Fix bugs from 5-2 code review

crates/components/src/lib.rs

@@ -59,6 +59,8 @@ pub mod compressor;
 pub mod expansion_valve;
 pub mod external_model;
 pub mod fan;
+pub mod flow_boundary;
+pub mod flow_junction;
 pub mod heat_exchanger;
 pub mod pipe;
 pub mod polynomials;
@@ -84,6 +86,14 @@ pub use polynomials::{AffinityLaws, PerformanceCurves, Polynomial1D, Polynomial2
 pub use port::{
     validate_port_continuity, Connected, ConnectedPort, ConnectionError, Disconnected, FluidId, Port,
 };
+pub use flow_boundary::{
+    CompressibleSink, CompressibleSource, FlowSink, FlowSource,
+    IncompressibleSink, IncompressibleSource,
+};
+pub use flow_junction::{
+    CompressibleMerger, CompressibleSplitter, FlowMerger, FlowSplitter, FluidKind,
+    IncompressibleMerger, IncompressibleSplitter,
+};
 pub use pump::{Pump, PumpCurves};
 pub use state_machine::{
     CircuitId, OperationalState, StateHistory, StateManageable, StateTransitionError,
@@ -499,6 +509,39 @@ pub trait Component {
     /// assert!(component.get_ports().is_empty());
     /// ```
     fn get_ports(&self) -> &[ConnectedPort];
+
+    /// Injects system-level context into a component during topology finalization.
+    ///
+    /// Called by [`System::finalize()`] after all edge state indices are computed.
+    /// The default implementation is a no-op; override this in components that need
+    /// to know their position in the global state vector (e.g. `MacroComponent`).
+    ///
+    /// # Arguments
+    ///
+    /// * `state_offset` — The index in the global state vector where this component's
+    ///   *internal* state block begins.  For ordinary leaf components this is never
+    ///   needed; for `MacroComponent` it replaces the manual `set_global_state_offset`
+    ///   call.
+    /// * `external_edge_state_indices` — A slice of `(p_idx, h_idx)` pairs for every
+    ///   edge incident to this component's node in the parent graph (incoming and
+    ///   outgoing), in traversal order.  `MacroComponent` uses these to emit
+    ///   port-coupling residuals.
+    fn set_system_context(
+        &mut self,
+        _state_offset: usize,
+        _external_edge_state_indices: &[(usize, usize)],
+    ) {
+        // Default: no-op for all ordinary leaf components.
+    }
+
+    /// Returns the number of internal state variables this component maintains.
+    ///
+    /// The default implementation returns 0, which is correct for all ordinary
+    /// leaf components. Hierarchical components (like `MacroComponent`) should
+    /// override this to return the size of their internal state block.
+    fn internal_state_len(&self) -> usize {
+        0
+    }
 }
 
 #[cfg(test)]