Sketch commands return the ids of the points, curves, constraints and dimensions they create as created: {points, curves, constraints, dimensions}, worked out in Session::execute from the sketch before and after, so a script can dimension and constrain new geometry right away; ids stay stable and are not reused after a delete (undo rewinds the counters with the design). The MCP execute tool describes the field

docs/book/src/guide/sketching.md

@@ -15,6 +15,11 @@ fillet, chamfer, offset (O), mirror, patterns, move/copy and scale.
 **Project** (P) and **Intersect** bring model edges into the sketch as linked geometry that
 follows later changes. Sketching on a face projects its edges automatically.
 
+Run from a script or the control channel, every command that adds sketch geometry returns the
+ids of what it added (`created: {points, curves, constraints, dimensions}`). Ids are stable and
+never reused within a sketch, even after a delete, so a script can dimension or constrain the new
+geometry right away.
+
 ## Constraints and dimensions
 
 The solver is SolveCraft's own (damped Gauss–Newton with degree-of-freedom analysis). Constraints:

docs/control-protocol.md

@@ -17,6 +17,18 @@ events, one pointer event per frame.
 
 Commands never open dialogs when run this way. `solvecraft-cli commands` prints the same registry.
 
+Every `sketch.*` command that changes a sketch adds `created: {points, curves, constraints,
+dimensions}` to its result (and `wires` for 3D curves): the ids of what it added, in creation
+order, next to whatever else the command returns (`curves`, `sides`, `corners`…). Sketch ids are
+stable and never reused, even after a delete (`l1`, `l2`, then `l3` once `l2` is gone; only undo
+rolls the numbering back with the design), so they can go straight into later commands:
+
+```text
+{"id":7,"method":"engine.execute","params":{"command":"sketch.line","params":{"points":[[0,0],[40,0]]}}}
+→ {"curves":["l1"],"created":{"points":["l1.start","l1.end"],"curves":["l1"],"constraints":["k1"],"dimensions":[]},…}
+{"id":8,"method":"engine.execute","params":{"command":"sketch.dimension","params":{"entities":["l1"],"value":50}}}
+```
+
 ## UI
 
 | Method | Params | Notes |