feat(httpclient): close the platform review's P0/P1/P2 findings

The review found one defect shape repeated across the platform: surfaces
that were declared, bound, and documented, but that nothing read. An
operator configuring fullUrlRecording, bodyLogging, retry.policy,
validatedDnsPinning, timeout.dns, or any of ten declared metric names got a
guarantee the code never delivered. Every such surface is now in exactly one
of three states -- wired for real, rejected at startup, or registered in a
test-enforced gap list with its reason. No silent no-ops remain.

P0:
- Activate the platform from bootstrap behind app.httpclient.enabled, with a
  single auto-configuration importing the nine child configurations.
- Give the platform a strict, repository-level ENV contract: 74 leaf fields
  derived from the settings record tree, unknown APP_HTTPCLIENT_* rejected.
- Route typed HTTP service clients through the call kernel via
  KernelHttpExchangeAdapter, so they stop bypassing platform policy.
- Pin dynamic-target DNS resolution to the socket for the life of a call,
  closing the resolve-then-connect TOCTOU / rebinding window.
- Actually transmit the idempotency key, and make retry eligibility depend on
  transmission rather than on merely holding one.
- Reject reactive authentication and reactive redirect at startup instead of
  declaring support that does not function.
- Fix the Reactor-only Stable contract row so the lane stops failing.
- Stop advertising HTTP/3 on a transport that negotiates HTTP/1.

P1 covers execution and retry accounting, redirect security (per-hop target
guarding, sensitive-header stripping, 303 body handling), runtime rotation
and transport resource ownership keyed by generation, dynamic-target
hardening (subdomain matching, global-unicast classification, strict CIDR
parsing), protocol intent, pool and timeout wiring, streaming and body
limits, observability parity, and OAuth single-flight refresh on a bounded
pool with a bounded wait.

P2 covers configuration and documentation drift, the Gradle check wiring for
the four hermetic lanes, and the CI gate matrix.

Two test-quality defects surfaced while closing these: the HTTP/2 stream
saturation test ran against cleartext HTTP/1.1 while asserting nothing about
the protocol, and an OAuth contention test slept on a latch that could fire
before the callers it meant to observe. Both now assert what their names
claim.

Verification run: :adapter:outbound:httpclient:check and :app-bootstrap:check
(checkstyle, spotless, spotbugs, and the four hermetic lanes),
verifyCleanArchitectureDependencies, verifyEnvKeys, verifyOneTypePerFile,
verifyDependencyLocks, the documentation and gate-matrix verifiers, and the
performance lane against a real TLS+ALPN HTTP/2 server.

Not executed, and tracked rather than claimed: Docker/Toxiproxy fault
injection, JMH, a real QUIC/HTTP3 server, a real Spring Framework 6.2
distribution (now a delegated-pending gate), live OAuth/TLS/proxy/DNS
integration, and a whole-repository check.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/httpclient/repository-adaptation.md

@@ -0,0 +1,87 @@
+# HTTP Client Platform — Repository Adaptation Contract
+
+**Design source:** `httpclient-superpowers-package/docs/superpowers/specs/2026-08-08-httpclient-platform-design.md`
+**Plan source:** `httpclient-superpowers-package/docs/superpowers/plans/2026-08-08-httpclient-platform-implementation-plan.md`
+
+The design package states its own adaptation rule:
+
+> 실제 Backend Skeleton 저장소가 제공되지 않았으므로 package 경로와 Gradle 구조는 설계서의 명시적
+> 구현 가정이다. 구현 전 저장소의 기존 convention과 root package에 맞춰 경로만 조정하고 공개 계약과
+> 정책 의미론은 유지한다.
+
+This file is the single record of *how* the design's assumed layout was mapped onto this repository.
+Only paths, build DSL, and composition-root ownership changed. Public contracts, policy order, and
+error semantics are implemented exactly as specified.
+
+## 1. Why the module layout differs
+
+The design assumes a greenfield library with 19 Gradle projects under `modules/httpclient/`.
+This repository is a Clean Architecture template whose **fail-closed registry**
+(`src/config/architecture/modules.json`, enforced by `src/settings.gradle` and
+`verifyCleanArchitectureDependencies`) declares **exactly 19 leaf identities**. Creating 19 more
+Gradle projects would violate HARD-STOP #5 in `AGENTS.md`.
+
+Therefore the design's 19 library modules become **package boundaries inside the registered leaf**
+`:adapter:outbound:httpclient`, with two exceptions driven by this repository's own rules:
+
+| Design module | Repository home | Reason |
+|---|---|---|
+| `httpclient-spring-boot-starter` | `:app-bootstrap` (`dev.caskeleton.bootstrap.autoconfigure.httpclient`) | This repository's composition root owns wiring and canonical activation; an adapter leaf must not auto-configure itself. |
+| `httpclient-testkit` | `:adapter:outbound:httpclient` `src/test/java/**/testkit` | The design forbids production modules depending on the testkit; a test source set gives the same guarantee without a new Gradle project. |
+
+The package boundary is enforced by ArchUnit rules (`PublicApiArchitectureTest`,
+`HttpClientModuleBoundaryTest`) that reproduce the design's module dependency table.
+
+## 2. Package mapping
+
+Root package: `io.backend.skeleton.httpclient` → `dev.caskeleton.adapter.outbound.httpclient`.
+
+| Design module | Design package | Repository package |
+|---|---|---|
+| `httpclient-core-api` | `…httpclient.api` (+ `.body`, `.error`, `.operation`, `.result`) | `dev.caskeleton.adapter.outbound.httpclient.api` (+ same subpackages) |
+| `httpclient-profile` | `…httpclient.profile` | `…outbound.httpclient.profile` |
+| `httpclient-transport-spi` | `…httpclient.transport` | `…outbound.httpclient.transport` |
+| `httpclient-transport-apache` | `…httpclient.apache` | `…outbound.httpclient.apache` |
+| `httpclient-transport-jdk` | `…httpclient.jdk` | `…outbound.httpclient.jdk` |
+| `httpclient-restclient` | `…httpclient.restclient` | `…outbound.httpclient.restclient` |
+| `httpclient-resilience` | `…httpclient.resilience` | `…outbound.httpclient.resilience` |
+| `httpclient-auth` | `…httpclient.auth` | `…outbound.httpclient.auth` |
+| `httpclient-security` | `…httpclient.security` | `…outbound.httpclient.security` |
+| `httpclient-observability` | `…httpclient.observation` | `…outbound.httpclient.observation` |
+| `httpclient-transport-reactor-netty` | `…httpclient.reactor` | `…outbound.httpclient.reactor` |
+| `httpclient-webclient` | `…httpclient.webclient` | `…outbound.httpclient.webclient` |
+| `httpclient-service-client` | `…httpclient.service` | `…outbound.httpclient.service` |
+| `httpclient-dynamic-target` | `…httpclient.dynamic` | `…outbound.httpclient.dynamic` |
+| `httpclient-resttemplate-migration` | `…httpclient.migration` | `…outbound.httpclient.migration` |
+| `httpclient-spring7-service-groups` | `…httpclient.spring7` | `…outbound.httpclient.spring7` |
+| `httpclient-jetty-http3-experimental` | `…httpclient.http3` | `…outbound.httpclient.http3` |
+| `httpclient-spring-boot-starter` | `…httpclient.autoconfigure` | `dev.caskeleton.bootstrap.autoconfigure.httpclient` |
+| `httpclient-testkit` | `…httpclient.testkit` | `…outbound.httpclient.testkit` (test source set) |
+
+## 3. Other deliberate substitutions
+
+| Design assumption | Repository reality | Adaptation |
+|---|---|---|
+| Gradle Kotlin DSL, `build-logic` convention plugin | Groovy DSL, root `build.gradle` conventions, `LockMode.STRICT` dependency locking | Dependencies declared in `src/adapter/outbound/httpclient/build.gradle`; `gradle.lockfile` regenerated. |
+| Spring Framework 6.2 baseline with 7.0 compatibility | Spring Boot 4.0.0 / Spring Framework 7.0 is the repository baseline | Common code targets the Spring 6.2 **API surface** (no 6.2-only or 7.0-only classes in common packages). The Spring 7 HTTP Service Group integration stays isolated in `…httpclient.spring7`, exactly as the design requires. |
+| `settings.gradle.kts` module registration | Fail-closed registry | No registry change; leaf identity, gradle path, allowed dependencies unchanged. |
+| Design §6.2 grades Apache HttpClient 5 as HTTP/2-capable | Spring's blocking factory drives Apache's **classic** client, which is HTTP/1.1 only; HTTP/2 lives in Apache's async client | `ApacheBlockingTransportProvider` declares HTTP/1.1 and rejects an HTTP/2 profile at startup. Blocking HTTP/2 is served by the JDK transport, measured by `NegotiatedProtocolContractTest`. |
+| Design §28.1 names WireMock for stateful fixtures | WireMock's Jetty modules bind a different Jetty 12 ABI than the Boot-managed one this module already needs for HTTP/3, and fail at server start | `StatefulUpstream` provides path-keyed stateful responses on the existing fixture server; the WireMock dependency was removed rather than worked around with a shaded jar |
+| Per-task `git commit` | `AGENTS.md`: commit policy is `human-only` | Implementation is delivered unstaged; commits are the human's action. This is the only plan step intentionally not executed, and it is recorded here. |
+| `docs/httpclient/**`, `.github/workflows/httpclient-*.yml`, `scripts/verify-httpclient-docs.py` | Repository already owns `docs/` and `.github/workflows/` | Created at the same repository-relative paths. |
+
+## 4. What is unchanged from the design
+
+- H1 / H2 / H3 / H4 exposure rules and the forbidden native-engine signatures.
+- `ExecutionEvidence`, `BodyReplayability`, `OperationIdempotency`, `AttemptStage`, `FailureCategory`.
+- `HttpOperation`, `HttpCallResult`, `BodySource`, `ResponseType`, `BlockingStreamingResponse`.
+- The complete stable exception hierarchy and `HttpFailureMetadata` redaction rules.
+- Named Client Profile schema, startup validation codes, and operation override direction.
+- Effective deadline formula, attempt budget, and streaming setup/idle split.
+- Retry eligibility inputs, the ordered decision table, retry budget, and backoff rules.
+- Circuit → Rate Limiter → Bulkhead attempt order and logical admission placement.
+- OAuth2 cache key, single-flight refresh, and the 401 replay-at-most-once rule.
+- TLS allow/forbid lists and permanent-failure classification.
+- Dynamic Target canonicalization → all-answer DNS validation → pinning → redirect revalidation.
+- Low-cardinality tag allowlist, forbidden labels, trace and logging rules.
+- Runtime generation swap and drain semantics.