mallinfo().fordblks counts only free bytes within the committed arena.
On STM32WL (newlib sbrk heap) the arena grows lazily from _end toward SP,
so fordblks reads near-zero at early boot even when ~48 KB of addressable
space remains. This caused NodeDB::isFull() to fire prematurely and evict
nodes on a freshly booted device.
Fix getFreeHeap() to include uncommitted sbrk headroom (SP - sbrk(0)) so
the returned value reflects true available memory throughout the boot
lifecycle.
Introduce MESHTASTIC_DYNAMIC_SBRK_HEAP as an opt-in build flag (set in
stm32.ini) so the fix is gated to platforms with a dynamic sbrk heap
rather than a static heap. Future platforms with the same heap model can
opt in by adding this flag.
Signed-off-by: Andrew Yong <me@ndoo.sg>
Assisted-by: Claude Sonnet 4.6 <noreply@anthropic.com>
Andrew YongandChloe Bethel
0ee5777c15