A Medium 7×7 Puzzle Solved with Shape Squeeze in 18 Steps

This 7×7 board rates as medium (difficulty score 876). Solving it from scratch takes 18 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, together, two regions have open cells only in rows 2 and 3; 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.
2. Next, every open cell left in this region sits in row 1, so its marker has to land there; that clears every other open cell in the row.
3. Then, 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.
4. After that, every open cell in column B belongs to the same region, so that region's marker has to be somewhere in this column; that clears every other open cell in the region.
5. Now, every remaining candidate in this region touches E2, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
6. From there, every open cell left in this region sits in column D, so its marker has to land there; that clears every other open cell in the column.
7. Following that, every remaining candidate in this region touches E3, so whichever candidate ends up marked will clear it, and it can be ruled out now regardless of which one wins.
8. First, 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.
9. Next, every remaining candidate in this region touches B4 and B5, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
10. Then, together, two regions have open cells only in rows 6 and 7; 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.
11. After that, every remaining candidate in this region touches C6 and C7, so whichever candidate ends up marked will clear them, and they can be ruled out now regardless of which one wins.
12. Now, place a marker at E7. Region has exactly one open cell left. Placing here clears the rest of row 7, column E, and its region.
13. From there, place a marker at B6. Region has exactly one open cell left. Placing here also clears its 1 touching neighbour.
14. Following that, place a marker at A4. Region has exactly one open cell left. Placing here clears the rest of row 4, column A, and its region.
15. First, place a marker at G5. Region has exactly one open cell left. Placing here clears the rest of row 5, column G, and its region.
16. Next, place a marker at C1. Region has exactly one open cell left. Placing here also clears its 1 touching neighbour.
17. Then, place a marker at D3. Region has exactly one open cell left. Placing here clears the rest of row 3, column D, and its region.
18. Finally, place a marker at F2. Region has exactly one open cell left.

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