes.

^{Reviewed by Cursor Bugbot for commit a90cb18. Configure here.}

[greptile-apps]

Greptile Summary

This PR fixes a zero-byte file preview crash by passing "" instead of undefined as streamingContent so file viewers enter skeleton/streaming mode rather than triggering a failing network fetch. It also adds mermaid diagram validation to the compiled-check flow, introduces a reusable ZoomablePreview component (extracted from ImagePreview), and improves the mermaid streaming experience with debounced rendering and a source-code fallback view during partial/invalid diagrams.

Confidence Score: 5/5

Safe to merge — all findings are P2; the core zero-byte fix is correct and the mermaid server-side issue was already known.

No P0 or P1 issues were found in the new code. The two P2 observations (blank flash on non-streaming mermaid re-render, and pointer-events loss on the SVG iframe) are minor UX concerns that don't affect correctness or data integrity.

apps/sim/app/workspace/[workspaceId]/files/components/file-viewer/preview-panel.tsx — blank flash regression and SvgPreview pointer-events change.

Important Files Changed

Filename	Overview
apps/sim/lib/mermaid/validate.ts	New server-side mermaid validation helper that imports browser-only mermaid package — will silently return {ok: false} in Node.js (already flagged in previous thread).
apps/sim/app/workspace/[workspaceId]/files/components/file-viewer/zoomable-preview.tsx	New reusable zoom/pan wrapper component extracted from ImagePreview; adds ResizeObserver-based clamping and a debounced zoom ref — well-structured but children are placed inside pointer-events-none, limiting use with interactive content like iframes.
apps/sim/app/workspace/[workspaceId]/files/components/file-viewer/preview-panel.tsx	Significant mermaid streaming improvements: debounced rendering, source-code fallback, streaming context propagation. Non-streaming re-renders produce a brief blank flash (P2) and SvgPreview iframe loses pointer interaction.
apps/sim/app/workspace/[workspaceId]/files/components/file-viewer/file-viewer.tsx	Adds a zero-byte buffer guard to the PDF streaming path so empty buffers show a skeleton instead of attempting to render.
apps/sim/app/workspace/[workspaceId]/home/components/mothership-view/components/resource-content/resource-content.tsx	Core zero-byte fix: pendingOrStreamingFilePreviewText now passes "" instead of undefined so FileViewer enters streaming/skeleton mode for empty files rather than triggering a failing network fetch.
apps/sim/app/api/workspaces/[id]/files/[fileId]/compiled-check/route.ts	Extends compiled-check route to support .mmd/.mermaid files via validateMermaidSource; will return {ok: false} for all diagrams in prod because mermaid is browser-only (already in previous thread).
apps/sim/lib/copilot/vfs/workspace-vfs.ts	Parallel server-side mermaid validation path added to VFS readFileContent; same browser-only concern as the route applies here.
apps/sim/app/workspace/[workspaceId]/files/components/file-viewer/image-preview.tsx	Simplified to delegate to ZoomablePreview; zoom/pan logic removed from this file with no behavior regression.
apps/sim/app/workspace/[workspaceId]/files/components/file-viewer/pdf-viewer.tsx	Adds .slice(0) defensive copy for buffer-based PDF sources to prevent detached-buffer crashes on re-renders.

Sequence Diagram

sequenceDiagram
    participant AI as AI Agent
    participant VFS as WorkspaceVFS
    participant Validate as validateMermaidSource
    participant RC as ResourceContent
    participant FV as FileViewer
    participant MP as PreviewPanel

    AI->>VFS: readFileContent(files/by-id/{id}/compiled-check)
    VFS->>Validate: validateMermaidSource(code)
    Note over Validate: imports mermaid (browser-only)
    Validate-->>VFS: {ok, error?}
    VFS-->>AI: JSON result

    RC->>RC: pendingOrStreamingFilePreviewText passes '' for zero-byte
    RC->>FV: streamingContent='' (was undefined before fix)
    FV->>FV: streamingContent !== undefined → streaming mode
    FV->>FV: buffer.byteLength === 0 → show skeleton

    FV->>MP: isStreaming=true + content
    MP->>MP: MermaidStreamingCtx.Provider value=true
    MP->>MP: MermaidDiagram(isStreaming=true)
    MP->>MP: 150ms debounce → mermaid.parse suppressErrors
    alt parse ok
        MP-->>FV: render SVG in ZoomablePreview
    else parse fails
        MP-->>FV: MermaidSourcePreview source code fallback
    end

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Cursor Bugbot has reviewed your changes and found 1 potential issue.

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