Fix bugs from 5-2 code review

_bmad-output/planning-artifacts/epics.md

@@ -112,6 +112,14 @@ This document provides the complete epic and story breakdown for Entropyk, decom
 
 **FR47:** Each refrigeration component natively exposes a complete thermodynamic state (Pressure, Temperature, T_sat, Quality, Superheat, Subcooling, Mass flow, Reynolds, Enthalpy, Entropy) easily accessible without complex recalculations.
 
+**FR48:** Hierarchical Subsystems (MacroComponents) - encapsulate complete systems into reusable blocks
+
+**FR49:** Flow Junctions (FlowSplitter 1→N, FlowMerger N→1) for compressible & incompressible fluids
+
+**FR50:** Boundary Conditions (FlowSource, FlowSink) for compressible & incompressible fluids
+
+**FR51:** Swappable Calibration Variables - swap calibration factors (f_m, f_ua, f_power, etc.) into solver unknowns and measured values (Tsat, capacity, power) into constraints for one-shot inverse calibration
+
 ### NonFunctional Requirements
 
 **NFR1:** Steady State convergence time < **1 second** for standard cycle in Cold Start
@@ -252,6 +260,9 @@ This document provides the complete epic and story breakdown for Entropyk, decom
 | FR46 | Epic 1 | Air Coils (EvaporatorCoil, CondenserCoil) |
 | FR47 | Epic 2 | Rich Thermodynamic State Abstraction |
 | FR48 | Epic 3 | Hierarchical Subsystems (MacroComponents) |
+| FR49 | Epic 1 | Flow Junctions (FlowSplitter 1→N, FlowMerger N→1) for compressible & incompressible fluids |
+| FR50 | Epic 1 | Boundary Conditions (FlowSource, FlowSink) for compressible & incompressible fluids |
+| FR51 | Epic 5 | Swappable Calibration Variables (inverse calibration one-shot) |
 
 ## Epic List
 
@@ -260,7 +271,7 @@ This document provides the complete epic and story breakdown for Entropyk, decom
 
 **Innovation:** Trait-based "Lego" architecture to add Compressors, Pumps, VFDs, Pipes, etc.
 
-**FRs covered:** FR1, FR2, FR3, FR4, FR5, FR6, FR7, FR8, FR46
+**FRs covered:** FR1, FR2, FR3, FR4, FR5, FR6, FR7, FR8, FR46, FR49, FR50
 
 ---
 
@@ -296,7 +307,7 @@ This document provides the complete epic and story breakdown for Entropyk, decom
 
 **Innovation:** Native Inverse Control via Residual Embedding - "One-Shot".
 
-**FRs covered:** FR22, FR23, FR24
+**FRs covered:** FR22, FR23, FR24, FR51
 
 ---
 
@@ -453,7 +464,58 @@ This document provides the complete epic and story breakdown for Entropyk, decom
 
 ---
 
-## Epic 2: Fluid Properties Backend
+### Story 1.11: Flow Junctions — FlowSplitter & FlowMerger
+
+**As a** system modeler,  
+**I want** `FlowSplitter` (1 inlet → N outlets) and `FlowMerger` (N inlets → 1 outlet) components,  
+**So that** I can build parallel branches in hydraulic and refrigerant circuits without manually writing junction equations.
+
+**Status:** ✅ Done (2026-02-20)
+
+**FRs covered:** FR49
+
+**Acceptance Criteria:**
+
+**Given** a refrigerant or water circuit with parallel branches  
+**When** I instantiate `FlowSplitter::compressible("R410A", inlet, vec![out_a, out_b])`  
+**Then** the splitter contributes `2N−1` equations (isobaric + isenthalpic constraints)  
+**And** validation rejects incompatible fluid types (`::incompressible` rejects refrigerants)  
+**And** `FlowMerger` contributes `N+1` equations with weighted enthalpy mixing via `with_mass_flows`  
+**And** both implement `Box<dyn Component>` (object-safe)  
+**And** type aliases `Incompressible/CompressibleSplitter` and `Incompressible/CompressibleMerger` are available
+
+**Implementation:**
+- `crates/components/src/flow_junction.rs` — `FlowSplitter`, `FlowMerger`, `FluidKind`
+- 16 unit tests passing
+
+---
+
+### Story 1.12: Boundary Conditions — FlowSource & FlowSink
+
+**As a** simulation user,  
+**I want** `FlowSource` and `FlowSink` boundary condition components,  
+**So that** I can define the entry and exit points of a fluid circuit without manually managing pressure and enthalpy constraints.
+
+**Status:** ✅ Done (2026-02-20)
+
+**FRs covered:** FR50
+
+**Acceptance Criteria:**
+
+**Given** a fluid circuit with an entry point  
+**When** I instantiate `FlowSource::incompressible("Water", 3.0e5, 63_000.0, port)`  
+**Then** the source imposes `P_edge − P_set = 0` and `h_edge − h_set = 0` (2 equations)  
+**And** `FlowSink::incompressible("Water", 1.5e5, None, port)` imposes a back-pressure (1 equation)  
+**And** `FlowSink` with `Some(h_back)` adds a second enthalpy constraint (2 equations)  
+**And** `set_return_enthalpy` / `clear_return_enthalpy` toggle the second equation dynamically  
+**And** validation rejects incompatible fluid + constructor combinations  
+**And** type aliases `Incompressible/CompressibleSource` and `Incompressible/CompressibleSink` are available
+
+**Implementation:**
+- `crates/components/src/flow_boundary.rs` — `FlowSource`, `FlowSink`
+- 17 unit tests passing
+
+---
 
 ### Story 2.1: Fluid Backend Trait Abstraction
 
@@ -884,6 +946,69 @@ This document provides the complete epic and story breakdown for Entropyk, decom
 
 ---
 
+### Story 5.5: Swappable Calibration Variables (Inverse Calibration One-Shot)
+
+**As a** R&D engineer calibrating a machine model against test bench data,
+**I want** to swap calibration coefficients (f_m, f_ua, f_power, etc.) into unknowns and measured values (Tsat, capacity, power) into constraints,
+**So that** the solver directly computes the calibration coefficients in one shot without external optimizer.
+
+**Context:** Each component has specific calibration factors. In normal simulation, f_ is fixed and outputs are computed. In calibration mode, measured values become constraints and f_ become unknowns.
+
+**Component → Calibration Factor Mapping:**
+
+| Component | f_ Factors | Measurable Values (can swap) |
+|-----------|------------|------------------------------|
+| Condenser | f_ua, f_dp | Tsat_cond, Q_cond (capacity), ΔP_cond |
+| Evaporator | f_ua, f_dp | Tsat_evap, Q_evap (capacity), ΔP_evap |
+| Compressor | f_m, f_power, f_etav | ṁ, Power, η_v |
+| Expansion Valve | f_m | ṁ |
+| Pipe | f_dp | ΔP |
+
+**Acceptance Criteria:**
+
+**Given** a Condenser with f_ua as calibration factor
+**When** I enable calibration mode and fix Tsat_cond to measured value
+**Then** f_ua becomes an unknown in solver state vector
+**And** residual added: Tsat_cond_computed - Tsat_cond_measured = 0
+**And** solver computes f_ua directly
+
+**Given** an Evaporator with f_ua as calibration factor
+**When** I enable calibration mode and fix Tsat_evap to measured value
+**Then** same swap mechanism: f_ua → unknown, Tsat_evap → constraint
+
+**Given** a Compressor with f_power as calibration factor
+**When** I enable calibration mode and fix Power to measured value
+**Then** f_power becomes unknown
+**And** residual: Power_computed - Power_measured = 0
+
+**Given** a Compressor with f_m as calibration factor
+**When** I enable calibration mode and fix mass flow ṁ to measured value
+**Then** f_m becomes unknown
+**And** residual: ṁ_computed - ṁ_measured = 0
+
+**Given** a machine in cooling mode calibration
+**When** I impose evaporator cooling capacity Q_evap_measured
+**Then** Q_evap becomes constraint (Q_evap_computed - Q_evap_measured = 0)
+**And** corresponding f_ (typically f_ua on evaporator) becomes unknown
+
+**Given** a machine in heating mode calibration
+**When** I impose condenser heating capacity Q_cond_measured
+**Then** Q_cond becomes constraint
+**And** corresponding f_ (typically f_ua on condenser) becomes unknown
+
+**Given** multiple calibration swaps on same system
+**When** solver runs
+**Then** all f_ unknowns solved simultaneously with cycle equations (One-Shot)
+**And** Jacobian includes ∂constraint/∂f_ partial derivatives
+**And** DoF validated: (equations + calibration_constraints) = (unknowns + swapped_f_factors)
+
+**Given** a calibration swap configuration
+**When** serializing system to JSON
+**Then** swap state persisted (which f_ are unknowns, which values are fixed)
+**And** deserialization restores exact calibration mode
+
+---
+
 ## Epic 6: Multi-Platform APIs
 
 ### Story 6.1: Rust Native API