v0.3.0 changelog

Added

• Added Agent Task as a first-class Agent Runtime contract.
• Added task lifecycle, attempts/runs, task graph, progress, delivery state, and task control-plane semantics.
• Added task orchestration events and attempt lifecycle events to the public event schema.
• Added task records, task attempts, task relationships, task summary, blocked tasks, and delivery state to the public snapshot schema.
• Added task-aware implementation guidance, acceptance scenarios, telemetry correlation, quickstart, examples, glossary, source analysis, and research sources.

Changed

• Clarified that job, subagent, run, step, and todo are related to task execution but do not replace task semantics.
• Expanded the latest specification's identity, event, control-plane, snapshot, completion/failure, and validation sections around Agent Task.