Add v0 networking governance foundation

[danieldilly]

Summary

Establishes foundational governance for v0 multiplayer networking.

• Add 4 invariants (INV-0003 to INV-0006): server authority, plane isolation, tick-indexed I/O, replay verifiability
• Add 6 domain concepts (DM-0005 to DM-0010): Entity, InputCmd, Snapshot, Session, Channel, Match
• Add acceptance criteria (AC-0001) and kill criteria (KC-0001, KC-0002) for v0 milestone
• Create 5 ADRs (ADR-0001 to ADR-0005) documenting architectural decisions
• Add networking parameters doc for tunable values (tick rates, validation thresholds)

Trace Block

Issue: N/A
Spec: N/A: governance
Constitution: INV-0003, INV-0004, INV-0005, INV-0006, DM-0010, AC-0001, KC-0001, KC-0002
ADRs: ADR-0001, ADR-0002, ADR-0003, ADR-0004, ADR-0005

Files Changed

Constitution documents:

• docs/constitution/invariants.md — Added INV-0003, INV-0004, INV-0005, INV-0006; added v0 determinism scope to INV-0006
• docs/constitution/domain-model.md — Added DM-0005 through DM-0010
• docs/constitution/acceptance-kill.md — Added AC-0001, KC-0001, KC-0002
• docs/constitution/tag-taxonomy.md — Added 14 networking/architecture tags
• docs/constitution/id-index.md — Generated (via just ids-gen)
• docs/constitution/id-index-by-tag.md — Generated (via just ids-gen)
• docs/constitution/id-catalog.json — Generated (via just ids-gen)

ADRs:

• docs/adr/0001-three-plane-architecture.md — Three-Plane Architecture
• docs/adr/0002-deterministic-simulation.md — Deterministic Simulation
• docs/adr/0003-fixed-timestep-simulation.md — Fixed Timestep Simulation Model
• docs/adr/0004-server-authoritative-architecture.md — Server-Authoritative Architecture (fixed dangling ADR-0011 reference)
• docs/adr/0005-v0-networking-architecture.md — v0 Networking Architecture

Parameters:

• docs/networking/v0-parameters.md — Tunable networking parameters (tick rates, validation thresholds)

Other:

• docs/vision.md — Minor formatting updates

Determinism / Simulation Impact

• This PR changes simulation-plane logic
  • No simulation-plane changes. This PR is governance-only (Constitution + ADRs + parameters).

Verification

What you ran and what passed.

• just ci — All checks passed (fmt, clippy, test, ids, spec-lint)
• just ids — Constitution IDs validated
• just ids-gen — Generated indices committed (id-index.md, id-index-by-tag.md, id-catalog.json)

Risk / Notes

This is a foundational governance package. All new IDs use Status: Proposed and will be flipped to Status: Active after merge.

Key additions:

• INV-0003 (Authoritative Simulation): Server is single source of truth; clients are untrusted
• INV-0004 (Simulation Plane Isolation): No I/O, networking, or side effects in simulation
• INV-0005 (Tick-Indexed I/O Contract): All inputs/outputs carry explicit Tick identifiers
• INV-0006 (Replay Verifiability): Replay artifacts must reproduce authoritative outcomes (v0 scope: same build/platform)
• DM-0010 (Match): Game instance scope with fixed tick rate and lifecycle
• AC-0001 (v0 Two-Client Multiplayer Slice): Composite acceptance criterion with 5 pass conditions (connectivity, WASD, plane integrity, validation, replay)
• KC-0001 (Plane Boundary Violation): Hard stop on Simulation Plane I/O violations
• KC-0002 (Replay Verification Blocker): Release blocker if replay fails
• ADR-0005 (v0 Networking Architecture): Two-layer design (semantic contract + transport adapters); ENet for v0, QUIC-aligned for future WebTransport

No implementation yet — this PR establishes the governance rules for upcoming v0 implementation work.

Follow-up: Consider updating governance-change template to handle composite/foundational governance packages.

Checklist

• Trace block is complete and accurate
• This PR stays within Constitution invariants (no silent weakening)
• No new dependencies added, or licensing intake updated under docs/licensing/
• Spec exists for non-trivial changes, or N/A: governance justified
• Gates added per spec's Gate Plan (N/A for governance-only PR)