feat: prefilter model for senstive content detection

[Jassu7082]

Implementation of Issue #150
Model used https://huggingface.co/urchade/gliner_small-v2.1#citation

Model Download Flow

Overview

Deep Mode relies on external assets hosted on Hugging Face.
To keep the initial APK size lightweight, these assets are downloaded dynamically at runtime.

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Download Pipeline & Logic

The download process is managed by PrefilterModelDownloadService, which displays a weighted progress bar to improve user experience.

Steps

1. Tokenizer (10%)

   • Downloads: gliner_tokenizer.json
   • Lightweight and quick to fetch

2. Model (90%)

   • Downloads: gliner_pii_small.onnx
   • Main model file (largest portion of the download)

---

Flow Diagram

graph TD
    A[User Selects 'Deep' Mode] --> B{isModelDownloaded?}
    B -- "Files Exist in App Support Dir" --> C[Set Mode to 'Deep']
    B -- "Files Missing" --> D[Show _PrefilterDownloadDialog]

    D --> E[startDownload]
    E --> F[Download Tokenizer: 0% → 10%]
    F --> G[Download Model: 10% → 100%]

    G --> H{HTTP 200?}
    H -- Yes --> I[Status: Completed]
    H -- No/Error --> J[Status: Error + Log Analytics]

    I --> K[Show 'Get Started' Button]
    J --> L[Show 'Retry' Button]

Loading

[Jassu7082]

Fail-Safe: Missing Assets

If Deep Mode is enabled but required assets are unavailable
(e.g., deleted manually or the application support directory is cleared),
the system automatically falls back to Light Mode during initialization.

if (mode == 'deep' && !isDownloaded) {
  _selectedMode = 'light';
  PrefilterService.setMode('light');
}

Source Attribution

The scanning engine uses optimized ONNX models provided by the onnx-community.

• Model: GLiNER Small v2.1
• Type: Open-source PII Entity Recognition
• Host: Hugging Face
• URL: https://huggingface.co/onnx-community/gliner_small-v2.1

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Used Dependencies

Package	Version	Description
onnxruntime	^1.4.0	Runs the GLiNER ONNX model on-device
http	^1.1.0	Handles streaming downloads from Hugging Face
path_provider	^2.1.0	Provides access to the Application Support Directory