test(sync-macros): prove public presence expansion

Exercise the proc-macro entry point from a real consumer crate so item preservation and argument routing are mutation-verified; record the clean 33-mutant package gate.

req: sync/003

req: sync/005

req: test/020

req: test/021

PLAN.md

@@ -18,10 +18,10 @@
 
 ## 2. Make mutation testing a reproducible release gate
 
-- [ ] **State:** In progress — the package-native capped xtask entry point is reachable, rejects unknown packages and invalid shards, propagates mutest failure, and mutation-tests `hemx`, `hemx-axum`, `hemx-build`, `hemx-core`, `hemx-derive`, `hemx-host`, `hemx-js`, `hemx-sync`, and `hemx-test` cleanly; full package closure remains.
+- [ ] **State:** In progress — the package-native capped xtask entry point is reachable, rejects unknown packages and invalid shards, propagates mutest failure, and mutation-tests `hemx`, `hemx-axum`, `hemx-build`, `hemx-core`, `hemx-derive`, `hemx-host`, `hemx-js`, `hemx-sync`, `hemx-sync-macros`, and `hemx-test` cleanly; full package closure remains.
 - **User value:** maintainers can run one bounded repository command and trust that meaningful Rust logic across every mutation-applicable library is either killed or explicitly justified.
 - **Build:** add a capped `hemx-xtask` mutation command that invokes `/opt/repositories/mutest`/`mutest` through package-native test targets rather than the broken workspace-wide example path; enumerate only current mutation-applicable library/proc-macro packages; finish adversarial tests or simplify code until every survivor is classified; keep equivalent, invariant-only, and infrastructure-inapplicable classifications inspectable and minimal; document the exact local release command in the existing readiness surface.
-- **Blocked by:** none; full package gates remain for `hemx-sync-macros` and `hemx-wasm`. `hemx-lsp` is a binary-only package and is deliberately outside the mutation-applicable library/proc-macro set elected by test/020; its package tests remain part of normal workspace verification. The complete `hemx` gate passes with 30 mutants (9 caught, 21 unviable), the complete `hemx-host` gate passes with 76 mutants (52 caught, 24 unviable), and the complete `hemx-sync` gate passes with 164 mutants (135 caught, 29 unviable). The xtask mutation runner creates shard output parents before invoking mutest, fixing first-use failure for newly sharded packages. All eight deterministic `hemx-derive` shards pass: 480 mutants total, 393 caught and 87 unviable, including final shard `8/8` with 54 mutants (42 caught, 12 unviable) after fail-closed malformed symbol-line handling, exact sorted/deduplicated component discovery, component filtering, non-handler exclusion, and direct quoted compile diagnostics. The mutation entry point accepts validated one-based `SHARD/TOTAL` operands, maps them to native zero-based shards, uses shard-specific output directories, grants repo-owned compiler probes a 120-second floor, and preserves the unsharded gate. All eight deterministic `hemx-build` shards now pass: 1,304 mutants total, 1,070 caught and 234 unviable, including final shard `8/8` with 159 mutants (139 caught, 20 unviable). The complete 470-mutant `hemx-axum` package gate passes with 262 caught and 208 unviable after public page/form/multipart/registry/response/runtime proofs and narrow classification of infallible header parsing and streamed multipart unwrap-equivalent mutants.
+- **Blocked by:** none; the full `hemx-wasm` package gate remains. `hemx-lsp` is a binary-only package and is deliberately outside the mutation-applicable library/proc-macro set elected by test/020; its package tests remain part of normal workspace verification. The complete `hemx` gate passes with 30 mutants (9 caught, 21 unviable), the complete `hemx-host` gate passes with 76 mutants (52 caught, 24 unviable), the complete `hemx-sync` gate passes with 164 mutants (135 caught, 29 unviable), and the complete `hemx-sync-macros` gate passes with 33 mutants (14 caught, 19 unviable) after a public proc-macro consumer proved that the attribute preserves and expands its item. The xtask mutation runner creates shard output parents before invoking mutest, fixing first-use failure for newly sharded packages. All eight deterministic `hemx-derive` shards pass: 480 mutants total, 393 caught and 87 unviable, including final shard `8/8` with 54 mutants (42 caught, 12 unviable) after fail-closed malformed symbol-line handling, exact sorted/deduplicated component discovery, component filtering, non-handler exclusion, and direct quoted compile diagnostics. The mutation entry point accepts validated one-based `SHARD/TOTAL` operands, maps them to native zero-based shards, uses shard-specific output directories, grants repo-owned compiler probes a 120-second floor, and preserves the unsharded gate. All eight deterministic `hemx-build` shards now pass: 1,304 mutants total, 1,070 caught and 234 unviable, including final shard `8/8` with 159 mutants (139 caught, 20 unviable). The complete 470-mutant `hemx-axum` package gate passes with 262 caught and 208 unviable after public page/form/multipart/registry/response/runtime proofs and narrow classification of infallible header parsing and streamed multipart unwrap-equivalent mutants.
 - **Proof:** the new xtask mutation command exits zero within its documented bound, covers each applicable package, emits no unexplained missed mutant, and a deliberate adjacent mutation makes it fail. `cargo run -p hemx-xtask -- test` remains green. req: test/020 req: test/021
 
 ## 3. Elect and enforce the release license policy

hemx-sync-macros/tests/presence.rs

@@ -0,0 +1,62 @@
+extern crate self as hemx_sync;
+
+use hemx_sync_macros::presence;
+
+pub trait IntoEffect {}
+
+impl IntoEffect for &'static str {}
+
+pub trait PresenceScope {
+    fn presence_channel(&self) -> String;
+}
+
+pub trait PresenceUpdate {
+    fn channel(&self) -> &str;
+    fn effect(&self) -> &str;
+}
+
+pub struct PresenceProjection<Effect> {
+    channel: String,
+    effect: Effect,
+}
+
+impl<Effect> PresenceProjection<Effect> {
+    pub fn new(channel: String, effect: Effect) -> Self {
+        Self { channel, effect }
+    }
+}
+
+impl PresenceUpdate for PresenceProjection<&'static str> {
+    fn channel(&self) -> &str {
+        &self.channel
+    }
+
+    fn effect(&self) -> &str {
+        self.effect
+    }
+}
+
+struct Signal(&'static str);
+
+impl PresenceScope for Signal {
+    fn presence_channel(&self) -> String {
+        self.0.to_owned()
+    }
+}
+
+#[presence]
+fn project(signal: Signal) -> impl IntoEffect {
+    if signal.0 == "board" {
+        "joined"
+    } else {
+        "left"
+    }
+}
+
+#[test]
+fn public_presence_attribute_preserves_the_item_and_expands_it() {
+    let update = project(Signal("board"));
+    assert_eq!(update.channel(), "board");
+    assert_eq!(update.effect(), "joined");
+    // test req: sync/003 req: sync/005
+}