v2.4.0

Added

• Distributed runtime extension layer — Added devsper.distributed package with controller and worker-runtime wrappers for clean orchestration composition.
• Agent pool — Added runtime/agent_pool.py with reusable, worker-aware concurrent agent leasing (acquire_agent, release_agent, run_agent, run_parallel).
• Model router (runtime layer) — Added runtime/model_router.py for planning/reasoning/validation model routing with fallback chains.
• Speculative planner (runtime layer) — Added runtime/speculative_planner.py to predict and stage speculative successor tasks.
• Runtime HITL manager — Added runtime/hitl.py for pause/resume and explicit human-input request lifecycle handling.
• Execution graph upgrades — Extended runtime execution graph with worker assignment metadata and distributed lineage tracking.

Changed

• Executor composition — Runtime executor now integrates AgentPool, ModelRouter, speculative planning hooks, and distributed assignment tracking while preserving default behavior.
• Task runner routing — Task execution now supports pool-backed agent execution, scoped model routing, and fallback chain handling.
• Tool execution control — Runtime ToolRunner now supports bounded concurrency, dependency-aware batching, per-call timeout, cancellation, and structured results.
• Event backpressure handling — Runtime event stream now uses bounded queues with controlled overflow behavior.
• Runtime docs — Updated runtime architecture docs in devsper/README.md with distributed flow, worker/controller lifecycle, and HITL/speculative execution details.

Full Changelog: v2.3.0...v2.4.0