Initial version

README.md

@@ -1,3 +1,106 @@
-# EonaCat.RdpColorizer
+# EonaCat RDP Colorizer
 
-EonaCat RdpColorizer
+A Windows utility that colors the title bar of Remote Desktop windows and
+overlays a small colored tag (e.g. `PROD`, `DEV-DB1`) on the caption, so you
+can tell multiple RDP sessions apart at a glance. It runs in the background,
+remembers which color/tag belongs to which server, and automatically
+re-applies that tag any time a matching RDP window shows up - including
+after you restart the app, and for windows opened outside the app entirely.
+
+## A note on "running as a service"
+
+A true Windows Service (the kind registered with the Service Control
+Manager) runs in **Session 0**, which has been isolated from the
+interactive desktop since Windows Vista. A Session 0 process cannot see or
+draw on windows in your logon session at all - this is an OS-level
+security boundary, not something that can be coded around. So a real SCM
+service could never color or overlay another window's title bar.
+
+What actually achieves the goal - always running, no manual relaunching,
+automatic re-tagging - is a background app that starts at logon inside
+your own session. That's what this app now does:
+
+- It starts hidden in the **system tray** (no window, no taskbar entry)
+  when launched with `--background`, or normally shows its control panel
+  when opened by hand.
+- Closing the window just hides it to the tray; the watcher keeps running
+  until you choose **Exit** from the tray icon's menu.
+- Check **Start with Windows** in the app to have it launch automatically
+  at logon (writes a `HKCU\...\Run` entry pointing at the exe with
+  `--background` - no admin rights required).
+
+If your environment specifically requires an SCM-registered service (e.g.
+for a policy or monitoring reason), that service could still exist to
+supervise/restart this tray app, but it would not be able to perform the
+window coloring itself.
+
+## How the coloring and tagging work
+
+1. **Native caption color** - `DwmSetWindowAttribute` with
+   `DWMWA_CAPTION_COLOR` / `DWMWA_TEXT_COLOR`. Only honored on **Windows 11
+   (build 22000+)**; ignored on Windows 10.
+2. **Overlay tag label** - a small always-on-top badge window positioned
+   over the caption bar, showing your text on your chosen color. Works on
+   any Windows version and follows the RDP window as it moves, resizes, or
+   restores (hidden while minimized).
+
+## Auto re-attach by server / IP
+
+- Whenever you tag a connection (Launch or Attach), the target
+  (server name or IP) plus your chosen label/color is saved to
+  `%AppData%\EonaCat.RdpColorizer\profiles.json`.
+- A background watcher scans for RDP windows **system-wide** every second.
+  For each one it doesn't recognize yet, it resolves the actual connection
+  target - first by reading the `mstsc.exe` process's command line
+  (`/v:target`) via WMI, falling back to parsing the window title if that
+  fails (e.g. if `mstsc.exe` is running elevated or under a different
+  account than this app).
+- If the resolved target matches a saved profile, the tag/color is applied
+  automatically - no manual step needed, including for connections opened
+  straight from the Start menu or a saved `.rdp` file.
+- Use **Manage saved profiles...** to review or delete remembered
+  server → tag mappings.
+
+## Requirements
+
+- Windows 10 or 11
+- [.NET 8 SDK](https://dotnet.microsoft.com/download) to build
+
+## Build & run
+
+```powershell
+cd EonaCat.RdpColorizer
+dotnet build
+dotnet run
+```
+
+Or publish a standalone exe:
+
+```powershell
+dotnet publish -c Release -r win-x64 --self-contained false
+```
+
+## Using it
+
+1. Enter a server name/IP and a short tag, pick a color, then click
+   **Launch new tagged connection** (runs `mstsc.exe /v:target`) or
+   **Tag active RDP window** to attach to one already open.
+2. That server/tag/color is now remembered - close and reopen the app (or
+   just leave it running in the tray) and any future RDP window to that
+   same server gets tagged automatically.
+3. Tick **Start with Windows** so this happens without you having to open
+   the app at all.
+
+## Notes / limitations
+
+- Windows caption theming (`DWMWA_CAPTION_COLOR`) is Windows 11 only;
+  there is no public equivalent for Windows 10 - the overlay tag is your
+  cross-version fallback.
+- The overlay tag is a separate always-on-top window layered over the
+  caption, so it will show up as its own tiny entry in things like Alt+Tab
+  previews - expected behavior, not a bug.
+- Command-line resolution via WMI requires the watcher to have permission
+  to query the `mstsc.exe` process; if it's elevated or owned by another
+  user, the watcher falls back to matching on the window title instead
+  (which shows the resolved computer name rather than the raw IP you
+  typed - keep that in mind when naming profiles for IP-based targets).