Add diagram workbench UI with Modelica DoF coaching and ISO glyphs.

Ship the Next.js cycle editor with CAD chrome, technical HX symbols, Fixed/Free boundary guidance, and secondary water/air pressure drop support in the solver stack.

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

docs/modelica-boundary-proof.md

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+# Modelica Fixed/Free — sources consulted (Entropyk alignment)
+
+## Official MSL (fetched)
+
+1. **Package** `Modelica.Fluid.Sources`  
+   https://doc.modelica.org/om/Modelica.Fluid.Sources.html
+
+2. **`MassFlowSource_T`** — prescribed **mass flow + temperature** (not pressure)  
+   https://doc.modelica.org/om/Modelica.Fluid.Sources.MassFlowSource_T.html  
+
+   Quote from OpenModelica HTML (fetched 2026-07-17):
+
+   > Models an ideal flow source, with prescribed values of flow rate, temperature…  
+   > - Prescribed mass flow rate.  
+   > - Prescribed temperature.
+
+   No “prescribed pressure” in the component description.
+
+3. **`Boundary_pT`** — prescribed **pressure + temperature** (not ṁ)  
+   https://doc.modelica.org/om/Modelica.Fluid.Sources.Boundary_pT.html  
+
+   Quote (fetched 2026-07-17):
+
+   > - Prescribed boundary pressure.  
+   > - Prescribed boundary temperature.
+
+4. **Context7** `/modelica/modelicastandardlibrary` — `SimplePipeline` example:
+
+   `Boundary_pT` → `StaticPipe` (wall friction / ΔP) → `Boundary_pT`  
+
+   Double Fixed P is legal **only** with hydraulic resistance between the ends.
+   An isobaric secondary path must **not** Fixed-P both ends.
+
+## Community
+
+Rene Just Nielsen — legal pipe-end combinations:  
+https://stackoverflow.com/questions/79349553/how-pressure-and-flow-ports-are-different-in-modelica
+
+| Inlet | Outlet | OK? |
+|-------|--------|-----|
+| Boundary_pT | Boundary_pT | Yes → ṁ from ΔP |
+| Boundary_pT | MassFlowSource_T | Yes |
+| MassFlowSource_T | Boundary_pT | Yes |
+| MassFlowSource_T | MassFlowSource_T | **No** |
+
+Quote: *“There is no boundary component specifying both mass flow rate and pressure.”*
+
+## Entropyk mapping
+
+| Mode | Source | Sink | HX secondary |
+|------|--------|------|--------------|
+| MassFlowSource_T (default) | Fixed T, Fixed ṁ, **Free P** | Fixed P (anchor), Free T_out | `P_out−P_in+ΔP_sec(ṁ)=0` |
+| Boundary_pT + friction | Fixed P, Fixed T, Free ṁ | Fixed P | Needs frictional ΔP (pipe / HX) |
+| T_out rating | Free ṁ, Free P | Fixed P + Fixed T_out | Same secondary momentum |
+
+Secondary water ΔP (quadratic, Modelica `dp_nominal` style):
+`secondary_rated_pressure_drop_pa` + `secondary_rated_m_flow_kg_s`
+— **not** refrigerant `dp_model=msh` (tube two-phase only).
+
+### Why HX secondary isobaric P was missing (bug)
+
+Entropyk stores **two edges** on a water loop (`source→HX`, `HX→sink`), each with its own `P`.  
+Without `P_out − P_in = 0` on the HX, Free P on the source left `P_in` unconstrained → DoF under by 1 per loop.
+
+Modelica closes that via the connection/pipe graph; Entropyk now closes it on Condenser / Evaporator / FloodedEvaporator secondary residuals.
+
+Implementation:
+
+- UI: `apps/web/src/lib/boundaryFix.ts`
+- Components: `condenser.rs`, `evaporator.rs`, `flooded_evaporator.rs` (`n_secondary` + residuals)
+- Ledger: `apps/web/src/lib/dofLedger.ts`