phase 20e: consolidate handle traits into SharedHandle<T>

[JustinKovacich]

Collapses the three near-identical handle traits introduced in 19f / 20b / 20c into a single generic trait pair:

pub trait SharedHandle<T: 'static>: Clone + 'static {
    fn get(&self) -> &T;
}
pub trait WrappableSharedHandle<T: 'static>: SharedHandle<T> {
    fn wrap(value: T) -> Self;
}

Two blanket impls cover the alloc and no-alloc paths:

impl<T: 'static> SharedHandle<T> for &'static T { ... }
impl<T: 'static> SharedHandle<T> for Arc<T> { ... }   // alloc-gated
impl<T: 'static> WrappableSharedHandle<T> for Arc<T> { ... }   // alloc-gated

Deleted (each was a slot-specific copy of this same shape):

• SocketHandle / WrappableSocketHandle (transport.rs).
• SdStateHandle / WrappableSdStateHandle (server/sd_state.rs).
• EventPublisherHandle<R, S, H> / WrappableEventPublisherHandle<R, S, H> (server/event_publisher.rs).
• StaticSocketHandle<T> (the &'static T blanket impl subsumes its only purpose: carrying the 'static lifetime).

Net trait count: 6 + 1 wrapper struct → 2 traits. ~60% less boilerplate across the three former trait modules.

Server's three handle bounds become uniform:

• H: SharedHandle<F::Socket>
• Hsd: SharedHandle<SdStateManager>
• Hep: SharedHandle<EventPublisher<R, S, H, F::Socket>>

EventPublisher gains an explicit T: TransportSocket parameter — the price of carrying T as a generic on SharedHandle<T> rather than as an associated type. The struct grows a PhantomData<T> field so the type parameter is well-formed without affecting drop-check.

Method calls collapse to one name everywhere:

• H::socket() / Hsd::sd_state() / Hep::publisher() → .get() (consistent across all three slot types).

Default type-param expressions adjust to spell the T:

• Hep = Arc<EventPublisher<R, S, H, <F as TransportFactory>::Socket>>.

Test type-aliases gain the new T slot:

• tests/client_server.rs::TestEventPublisher
• event_publisher.rs::TestEventPublisher (internal)
• The AlwaysFailSocket regression-test type alias.

Pure rename / shape-change patch — no behavior change. The runtime behavior of every public API call is identical to 20d's; this is type-system tidying motivated by the adversarial review.

Adversarial-review observations addressed:

• "Three near-identical handle traits is a code smell" — fixed.
• "We didn't generalize this into a single Shared trait" — done.

Trade-off accepted: EventPublisher signature widens from <R, S, H> to <R, S, H, T>. The cost is one extra type parameter at the EventPublisher layer; the win is removing six trait definitions and one wrapper struct.

Gates green:

• cargo fmt --check
• cargo clippy --tests (2 pre-existing warnings, unrelated)
• cargo build --workspace --all-targets
• cargo build --no-default-features --features client,server,bare_metal
• cargo build -p simple-someip-embassy-net --target thumbv7em-none-eabihf
• cargo test --features client-tokio,server-tokio --test client_server -- --test-threads=1 (11/11)
• cargo test --features client,server,bare_metal --test bare_metal_e2e (2/2)
• cargo test -p simple-someip-embassy-net --test loopback (3/3)

[Copilot]

Pull request overview

This PR consolidates the server-side “shared handle” abstractions into a single generic SharedHandle<T> / WrappableSharedHandle<T> pair, replacing the prior slot-specific handle traits and updating Server/EventPublisher generics and call sites to use a uniform .get() accessor.

Changes:

• Introduces SharedHandle<T> + WrappableSharedHandle<T> with blanket impls for &'static T and (alloc-gated) Arc<T>.
• Updates Server and EventPublisher to use the unified handle traits (including widening EventPublisher to carry an explicit socket type parameter T).
• Adjusts test type aliases to the new EventPublisher<..., T> signature.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
tests/client_server.rs	Updates TestEventPublisher alias to include the new socket type parameter.
src/transport.rs	Adds SharedHandle<T>/WrappableSharedHandle<T> and removes SocketHandle/StaticSocketHandle boilerplate.
src/server/sd_state.rs	Removes SD-state-specific handle traits in favor of SharedHandle<SdStateManager>.
src/server/mod.rs	Updates Server bounds/defaults and replaces .socket()/.sd_state() call sites with .get().
src/server/event_publisher.rs	Widens EventPublisher generics to include socket type T, switches to SharedHandle<T>, and removes publisher-specific handle traits.

Comments suppressed due to low confidence (1)

src/transport.rs:892

• This module-level doc comment still mentions SocketHandle, which was removed in favor of SharedHandle<T>. Please update the list of traits/types covered by std_handle_impls so it reflects the current handle traits (or drop the SocketHandle mention if SharedHandle is now provided via blanket impls outside this module).

/// Default `std`-flavoured impls of [`E2ERegistryHandle`] /
/// [`InterfaceHandle`] / [`SocketHandle`] backed by
/// `std::sync::{Arc, Mutex, RwLock}`. Pure std — no tokio
/// dependency — so they live in the executor-agnostic transport

---

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[Copilot]

With SdStateHandle/WrappableSdStateHandle no longer re-exported, please ensure any remaining doc comments in this module (or public docs) that reference those traits are updated to SharedHandle<SdStateManager> / WrappableSharedHandle<SdStateManager> to keep rustdoc accurate.

[Copilot]

The ServerHandles section immediately above this bound still mentions the removed StaticSocketHandle/Wrappable*Handle traits. Please update that doc comment to describe the new SharedHandle<T> / WrappableSharedHandle<T> model and the no-alloc &'static T usage, so the docs match the new bounds here.

[Copilot]

The field docs in this struct still reference StaticSocketHandle<T> and the old EventPublisher<R, S, H> 3-parameter shape. Since this struct now uses SharedHandle<F::Socket> and EventPublisher<R, S, H, F::Socket>, please update the nearby doc comments to reflect &'static T (no-alloc) and the new EventPublisher<..., T> signature.

[Copilot]

This impl switches the bounds to WrappableSharedHandle<...>, but the method docs/comments in the same impl (e.g., new_with_deps) still refer to WrappableSocketHandle / SocketHandle and StaticSocketHandle. Please update that text so users reading the docs see the new WrappableSharedHandle/SharedHandle terminology.

[Copilot]

Arc is only used inside the #[cfg(all(test, feature = "server-tokio"))] test module below, but the import is gated with just #[cfg(test)]. This will produce an unused_imports warning when compiling unit tests without server-tokio enabled. Consider moving the Arc import into the test module or gating it with the same all(test, feature = "server-tokio") condition.

Suggested change

	#[cfg(test)]
	#[cfg(all(test, feature = "server-tokio"))]

[Copilot]

Now that EventPublisherHandle/WrappableEventPublisherHandle are no longer re-exported, there are still doc comments in this module that mention/link to EventPublisherHandle (e.g. the publisher() docs later in the file). Those references should be updated to the new SharedHandle<EventPublisher<...>> / Hep terminology to avoid stale docs and potential broken intra-doc links.