Comment/docstring cleanup only, no functional changes

- Fix stale claim in RustRuntime's doc: with skip_from_py_object, pyo3
  does not clone-extract the pyclass; callers clone explicitly.
- Fix changelog grammar and 'per-reactor' -> 'per-homeserver'.
- Fix garden-path sentence in runtime.pyi docstring.
- Minor punctuation fixes in new doc comments.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

changelog.d/20011.misc

@@ -1 +1 @@
-Refactor Rust code have a single place to store per-reactor state.
+Refactor the Rust code to have a single place to store per-homeserver state.

rust/src/homeserver.rs

@@ -23,7 +23,7 @@ use crate::runtime::RustRuntime;
 /// The Python `HomeServer`, as seen from Rust.
 ///
 /// Like [`crate::reactor::Reactor`], this is a typed facade over a foreign
-/// Python object: it does no validation of the object it wraps (the Python
+/// Python object. It does no validation of the object it wraps (the Python
 /// side is type-checked by mypy), but it is the single place that names the
 /// `HomeServer` API surface that Rust code depends on.
 pub struct HomeServer(Py<PyAny>);

rust/src/reactor.rs

@@ -19,7 +19,7 @@ use pyo3::{call::PyCallArgs, intern, prelude::*};
 
 /// The Twisted reactor, as seen from Rust.
 ///
-/// A typed facade over a foreign Python object: it does no validation of the
+/// A typed facade over a foreign Python object. It does no validation of the
 /// object it wraps (the Python side is type-checked by mypy), but it is the
 /// single place that names the Twisted API surface that Rust code depends
 /// on.

rust/src/runtime.rs

@@ -125,9 +125,8 @@ impl Drop for RustRuntimeInner {
 ///
 /// One instance is constructed per homeserver by
 /// `HomeServer.get_rust_runtime()`. Rust classes that need it take it as a
-/// constructor argument — pyo3 extracts a `#[pyclass]` that is `Clone` by
-/// cloning, which here is just an `Arc` refcount bump — and hold their own
-/// clone. Derefs to [`RustRuntimeInner`].
+/// constructor argument and store their own clone, which is just an `Arc`
+/// refcount bump. Derefs to [`RustRuntimeInner`].
 #[pyclass(frozen, skip_from_py_object)]
 #[derive(Clone)]
 pub struct RustRuntime {
@@ -154,7 +153,7 @@ impl RustRuntime {
         });
 
         // Shut the tokio runtime down when the reactor does. The trigger
-        // holds only a `Weak` reference: Twisted keeping the hook alive must
+        // holds only a `Weak` reference. Twisted keeping the hook alive must
         // not keep the runtime (nor, via it, the reactor) alive, as that
         // would be a reference cycle passing through a Rust field that
         // Python's GC cannot see into.

synapse/synapse_rust/runtime.pyi

@@ -5,7 +5,7 @@ class RustRuntime:
 
     Holds the tokio thread pool (started lazily on first use, shut down by a
     reactor shutdown trigger) and a handle to the reactor. Rust classes that
-    need either take this as a constructor argument; get it from
+    need them take this as a constructor argument. Get it from
     `hs.get_rust_runtime()`.
     """