Add new Spinscale C++ Coroutine support

include/spinscale/co/promiseChainWalker.h

@@ -0,0 +1,49 @@
+#ifndef PROMISE_CHAIN_WALKER_H
+#define PROMISE_CHAIN_WALKER_H
+
+#include <cstddef>
+
+#include <spinscale/co/promiseChainLink.h>
+
+namespace sscl::co {
+
+/**
+ * Upper bound on caller-chain links visited after the root (guards cycles / bugs).
+ *
+ * Design posture (cf. docs/3rdParty/smo/libspinscale — continuation tracing vs
+ * interpretation): this header performs trace-only walks along
+ * PromiseChainLink::callerPromiseChainLink(); deadlock interpretation stays at
+ * call sites / later policy.
+ */
+inline constexpr std::size_t kMaxCallerPromiseChainTraversalSteps = 4096;
+
+inline const PromiseChainLink *nextOnCallerPromiseChain(
+	const PromiseChainLink &link) noexcept
+{
+	return link.callerPromiseChainLink();
+}
+
+inline bool callerChainHopUnderStepLimit(
+	std::size_t hopIndex) noexcept
+{
+	return hopIndex < kMaxCallerPromiseChainTraversalSteps;
+}
+
+template <typename Visitor>
+void walkCallerPromiseChainFrom(
+	const PromiseChainLink &root, Visitor &&visitor)
+{
+	visitor(root);
+	const PromiseChainLink *next = nextOnCallerPromiseChain(root);
+	for (std::size_t hopIndex = 0;
+		next != nullptr && callerChainHopUnderStepLimit(hopIndex);
+		++hopIndex)
+	{
+		visitor(*next);
+		next = nextOnCallerPromiseChain(*next);
+	}
+}
+
+} // namespace sscl::co
+
+#endif // PROMISE_CHAIN_WALKER_H