CD: resolve same-app includes in-process, with per-type transport (IN_PROCESS | HTTP) #220

Problem

The CD plugin fetches every included type over HTTP, including the types the app serves itself, by calling itself on loopback. Each same-app include:

• pays a full round trip: a socket, every servlet filter, and the JSON serialised and parsed again;
• holds a second worker thread while the original request waits, so a bounded pool can starve under load;
• breaks wherever loopback can't reach the app: TLS terminated in the app, a server bound to one address, mTLS, graceful shutdown, MockMvc.

Solution

Resolve same-app types in-process, through JsonApi4j.execute(...), as the client's principal. Validation and the AC plugin still apply.

Types mapped to another service's url stay over HTTP. HTTP for same-app types becomes an explicit, per-type choice:

jsonapi4j:
  cd:
    mapping:
      default:
        url: http://127.0.0.1:8080/jsonapi   # this app's own address
        transport: HTTP                      # same-app types over HTTP by default
      users:
        transport: IN_PROCESS                # except users
      orders:
        url: https://orders.internal/jsonapi # another service: always HTTP

• transport: IN_PROCESS | HTTP per mapping entry. An unset transport falls back to mapping.default.transport, then to IN_PROCESS.
• Startup validation:
  • HTTP without mapping.default.url is rejected;
  • IN_PROCESS on a type with a url is rejected;
  • default takes only url and transport.
• No more loopback-URL detection.
• In-process results bypass the include cache: they're cheap to read and always fresh.

A rough benchmark on a 3-hop include: in-process is ~1.8× faster per request, at ~1.6× the throughput.

Refactoring (resolver)

• DomainSettings is a sealed interface with two kinds: overHttp(...) and inProcess(...).

• Fetching is split into composable BatchFetcher<R> decorators:

  OverHttp  → Caching → Chunking → ErrorStrategyAware → HTTP client
  InProcess →           Chunking → ErrorStrategyAware → InProcessBatchFetcher
  

  RoutingBatchFetcher dispatches by the route kind and stands in a null object when there is no in-process fetcher.

• HttpFetchResult is renamed to FetchResult. CachingCompoundDocsFetcher, BatchFetchResult and PrimaryResource are removed. Resource parsing is unified in JsonApiResponseParser.

• CompoundDocsRequest carries the principal. ResponseHeaders and ResponseStatus gain clear(), and ResponseHeaders also gains takeCacheControl().

Breaking changes

• Same-app includes no longer pass through servlet filters or URL-based security rules. To keep that, set transport: HTTP.
• mapping.default.url alone no longer switches to HTTP; it now also needs mapping.default.transport: HTTP.
• SelfFallbackRouting.forRequest is removed.
• The resolver API renames listed above (HttpFetchResult → FetchResult, and the removed classes).

Docs

• compound-docs-plugin.md: how includes are fetched, the transport settings, and the Limitations section.
• performance.md: prefer IN_PROCESS.
• compound-docs.md.
• The Claude Code plugin references.