docs: missing_docs sweep — 0 warnings + deny gate + publish-prep decisions (HY-02, HY-04, HY-11)

- document every public-API item across 18 files (openapi_spec model,
  HttpAuthScheme/HttpServiceConfig, HttpClientBuildError + SharedHttpClient
  accessors, RetryAfterMiddleware, GatewayDispatch, gateway error
  mapping, CallRequest/SchemaQuery/SubscribeStream, HttpAdapter +
  ALPNs + builders, decoy/healthz/state, WsSessions/WsPumps,
  from_openapi/from_jsonschema/from_mcp/from_wss/to_mcp, lib.rs module
  docs)
- enforcement: #![deny(missing_docs)] at crate root — stronger than CI
  rustdocflags (every build incl. cfg(test), where rustdoc misses the
  test-support module docs)
- HY-10 (opportunistic): all 8 docs.rs/alkhttp placeholder ADR links +
  the one relative ../docs link converted to plain text; the 10
  pre-existing private/redundant intra-doc-link warnings fixed —
  RUSTDOCFLAGS="-D warnings" cargo doc is fully clean
- HY-11 decision: docs/ + tasks/ excluded from the published package
  (contributor-facing design/process material; ADR references degrade
  to plain text uniformly). cargo publish --dry-run: 38 files, ~889 KiB,
  zero docs/ or tasks/ entries
- HY-04 decision: keep + document — frame_channel0_chunk's unwrap is
  on serializing the acyclic EventEnvelope (unreachable failure);
  # Panics on it and the adjacent WsClient senders state the contract

Verified: cargo test (299 + 5 TLS), --all-features (370 + suites),
--no-default-features (299), clippy --all-targets -D warnings
(default + all-features), fmt --check, cargo doc -D warnings clean,
cargo publish --dry-run --allow-dirty clean.

Tasks: review-001-missing-docs-sweep (final pending task; 42/42)

src/adapters/from_jsonschema.rs

@@ -35,6 +35,10 @@ use serde_json::Value;
 use super::forward::{forward, forward_stream, HttpServiceConfig};
 use crate::client::SharedHttpClient;
 
+/// The HTTP-backed single-endpoint adapter (ADR-066): one caller-built
+/// [`OperationSpec`] forwarded to one HTTP endpoint. Eagerly validated
+/// at construction; the caller's spec visibility is forced to
+/// `Internal` (ADR-015).
 pub struct FromJsonSchema {
     spec: OperationSpec,
     config: HttpServiceConfig,
@@ -61,7 +65,7 @@ impl FromJsonSchema {
     /// are rejected at call time. Mark a property with
     /// `"wire": "header"` to route it as an upstream HTTPS header
     /// instead of a query parameter (review 001 OAI-03). Input key
-    /// [`GATEWAY_BODY_KEY`](super::forward::GATEWAY_BODY_KEY) carries
+    /// `GATEWAY_BODY_KEY` ("body") carries
     /// the request body.
     pub fn new(
         spec: OperationSpec,