v0.4.0

• Adds named simulation profiles (baseline, swarm, replay, and
  performance) that expand into run metadata, simulator options, and explicit
  runtime-control application. The replicated-register swarm now uses the
  shared profile and reports the expanded profile values in traces and failure
  summaries.
• Adds a durable-broadcast bug-search test that finds the planted
  broadcast-before-sync bug under probabilistic crash-loss faults while keeping
  the deterministic single-seed failure for readable traces.
• Adds scheduler-backed Io.Group async/concurrent/await/cancel behavior with
  deterministic task ownership, reuse, and process-kill cleanup.
• Adds the simulated directory operations needed by ordinary storage engines:
  absolute and handle-relative paths, create/open/access/stat, iteration,
  directory syncing through File.sync, and process-coordinated blocking and
  non-blocking advisory file locks. Directory namespace state now lives in
  SimDisk, so processes share it and crash metadata faults apply to it.
• Adds a pinned lazy Ochi validation that starts the unmodified store, ingests
  a line, flushes index/data tables, queries the line, crashes and reopens the
  store, and verifies the same line through recovery.
• Fixes a same-directory SimDisk.rename metadata allocation leak.
• Fixes sector read-modify-write handling so short std.Io writes retain their
  logical file length across crashes, and atomic rename discards pending writes
  belonging to the replaced destination.
• Fixes cross-process file-lock rekeying on rename so open lock holders release
  the renamed path and source/destination waiters are preserved.
• Adds process-scoped simulation std.Io backends with stable per-node
  identity, shared listener/connection registration, and process-local futex
  namespaces.
• Adds logical process lifecycle controls: killProcess, registered process
  initializers, and restart semantics that discard volatile state while
  preserving durable disk state.
• Fixes cross-process async closure cleanup so awaits release task closures
  through the owning backend.
• Requires callers to pass an allocator to Production.init, removing the
  production default to std.heap.smp_allocator.
• Retires completed scheduler task records after completion while preserving
  stable task counts.
• Narrows the public/internal module boundary so backend coordinators, task
  runtimes, process runtimes, and teardown hooks are kept under explicit
  internal roots.
• Adds a release-symbol readiness check that verifies simulation-only symbols
  are absent from release binaries.
• Adds a contributor-facing repository layout guide.