HAL capability audit — independent per-chain TX (CSD/STBC/beam-steer vs RF-path enable)

[josephnef]

Part of the spatial-diversity roadmap #127.

Goal

Establish what the Realtek Jaguar / 8814 HAL actually lets us drive on a
per-chain basis, since every downstream spatial technique depends on it. The
question is whether the chip exposes independent per-chain TX (each RF path
fed a controlled, phase-related copy of one stream — the substrate for cyclic
shift diversity, space-time coding, and beam-steer) or only a coarse
RF-path enable/disable.

Scope

• Enumerate the per-path controls the HAL surfaces on 2T2R (8812) and 4T4R (8814):
  path enable, per-path TX power, per-path phase/delay, per-path RF gain.
• Determine which spatial modes are reachable today (CSD is chip-validated; STBC
  is wired in the radiotap path but unresolved on-air) and which need new HAL work.
• Document the 8814's 4-path model vs the 8812's 2-path model, and the 3-SS
  baseband ceiling.

Deliverable

A capability matrix (mode x chip x "reachable today / needs HAL work") that gates
issues #C–#J. No hardware behaviour change in this issue — audit only.