Immediate PATH_RESPONSE for local clients: On ESP32, continuous TCP
backbone data can starve the jobs() loop for many seconds, causing
path discovery timeouts for local TCP clients. When a local client's
path request is satisfied by a cached announce, send the PATH_RESPONSE
immediately rather than queuing it for the next jobs() cycle.
Remove boundary-mode announce echo blocking: The boundary-specific
code that prevented backbone announces from overwriting LoRa paths
was redundant (the standard random_blob check already prevents echoes)
and harmful (it blocked TCP clients from learning backbone paths and
prevented correct transport routing for LINKREQUESTs).
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