sdk, agent: review fixes (T18R)

- The serve loop ends the process after EOF or exit_after_response,
  also with background tasks or listeners.
- One schema generator per direction for the whole document, so types
  with the same name get distinct names.
- The agent gives the complete error (code, message, data) to the
  model, writes SKIP only after a successful request, caps tool output
  at 64 KiB, writes each history line in one write, and skips a damaged
  line.
- Endpoints skip blank and non-RPC lines. client_rs does not panic.
- #[must_use] on builders and the lock guard; #[schemars] attributes
  and duplicate hooks are compile errors; raw identifiers; -32000 for
  local SDK errors; x-sausage-params only for methods with params.

sdk/src/calls.rs

@@ -1,6 +1,7 @@
 //! Outgoing core calls and notification callbacks.
 use super::*;
 /// An outgoing request builder.
+#[must_use = "await the call to send it"]
 pub struct Call {
     method: String,
     params: Value,
@@ -43,7 +44,7 @@ impl IntoFuture for Call {
                 let mut s = s.borrow_mut();
                 if !s.active || s.stopping {
                     return Err(Error::new(
-                        -32002,
+                        -32000,
                         "no core transport (or stdin reached EOF)",
                     ));
                 }
@@ -72,7 +73,7 @@ impl IntoFuture for Call {
                 return Err(e);
             }
             rx.await
-                .unwrap_or_else(|_| Err(Error::new(-32002, "core transport closed")))
+                .unwrap_or_else(|_| Err(Error::new(-32000, "core transport closed")))
         })
     }
 }