P3-H P0: centralize Process Bus VLAN invariants

[masarray]

Tracks #139. Continues #24 / #33 / #36 from exact main baseline c7238d3a8ff86b30b397164c5fcbed820562b3e0.

Why

The core Ethernet encoder already rejects IEEE 802.1Q VID 4095, but several upstream SV/Studio/embedded gates accepted it. That allowed an invalid profile to survive configuration/deployment validation and fail only when the frame/template reached the encoder. The generic PTP Ethernet builder had the same off-by-one inconsistency.

This PR removes that split authority.

Architecture

• Ethernet core owns the generic 802.1Q invariant:
  • PCP 0..7
  • VID 0..4094
  • VID 4095 reserved
• SV compiler, SV frame codec, Studio device bridge and ESP32-P4 runtime consume that authority.
• Generic PTP Ethernet framing consumes the same Ethernet invariant.
• PTP runtime policy remains separate and may still intentionally reject VID 0 for its own profile; this PR does not broaden that policy.
• SV priority-tagged VID 0 remains valid.
• No change to current 4I+4V packet layout, scheduler, waveform engine, smpCnt policy or synchronization policy.

Regression coverage

• SCL/SV profile compiler: VID 0 remains valid through the existing 4800 fixture, VID 4094 accepted, VID 4095 rejected before a profile is produced.
• SV frame codec: VID 0 and 4094 encodable; VID 4095 fails closed.
• Generic PTP Ethernet builder: VID 0 and 4094 accepted; VID 4095 and PCP 8 rejected.
• Existing golden SV bytes remain unchanged for valid reference traffic.

Multi-thread / recovery boundary

This is only P0 of #139. Do not fold P0.1 WirePlan, multi-ASDU, IEC 61869-9 profile expansion, scaling, PRP/HSR or admission planning into this PR.

Next node after this PR is accepted: P0.1 deterministic encoder-produced WirePlan/patch metadata, replacing find_fixed_field() without adding a second BER parser.

Merge gate

Keep Draft until exact-head required CI is green. Physical bench evidence is not required for this pure validation invariant change, but no product/release conformance claim is made by this PR.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-06T12:44:46.241978Z	a09e031	Draft marked ready

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