diff --git a/docs/GUIDELINES.md b/docs/GUIDELINES.md
index 9e29fe1..6ffb3b1 100644
--- a/docs/GUIDELINES.md
+++ b/docs/GUIDELINES.md
@@ -17,4 +17,12 @@ type: guidelines
 ## 3. Design for a split screen
 - The screen may be shared with another app. Do not assume full width.
 
-## 4. To be added
+## 4. Bind to the Orin's network explicitly
+- Android's default network is never the Orin link (it has no internet). Request
+  `TRANSPORT_ETHERNET` and bind to it; never rely on the default route.  
+
+## 5. Keep the device awake while displaying
+- A sleeping tablet is indistinguishable from a dead link. Hold the screen on
+  while the app is the display, and treat every reconnect as routine, not an error.  
+
+## 6. To be added
diff --git a/docs/impl/plans/INITIAL.md b/docs/impl/plans/INITIAL.md
index 54e550d..9f08025 100644
--- a/docs/impl/plans/INITIAL.md
+++ b/docs/impl/plans/INITIAL.md
@@ -1,7 +1,7 @@
 ---
 type: plan
 status: active
-updated: 2026-09-04
+updated: 2026-10-09
 ---
 # Initial plan
 
@@ -19,9 +19,9 @@ needs no routing engine at all. Routing is the expensive last fraction.
 
 ## Open
 
-- **Transport.** Over USB the tablet has an IP link via RNDIS, so it can reach the
-  broker directly. Whether it should, or should go through `svc-gw`, is decided in
-  that repo — see its initial plan.
+- **Transport.** Whether the app reaches the broker directly or goes through
+  `svc-gw` is decided in that repo — see its initial plan. The physical link is
+  settled (below).
 - **CJK labels.** MapLibre cannot ship Japanese glyph sets as SDF ranges. Local
   font rendering must be configured, or labels will be slow or absent.
 - **Sunlight.** A typical tablet is unreadable through a windscreen in daylight.
@@ -38,7 +38,29 @@ Two channels with different guarantees, not one socket:
 | On reconnect | expect current state immediately | resend anything pending |
 
 This client always initiates and owns reconnection — the Orin never dials out.
-Assume the link drops constantly: cable knocked, screen off, WiFi lost.
+Assume the link drops constantly: cable knocked, screen off, power changes.
+
+## The USB link, as measured (2026-10-09)
+
+Tested with the actual tablet (Redmi Pad SE 8.7 4G, Android 16) against the car
+Orin. Details: [USB tablet link report](gitea:yukart/orin-nano-env-setup).
+
+- **Physical:** tablet USB-C → PD hub (charging from the car) → Orin's USB-C port.
+  The tablet is the USB host; the Orin is a USB network gadget. The tablet picks
+  **NCM** and gets `192.168.55.100`; the Orin is **`192.168.55.1`**.
+- **Android won't route over it by default.** The link has no internet, so it never
+  becomes the default network while WiFi or cellular is up, and ordinary sockets go
+  elsewhere. Verified: the Orin was unreachable until WiFi and cellular were off.
+  The app must request the Ethernet network (`ConnectivityManager.requestNetwork`
+  with `TRANSPORT_ETHERNET`) and bind its sockets to it.
+- **About 3 s blank per power change.** Cutting the hub's PD costs ~3.5 s (full
+  USB detach); restoring it ~2.2 s. Ignition and cranking produce these.
+- **An asleep tablet is a dead link.** Off charger and idle, Android suspends about
+  a minute after screen-off and answers nothing, while the Orin still sees the USB
+  link up. The app keeps the device awake while it is the display (screen-on flag
+  in the full UI; the same for any overlay widget).
+- Reconnect without user action, and expect the Orin to drop a silent client by
+  heartbeat (project-yukart decision 24).
 
 ## Session marking is worth building early