Render R2: persist named render setups without re-evaluating geometry (#667)

render.settings.set saves validated named render setups (camera, output size, exposure, environment) as one undo step, and render.settings.get reads them back without applying a camera. When validated render settings are the only change, the engine keeps the evaluated model instead of rebuilding it. Setups are saved under design format 21; format-20 designs read as having none. Fixes #658; refs #620.

Contributed by @0xlillith.

Co-authored-by: lillith <35337584+0xlillith@users.noreply.github.com>

crates/engine/src/cmd/render.rs

@@ -1,15 +1,75 @@
-//! Render capability discovery. No rendering, host probing or document mutation occurs here.
+//! Render capability discovery and persistent intent. No rendering or host probing.
 
+use std::sync::Arc;
+
+use serde::Deserialize;
 use serde_json::{Value, json};
+use solidcraft_doc::render_settings::{RenderSettings, RenderSetup};
 
 use super::CommandSpec;
 use crate::params::bad;
 use crate::{Result, Session};
 
-pub static COMMANDS: &[CommandSpec] = &[CommandSpec::new("render.backends", "Render Backends", backends)
+pub static COMMANDS: &[CommandSpec] = &[
+CommandSpec::new("render.backends", "Render Backends", backends)
     .noundo()
     .doc_only()
-    .params("No parameters. Returns {schema_version: 1, default_backend: builtin, backends: [{id, label, availability, executors: [{id, availability, profiles, limits, scratch}]}]}. Metadata only; does not start rendering or probe a GPU. See docs/render-backends.md")];
+    .params("No parameters. Returns {schema_version: 1, default_backend: builtin, backends: [{id, label, availability, executors: [{id, availability, profiles, limits, scratch}]}]}. Metadata only; does not start rendering or probe a GPU. See docs/render-backends.md"),
+CommandSpec::new("render.settings.get", "Render Settings", get_settings).noundo().doc_only()
+    .params("name?: saved setup. Without name returns {setups, defaults}; with name returns {name, setup}. Does not evaluate the model or apply a camera. See docs/render-settings.md"),
+CommandSpec::new("render.settings.set", "Save Render Settings", set_settings).doc_only()
+    .params("name: setup name, set: object of fields to replace (backend, mode, camera, width, height, format, exposure_ev, environment_rotation, environment_intensity, background). Creates from defaults, validates atomically, one undo step; identical edits are no-ops. See docs/render-settings.md"),
+];
+
+#[derive(Deserialize)]
+#[serde(deny_unknown_fields)]
+struct GetSettings {
+    name: Option<String>,
+}
+
+fn get_settings(s: &mut Session, params: &Value) -> Result<Value> {
+    let cmd = "render.settings.get";
+    let request: GetSettings = serde_json::from_value(params.clone()).map_err(|e| bad(cmd, e.to_string()))?;
+    match request.name {
+        None => Ok(json!({"setups": s.doc.render.setups, "defaults": RenderSetup::default()})),
+        Some(name) => {
+            RenderSettings::validate_name(&name).map_err(|e| bad(cmd, e.to_string()))?;
+            let setup = s.doc.render.setups.get(&name).ok_or_else(|| bad(cmd, "no saved render setup with that name"))?;
+            Ok(json!({"name": name, "setup": setup}))
+        }
+    }
+}
+
+#[derive(Deserialize)]
+#[serde(deny_unknown_fields)]
+struct SetSettings {
+    name: String,
+    set: Value,
+}
+
+fn set_settings(s: &mut Session, params: &Value) -> Result<Value> {
+    let cmd = "render.settings.set";
+    let request: SetSettings = serde_json::from_value(params.clone()).map_err(|e| bad(cmd, e.to_string()))?;
+    RenderSettings::validate_name(&request.name).map_err(|e| bad(cmd, e.to_string()))?;
+    let patch = request.set.as_object().filter(|p| p.len() <= 10).ok_or_else(|| bad(cmd, "`set` must be an object with at most 10 fields"))?;
+    let current = s.doc.render.setups.get(&request.name).cloned().unwrap_or_default();
+    let mut value = serde_json::to_value(&current).map_err(|e| bad(cmd, e.to_string()))?;
+    let object = value.as_object_mut().ok_or_else(|| bad(cmd, "invalid render setup"))?;
+    for (key, value) in patch {
+        object.insert(key.clone(), value.clone());
+    }
+    let setup: RenderSetup = serde_json::from_value(value).map_err(|e| bad(cmd, e.to_string()))?;
+    setup.validate().map_err(|e| bad(cmd, e.to_string()))?;
+    let reply = json!({"name": request.name, "setup": setup});
+    if s.doc.render.setups.get(&request.name) == Some(&setup) {
+        return Ok(reply);
+    }
+    let mut settings = (*s.doc.render).clone();
+    settings.setups.insert(request.name, setup);
+    settings.validate().map_err(|e| bad(cmd, e.to_string()))?;
+    s.doc_mut().render = Arc::new(settings);
+    Ok(reply)
+}
 
 fn backends(_: &mut Session, params: &Value) -> Result<Value> {
     if !params.as_object().is_some_and(|p| p.is_empty()) {
@@ -89,3 +149,6 @@ mod tests {
         assert_eq!(s.evaluations, 0);
     }
 }
+
+#[cfg(test)]
+mod settings_tests;