Verification oracle: tests/oracle cases, cargo xtask oracle, fixtures, docs/oracle.md, CI job

The oracle binary (modelcraft-testkit) runs each case's recipe through the
command engine, measures its quantities by JSON pointers into step outputs
or commands, compares them with the cited references and the frozen
fixtures, and writes docs/oracle.md. 20 theory cases (patch tests of every
solid element, Timoshenko cantilevers, Lame, Kirsch, beam frequencies,
torsion and bending through couplings, explicit waves and impact, CDT
invariants), 8 published benchmarks (MacNeal-Harder patch, straight and
curved cantilevers, thick cylinder, Scordelis-Lo with solids, NAFEMS LE1,
LE10, FV32) and 10 pending cases with citations.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

xtask/src/main.rs

@@ -37,6 +37,11 @@ commands:
   corpus [--part NAME] [--no-write]
                   build every meshing test corpus part (tests/corpus, analytic shapes), tessellate
                   and mesh it, and write the results to docs/meshing/corpus.md (release build)
+  oracle [--case NAME]... [--bless NAME|all]... [--quick] [--no-write]
+                  run the verification and validation cases (tests/oracle, docs/verification.md)
+                  against their references and fixtures; write docs/oracle.md after a full run;
+                  --bless freezes a passing case's results in its fixture.json; --quick skips
+                  cases marked slow (release build)
   wasm            cargo check every library crate for wasm32-unknown-unknown
   ci              fmt --check, assets, licences --check, layers, clippy -D warnings, then the tests
                   (not the heavy ones) with the wasm check alongside (stops at the first failing
@@ -72,6 +77,12 @@ fn main() -> ExitCode {
             c.args(["run", "--release", "-p", "modelcraft-testkit", "--bin", "corpus", "--"]).args(&rest);
             run(c, "corpus")
         }
+        Some("oracle") => {
+            // A binary of the testkit, which has the engine and SolidCraft scripts for geometry.
+            let mut c = cargo();
+            c.args(["run", "--release", "-p", "modelcraft-testkit", "--bin", "oracle", "--"]).args(&rest);
+            run(c, "oracle")
+        }
         Some("wasm") => cmd_wasm(),
         Some("-h" | "--help" | "help") | None => {
             print!("{USAGE}");