Seed from go-template-repo, renamed to simplexcalc

The template's files at a77fd30, without its history or LICENSE, after
script/rename simplexcalc.

Model: opus-5-5

script/test

@@ -0,0 +1,21 @@
+#!/bin/sh
+# script/test: run the test suite. Quiet on success; on failure, rerun
+# with -v for full diagnostic output (and still fail — the first run
+# already proved the tests are broken).
+set -eu
+
+ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
+
+main() {
+    cd "$ROOT"
+    # -count=1 disables the test result cache. Without it a repeat run on
+    # an unchanged tree reports every package `ok ... (cached)` and exits
+    # 0 having executed nothing — a gate that cannot fail.
+    go test -count=1 -timeout 90s -race -cover ./... || {
+        echo "--- Rerunning with -v for details ---"
+        go test -count=1 -timeout 90s -race -v ./...
+        exit 1
+    }
+}
+
+main "$@"