feat(http1): ClientHTTP1::Fetch follows redirects by the RFC, on a URL type

One request to an http(s) URL with redirects followed by RFC 9110 §15.4:
301, 302, 303, 307 and 308 for every method; a 303 makes the request a
GET without its body and content headers, a 301 or 302 does so for a POST
alone, a 307 or 308 keeps the method and the body. The Location is
resolved against the sending URL by RFC 3986, a hop between http and
https is allowed, Authorization, Proxy-Authorization and Cookie are
dropped on a change of origin, and each hop is a client of its own, since
one ClientHTTP1 is one origin. A redirect without a usable Location, to
another scheme, back to a URL already visited or past maxRedirects comes
back as the response, with `stop` saying why.

The new :URL partition is the URL type behind it, exported: Parse,
Resolve (RFC 3986 §5.2; its §5.4 examples are the test), ToString, and
the pieces a request is built from.

This replaces the FetchHTTP1 free function, which followed redirects the
way Python's urllib did (its repeat limit, its quoting of the Location, a
POST turned back on a 307) for a port that no longer needs the fidelity.

Breaking: FetchHTTP1, FetchOptionsHTTP1 and FetchResultHTTP1 are gone;
use ClientHTTP1::Fetch, FetchOptions and FetchResult, whose `url` is a
URL and whose `limited` became `stop`.

AGENTS.template.md

@@ -4,13 +4,13 @@ Guidance for coding agents and contributors working on Crafter.Network itself. T
 
 ## Project overview
 
-Crafter.Network is the Crafter engine's networking library: one C++ module, `Crafter.Network`, with fourteen partitions behind its primary interface (fifteen interface files), with TCP, a byte-stream seam and a libssl TLS transport, HTTP/1.1 (client, listener and a transport-free codec), QUIC over msquic, HTTP/3 (client, listener and a wire-format partition) and WebTransport on the HTTP/3 listener. One source tree builds three libraries: native Linux (everything), native with `--no-quic` (TCP, TLS and HTTP/1.1, no msquic), and the browser (`wasm32-*`: the client half of HTTP and WebTransport over `fetch()` and the `WebTransport` API, `*Async` only). The only crafter-build dependency is Crafter.Thread, whose `ThreadPool` runs every callback and `*Async` call; msquic is an `ExternalDependency` built with CMake, and OpenSSL 3 is a system package.
+Crafter.Network is the Crafter engine's networking library: one C++ module, `Crafter.Network`, with fifteen partitions behind its primary interface (sixteen interface files), with TCP, URLs, a byte-stream seam and a libssl TLS transport, HTTP/1.1 (client, listener and a transport-free codec), QUIC over msquic, HTTP/3 (client, listener and a wire-format partition) and WebTransport on the HTTP/3 listener. One source tree builds three libraries: native Linux (everything), native with `--no-quic` (TCP, TLS and HTTP/1.1, no msquic), and the browser (`wasm32-*`: the client half of HTTP and WebTransport over `fetch()` and the `WebTransport` API, `*Async` only). The only crafter-build dependency is Crafter.Thread, whose `ThreadPool` runs every callback and `*Async` call; msquic is an `ExternalDependency` built with CMake, and OpenSSL 3 is a system package.
 
 | Path | What lives there |
 |---|---|
 | `interfaces/Crafter.Network.cppm` | The umbrella: `export import`s every partition, under `#ifndef CRAFTER_NETWORK_NO_QUIC` and `#ifndef CRAFTER_NETWORK_BROWSER` for the ones a build leaves out. |
 | `interfaces/Crafter.Network-<Partition>.cppm` | One partition per file. The native-only ones wrap their whole body in `#ifndef CRAFTER_NETWORK_BROWSER`, so the browser build compiles them as empty modules. |
-| `implementations/Crafter.Network-<Partition>.cpp` | The native implementation units, `Crafter.Network:<Partition>_impl`. `HTTP`, `HTTP1` and `HTTP3` have none: they are inline. |
+| `implementations/Crafter.Network-<Partition>.cpp` | The native implementation units, `Crafter.Network:<Partition>_impl`. `HTTP`, `HTTP1`, `HTTP3` and `URL` have none: they are inline. |
 | `implementations/Crafter.Network-ClientHTTP-Browser.cpp`, `-ClientQUIC-Browser.cpp` | The browser implementations of those two partitions, over the JS bridge. |
 | `additional/network-env.js` | The JS bridge: `fetch()` and `WebTransport` behind the `env` imports the wasm declares, shipped next to a consumer's `.wasm` through `cfg.files`. |
 | `project.cpp` | The build description: one static library, `crafter-network`, in its three variants, the msquic external, the OpenSSL link flags and the test declarations. |
@@ -25,8 +25,9 @@ Partitions and what they own:
 - `:Stream`: `ByteStream` (`ReadSome` and `Write` with a timeout per call, `Shutdown`, `Descriptor`, `Protocol`, `Secure`) and `PlainStream`, so one HTTP/1.1 implementation serves `http://` and `https://`. `SetNonBlocking`, `PollDescriptor`.
 - `:TLS`: `TLSContext`, `TLSStream`, both credential structs, `GetSelfSignedCertificatePem`. OpenSSL stays behind the `Impl` pointers; no OpenSSL header reaches an importer.
 - `:HTTP`: `HTTPRequest`, `HTTPResponse`, the `Create*` helpers, `PathWithoutQueryHTTP`. Shared by both HTTP versions and by every build.
+- `:URL`: `URL`, an absolute URL as RFC 3986 reads it (`Parse`), the resolution of a reference against it (`Resolve`, RFC 3986 §5.2, dot segments removed), the recomposition, and the pieces a request is built from. Inline, native only; what `ClientHTTP1::Fetch` follows a Location with.
 - `:HTTP1`: the RFC 9112 codec, inline: `SerializeRequest`, `SerializeResponse`, `SerializeContinue`, `MessageParser`, `MessageLimits`, `HTTP1ProtocolError`, and the framing it refuses to guess at.
-- `:ClientHTTP1`, `:ListenerHTTP1`: HTTP/1.1 over a `ByteStream&`. The listener is a `ListenerTCP` with a thread per accepted connection; the client keeps one pooled connection with a replay-once rule.
+- `:ClientHTTP1`, `:ListenerHTTP1`: HTTP/1.1 over a `ByteStream&`. The listener is a `ListenerTCP` with a thread per accepted connection; the client keeps one pooled connection with a replay-once rule, and `ClientHTTP1::Fetch` is the URL fetch that follows redirects by RFC 9110 §15.4 with a client per hop (`FetchOptions`, `FetchResult`, `FetchStop`).
 - `:ClientQUIC`: `ClientQUIC` and `QUICStream` for both ends of a connection, `QUICSettings`, both QUIC credential structs, `QUICException`, `QUICClosedException`. The native unit holds the process-wide `MsQuicRuntime` (API table and registration, closed by a static destructor at exit), the stream registry with its refcounted handles, and the drain in `~ClientQUIC`.
 - `:ListenerQUIC`: the msquic listener, its four `Listen*` variants, the self-signed certificate (made by the `openssl` CLI and cached under `/tmp/crafter-network-quic-cert/`), `ComputeCertificateHashSHA256`, `GetSelfSignedCertificatePath`.
 - `:HTTP3`: QUIC varints, HTTP/3 frames, the QPACK static table, Huffman decoding, the control-stream preludes and the WebTransport stream prefixes. Native only: it throws for protocol errors.
@@ -50,9 +51,9 @@ crafter-build                                  # native: TCP, TLS, HTTP/1.1, QUI
 crafter-build --no-quic                        # native without QUIC, HTTP/3, WebTransport and msquic
 crafter-build --local                          # Crafter.Thread from ../Crafter.Thread
 crafter-build --target=wasm32-wasip1           # the browser library
-crafter-build test                             # the suite, native: 23 tests
+crafter-build test                             # the suite, native: 30 tests
 crafter-build test 'Should*HTTP1'              # a name glob
-crafter-build test --no-quic                   # the TCP, TLS and HTTP/1.1 tests plus ShouldBuildWithoutQUIC: 12
+crafter-build test --no-quic                   # the TCP, URL, TLS and HTTP/1.1 tests plus ShouldBuildWithoutQUIC: 19
 crafter-build test --list
 crafter-build test --jobs=1 --timeout=120
 crafter-build clean