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/tests/ui/hooks.rs

@@ -0,0 +1,22 @@
+use sausage_plugin::{rpc, on_stop, on_retired, Result};
+struct Stops;
+#[rpc]
+impl Stops {
+    /// First stop hook.
+    #[on_stop]
+    fn a(&self) {}
+    /// Second stop hook.
+    #[on_stop]
+    fn b(&self) {}
+}
+struct Retires;
+#[rpc]
+impl Retires {
+    /// First retired hook.
+    #[on_retired]
+    fn a(&self) -> Result<()> { Ok(()) }
+    /// Second retired hook.
+    #[on_retired]
+    fn b(&self) -> Result<()> { Ok(()) }
+}
+fn main() {}

sdk/tests/ui/hooks.stderr

@@ -0,0 +1,19 @@
+error: only one on_stop method is allowed
+ --> tests/ui/hooks.rs:8:5
+  |
+8 |     /// Second stop hook.
+  |     ^^^^^^^^^^^^^^^^^^^^^
+
+error: only one on_retired method is allowed
+  --> tests/ui/hooks.rs:18:5
+   |
+18 |     /// Second retired hook.
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^
+
+warning: unused imports: `Result`, `on_retired`, and `on_stop`
+ --> tests/ui/hooks.rs:1:27
+  |
+1 | use sausage_plugin::{rpc, on_stop, on_retired, Result};
+  |                           ^^^^^^^  ^^^^^^^^^^  ^^^^^^
+  |
+  = note: `#[warn(unused_imports)]` (part of `#[warn(unused)]`) on by default

sdk/tests/ui/must_use.rs

@@ -0,0 +1,11 @@
+#![deny(unused_must_use)]
+use sausage_plugin::{call, lock, Endpoint, Guard, TypedCall};
+fn builders(endpoint: Endpoint) {
+    call("p.m", ());
+    TypedCall::<()>::new(call("p.m", ()));
+    lock("/state/file");
+    endpoint.call::<()>("m", ());
+}
+fn guard(g: Guard) -> Guard { g }
+fn dropped(g: Guard) { guard(g); }
+fn main() {}

sdk/tests/ui/must_use.stderr

@@ -0,0 +1,64 @@
+error: unused `Call` that must be used
+ --> tests/ui/must_use.rs:4:5
+  |
+4 |     call("p.m", ());
+  |     ^^^^^^^^^^^^^^^
+  |
+  = note: await the call to send it
+note: the lint level is defined here
+ --> tests/ui/must_use.rs:1:9
+  |
+1 | #![deny(unused_must_use)]
+  |         ^^^^^^^^^^^^^^^
+help: use `let _ = ...` to ignore the resulting value
+  |
+4 |     let _ = call("p.m", ());
+  |     +++++++
+
+error: unused `TypedCall` that must be used
+ --> tests/ui/must_use.rs:5:5
+  |
+5 |     TypedCall::<()>::new(call("p.m", ()));
+  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+  |
+  = note: await the call to send it
+help: use `let _ = ...` to ignore the resulting value
+  |
+5 |     let _ = TypedCall::<()>::new(call("p.m", ()));
+  |     +++++++
+
+error: unused `Lock` that must be used
+ --> tests/ui/must_use.rs:6:5
+  |
+6 |     lock("/state/file");
+  |     ^^^^^^^^^^^^^^^^^^^
+  |
+  = note: await the lock to acquire it
+help: use `let _ = ...` to ignore the resulting value
+  |
+6 |     let _ = lock("/state/file");
+  |     +++++++
+
+error: unused `EndpointCall` that must be used
+ --> tests/ui/must_use.rs:7:5
+  |
+7 |     endpoint.call::<()>("m", ());
+  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+  |
+  = note: await the endpoint call to send it
+help: use `let _ = ...` to ignore the resulting value
+  |
+7 |     let _ = endpoint.call::<()>("m", ());
+  |     +++++++
+
+error: unused `Guard` that must be used
+  --> tests/ui/must_use.rs:10:24
+   |
+10 | fn dropped(g: Guard) { guard(g); }
+   |                        ^^^^^^^^
+   |
+   = note: bind the guard to hold the lock
+help: use `let _ = ...` to ignore the resulting value
+   |
+10 | fn dropped(g: Guard) { let _ = guard(g); }
+   |                        +++++++

sdk/tests/ui/params.stderr

@@ -12,7 +12,7 @@ help: the trait `Params` is implemented for `sausage_plugin::Empty`
 note: required by a bound in `sausage_plugin::method`
  --> src/discovery.rs
   |
-  | pub fn method<P: Params, R: SchemaType>(doc: &mut Value, name: &str, docs: &str) {
+  | pub fn method<P: Params, R: SchemaType>(doc: &mut Discovery, name: &str, docs: &str) {
   |                  ^^^^^^ required by this bound in `method`
 
 error[E0277]: RPC params must be a #[schema] struct with named fields

sdk/tests/ui/schemars.rs

@@ -0,0 +1,9 @@
+use sausage_plugin::schema;
+/// A documented object.
+#[schema]
+struct Object {
+    /// A documented field.
+    #[schemars(with = "std::collections::HashMap<String, String>")]
+    value: String,
+}
+fn main() {}

sdk/tests/ui/schemars.stderr

@@ -0,0 +1,5 @@
+error: schemars attributes are outside the schema subset
+ --> tests/ui/schemars.rs:6:5
+  |
+6 |     #[schemars(with = "std::collections::HashMap<String, String>")]
+  |     ^