P3 async — static stream validation at build time (#94 sub-B)

[avrabe]

Sub-issue of #94 — outstanding deliverable B from the audit.

Four build-time checks the umbrella calls for. None are implemented today.

Scope

Check	What it catches
(i) Stream type compatibility	Source `stream` connected to sink `stream` where A ≠ B — currently silently mis-types at runtime.
(ii) Bounded-channel capacity	Components that opt into bounded channels but don't declare capacity — currently UB.
(iii) Circular stream dependencies	Two streams whose endpoints form a closed cycle — would deadlock at runtime. Note: `resolver.rs` has module-level cycle detection (`test_topological_sort_circular_fallback`) but not stream-level.
(iv) Resource lifetime across async boundaries	An `own` handle escaping into a `stream` then dropped while still referenced — Mythos-class hazard.

Deliverables

• `resolver.rs` additions: stream graph build (analogous to existing resource graph), cycle detection on the stream subgraph, type-compatibility pass.
• New error variants in `Error::ValidationError` for each of (i)–(iv).
• Regression tests + Kani harness for cycle detection.
• LS-N entries: each of (i)–(iv) gets its own approved loss scenario.

Dependencies

• Blocked by P3 async — cross-component stream adapter (#94 sub-A) #141 (sub-A) — needs concrete cross-component stream pairs to validate against. If sub-A lands in v0.9, this can ride v0.9 too; otherwise slip to v0.10.

Rivet artifact

• New requirement SR-34 — "Static `stream` validation (type / capacity / cycle / lifetime)".

Milestone

v0.9.0 (target — slips to v0.10.0 if sub-A doesn't land in time)