Add session restore support

[cheerfulScumbag]

Adds opt-in session save/restore support to Mango.

When session_restore=1:

• Mango saves a restorable snapshot on clean shutdown
• Mango loads that snapshot on next startup
• Mango relaunches supported apps from persisted launch_command
• Mango restores tag, monitor, floating/fullscreen state, and floating geometry as windows map

When session_restore=0:

• Mango behaves as before
• no session file is written
• no restore or relaunch path runs

Supported config:
'session_restore=0|1'

Optional override config:
'session_launch=app_id|command'
'session_launch=app_id|title|command'

Current launch-command priority:

1. exact command Mango itself used to spawn the app
2. normalized higher-level launcher command recovered from process metadata
3. raw process argv fallback
4. title-specific session_launch
5. app-only session_launch
6. plain app_id

Normalization currently implemented:

• Flatpak apps normalize to desktop-entry launcher command
• desktop-entry-backed apps normalize to the desktop file Exec= command

Validated:

• disabled path writes no session file
• clean shutdown save
• self-relaunch on next Mango startup
• duplicate foot windows with title-specific mappings
• exact command capture for Mango-owned exec-once launches
• process-based recovery for apps Mango did not spawn directly
• single-monitor restore
• floating geometry restore
• tag restore
• two-monitor restore when outputs already exist before clients map

[cheerfulScumbag]

current implementation works, but I want to improve automatic launch recovery so common apps do not require as much manual session_launch configuration

[cheerfulScumbag]

Updated this draft with a stronger automatic launch-command recovery path.

Since the original draft, Mango now:

• tracks exact commands for apps it launches itself
• recovers commands from client process metadata for apps it did not launch directly
• normalizes Flatpak apps to desktop-entry launcher command
• normalizes desktop-entry-backed apps to the desktop file Exec= command

That reduces the need for manual session_launch rules for common apps.

[cheerfulScumbag]

tested on multiple programs and they all restore with no issues
so when session_restore=1:

• Mango saves a restorable snapshot on clean shutdown
• Mango loads that snapshot on next startup
• Mango relaunches supported apps from persisted launch_command
• Mango restores tag, monitor, floating/fullscreen state, and floating geometry as windows map

Give it a test and let me know what you think