A Steady 9×9 Puzzle Solved with Shape Squeeze in 19 Steps

This 9×9 board rates as steady (difficulty score 847). Solving it from scratch takes 19 logical steps, using 7 techniques: Single cell, Row/column exclusion, Adjacency clear, Region confinement, Line confinement, Paired regions, Shape squeeze. Every step below is forced: nothing here is a guess.

1. First, every open cell left in this region sits in column A, so its marker has to land there; that clears every other open cell in the column.
2. Next, every open cell left in this region sits in column B, so its marker has to land there; that clears every other open cell in the column.
3. Then, every open cell left in this region sits in row 9, so its marker has to land there; that clears every other open cell in the row.
4. After that, together, two regions have open cells only in rows 1 and 2; with one marker each, those two markers have to fill exactly those two rows, so every other region's open cells there can be cleared.
5. Now, together, two regions have open cells only in columns C and D; with one marker each, those two markers have to fill exactly those two columns, so every other region's open cells there can be cleared.
6. From there, every open cell left in this region sits in column E, so its marker has to land there; that clears every other open cell in the column.
7. Following that, every open cell left in this region sits in column F, so its marker has to land there; that clears every other open cell in the column.
8. First, place a marker at B2. Row 2 has exactly one open cell left. Placing here clears the rest of row 2, column B, and its region.
9. Next, every remaining candidate in this region touches C8 and D8, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
10. Then, place a marker at C7. Region has exactly one open cell left. Placing here clears the rest of row 7, column C, and its region.
11. After that, place a marker at A6. Region has exactly one open cell left. Placing here clears the rest of row 6, column A, and its region.
12. Now, place a marker at D9. Region has exactly one open cell left.
13. From there, every open cell in row 8 belongs to the same region, so that region's marker has to be somewhere in this row; that clears every other open cell in the region.
14. Following that, every remaining candidate in this region touches F3 and F4, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
15. First, place a marker at F5. Region has exactly one open cell left. Placing here clears the rest of row 5, column F, and its region. Placing here also clears its 2 touching neighbours.
16. Next, place a marker at E3. Region has exactly one open cell left. Placing here clears the rest of row 3, column E, and its region.
17. Then, place a marker at H4. Region has exactly one open cell left. Placing here clears the rest of row 4, column H, and its region.
18. After that, place a marker at G1. Region has exactly one open cell left. Placing here clears the rest of row 1, column G, and its region.
19. Finally, place a marker at I8. Region has exactly one open cell left.

The key move here was Shape squeeze. Once you can spot that, this board falls quickly. ∎