Context

#841 (PR #842) made async(Http.get/post(...)) with call-free arguments concurrent, and W002 warns when the argument's effect row is outside the commutative whitelist — the semantic case where concurrency is impossible without observable reordering.

The gap CodeRabbit flagged (PR #842 review)

Two natural shapes are effect-eligible but never fuse, silently staying eager with no diagnostic:

1. async(fetch(url)) where fetch is effects(<Http>) and wraps Http.get — fusion requires a direct Http.get/Http.post call.
2. async(Http.get(build_url(id))) with a pure build_url — fusion requires call-free request arguments.

Both are per-design in v1 (spec §9.5.4 documents the exact fused shapes, and the MAY-evaluate-concurrently wording means silence promises nothing), and W002's semantic contract is commutativity, not fusion reporting — tests/test_checker_effects.py::test_async_over_http_via_fn_call_no_warning pins that deliberately. But a user writing these shapes plausibly expects concurrency, and an advisory would surface the miss at check time instead of at the profiler.

Proposal

A separate advisory (W003, "async argument is not a fusable shape; evaluates eagerly"), firing only when the argument's effect row intersects {Http} (so async(41 + 1) stays silent) but the shape is not the direct call-free form. Notes:

• The checker cannot import vera/wasm/async_fusion.py without inverting the layer direction (vera/checker → vera/wasm); the shape predicate would need a neutral home (e.g. alongside the AST helpers) consumed by both, preserving the single-source-of-truth invariant from PR feat(async): concurrent async(Http.get/post) on host worker threads — release v0.0.192 #842.
• Requires flipping the pinned no-warning tests, a registry entry, spec/SKILL wording, and deciding whether an advisory that fires on idiomatic wrapper functions is more signal than noise — a design call beyond the Host-threaded concurrent <Async> for commutative effect rows #841 scope, which is why this is an issue rather than an in-PR change.

Refs #841.