Closes Tier 1 #5. The previous §7.2 was four bullet points naming the
"answer with an announce" rule but missing every wire detail —
implementation-time the SF mobile client got steps 4 (dedup) and 5
(local-destination check) wrong on its first cut and the bug only
surfaced as "I can message my own destination but no one else can
reply".
§7.2 is now six sub-sections:
§7.2.1 Path-request packet parse rules. The handler's slice
recipe with branching on payload length (32B = leaf form
target||tag; 48B+ = transport form target||transport_id||
tag); tag cap at 16B; tagless-request rejection.
§7.2.2 Tag-based dedup via Transport.discovery_pr_tags. The
unique_tag = dest_hash || tag construction, the 32000-
entry cap, why missing this turns a leaf into a broadcast-
storm amplifier on retransmits.
§7.2.3 The five-way dispatch in Transport.path_request:
local-destination / transit-knows-path / local-client-
forward / discovery-recursive / drop. Branches 1 and 5
are the only ones a leaf needs.
§7.2.4 Path-response announce wire format. Body byte-identical
to a regular announce (§4.1); only the outer packet
context byte differs (NONE → PATH_RESPONSE 0x0B).
PR_TAG_WINDOW=30s body-cache that serves identical wire
bytes to racing relays so transit dedup converges.
§7.2.5 Timing constants: PATH_REQUEST_GRACE = 0.4s, +
PATH_REQUEST_RG = 1.5s for roaming-mode interfaces.
Local-destination and local-client originator branches
bypass the grace.
§7.2.6 Minimum responsibility for a non-transport leaf — the
six-step protocol-level recipe.
flows/path-discovery.md: 9-step chronology covering both
single-hop leaf-owns-target and two-hop transit-relay-knows-path
cases. Wire-byte ladder diagrams for both. Notes the ingress-limit
bypass for path-responses (Transport.py:1632-1639), the
receive_path_responses opt-in for handler dispatch
(Transport.py:1989-1991), and the timeout/escalation path through
LXMRouter.process_outbound's MAX_PATHLESS_TRIES retry counter.
flows/README.md status table updated.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
