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/imports.rs

@@ -14,6 +14,7 @@ pub struct Import {
 inventory::collect!(Import);
 
 /// An outgoing call whose result decodes to a generated Rust type.
+#[must_use = "await the call to send it"]
 pub struct TypedCall<T> {
     call: Call,
     result: PhantomData<T>,