feat(eve): stamp schedule-dispatched sessions with $eve.schedule

[warmwind]

Closes #708

Problem

Sessions started by a schedule dispatch carry no record of which schedule fired. The markdown form only gets $eve.trigger = "schedule", and sessions a handler starts through args.receive(...) carry the target channel's kind instead — so trigger-based filtering can neither attribute runs to a specific schedule nor see channel-dispatched schedule work at all.

Change

• New ScheduleIdKey (eve.scheduleId) context key.
• ScheduleDispatcher.trigger wraps the whole dispatch in an eve context scope (the unified contextStorage, per the rule-19 invariant — no new AsyncLocalStorage) carrying the schedule name.
• buildRunContext inherits the key from the ambient scope into every run started inside the dispatch. This is what covers the args.receive(...) path: those RunInputs are built by the target channel's authored receive hook, out of the dispatcher's hands, so the value cannot be threaded through explicitly.
• buildSessionAttributes emits it as $eve.schedule. $eve.trigger semantics are unchanged — channel-dispatched sessions keep the channel kind and carry provenance alongside it.

Pure metadata addition, backward compatible: attributes ->> '$eve.schedule' = <name> now yields a schedule's complete run history regardless of dispatch path.

Testing

• ScheduleDispatcher tests assert the scope is active when runtime.run fires for both the markdown form and the args.receive(...) path, and cleared after the dispatch.
• Attribute builder tests cover readScheduleId well-formed/missing/malformed slots and the stamped session payload.
• pnpm test:unit (4435), pnpm test:integration (385), package typecheck, lint, guard:invariants, docs:check all pass.

🤖 Generated with Claude Code

https://claude.ai/code/session_0164WUaSv9mN58wgnnoN2vKG

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