Design for PowerFlow and PhasorDynamics Interoperability

GridKit/Model/PhasorDynamics/STATE.md

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+# State Input Format
+
+A representation of the models state from which it can be initialized. This decouples the model definition from the model state.
+
+In addition to making model initialization easier, it also lets us seperate the case from the dispatch. With one canonical `texas.case.json` we might have multiple operating points provided in `examples/`:
+- `texas-summer2025.state.json`
+- `texas-winter2025.state.json`
+- `texas-summer2026.state.json`
+
+For example `texas-summer2025.state.json` might be structured as:
+
+```json
+"header":{
+    ...
+},
+"buses":{
+    ...
+},
+"devices":{
+    ...
+}
+```
+
+Inside the `buses` and `devices` the relevant boundary states needed for intiailziation are given for each component. Then Model initialization at a higher or lower fidelity `PowerFlow`$\leftrightarrow$ `PhasorDynamics`$\leftrightarrow$ `EMT` requires no direct API.
+
+## Bus
+
+### RMS State (PowerFlow & PhasorDynamics)
+
+RMS state initialization/storage is written with real and imaginary parts:
+
+```json
+"bus_id_2533":{
+    "vr": 0.9289638822595822,
+    "vi": -0.39534548980249884,
+    "injections": {
+        "6533_C":{
+            "ir": 13.185009956359863,
+            "ii": 0.785739004611969
+        },
+        "6533_G":{
+            "ir": 12.132010459899902,
+            "ii": 0.785739004611969
+        }
+    }
+},
+```
+
+### ABC State (EMT)
+
+EMT should support balanced initialization (see previous section) but also unbalanced initialization, which would require higher fidelity. This would also specifiy branch injections for distirbuted network models.
+
+```json
+"bus_id_2533":{
+    "va": 0.9289638822595822,
+    "vb": -0.39534548980249884,
+    "vc": -0.39534548980249884,
+    "injections": {
+        "gen_325":{
+            "ia": 13.185009956359863,
+            "ib": 0.785739004611969,
+            "ic": 0.785739004611969
+        },
+        "branch_6533":{
+            "ia": 13.185009956359863,
+            "ib": 0.785739004611969,
+            "ic": 0.785739004611969
+        }
+    }
+},
+```
+
+## Devices
+
+This is where we store stateful information like connectivity and dispatch, which can be shared across all domains (PowerFlow & PhasorDynamics & EMT). This would also let us specify non steady state initialziations with `"omega": 0.0`
+
+
+```json
+"gen_id_2":{
+    "online": true,
+    "p": 55,
+    "q": -12
+}
+"br_id_2":{
+    "open": false,
+    "tap": 1,
+    "phase": 0
+}
+```
+
+
+# Migration
+
+`Bus`:
+- Remove the `init` fields from `Bus` in the `INPUT_FORMAT.md`
+- make an interface `setVr(..)` and `setVi(..)`.
+
+`Branch`:
+- Remove `tap` and `phase` as parameters
+- make an interface `setTap(..)` and `setPhase(..)`.
+- add `setOpen(..)` interface
+
+`LoadZIP`, `GENROU`, `GENSAL`, `GenClassical`:
+- Remove `p0` and `q0` as parameters
+- make an interface `setP(..)` and `setQ(..)`.
+- add `setOnline(..)` interface