Root cause: heltec_V4_boundary build was missing -DRNS_USE_TLSF=1 and
-DRNS_USE_ALLOCATOR=1 flags, causing ALL C++ new/delete to use internal
SRAM (239KB) instead of the PSRAM-backed TLSF pool (~1.6MB). Transport
data structures consumed internal heap until WiFi driver could not
allocate RX buffers (ESP_ERR_NO_MEM).
Changes:
- platformio.ini: Add TLSF/allocator flags to heltec_V4_boundary env,
re-enable NDEBUG
- Transport.cpp: Add periodic culling of _path_requests (was unbounded,
grew one entry per unique destination forever). Cull entries older than
DESTINATION_TIMEOUT. Also cull _pending_local_path_requests for removed
interfaces, and fix missing .erase() (Python .pop() equivalent).
- RNode_Firmware.ino: Replace WiFi watchdog halt-serial with auto-reboot.
Add heap pressure check (reboot if free heap < 20KB). Increase WiFi
grace period from 5s to 15s. Remove orphaned boundary_done label.
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