Saves the comprehensive OTA pipeline reference written by another
agent so future sessions don't lose the diagnostic flowchart or the
"three FW prerequisites" causal chain.
Tested live against current FW (v0.6.4): port 8032 reachable on both
sensors, scripts/ota-deploy.sh round-trip works, both nodes
successfully switched partitions (ota_0 ↔ ota_1) without USB+BOOT
dance. OTA is the supported path for future FW changes from this
session — sensor µs timestamp (ADR-106 open item), NVS persistence
of gain-lock (gap-analysis #5), and any larger FW work.
Kept whole (329 lines, over the usual 200 line cap for docs) because
the flowchart and pitfall table lose meaning if split. The cap is a
guideline for new project ADRs; a verbatim recipe is justified by
diagnostic value.
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