"Repack Atlas" after replacing frames.

How it works end-to-end:

1. Atlas Manager replaces a frame — stores replacement in replacedFrames[frameName] (in-memory canvas)
2. "Repack Atlas" button — calls repackAtlas() → buildAtlasWithReplacements() which composites all original + replaced frames into a new atlas PNG + JSON
3. Saved with _ prefix — e.g. _game_ui.png / _game_ui.json (or _game_asset.* for explosions)
4. On next game launch — phaser-game.html:checkEditorAtlases() does HEAD requests to detect _prefixed files, sets window.__editorAtlases
5. BootScene.preload() — checks window.__editorAtlases and loads _game_ui.png instead of game_ui.png (likewise for game_asset)
6. All sprites using that atlas automatically show the new frames because Phaser looks up frames by key name from the loaded atlas texture

titleCopyright.gif (game_ui atlas)

• PhaserTitleScene creates: this.add.sprite(0, 0, "game_ui", "titleCopyright.gif")
• After repack, the _game_ui.png contains the replacement image at the frame coordinates specified in _game_ui.json
• Result: Title scene shows the updated copyright image automatically

explosion0.gif–explosion06.gif (game_asset atlas)

• Explosions.js:showExplosion() creates animation from generateFrameNames("game_asset", { prefix: "explosion", start: 0, end: 6, zeroPad: 2, suffix: ".gif" })
• After repack, _game_asset.png contains replacement explosion frames
• Result: Explosions in-game automatically show updated frames

Key requirement

• The frame key names must stay the same (e.g. "titleCopyright.gif", "explosion00.gif") — the Atlas Manager preserves these during replacement
• Frame dimensions can change — the repacker re-bins with MaxRects algorithm
• You must reload the game after repacking (the atlas is loaded once at boot)