Closes #24.

What

Automatic OpenTelemetry instrumentation for Symfony Scheduler (https://symfony.com/doc/current/scheduler.html). One CONSUMER span per
scheduled-task run, emitted by SchedulerSubscriber listening to PreRunEvent / PostRunEvent / FailureEvent.

Attributes

OTel messaging semconv:

• messaging.system = symfony_scheduler
• messaging.operation.name = process, messaging.operation.type = process
• messaging.message.id (from MessageContext::$id)
• messaging.message.class (FQCN of the dispatched message)
• messaging.destination.name (schedule name)

Traceway-specific scheduler.* namespace (anticipating any future OTel scheduler semconv):

• scheduler.schedule.name
• scheduler.trigger.type (short class name of the trigger, e.g. CronExpressionTrigger, PeriodicalTrigger)
• scheduler.trigger.expression ((string) $trigger — cron expression, interval, etc.)
• scheduler.triggered_at (ATOM-formatted)
• scheduler.trigger.next_run_at (ATOM-formatted, only set when known)
• scheduler.cancelled = true when a listener calls PreRunEvent::shouldCancel(true)

Errors: recordException + error.type via ErrorTypeResolver. FailureEvent::shouldIgnore() is honored — ignored failures end with STATUS_OK.

Coordination with Messenger middleware

Scheduler dispatches go through the Messenger bus, which would otherwise produce duplicate PRODUCER/CONSUMER spans alongside the scheduler span.
OpenTelemetryMiddleware now skips any envelope carrying Symfony's ScheduledStamp when scheduler instrumentation is active (toggled via
$excludeScheduledMessages, wired automatically in the extension). The stamp class is referenced by string + class_exists guard so Messenger
users without symfony/scheduler aren't affected.

Configuration

open_telemetry:
scheduler_enabled: true # default

Service definition is only registered when symfony/scheduler is installed (checked via interface_exists(ScheduleProviderInterface::class),
matching the bundle's pattern for optional-dep gating).

Lifecycle

• Spans are keyed by message object identity (SplObjectStorage) to handle nested/concurrent runs.
• Implements ResetInterface: reset() drains any in-flight spans (long-running workers, container resets).
• __destruct() drains as a last-resort safety net with scope-detach notices suppressed.
• Cancellation is observed via a low-priority (-256) PreRun listener so any user listener has already had a chance to set shouldCancel(true)
  before we end the span.

Tests

• SchedulerSubscriberTest (235 LOC) covers PreRun/PostRun success, FailureEvent (recorded vs ignored), cancellation, nested runs, reset
  behavior.
• OpenTelemetryMiddlewareTest adds 77 LOC verifying ScheduledStamp envelopes bypass the middleware on both dispatch and consume paths.