feat(plugin): carry Http\Response across as a materialized value

A response is built for one request and the graph never retains it, so there
is no entity for a handle to point at. The child holds a real instance
instead, revived from the object record the wire carries, and collect() frees
the copy each world holds — which is what that method is for. The
value-object rule rejects the class only because collect() assigns to $this,
so the category comes from an overrides.list entry.

HttpDownloader::get() and copy() answer with one.

Two gaps stay: decodeJson() reaches Composer\Json\JsonFile, which a guard
shadows, and Composer answers a curl request with the CurlResponse subclass
where this port flattens the value into a Response.

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

2 files changed, 33 insertions, 1 deletions

diff --git a/crates/shirabe/tests/plugin/e2e_http_downloader_test.rs b/crates/shirabe/tests/plugin/e2e_http_downloader_test.rs
index ecb0b34c..42471b61 100644
--- a/crates/shirabe/tests/plugin/e2e_http_downloader_test.rs
+++ b/crates/shirabe/tests/plugin/e2e_http_downloader_test.rs
@@ -61,7 +61,8 @@ fn test_plugin_owned_http_downloader_matches_upstream_composer() {
 
     // Pinned as well as compared, so a run where neither side wrote a trace cannot pass. The
     // second options line is the evidence that both worlds merge into one value rather than each
-    // holding its own copy of the map.
+    // holding its own copy of the map, and the response lines are the evidence that the value the
+    // request answers with is a real instance of the class rather than something shaped like one.
     assert_eq!(
         "\
 event=post-update-cmd
@@ -71,6 +72,11 @@ options merged=[\"X-Probe: 2\"]
 isCurlEnabled=true
 hints other=null transport=null
 outputWarnings=ok
+get=ok
+response class=\"Composer\\\\Util\\\\Http\\\\Response\" body=\"{\\\"probe\\\":true,\\\"n\\\":42}\" headers=[]
+getHeader=null
+copy=ok file=\"{\\\"probe\\\":true,\\\"n\\\":42}\"
+collect=ok
 ",
         upstream.trace
     );
diff --git a/crates/shirabe/tests/plugin/fixtures/e2e-http-downloader/plugin/src/Plugin.php b/crates/shirabe/tests/plugin/fixtures/e2e-http-downloader/plugin/src/Plugin.php
index 504c2108..054a47ca 100644
--- a/crates/shirabe/tests/plugin/fixtures/e2e-http-downloader/plugin/src/Plugin.php
+++ b/crates/shirabe/tests/plugin/fixtures/e2e-http-downloader/plugin/src/Plugin.php
@@ -78,6 +78,32 @@ class Plugin implements PluginInterface, EventSubscriberInterface
             );
         });
 
+        // A file:// url keeps the probe offline and off the curl path, so the trace is the same
+        // on a machine with no network. Paths stay out of the trace: the two runs work in
+        // different temporary directories.
+        $payload = getcwd() . '/probe-payload.json';
+        file_put_contents($payload, '{"probe":true,"n":42}');
+
+        $response = null;
+        $lines[] = 'get=' . $this->describe(static function () use ($downloader, $payload, &$response): void {
+            $response = $downloader->get('file://' . $payload);
+        });
+        $lines[] = 'response class=' . json_encode($response === null ? null : \get_class($response))
+            . ' body=' . json_encode($response === null ? null : $response->getBody())
+            . ' headers=' . json_encode($response === null ? null : $response->getHeaders());
+        $lines[] = 'getHeader=' . json_encode($response === null ? null : $response->getHeader('Content-Type'));
+
+        $target = getcwd() . '/probe-copy.json';
+        $lines[] = 'copy=' . $this->describe(static function () use ($downloader, $payload, $target): void {
+            $downloader->copy('file://' . $payload, $target);
+        }) . ' file=' . json_encode(@file_get_contents($target));
+
+        // collect() unsets the response's own properties, so the object is spent afterwards and
+        // nothing may read it again.
+        $lines[] = 'collect=' . $this->describe(static function () use ($response): void {
+            $response->collect();
+        });
+
         file_put_contents('http-downloader-trace.txt', implode("\n", $lines) . "\n");
     }