Large sketches: the solver works on each component's own Jacobian (block-diagonal DOF analysis, no dense whole-sketch matrices), component grouping by map, and profile finding uses its grid for end checks and keyed sorting. A 10 000-entity sketch solves in 65 ms instead of 1.3 s and commands on it take ~0.2 s instead of 5 s; numbers in docs/perf.md

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

docs/perf.md

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+# Performance
+
+## Large sketches
+
+Measured with `cargo test -p solvecraft-engine --release sketch_perf -- --ignored --nocapture`
+(`crates/engine/src/cmd/sketch_perf_tests.rs`). The sketch holds `n` rectangles (four lines,
+horizontal/vertical constraints and two length dimensions each) and `n` circles. All times are
+wall-clock milliseconds on the development machine while other builds were running (load
+average around 60), so treat them as upper bounds.
+
+| n | curves | points | constraints | solve | profiles | draw lists | snap query | add a line (command) | drag a point (command) |
+|---:|---:|---:|---:|---:|---:|---:|---:|---:|---:|
+| 250 | 1 250 | 1 251 | 1 500 | 15 | 30 | 12 | 0.1 | 68 | 48 |
+| 500 | 2 500 | 2 501 | 3 000 | 35 | 47 | 10 | 0.1 | 123 | 100 |
+| 1000 | 5 000 | 5 001 | 6 000 | 65 | 134 | 1 | 0.3 | 232 | 100 |
+
+"Add a line" and "drag a point" are whole commands: they copy the sketch, solve it, store it and
+re-evaluate the timeline (a second solve, plus profile finding). "Draw lists" is
+`view::sketch_lines`, the polylines the viewport draws.
+
+Before the 2026-10-08 changes the n = 1000 sketch took 1 280 ms to solve, 590 ms to find
+profiles and 5.1 s per command:
+
+- The solver built one dense Jacobian over every variable of the sketch, for each connected
+  component's iterations and again for the degree-of-freedom analysis (5 000 × 10 000 entries,
+  then reduced row echelon form). It now builds each component's Jacobian over that component's
+  own variables. The sketch's Jacobian is block diagonal, so its rank is the sum of the
+  components' ranks, and components were already solved separately.
+- Grouping variables into components searched a list per variable. It now uses a map.
+- Profile finding looked at every curve end for each crossing it found, and sorted profiles with
+  a linear id lookup in the comparison. It now uses the grid it already builds for crossings,
+  and sorts on precomputed keys.
+
+Projection (linked reference geometry) is cached per model state, so edits to a sketch with
+projected silhouettes or sections on a ~20 000-triangle model cost about 3 ms each instead of
+about 80 ms.