Snapshot WIP: solver HP epic progress, BPHX/HX physics, BMAD skill refresh.

Capture uncommitted solver robustness work (regularization, domain errors, linear solver lifecycle, tube DP/MSH), web workbench updates, and synced BMAD skills across IDE agent folders before starting BPHX pressure-drop.

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/components/drum.md

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+# Drum (separator / recirculation drum)
+
+Config type: `"Drum"`  
+Source: `crates/components/src/drum.rs`
+
+---
+
+## EN
+
+### Purpose & model
+
+Liquid/vapor **separator** used in flooded recirculation architectures. Splits a two-phase feed into liquid and vapor outlets; may accept an evaporator return.
+
+Thermodynamics: equilibrium separation at drum pressure (quality split toward x≈0 liquid / x≈1 vapor legs), mass and energy balances across ports.
+
+### Residuals & `n_equations()`
+
+Multi-port balance residuals (mass + energy + pressure consistency). Exact count depends on active ports and edge wiring; treat as a multi-equation node — see unit tests and `n_equations()` in source.
+
+### Ports (4-port naming)
+
+| Port | Role |
+|------|------|
+| `feed_inlet` | two-phase feed |
+| `evaporator_return` | return from flooded evaporator |
+| `liquid_outlet` | liquid to pump / recirculation |
+| `vapor_outlet` | vapor to compressor suction |
+
+### Calibration
+
+No primary Z-factor set; geometry/level control may be added in specialized builds.
+
+### JSON (main)
+
+| Key | Meaning | Default |
+|-----|---------|---------|
+| `fluid` / refrigerant | working fluid | primary |
+| level / volume options | if exposed | – |
+
+### System note
+
+A **flooded plate** topology is often Drum + recirculation + DX exchanger — not a mode of BPHX alone. Shell-and-tube flooded use `FloodedEvaporator`.
+
+---
+
+## FR
+
+### But & modèle
+
+**Ballon séparateur** liquide/vapeur pour architectures noyées / recirculation.
+
+### Ports
+
+Alimentation, retour évap, sortie liquide, sortie vapeur.
+
+### DoF
+
+Nœud multi-équations ; équilibrer avec le reste du circuit.
+
+### JSON
+
+Voir EN.