docs(handoff): node-side mesh diagnosis — nginx v6 fixed, real blocker is session path quality

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/HANDOFF-2026-07-23-companion-apk-deploy.md

@@ -85,3 +85,44 @@ what remains to the node side. State as of vc24:
     - `ip addr show fips0` + confirm the web server listens on `[::]:80`
   Report whether the node ever sees a session attempt from
   `npub132c5whrsa6ccs0eylcpzaejq9uxul5ldvczz0axq78dh7fxkqj9st4uvzu`.
+
+## Node-side diagnosis complete (23:00–23:30, archi-dev-box agent)
+
+Chain of findings, each verified live:
+
+1. **FIXED: nginx had no IPv6 listener anywhere** — every shipped config
+   listened on 0.0.0.0 only, so `http://[<ULA>]` could NEVER connect on any
+   node, ever. Live-fixed on framework-pt + .116, canonical conf + bootstrap
+   self-heal shipped (`1e89362e`), heal binary deployed. ULA HTTP verified
+   answering on both nodes (local + over-mesh).
+2. Firewall clean, fd00::/8 routes correct both ends, wire compat proven
+   (node + vps2 anchor both run fips 0.4.1 rev 15db6471db — the latest
+   upstream stable; nothing newer exists).
+3. **THE REMAINING PROBLEM IS MESH SESSION PATH QUALITY.** From the vps2
+   anchor — a DIRECT connected peer — `GET /health` on the node's ULA takes
+   **15–17 s per request and intermittently fails outright** (nginx logs
+   show 499 client-gave-up then 200; TCP SYN-retransmit backoff signature).
+   Session MMP is wildly asymmetric: node→vps2 srtt 204 ms, **vps2→node
+   srtt 4270 ms** — on a direct link whose raw RTT is 4 ms. Session traffic
+   is not riding the direct link; it appears to route through the ~1271-node
+   public tree (node's tree root is the public 00001a8c, depth 8; the node's
+   log also shows chronic "Discovery lookup timed out" for other targets).
+4. The phone's npub never appears in the node's sessions — consistent with
+   discovery/handshake dying on the same degraded tree path, and the app's
+   ~8 s probe window being far smaller than the observed 15 s+ first-request
+   latency even on the GOOD path.
+
+### Recommendations
+
+- **App side (Mac agent):** widen the ULA probe/connect window to ≥30 s
+  with retransmit-friendly pacing, and PRE-WARM the mesh session (start
+  pinging the node ULA as soon as the VPN is up, decoupled from the UI
+  probe) so the WebView hits a warm session.
+- **Infra decision (user):** consider detaching the fleet from the public
+  v0l mesh — private tree rooted at the vps2 anchor (drop the legacy
+  185.18.221.160 seed anchor fleet-wide AND vps2's public peering). A
+  2-hop private tree would make session paths ride the direct links and
+  should collapse latency to ms. Trade-off: no reachability to/from the
+  broader public mesh.
+- **Upstream:** report the direct-peer session-path asymmetry to
+  jmcorgan/fips (0.4.1).