digraph writer_insert_flow {
    rankdir=TB;
    fontname="Helvetica";
    node [fontname="Helvetica", fontsize=10, style=filled, shape=box];
    edge [fontname="Helvetica", fontsize=9];

    label="Writer: Insert Data Flow (e.g. region)";
    labelloc=t;
    fontsize=14;

    start [label="writer_t::insert_region_data()", fillcolor="#c8ddf0"];
    impl [label="m_impl->insert_region_data()", fillcolor="#c8ddf0"];
    dispatch [label="m_region_writer->insert()", fillcolor="#c0e0c0"];
    crtp [label="region_writer_interface::insert()\n→ self().insert_impl()", fillcolor="#ddd0f0"];
    insert_impl [label="region_writer<schema_v3_tag>::insert_impl()", fillcolor="#f0dcc0"];

    begin_tx [label="1. backend->begin_transaction()", fillcolor="#ffffc0"];
    validate [label="2. validator->require_node()\n   .require_process()\n   .require_thread()", fillcolor="#ffffc0"];
    resolve [label="3. resolve foreign keys\n   (process_pk, thread_pk, name_pk)", fillcolor="#ffffc0"];
    event [label="4. common_ops->insert_event()\n   (if event metadata present)", fillcolor="#ffffc0"];
    get_pk [label="5. key_providers->region_data().next()", fillcolor="#ffffc0"];
    execute [label="6. stmts->region_statement()(pk, ...)", fillcolor="#ffffc0"];
    args [label="7. common_ops->insert_arg()\n   (for each argument)", fillcolor="#ffffc0"];
    sample [label="8. common_ops->maybe_insert_sample()\n   (timeline correlation)", fillcolor="#ffffc0"];
    commit [label="9. transaction_guard destructor\n   → COMMIT", fillcolor="#ffffc0"];

    start -> impl;
    impl -> dispatch;
    dispatch -> crtp;
    crtp -> insert_impl;

    insert_impl -> begin_tx;
    begin_tx -> validate;
    validate -> resolve;
    resolve -> event;
    event -> get_pk;
    get_pk -> execute;
    execute -> args;
    args -> sample;
    sample -> commit;
}