feat(net): Retry resilience layer (Slice 1, PR 3)

CHANGELOG.md

@@ -62,6 +62,15 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   layer default). Response-future-only (ADR-0031 §1's "bounds the send, not the permit
   wait"); a streaming-body timeout is deferred. No new dependency. (ADR-0031 §1,
   ADR-0034.)
+- `oath-adapter-net-http-api` `Retry` resilience layer (Slice 1 PR 3) — the
+  `Retry<S, T>` service + `RetryLayer<T>` factory (`net-api::Layer`): re-issues an
+  explicitly-eligible request (a `Retryable` marker extension; absent → never retried,
+  fail-safe) on a transient failure (`HttpError::{Timeout, Connection}`) or a `5xx`
+  response, with capped-exponential full-jitter backoff up to `max_attempts`. Never
+  retries a 429 / other 4xx / `Auth` / `Throttled`; returns the last outcome verbatim on
+  exhaustion; body-transparent (drops a superseded response, releasing its `Guarded`
+  permit). Adds the `Retryable` marker + `RetryConfig` schedule; jitter via an internal
+  seeded `SplitMix64` — no new dependency. (ADR-0031 §2, ADR-0034.)
 - net-http construction-surface design refinements (ADR-0034 append-only
   Amendments 2026-07-04, spec updated) — an absent `RateLimit<K>` directive now
   **fails closed** (not "defaults to `Global`"), closing the last silent

crates/adapter/net/http/api/src/lib.rs

@@ -12,6 +12,8 @@
 //!   `RateLimitConfig`, and the boot-time `validate_coverage` check
 //! - [`rate_limit`] — the `RateLimit` layer, its `RateLimitLayer` factory, and
 //!   the `RateScope`/`Scope` per-request directive
+//! - [`retry`] — the `Retry` layer, its `RetryLayer` factory, and the
+//!   `Retryable`/`RetryConfig` retry directive + schedule
 //! - [`timeout`] — the `Timeout` layer, its `TimeoutLayer` factory, and the
 //!   `RequestTimeout` per-request override
 //!
@@ -25,6 +27,7 @@ pub mod client;
 pub mod error;
 pub mod rate;
 pub mod rate_limit;
+pub mod retry;
 pub mod service;
 pub mod timeout;
 
@@ -37,5 +40,6 @@ pub use rate::{
     validate_coverage,
 };
 pub use rate_limit::{RateLimit, RateLimitLayer, RateScope, Scope};
+pub use retry::{Retry, RetryConfig, RetryLayer, Retryable};
 pub use service::Service;
 pub use timeout::{RequestTimeout, Timeout, TimeoutLayer};