Route invalidation through PSR-14 events

[Firehed]

Closes #642.

The invalidator fan-out (InvalidatableInterface, CompositeInvalidatable) is replaced with a PSR-14 event bus. Two file-shaped events are published by the LSP handlers, and one internal event is published by the map reader when it detects a vendor/composer/ change:

• WatchedFileChangedEvent — from workspace/didChangeWatchedFiles
• OpenDocumentClosedEvent — from textDocument/didClose
• AutoloadMapRegeneratedEvent (in Knowledge; carries the fresh map) — from the map reader

Subscribers register against each concrete event type. Backends stop polling ComposerAutoloadMapReader::current() on every invalidation to check for map identity changes; instead they receive the new map on the event and rebuild their derived indexes on the next query.

Notes

• PSR-14 dispatcher and provider are home-grown, ~40 LoC together in src/Events/. Sufficient for one composition root; nothing depends on Symfony or Tukio.
• Subscription is exact-string match on EventInterface::$type (each event sets it to self::class). No is_a, get_class, $event::class, or $event instanceof $var on the dispatch path — those are all disallowed as kind inspection (RFC 1 §4.5). A subscriber that treats two events the same way registers the same callable against each concrete type. FileEventInterface still exists as a listener parameter type for narrowing; it is not a subscription target.
• EventDispatcher is typed on the concrete ListenerProvider, not Psr\EventDispatcher\ListenerProviderInterface. The PSR interface's getListenersForEvent() returns iterable with no value type, so an interface-typed field forces every dispatch site to widen through mixed. This is one call site; the concrete typing avoids that.
• AutoloadMapRegeneratedEvent lives in Knowledge/, not Events/, because it carries ComposerAutoloadMap (confined to backends by SymbolDiscoveryAuthorityExtension). Keeps the exempt-namespaces list unchanged.
• Nesting is synchronous: the map reader dispatches AutoloadMapRegeneratedEvent from inside its WatchedFileChangedEvent handler; downstream listeners run in the same tick before control returns.
• Container-compatibility: every new class is a plain-constructor service with typed deps. The step-12 migration moves the assembly body from KnowledgeStack::assemble() into a container factory closure (or a bootstrap seam) with no shape changes.

Enforcement edits, made at Eric's direction

deptrac.yaml: new Events layer covering src/Events/; edges Handler -> Events and Knowledge -> Events; Handler -> Cache edge removed (no Handler file references Cache after this change).

Test plan

• composer test (phpstan, deptrac, layer-coverage, phpunit, phpcs) green
• Unit tests updated for the new API: CachingSymbolSourceTest, ComposerAutoloadMapReaderTest, ComposerMapBackendTest, AutoloadFilesBackendTest, DidChangeWatchedFilesHandlerTest, TextDocumentSyncHandlerTest, plus new ListenerProviderTest and EventDispatcherTest
• Integration tests kept and updated: ExternalFileChangeInvalidationTest, ComposerRegenerationInvalidationTest

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 95.09804% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 99.55%. Comparing base (4c534ba) to head (82341dd).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/Knowledge/AutoloadFilesBackend.php	70.00%	3 Missing ⚠️
src/Events/OpenDocumentClosedEvent.php	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #643      +/-   ##
============================================
- Coverage     99.65%   99.55%   -0.10%     
- Complexity     1913     1922       +9     
============================================
  Files           134      138       +4     
  Lines          4940     4968      +28     
============================================
+ Hits           4923     4946      +23     
- Misses           17       22       +5     

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