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 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

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]