Add Dropbox/iCloud sync status icons

Detect and display cloud sync status (synced, online-only, uploading, downloading) for files and folders in both Full and Brief view modes.

Backend:
- Add `sync_status.rs` with macOS `SF_DATALESS` flag and NSURL detection
- Expose `get_sync_status` Tauri command with parallel fetching

Frontend:
- Add 4 SVG sync status icons
- Display icons in FileList (Full mode) and BriefList (Brief mode)
- Poll visible files every 2s for real-time status updates

Author: vdavid

docs/notes/dropbox-statuses-and-formats.md

@@ -0,0 +1,222 @@
+# Dropbox sync status detection on macOS
+
+Dropbox does not document how to programmatically detect file sync status. This document captures our
+reverse-engineering findings from December 2025.
+
+## Overview
+
+On macOS 12.5+, Dropbox uses Apple's **File Provider API**. Files live in `~/Library/CloudStorage/Dropbox/` (with
+`~/Dropbox` as a symlink). Sync status can be detected via:
+
+1. **File system metadata** (`stat()`) - fast, no API calls
+2. **Spotlight metadata** (`mdls` / `NSMetadataItem`) - slower but more detailed
+3. **Extended attributes** (`com.dropbox.attrs`) - undocumented binary format
+
+---
+
+## Detection methods
+
+### Method 1: stat() - fastest
+
+The `stat()` system call provides two key indicators:
+
+| Field       | Access in Rust                            | Meaning                             |
+| ----------- | ----------------------------------------- | ----------------------------------- |
+| `st_blocks` | `metadata.blocks()`                       | Number of 512-byte blocks allocated |
+| `st_flags`  | `metadata.st_flags()` (via `MetadataExt`) | File flags including `SF_DATALESS`  |
+
+**Key insight**: Online-only files have `blocks = 0` and `SF_DATALESS` flag set.
+
+```rust
+use std::os::unix::fs::MetadataExt;
+
+const SF_DATALESS: u32 = 0x40000000;
+
+fn is_online_only(metadata: &std::fs::Metadata) -> bool {
+    metadata.blocks() == 0 || (metadata.st_flags() & SF_DATALESS != 0)
+}
+```
+
+### Method 2: Spotlight metadata - for sync progress
+
+Spotlight indexes Dropbox files with these relevant keys:
+
+| Key                    | Type       | Meaning                                        |
+| ---------------------- | ---------- | ---------------------------------------------- |
+| `kMDItemIsUploaded`    | Bool (0/1) | File content fully uploaded to Dropbox servers |
+| `kMDItemIsUploading`   | Bool (0/1) | File is currently uploading                    |
+| `kMDItemIsDownloading` | Bool (0/1) | File is currently downloading                  |
+| `kMDItemIsDownloaded`  | Bool       | File content fully downloaded (often null)     |
+
+**Note**: Spotlight indexing may lag behind actual state. New/temporary files may show `(null)` for all values.
+
+Query via command line:
+
+```bash
+mdls -name kMDItemIsUploaded -name kMDItemIsUploading /path/to/file
+```
+
+### Method 3: Extended attributes - undocumented
+
+Dropbox stores sync metadata in `com.dropbox.attrs` (26 bytes, binary format):
+
+```bash
+xattr -px com.dropbox.attrs /path/to/file
+# Output: 0A 12 0A 10 FB 39 37 41 16 17 ED F2 00 00 00 00 00 8E E5 7E 10 ...
+```
+
+The format appears to be a protobuf or custom binary encoding. First 16 bytes are consistent across files (possibly
+account/folder ID). Last 10 bytes vary by file/state. **Not recommended** for detection due to lack of documentation.
+
+---
+
+## Observed file states
+
+### Synced (downloaded and up-to-date)
+
+```
+stat:  blocks=224, flags=0x40 (64)
+mdls:  kMDItemIsUploaded=1, kMDItemIsUploading=0
+Finder: Green checkmark ✅
+```
+
+### Online-only (cloud stub)
+
+```
+stat:  blocks=0, flags=0x40000060 (1073741920)
+       Flags include: SF_DATALESS, UF_COMPRESSED, UF_TRACKED
+mdls:  kMDItemIsUploaded=1, kMDItemIsUploading=0
+Finder: Cloud icon ☁️
+```
+
+### Uploading (syncing to cloud)
+
+```
+stat:  blocks>0, flags=0x40 (64)
+mdls:  kMDItemIsUploaded=0, kMDItemIsUploading=1
+Finder: Circular arrows 🔄
+```
+
+### Downloading (syncing from cloud)
+
+```
+stat:  blocks=0, flags=0x40000060 (SF_DATALESS)
+       Size shows expected final size, blocks still 0
+mdls:  All values may be (null) during download
+Finder: Pie chart progress indicator 🥧
+```
+
+### Download progress calculation
+
+Finder shows a pie-chart progress indicator during downloads. We can potentially calculate progress using:
+
+```
+progress = (blocks * 512) / size
+```
+
+Where:
+
+- `blocks` = `stat().st_blocks` (number of 512-byte blocks allocated)
+- `size` = `stat().st_size` (total file size)
+
+**Caveat**: In our testing, `blocks` remained 0 during download (File Provider may buffer to temp location). This
+approach may not work with Dropbox's File Provider implementation. There is no public API to query per-file download
+progress from a third-party File Provider extension – the `NSProgress` is internal to Dropbox's extension.
+
+**Recommendation**: Show syncing icon 🔄 without progress percentage. Displaying accurate progress would require
+reverse- engineering Dropbox's internal progress mechanism, which is not feasible.
+
+---
+
+## Recommended detection algorithm
+
+```rust
+pub enum DropboxSyncStatus {
+    Synced,        // Fully downloaded and uploaded
+    OnlineOnly,    // Stub file, content in cloud
+    Uploading,     // Local changes being uploaded
+    Downloading,   // Cloud content being downloaded
+    Unknown,       // Not a Dropbox file or status unclear
+}
+
+pub fn get_sync_status(path: &Path) -> DropboxSyncStatus {
+    let metadata = match std::fs::metadata(path) {
+        Ok(m) => m,
+        Err(_) => return DropboxSyncStatus::Unknown,
+    };
+
+    let blocks = metadata.blocks();
+    let flags = metadata.st_flags();
+    let is_dataless = (flags & 0x40000000) != 0 || blocks == 0;
+
+    // Fast path: check stat() first
+    if is_dataless {
+        // Could be online-only OR downloading
+        // To distinguish, would need Spotlight query (slower)
+        return DropboxSyncStatus::OnlineOnly;
+    }
+
+    // File has local content - check if uploading via Spotlight
+    // (This part requires NSMetadataItem query - omitted for brevity)
+    // if is_uploading { return DropboxSyncStatus::Uploading; }
+
+    DropboxSyncStatus::Synced
+}
+```
+
+---
+
+## File flags reference
+
+Relevant macOS file flags from `<sys/stat.h>`:
+
+| Flag            | Value      | Meaning                                |
+| --------------- | ---------- | -------------------------------------- |
+| `UF_NODUMP`     | 0x00000001 | Don't dump file                        |
+| `UF_COMPRESSED` | 0x00000020 | File is compressed                     |
+| `UF_TRACKED`    | 0x00000040 | File changes tracked (File Provider)   |
+| `UF_DATAVAULT`  | 0x00000080 | Entitlement required for access        |
+| `SF_DATALESS`   | 0x40000000 | **File is a stub** - content not local |
+
+Online-only Dropbox files typically have flags: `SF_DATALESS | UF_COMPRESSED | UF_TRACKED` = `0x40000060`
+
+---
+
+## Open questions
+
+1. **Downloading vs online-only**: Both show `blocks=0` and `SF_DATALESS`. During active download, Spotlight metadata
+   may be `(null)`. Need to find a reliable way to distinguish "static online-only" from "currently downloading".
+
+2. **Sync errors**: How are sync errors (conflicts, permission issues) indicated? Need test files with error states.
+
+3. **Ignored files**: Files with `com.dropbox.ignored` xattr are not synced. Detection is straightforward:
+
+    ```bash
+    xattr -p com.dropbox.ignored /path/to/file  # Returns "1" if ignored
+    ```
+
+4. **Shared folders**: Do shared folder files have different status indicators?
+
+5. **Spotlight latency**: How quickly does Spotlight update after state changes? Is there a faster notification
+   mechanism?
+
+---
+
+## Test files used
+
+All in `~/Dropbox/sharing/`:
+
+| File                     | State       | Notes                               |
+| ------------------------ | ----------- | ----------------------------------- |
+| `edlevo-downloaded.png`  | Synced      | blocks=224, flags=0x40              |
+| `edlevo-online-only.png` | Online-only | blocks=0, flags=0x40000060          |
+| `edlevo-syncing.png`     | Uploading   | blocks>0, kMDItemIsUploading=1      |
+| `.../tmp.a`              | Downloading | blocks=0, size=571MB, mdls all null |
+
+---
+
+## References
+
+- Apple File Provider documentation: https://developer.apple.com/documentation/fileprovider
+- Dropbox help article on sync icons: https://help.dropbox.com/sync/icons
+- macOS `stat.h` flags: `/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/stat.h`

docs/todo.md

@@ -16,12 +16,24 @@
 - [x] Add file watching to auto-update changes. It should be as close to immediate as possible
 - [x] Implement proper Full view (with fixed columns)
 - [x] Add Brief view with view switching option
+- [x] Make sure it lists Dropbox files correctly, incl. files that are loaded on the fly
 - [ ] Add different sorting options
-- [ ] Make sure it lists Dropbox files correctly, incl. files that are loaded on the fly
 - [ ] When sorting alphabetically, sort numbers ascending, not alphabetically
 - [ ] Add "change drive" feature
 - [ ] Tweak chunked loading to load in chunks on the backend based on drive speed. So far, we've only tested with fast
       drives, and chunk sizes are constant.
+- [ ] Load iCloud sync statuses, too
+- [ ] Load Google Drive sync statuses, too
+- [ ] Load OneDrive sync statuses, too?
+- 
+## Cleanup
+
+- Rename FileList to FullList
+- In Full mode, size display coloring is ugly, fix it
+- When the app starts, it's temporarily all white bg for like 1 second. Go around this by delaying opening the window,
+  or show a nice loading screen via normal HTML (no svelte) if that solves it. What can we do?
+- Big dir reading is wrong: takes 7 seconds for the 50k dir, and it looks weird: it shows 45k files Loading but then it
+  loads immediately
 
 ## Settings