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/lib.rs

@@ -44,6 +44,8 @@
 //! [`listen`] publishes a declared interface at an endpoint file.
 //! [`connect`] verifies its owner before it returns an [`Endpoint`].
 //! Endpoint calls report progress through [`EndpointCall::on_notify`].
+//! Local transport errors use code -32000: no transport, stdin EOF, a closed endpoint,
+//! or an endpoint identity or interface mismatch. Code -32002 belongs to core process failures.
 //! Log with `eprintln!`. Stdout belongs to JSON-RPC.
 #![warn(missing_docs)]
 mod discovery;