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## Problem The firmware computes packet content hash as: ``` SHA256(payload_type_byte + [path_len for TRACE] + payload) ``` Where `payload_type_byte = (header >> 2) & 0x0F` — just the payload type bits (2-5). CoreScope was using the **full header byte** in its hash computation, which includes route type bits (0-1) and version bits (6-7). This meant the same logical packet produced different content hashes depending on route type — breaking dedup and packet lookup. **Firmware reference:** `Packet.cpp::calculatePacketHash()` uses `getPayloadType()` which returns `(header >> PH_TYPE_SHIFT) & PH_TYPE_MASK`. ## Fix - Extract only payload type bits: `payloadType := (headerByte >> 2) & 0x0F` - Include `path_len` byte in hash for TRACE packets (matching firmware behavior) - Applied to both `cmd/server/decoder.go` and `cmd/ingestor/decoder.go` ## Tests Added - **Route type independence:** Same payload with FLOOD vs DIRECT route types produces identical hash - **TRACE path_len inclusion:** TRACE packets with different `path_len` produce different hashes - **Firmware compatibility:** Hash output matches manual computation of firmware algorithm ## Migration Impact Existing packets in the DB have content hashes computed with the old (incorrect) formula. Options: 1. **Recompute hashes** via migration (recommended for clean state) 2. **Dual lookup** — check both old and new hash on queries (backward compat) 3. **Accept the break** — old hashes become stale, new packets get correct hashes Recommend option 1 (migration) as a follow-up. The volume of affected packets depends on how many distinct route types were seen for the same logical packet. Fixes #786 --------- Co-authored-by: you <you@example.com>