[h2zero]

…mBLE host task

Summary

• Adds a public utility, bool NimBLEUtils::runOnHostTask(std::function<void()> func). It lets library users run code on the NimBLE host task. Callers capture whatever context they need in the callable instead of passing a void* plus a lifetime contract.

Behavior

• Already on the host task: func runs immediately and the call returns true.
• Any other task: func is moved into a heap-owned context and queued on the default NimBLE event queue. The host task runs it asynchronously, then frees the context.
• Host task not running (before NimBLEDevice::init() or after deinit): the call returns false and the callable is dropped.
• Empty std::function: returns false.

Design notes

• Ownership: the callable and its ble_npl_event live in one heap-allocated HostTaskContext. This replaces a stack-local event and a pointer to the caller's std::function, which were both dangling hazards.
• Captured state: values captured by the callable are copied or moved into the context. Anything captured by reference or raw pointer must stay valid until the callable runs. Use values or a shared_ptr when lifetime is uncertain.
• Pending-task tracking: queued contexts are kept in a spinlock-protected intrusive list and unlinked in executeHostTask.
• Shutdown: NimBLEUtils::deinit() calls the new drainHostTasks(). It clears the host-task handle and removes queued events with ble_npl_eventq_remove. It then frees the contexts without running them. Queueing and the handle check share one lock, so a call racing with deinit is either rejected or drained, never leaked.

API contract

• The callable runs asynchronously unless the caller is already on the host task. This is not a completion or wait mechanism.
• The callable must not throw. It runs inside NimBLE's C event loop.
• Work queued but not yet run when the stack is deinitialized is discarded.
• A false return means the work was not run or queued.

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