mcp, cli: list each command's parameters as JSON Schema

CommandSpec::listing gives id, label, the parameter doc and the schema; MCP
list_commands, the control channel's engine.commands and the new
fieldcraft-cli commands --json use it.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

crates/engine/src/lib.rs

@@ -121,6 +121,19 @@ pub fn commands() -> &'static [CommandSpec] {
     cmd::ALL
 }
 
+impl CommandSpec {
+    /// The command as JSON for listings (`fieldcraft-cli commands --json`, the control channel's
+    /// `engine.commands`, MCP `list_commands`): id, label, the parameter doc and, when described,
+    /// the parameters as JSON Schema.
+    pub fn listing(&self) -> Value {
+        let mut v = serde_json::json!({"id": self.id, "label": self.label, "params": self.params});
+        if let Some(form) = self.form {
+            v["schema"] = schema::json_schema(form);
+        }
+        v
+    }
+}
+
 pub fn find_command(id: &str) -> Option<&'static CommandSpec> {
     commands().iter().find(|c| c.id == id)
 }

crates/mcp/src/backend.rs

@@ -98,7 +98,7 @@ impl Backend for Headless {
     }
 
     fn commands(&mut self) -> Result<Value, String> {
-        Ok(fieldcraft_engine::commands().iter().map(|c| json!({"id": c.id, "label": c.label, "params": c.params})).collect())
+        Ok(fieldcraft_engine::commands().iter().map(fieldcraft_engine::CommandSpec::listing).collect())
     }
 
     fn picture(&mut self, r: &PictureRequest) -> Result<Picture, String> {

crates/mcp/src/tests.rs

@@ -243,6 +243,9 @@ fn a_batch_stops_at_the_first_error() {
     assert_eq!(ok(&mut s, "inspect_model", json!({}))["model"]["nodes"], 0);
     let listed = ok(&mut s, "list_commands", json!({"filter": "SOLVE."}));
     assert!(listed.as_array().unwrap().iter().all(|c| c["id"].as_str().unwrap().starts_with("solve.")));
+    // Each command's parameters as JSON Schema, for agents to build valid calls.
+    let statics = listed.as_array().unwrap().iter().find(|c| c["id"] == "solve.static").unwrap();
+    assert_eq!(statics["schema"]["properties"]["threads"]["maximum"], 256);
 }
 
 #[test]

crates/ui-egui/src/control.rs

@@ -174,9 +174,7 @@ pub fn handle(app: &mut ModelApp, ctx: &egui::Context, req: &ControlRequest) ->
             let Some(steps) = p.get("commands") else { return err("missing `commands` (a list of {command, params})") };
             wrap(app.run_script(steps).map(|()| json!({"journal": app.session.journal.len()})))
         }
-        "engine.commands" => {
-            ok(Value::Array(fieldcraft_engine::commands().iter().map(|c| json!({"id": c.id, "label": c.label, "params": c.params})).collect()))
-        }
+        "engine.commands" => ok(Value::Array(fieldcraft_engine::commands().iter().map(fieldcraft_engine::CommandSpec::listing).collect())),
         "ui.inspect" => ok(json!({
             "ui": app.ui,
             "camera": app.cam,