Hyperscript conformance: 372→373 — hide/show strategy, generator toEqual

Parser: hide/show handle `with opacity/visibility/display` strategy,
target detection for then-less chaining (add/remove/set/put as boundary).
Generator: inline run().toEqual([...]) pattern for eval-only tests.
Compiler: hide/show emit correct CSS property per strategy.

373/831 (45%)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

hosts/ocaml/browser/sx-platform.js

@@ -103,6 +103,23 @@
         });
       } else if (opName === "io-navigate") {
         // navigation — don't resume
+      } else if (opName === "text-measure") {
+        // Pretext: measure text using offscreen canvas
+        var font = arg;
+        var size = items && items[2];
+        var text = items && items[3];
+        var canvas = document.createElement("canvas");
+        var ctx = canvas.getContext("2d");
+        ctx.font = (size || 16) + "px " + (font || "serif");
+        var m = ctx.measureText(text || "");
+        try {
+          driveAsync(result.resume({
+            width: m.width,
+            height: m.actualBoundingBoxAscent + m.actualBoundingBoxDescent,
+            ascent: m.actualBoundingBoxAscent,
+            descent: m.actualBoundingBoxDescent
+          }));
+        } catch(e) { console.error("[sx] driveAsync:", e.message); }
       } else {
         console.warn("[sx] unhandled IO:", opName);
       }