fix(export): keep large exports off in-memory save path

[meiiie]

Description

Fixes #445 by keeping MP4 export saves on the temp-file streaming/finalize path instead of silently falling back to renderer/main-process ArrayBuffer saves when the output is large or when Electron MP4 streaming fails.

Motivation

The v1.3.0 beta still had a legacy in-memory save path that could be reached after a Blob export. For outputs over Node/Electron's Buffer limit, that path can fail with the same >2 GiB class of error reported in #445.

Type

Bug fix

Related Issue(s)

Fixes #445

Changes Made

• Added an explicit export-save policy for the in-memory fallback limit.
• Blocked Electron MP4 saves from falling back to the legacy blob.arrayBuffer() path after temp-file streaming fails.
• Added main-process guards so old IPC paths reject oversized ArrayBuffer saves with a clear message.
• Added focused tests for the save policy and kept existing export stream/muxer tests green.

Scope Note

This does not change rendering, muxing quality, or native CUDA/D3D11 selection. It only hardens the final save/mux handoff so large exports stay on disk-backed paths.

Testing Guide

1. Export a small MP4 through Lightning and confirm the save dialog still works.
2. Export a large MP4 expected to exceed 2 GiB and confirm it completes through the temp-file path instead of throwing a Buffer/ArrayBuffer size error.
3. If a large MP4 still fails, collect the export error and whether it failed during render, mux/finalize, or save dialog.

Validation

• npm test -- src/lib/exporter/exportSavePolicy.test.ts electron/ipc/export/exportStream.test.ts electron/ipc/register/export.test.ts src/lib/exporter/muxer.test.ts
• npm exec -- tsc --noEmit
• npx biome check --formatter-enabled=false src/lib/exporter/exportSavePolicy.ts src/lib/exporter/exportSavePolicy.test.ts src/components/video-editor/VideoEditor.tsx electron/ipc/register/export.ts
• npx vite build --config vite.config.ts
• npm run normalize:electron-main-cjs
• npm run smoke:electron-main-cjs

Checklist

• Focused scope for [Bug]: can not export more than 2gb #445
• Local tests added/updated
• Production build and Electron CJS smoke pass
• Draft PR opened for review/checks

Summary by CodeRabbit

• New Features

  • Added file-size validation for video exports to prevent processing failures
  • Implemented intelligent fallback logic that selects the appropriate save method based on video size and format

• Bug Fixes

  • Improved handling of large video exports by utilizing streaming-based processing instead of memory-intensive operations
  • Enhanced error messaging when exports exceed system limitations
  • Better MP4 export handling when streaming capabilities are available

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: 940c7ba3-861b-4d1c-8ce8-c29de3d89085

📥 Commits

Reviewing files that changed from the base of the PR and between 144698c and 4f89a6d.

📒 Files selected for processing (4)

• electron/ipc/register/export.ts
• src/components/video-editor/VideoEditor.tsx
• src/lib/exporter/exportSavePolicy.test.ts
• src/lib/exporter/exportSavePolicy.ts

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📝 Walkthrough

Walkthrough

This PR adds size constraints for in-memory video exports by introducing a 2GB limit and conditional fallback policy. It defines size-checking utilities and applies them across IPC handlers and client-side fallback logic, with tests validating the policy behavior.

Changes

In-Memory Export Size Guards

Layer / File(s)	Summary
Policy Definitions src/lib/exporter/exportSavePolicy.ts	Introduces MAX_IN_MEMORY_EXPORT_BYTES (0x7fffffff), normalizeExportExtension(), isExportTooLargeForInMemorySave(), canUseInMemoryExportSaveFallback(), and describeBlockedInMemoryExportSave() to define export save-path eligibility based on size and streaming API availability.
IPC Handler Guards electron/ipc/register/export.ts	Adds local size guard constant and helper; updates mux-exported-video-audio, save-exported-video, and write-exported-video-to-path handlers to reject oversized videoData early with descriptive errors before processing.
Client-Side Fallback Logic src/components/video-editor/VideoEditor.tsx	Imports policy helpers; saveBlobExport now detects streaming API availability, catches temp-file failures, and conditionally gates in-memory fallback via policy check, throwing detailed errors when fallback is blocked.
Policy Tests src/lib/exporter/exportSavePolicy.test.ts	Vitest suite validates extension normalization, size-limit rejection, MP4 format blocking with streaming APIs, small-export fallback allowance, and error message correctness.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• webadderallorg/Recordly#278: Modifies electron/ipc/register/export.ts to handle user path approval and path normalization in the same export handlers.
• webadderallorg/Recordly#404: Updates the mux-exported-video-audio IPC handler to use a temp-file path instead of in-memory reads, directly affected by this PR's size guard injection.
• webadderallorg/Recordly#284: Modifies the same mux-exported-video-audio handler path in electron/ipc/register/export.ts.

Suggested labels

Checked

Poem

🐰 Two gigs! That's quite the haul to hoard,
In memory's vault, we've set a new board!
When buffers grow large beyond our small space,
We fallback with grace—a safe, steady pace.
No crashing exports, no sizes run wild,
Your videos now save—forever beguiled! ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely summarizes the main change: preventing large exports from using the in-memory save path.
Description check	✅ Passed	The description is comprehensive, covering motivation, type, related issues, changes made, scope, testing guide, and validation commands, closely following the template structure.
Linked Issues check	✅ Passed	The PR addresses issue #445 by implementing disk-backed temp-file paths for large exports and blocking in-memory fallback, directly solving the >2 GiB export failure reported.
Out of Scope Changes check	✅ Passed	All changes are focused on export save-path routing and in-memory limit guards; no unrelated modifications to rendering, muxing, or GPU selection are present.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/issue445-large-export-stream-save

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