refactor: harden distributed_macros expansion and diagnostics

[patrickleet]

Summary

Hardens the distributed_macros proc-macro crate to make expansion testable and misuse produce pointed, spanned diagnostics. Brings the four macros in lib.rs (sourced, aggregate!, digest, enqueue) up to the pattern already used by snapshot.rs / read_model.rs.

Generated output is unchanged. The refactor only changes how the code is structured and how errors are produced — not what the macros emit. This is verified by the full main-crate test suite (250+ tests, including tests/sourced*, tests/enqueue, tests/todos, tests/upcasting, tests/snapshots) all passing unmodified.

Changes

1. Testable shape — each macro now has an expand_* -> syn::Result<TokenStream2> core, with a thin #[proc_macro*] entry point that calls it and converts errors via .unwrap_or_else(|e| e.to_compile_error()). This mechanical change enables unit testing of expansion.

2. Explicit unknown-key diagnostics — parse_digest_args, parse_sourced_args, parse_event_args, and parse_enqueue_args previously left unknown keyword args silently unconsumed (surfacing later as a bare "unexpected token"). They now reject unknown keys with a spanned syn::Error naming the bad key and listing the valid ones, e.g.:
   unsupported key versoinin #[digest(...)]; expectedwhenorversion``
   Also added up-front checks for duplicate #[event] names, `#[event]` methods missing a `self` receiver, and a clear message for bare `#[sourced()]` with no entity field.

3. #[enqueue] renamed-entity fix — the replay guard was hardcoded to self.entity.is_replaying(). A renamed entity field produced a confusing "no field entity" error pointing at the user's method. #[enqueue] now accepts entity = field (defaulting to entity), matching how the other macros configure the entity field.

4. trybuild compile-fail suite — new distributed_macros/tests/ with a trybuild dev-dependency and five fixtures covering: unsupported #[event] signature, duplicate event names, unknown attribute keys, #[sourced] missing the entity field, and the renamed-entity #[enqueue] footgun. Plus unit tests for the new expand_*/parse_* functions.

5. ReplayError decision — kept as String. Replay errors are flattened from heterogeneous sources (per-event decode() errors, user method errors of arbitrary E, unknown-event messages) via e.to_string(). A typed error would have to be generic over each method's error type or erase them anyway, so String is the smaller, honest representation. Rationale documented inline at both impl Aggregate blocks.

Note on dev-dependency cycle

trybuild fixtures need the distributed runtime crate to type-check generated distributed::... code, so distributed_macros now dev-depends on distributed (which depends on distributed_macros). Cargo permits dev-dependency cycles; this does not affect the normal dependency graph.

Testing

• cargo fmt --all — clean
• cargo clippy -p distributed_macros — clean
• cargo test -p distributed_macros — 46 unit tests + 1 trybuild harness (5 fixtures) pass. .stderr snapshots generated with TRYBUILD=overwrite and reviewed (all pointed/spanned).
• cargo build (default features) — clean
• cargo test (default features) — entire workspace passes, including all macro-using integration tests with no changes to their expected behavior, confirming generated output is unchanged.

🤖 Generated with Claude Code

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: abec62a5-f5c8-47f5-aca0-116c12f917ec

📥 Commits

Reviewing files that changed from the base of the PR and between 55c2674 and 1862fed.

📒 Files selected for processing (13)

• distributed_macros/Cargo.toml
• distributed_macros/src/lib.rs
• distributed_macros/tests/compile_fail.rs
• distributed_macros/tests/compile_fail/duplicate_event_names.rs
• distributed_macros/tests/compile_fail/duplicate_event_names.stderr
• distributed_macros/tests/compile_fail/enqueue_renamed_entity.rs
• distributed_macros/tests/compile_fail/enqueue_renamed_entity.stderr
• distributed_macros/tests/compile_fail/event_bad_signature.rs
• distributed_macros/tests/compile_fail/event_bad_signature.stderr
• distributed_macros/tests/compile_fail/sourced_missing_entity.rs
• distributed_macros/tests/compile_fail/sourced_missing_entity.stderr
• distributed_macros/tests/compile_fail/unknown_digest_key.rs
• distributed_macros/tests/compile_fail/unknown_digest_key.stderr

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch hardening/macro-crate-hardening

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