fix: review follow-ups on the php_server refactor

[nicolas-grekas]

Follow-up to #2499, targeting refactor/phpserver. Four commits, each independently reviewable.

Findings from a close read of the branch. Nothing here changes the direction of the refactor; the first two are the ones I would not want to ship.

1. The per-worker Mercure hub is dropped

assignMercureHub() fills workerConfig.options, but the new toWorkerOptions() builds a fresh slice and never appends it, where Start() used to pass w.options directly. The field is now written and never read.

WithWorkerMercureHub() appends WithMercureHub() to the worker request options, which is what lets a worker publish from its startup code, outside frankenphp_handle_request(). Request-scoped publishing kept working because the module carries WithMercureHub() in its own request options, which is why no test noticed. #2543 extends the same function and inherits the bug.

2. FrankenPHPModule.server can be nil in ServeHTTP()

It is assigned by FrankenPHPApp.Start(), but caddy starts apps by ranging over a map, so the http app can begin serving first. The handler dereferenced it unconditionally, turning that window into a nil pointer panic where main returned a clean ErrNotRunning.

Two neighbouring lifecycle issues are fixed in the same commit: modules left in app.modules by a config that failed to provision are registered again by the next reload (the app is a process singleton and reset() only runs at the end of Start()), and match in a global worker block was parsed then silently ignored, so it is now rejected at parse time as docs/config.md already documents.

3. A Server could not be registered twice

unregisterServers() only flipped isRegistered, so the worker slices and maps kept the previous run's entries and a second Init() with the same *Server failed with two workers in a server cannot have the same filename. Caddy dodges this by building a fresh NewServer per Start(), but docs/library.md presents NewServer + Init as the library pattern with no hint the instance is single-use.

Same commit: the server_<idx> default was written into s.name permanently, servers were marked registered about a hundred lines before initWorkers() and the thread setup (a request in that window found neither a worker nor a regular thread, so activateServers() is split out), and WithWorkerMatcher() without WithWorkerServerScope() was a silent no-op that still got path-matched via globalWorkersByPath, the opposite of what the matcher asked for.

4. Logger and prepared env

Worker startup contexts hardcoded globalLogger even though the worker's server was at hand, so worker boot messages and worker stdout bypassed the per-php_server logger this branch introduces. The module used to append WithRequestLogger() to each worker's request options and that line is gone, so nothing else covered it.

go_register_server_variables() merged the prepared env whenever the server had one, but registerPreparedEnv() only runs from go_update_request_info(), which returns early without a request. For a server-scoped extension worker handling a message the merge copied whatever the thread-local prepared env held from an earlier request.

Tests

Added: toWorkerOptions() keeps provisioned options, a Server re-registered after Shutdown() still serves its worker and keeps its name, and a request matcher without a server scope is rejected.

Both modules pass go vet including test files. The runtime tests need CI: on my box (WSL2) per-thread engine bootstrap of an embed ZTS build is pathologically slow and linking needs dev libs I do not have, so every Init()-based test is unrunnable locally, including on unmodified base commits.

Not included

worker.mercureHub is assigned by configureMercure() and never read anywhere; removing the dead field touches the nomercure build-tag pair, so I left it alone. Say the word and I will fold it in.