Validate and expand dock, USB-C, PD, Ethernet, and external-display diagnostics

[deucebucket]

Current prototype

This branch inventories USB topology, Type-C roles/partner exports, PD telemetry, DP Alt Mode, external DRM connectors, USB Ethernet, and current-boot UCSI/xHCI/USB/display-link errors.

Scope

Build a repeatable direct-vs-dock A/B workflow that can locate failures to the Deck, upstream cable, PD supply, dock hub, Ethernet adapter, display/EDID path, or one peripheral.

Acceptance criteria

• Produce a privacy-safe dock identity/capability record without serial numbers.
• Record topology, negotiated USB speed, Type-C roles, PD revision/contract when exported, Alt Mode, connector/mode/EDID state, Ethernet driver/link, and aligned resets.
• Compare direct charger/display/network paths with docked paths and generate a differential summary.
• Test official and representative third-party docks, multiple PSUs/cables, HDMI/DP, Ethernet, suspend/resume, and hotplug.
• Distinguish a deliberate unplug from repeated topology resets or correlated path errors.
• Document inaccessible kernel exports and measurement limits.
• Add fixtures for one-function failure, shared-path failure, underpowered negotiation, flapping Ethernet, bad EDID, and healthy dock.

Safety boundary

Software telemetry can observe exported voltage/current/power and negotiation; it cannot certify transient rail quality, electrical safety, or advertised dock wattage. Do not flash unofficial firmware or force Type-C/PD state.

Docs

docs/wiki/Dock-USB-C-and-External-Displays.md