feat(plugin): serve ProcessExecutor as a proxy stub

Composer reaches this class two ways: the object graph hands one out through
Composer::getLoop()->getProcessExecutor(), and plugins write
`new ProcessExecutor($io)` freely. Both bind to a Rust-side entity, so the
timeout the run shares -- seeded from process-timeout and rewritten while the
run is in flight -- has one value instead of one per world, and the executor
can still be passed to the classes that take one (`new Filesystem($process)`).

Three things the stub generator was missing came with it:

- By-ref parameters. The call carries their positions and the answer carries
  what each holds afterwards; a position the answer omits was never assigned
  to, which is what PHP does with an untouched by-ref parameter.
  ProcessExecutor::execute is the only one on a proxied class.
- Argument arity, reproduced where the real body reads func_num_args().
  execute($cmd) forwards the child's output and execute($cmd, $out) captures
  it, and nothing but the argument count separates the two.
- Static methods that cannot run in the worker. One that reads a static
  property the Rust side owns, or that reaches a guarded class, forwards
  through __shirabeCallStatic instead of being materialized. That also fixes
  Filesystem::isLocalPath and getPlatformPath, whose materialized bodies
  called the guarded Composer\Util\Platform.

The async surface stays an explicit error. executeAsync resolves its promise
with a Symfony Process, whose proc_open() resource and pipes belong to
whichever process called start(), so a Rust-side spawn has none to hand back;
running the real start() in the worker needs a promise representation that
crosses the boundary unresolved.

The fixture project drives the whole synchronous surface from plugin code and
compares the trace against upstream Composer byte for byte.

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

1 files changed, 25 insertions, 0 deletions

diff --git a/crates/shirabe/tests/plugin/fixtures/e2e-process-executor/project/composer.json b/crates/shirabe/tests/plugin/fixtures/e2e-process-executor/project/composer.json
new file mode 100644
index 00000000..61ca9a5a
--- /dev/null
+++ b/crates/shirabe/tests/plugin/fixtures/e2e-process-executor/project/composer.json
@@ -0,0 +1,25 @@
+{
+    "name": "shirabe/e2e-process-executor",
+    "description": "E2E fixture project: record what a plugin's own ProcessExecutor reports.",
+    "repositories": [
+        {
+            "type": "path",
+            "url": "../plugin",
+            "options": {
+                "symlink": false
+            }
+        },
+        {
+            "packagist.org": false
+        }
+    ],
+    "require": {
+        "shirabe-test/process-executor-probe": "1.0.0"
+    },
+    "config": {
+        "process-timeout": 42,
+        "allow-plugins": {
+            "shirabe-test/process-executor-probe": true
+        }
+    }
+}