# Entropyk Model IR (unified schema)

Entropyk uses **one declarative Model IR** — a schema-versioned JSON document —
as the single source of truth shared by the CLI, the web UI, and (once present)
the Python and WASM bindings. There is no divergent per-frontend schema: the web
graph editor serializes to the same document the CLI loads.

The IR is defined by the Rust types in [`crates/cli/src/config.rs`](../crates/cli/src/config.rs).
The machine-readable JSON Schema is **generated from those types** (via `schemars`)
so it can never drift from what the loader accepts.

## Getting the schema

```bash
# Print the canonical JSON Schema (draft-07) to stdout
cargo run -p entropyk-cli -- schema

# …or write it to a file (the committed copy lives at docs/model-ir.schema.json)
cargo run -p entropyk-cli -- schema --output docs/model-ir.schema.json
```

External tools and the UI can validate documents against
[`model-ir.schema.json`](./model-ir.schema.json).

## Versioning

Every document carries a `schema_version`. This lets the schema — and any embedded
standard/norm references (SEER/SCOP/IPLV/NPLV) — evolve without silently
misreading older files.

| `schema_version` | Meaning |
| ---------------- | ------- |
| absent           | Treated as `"1"` (legacy). |
| `"1"`            | Flat `circuits` / `components` / `edges` graph. |
| `"2"`            | Adds `controls`, `subsystems`, `instances`, `connections`. |

The loader accepts every version listed in `SUPPORTED_SCHEMA_VERSIONS`
(currently `1`, `2`) and rejects anything else with a clear error. `v1` documents
load unchanged — the new fields are all optional and default to empty.

## Top-level fields

```jsonc
{
  "schema_version": "2",
  "fluid": "R134a",
  "fluid_backend": "CoolProp",

  "circuits":    [ /* flat refrigerant loops (v1) */ ],
  "thermal_couplings": [ /* inter-circuit UA links (v1) */ ],

  "subsystems":  { /* reusable parameterized templates (v2) */ },
  "instances":   [ /* template instantiations (v2) */ ],
  "connections": [ /* external edges between instance ports (v2) */ ],

  "controls":    [ /* co-solved steady-state control loops (v2) */ ],

  "solver": { "strategy": "fallback", "max_iterations": 300, "tolerance": 1e-6 }
}
```

### `subsystems` + `instances` (hierarchical templates)

A `SubsystemTemplate` is a parameterized assembly of components and internal
edges, exposing a reduced set of external `ports`. It is declared once and
instantiated any number of times. At **load time** each instance is *flattened*
into the flat `circuits/components/edges` graph — the solver never sees the
hierarchy — with component names prefixed `"{instance}."`.

Parameter substitution: any component parameter whose value is a string `"$name"`
is replaced by the resolved parameter (instance override → template default).
Because `ua`, `secondary_*`, `isentropic_efficiency`, `t_cond_k`, … all flow
through the component parameter catch-all, essentially every physical knob is
parameterizable.

```jsonc
"subsystems": {
  "EmergentCircuit": {
    "params": { "ua_cond": 766.0, "ua_evap": 1468.0 },
    "components": [
      { "type": "IsentropicCompressor", "name": "comp", "isentropic_efficiency": 0.7 },
      { "type": "Condenser", "name": "cond", "ua": "$ua_cond" },
      { "type": "IsenthalpicExpansionValve", "name": "exv" },
      { "type": "Evaporator", "name": "evap", "ua": "$ua_evap" }
    ],
    "edges": [
      { "from": "comp:outlet", "to": "cond:inlet" },
      { "from": "cond:outlet", "to": "exv:inlet" },
      { "from": "exv:outlet", "to": "evap:inlet" },
      { "from": "evap:outlet", "to": "comp:inlet" }
    ],
    "ports": { "suction": "evap:outlet", "discharge": "comp:outlet" }
  }
},
"instances": [
  { "of": "EmergentCircuit", "name": "A", "circuit": 0, "params": { "ua_cond": 766.0 } },
  { "of": "EmergentCircuit", "name": "B", "circuit": 1, "params": { "ua_cond": 900.0 } }
]
```

This unlocks multi-circuit machines (e.g. 61XW `System_2C`, multi-module 61AQ):
define the circuit once, instantiate `A`/`B` with different parameters. See
[`crates/cli/examples/chiller_2circuit_subsystems.json`](../crates/cli/examples/chiller_2circuit_subsystems.json).

`connections` wire external ports together (or literal `component:port` endpoints):

```jsonc
"connections": [ { "from": "A.discharge", "to": "B.suction" } ]
```

### `controls` (co-solved steady-state control loops)

Each control loop is solved **inside the same Newton system** as the physics — no
time integration. A `SaturatedController` is a saturated-PI loop with exact
anti-windup that drives a measured plant output (`measure`) to `target` by
manipulating an actuator factor (`actuator`) within `[min, max]`.

```jsonc
"controls": [
  {
    "type": "SaturatedController",
    "id": "evap_capacity",
    "measure":  { "component": "evap", "output": "capacity" },
    "actuator": { "component": "comp", "factor": "z_flow", "initial": 1.0, "min": 0.5, "max": 1.5 },
    "target": 7000.0,
    "gain": 0.01,
    "band": 1.0
  }
]
```

Measurable outputs: `capacity`, `heatTransferRate`, `superheat`, `subcooling`,
`saturationTemperature`, `massFlowRate`, `pressure`, `temperature`.
Actuator Z-factors (canonical): `z_flow`, `z_dp`, `z_ua`, `z_power`, `z_etav`
(BOLT equivalents: `Z_flow_suc`, `Z_dpc`, `Z_UA`, `Z_power`; legacy `f_*` names still accepted).

When an instance is involved, reference the prefixed name, e.g.
`"component": "A.evap"`. See
[`crates/cli/examples/chiller_r134a_capacity_control.json`](../crates/cli/examples/chiller_r134a_capacity_control.json).

## One IR, every frontend

- **CLI** — `entropyk-cli run|validate|rate|scop|seer …` load this IR directly.
- **Web UI** (`apps/web`) — the React-Flow graph serializes to this exact IR via
  `buildScenarioConfig` (`apps/web/src/lib/configBuilder.ts`); it emits
  `schema_version` from the shared `SCHEMA_VERSION` constant.
- **Python / WASM bindings** — consume the same JSON document, no separate schema.