Prove a write by compare-and-set loses no update under contention, on a real bus (hq research 042)

The issues module will hand out numbers through mesh/state.create and update. Two writers incrementing one
counter a thousand times each through the module's bus now end at two thousand with every number handed out
once; a stale, zero or future revision is refused with the lost-write code and writes nothing; a deleted key
can be created again; and the lost-write code reaches a bundle wrapped or not, and no other refusal carries it.
Both runtime tests run in the check's bundleless list, so mesh/repo-check runs them.

Part of the issue tracker decision, hq research 042.

node-tools/internal/launch/error_code_test.go

@@ -0,0 +1,30 @@
+package launch
+
+import (
+	"errors"
+	"fmt"
+	"testing"
+)
+
+type lostWrite struct{}
+
+func (lostWrite) Error() string {
+	return "issues.numbers.issue: the key was written by another writer first"
+}
+func (lostWrite) ErrorCode() int { return CodeChanged }
+
+// A lost compare-and-set is answered to a bundle with its own code, wrapped or not, and the SDK tells it by
+// that code alone (mesh-sdk's stdio.CodeChanged); every other refusal is the general code, never that one.
+func TestALostWriteIsAnsweredWithItsOwnCodeAndNothingElseIs(t *testing.T) {
+	if CodeChanged != -32010 {
+		t.Fatalf("the lost-write code is %d; mesh-sdk tells it by -32010", CodeChanged)
+	}
+	for _, err := range []error{lostWrite{}, fmt.Errorf("asked by issues: %w", lostWrite{})} {
+		if got := errorCode(err); got != CodeChanged {
+			t.Errorf("%v is answered %d", err, got)
+		}
+	}
+	if got := errorCode(errors.New("issues keeps no state numbers")); got == CodeChanged || got != -32000 {
+		t.Errorf("a plain refusal is answered %d", got)
+	}
+}