Sheet metal: tear as a fourth corner relief shape (#809)

A sheet metal rule's corner relief shape can now be tear; saved under format 17 with a note.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/cmd/sheet.rs

@@ -43,7 +43,8 @@ pub static COMMANDS: &[CommandSpec] = &[
     CommandSpec::new("sheet.manage_rules", "Sheet Metal Rules", rules).at("SHEET METAL", "MODIFY").icon("sheet_rules").params(
         "name (new or existing); thickness?, k_factor?, bend_radius?, relief_width?, relief_depth?, corner_relief?, hem_gap?, gap? (expressions; `Thickness` is the rule's; \
          gap: between flanges that meet at a corner, whose ends are closed toward each other at any angle); \
-         corner_relief_shape?: notch|round|rectangular (what is cut where two bends meet at a corner of the base, `corner_relief` across; default notch); \
+         corner_relief_shape?: notch|round|rectangular|tear (what is cut where two bends meet at a corner of the base: round and rectangular a relief \
+         `corner_relief` across; tear none, each bend's end is cut straight from the corner to its flange's end; default notch); \
          active?: bool; delete?: bool",
     ),
     CommandSpec::new("sheet.rules", "List Sheet Metal Rules", list_rules).noundo().doc_only().params("→ rules with their expressions and values, and the active one"),
@@ -323,7 +324,7 @@ fn rules(s: &mut Session, p: &Value) -> Result<Value> {
     }
     if let Some(shape) = p.get("corner_relief_shape").filter(|v| !v.is_null()) {
         let shape = shape.as_str().and_then(solidcraft_doc::sheet::ReliefShape::parse);
-        rule.corner_relief_shape = shape.ok_or_else(|| bad(cmd, "`corner_relief_shape` must be notch, round or rectangular"))?.name().into();
+        rule.corner_relief_shape = shape.ok_or_else(|| bad(cmd, "`corner_relief_shape` must be notch, round, rectangular or tear"))?.name().into();
     }
     let (vals, _) = s.doc.param_values();
     let values = s.doc.rule_values(&vals, &rule).map_err(|e| bad(cmd, e.to_string()))?;