Basic implementation of /commit, /version, and /status

No precondition checking, persistence, or log scanning yet.

src/pipeline_entry.hpp

@@ -0,0 +1,47 @@
+#pragma once
+
+#include "connection.hpp"
+#include <memory>
+#include <variant>
+
+/**
+ * Pipeline entry for commit requests that need full 4-stage processing.
+ * Contains connection with parsed CommitRequest.
+ */
+struct CommitEntry {
+  std::unique_ptr<Connection> connection;
+  int64_t assigned_version = 0; // Set by sequence stage
+  bool resolve_success = false; // Set by resolve stage
+  bool persist_success = false; // Set by persist stage
+
+  CommitEntry() = default; // Default constructor for variant
+  explicit CommitEntry(std::unique_ptr<Connection> conn)
+      : connection(std::move(conn)) {}
+};
+
+/**
+ * Pipeline entry for status requests that need sequence stage processing
+ * then transfer to status threadpool.
+ */
+struct StatusEntry {
+  std::unique_ptr<Connection> connection;
+  int64_t version_upper_bound = 0; // Set by sequence stage
+
+  StatusEntry() = default; // Default constructor for variant
+  explicit StatusEntry(std::unique_ptr<Connection> conn)
+      : connection(std::move(conn)) {}
+};
+
+/**
+ * Pipeline entry for coordinated shutdown of all stages.
+ * Flows through all stages to ensure proper cleanup.
+ */
+struct ShutdownEntry {
+  // Empty struct - presence indicates shutdown
+};
+
+/**
+ * Pipeline entry variant type used by the commit processing pipeline.
+ * Each stage pattern-matches on the variant type to handle appropriately.
+ */
+using PipelineEntry = std::variant<CommitEntry, StatusEntry, ShutdownEntry>;