Chunk blending does not resume after reloading a world

Quitting the game while generating blended chunks may cause the blending process to cancel. The next time the world is loaded, regular world generation occurs where blended chunks are expected. This happens as soon as the blending_data tag is added to the chunk that the game is blending to. The earliest version where this issue appears is 25w09a.

To reproduce this easily, a world has been setup to blend 1.21.5 chunks into a single 1.21.4 chunk.

Instructions to reproduce:

1. Start the game.

2. Set render distance to the minimum 2 chunks.

3. Load the provided world in Singleplayer. Do NOT move. Teleport to 1194 95 -823 if not already there and wait a few seconds for the terrain to generate.

4. Save and Quit to Title.

5. Increase render distance again (e.g. to 16 chunks).

6. Load the world again in Singleplayer. Move over the mountain and observe a hard edge in the terrain.

Additional Images:

1. Top-Down view of the initial setup in MCA Selector.

2. Top-Down view in MCA Selector, after Saving and Quitting to Title (step 4).

3. Top-Down view in MCA Selector, after step 6.

4. Demonstration of cut terrain, after step 6.

5. Expected blending, achieved by not setting the render distance to 2 chunks (skipping step 2).