Feat: Add real-time scan progress via SSE to prevent UI freeze during large photo processing

[VasuS609]

Describe the feature

I’ve observed that when scanning large folders (e.g., 100+ photos), the frontend remains stuck on “No Images to Display” until the entire process completes — even though the backend is actively processing images (confirmed via debug logs).

This creates a poor user experience, as users have no feedback that work is in progress and may assume the app has frozen or crashed.

Root Cause
The current flow:

• Frontend calls POST /scan → waits for full JSON response.
• Backend uses ProcessPoolExecutor → processes images in parallel.
• No intermediate progress is streamed → UI stays static until completion.

Proposed Solution: Server-Sent Events (SSE)
Add an SSE endpoint /scan/progress/{scan_id} that streams real-time updates like:

{"processed": 42, "total": 500}

Frontend will use EventSource to listen and update a progress indicator dynamically.

Benefits:

• No UI freeze — user sees live progress.
• Zero changes to Tauri/Rust layer — leverages existing HTTP architecture.
• Lightweight & simple — no WebSocket complexity.
• Scalable — works for 10 or 10,000 photos.

Implementation Plan (Minimal Scope)

1. Backend (FastAPI):

• Add POST /start-scan → returns scan_id.
• Add GET /scan/progress/{scan_id} → SSE stream of {processed, total}.
• Use shared state (e.g., multiprocessing.Manager().dict()) to track progress from ProcessPoolExecutor.

2. Frontend (React):

• Create hook useScanProgress(scanId) using EventSource.
• Display progress bar + text (“Processed 42/500”) during scan.
• Gracefully handle disconnects/retries.

Let me know:

• Is SSE preferred over WebSocket or polling?
• Any naming conventions for endpoints?

I’ve already readied with the setup and am ready to implement this — give me the green light!

Added Proof of Issue

This is the behaviour of 100 photos:
https://github.com/user-attachments/assets/bbdf16cd-3c35-42b9-9762-b7993d61827f

This is the behaviour of 650 photos: (took 2+ minutes)
https://github.com/user-attachments/assets/b21667c0-b7a7-4160-89d1-a386b26b7e7d

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• Have you updated docs for it?.
• Have you added unit tests?.
• Have you made sure unit tests pass?
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• Does it contain any style related issues?

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🔗 Related PRs

#574 - Implement live progress tracking with 1s polling, animated progress b… [merged]

👤 Suggested Assignees

• SiddharthJiyani

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[VasuS609]

Hi @rahulharpal1603 , I’ve completed the setup and will submit a PR within the next 2–3 days. I’ll ensure it includes proper proof of work and that the code is clean and ready for a smooth merge.