tessera-ctl/.planning/quick/260929-d37-desktop-client-nur-einmal-starten-single/260929-d37-PLAN.md

quick_id, type, wave, autonomous, files_modified

quick_id	type	wave	autonomous	files_modified
260929-d37	quick	1	true	apps/desktop/src-tauri/Cargo.toml apps/desktop/src-tauri/Cargo.lock apps/desktop/src-tauri/src/lib.rs CHANGELOG.md

Quick 260929-d37: Desktop-Client nur einmal starten (Single-Instance)

Problem

User report (29.09.2026, Windows 11): at system start Tessera launches twice and two tray icons appear. apps/desktop/src-tauri/src/lib.rs has no single-instance guard. Autostart via tauri-plugin-autostart (HKCU Run key, only set when the user ticks "Mit Windows starten"); a second launch source (Windows 11 "restart restartable apps after sign-in", a stale Run/Startup entry from an older install, or a manual double-click) starts a second full process with its own tray icon.

Goal

Only one Tessera desktop process runs per user session. A second launch hands off to the running one (show + unminimize + focus the main window) and exits immediately — no second tray icon.

Task 1: Single-instance plugin

• files: apps/desktop/src-tauri/Cargo.toml, apps/desktop/src-tauri/Cargo.lock, apps/desktop/src-tauri/src/lib.rs
• action:
  • Add tauri-plugin-single-instance = "2" to [dependencies] (resolve with cargo; lockfile updated).
  • Register it as the FIRST plugin in tauri::Builder (plugin docs require it to be registered first): .plugin(tauri_plugin_single_instance::init(|app, _argv, _cwd| { focus main window })).
  • Callback: reuse the exact show/unminimize/set_focus sequence already used by the tray "open" handler (around lib.rs:820-835). If that sequence is duplicated 3x already, extract a small helper fn show_main_window(app: &AppHandle) and use it in all places (keep behavior identical).
  • Short German comment above the plugin line explaining why (double start at Windows sign-in, two tray icons).
  • No capabilities/permissions change needed (plugin has no JS API); verify by building.
• verify: cd apps/desktop/src-tauri && cargo build succeeds; cargo test (existing unit tests) green; cargo clippy no new warnings if clippy is available.
• done: builds, tests green, commit fix(desktop): nur eine Instanz — zweiter Start holt das Fenster nach vorne.

Task 2: CHANGELOG

• files: CHANGELOG.md
• action: under ## Unveröffentlicht add a ### Behoben section (after ### Neu) with one plain-German bullet (app text uses "Sie"), e.g.: "Desktop-App: Tessera startet nicht mehr doppelt. Wird die App ein zweites Mal gestartet – etwa beim Anmelden an Windows –, holt sie nur das vorhandene Fenster nach vorne; im Infobereich erscheint nur noch ein Symbol." Follow existing CHANGELOG style; run the repo's changelog/umlaut checks if any exist (web tests touching CHANGELOG, e.g. pnpm --filter web test -- changelog).
• done: commit docs(changelog): Desktop-App startet nicht mehr doppelt.

Constraints

• Commit locally only. NEVER git push.
• Do not touch the desktop version numbers (release process handles them).
• Real Windows verification is not possible from here; state in SUMMARY that the Windows check (VM 8233 or user's PC after next desktop release) is open.