Approve FS-0007: v0 Two-Client Multiplayer Slice

[danieldilly]

Summary

Approves FS-0007 v0 Two-Client Multiplayer Slice specification after extensive iterative review with multiple senior reviewers. Changes spec status from Draft to Approved, marking it implementation-ready.

Key refinements:

• Complete wire schemas for all protocol messages (ClientHello, ServerWelcome, JoinBaseline, SnapshotProto)
• Explicit detectability data contract with tie evolution semantics for InputSeq selection
• Byte-identical snapshot broadcast for v0 floor coherency
• 20 Tier-0 gates with concrete, testable acceptance criteria
• Constitution and ADR updates to close governance gaps

Trace Block

Issue: #7
Spec: docs/specs/FS-0007-v0-multiplayer-slice.md
Constitution: AC-0001, INV-0001, INV-0002, INV-0003, INV-0004, INV-0005, INV-0006, INV-0007, DM-0001, DM-0002, DM-0003, DM-0005, DM-0006, DM-0007, DM-0008, DM-0009, DM-0010, DM-0011, DM-0014, DM-0015, DM-0016, DM-0017, DM-0018, DM-0019, DM-0020, DM-0021, DM-0022, DM-0023, DM-0024, DM-0025, DM-0026, DM-0027, KC-0001, KC-0002
ADRs: ADR-0001, ADR-0002, ADR-0003, ADR-0004, ADR-0005, ADR-0006, ADR-0007

Files Changed

• docs/specs/FS-0007-v0-multiplayer-slice.md (status: Draft → Approved; +263/-57 lines)
• docs/constitution/acceptance-kill.md (AC-0001 clarifications: testable synchronization definition, entity binding requirement)
• docs/adr/0006-input-tick-targeting.md (added v0 floor coherency normative constraint)
• docs/networking/v0-parameters.md (minor parameter documentation updates)

Determinism / Simulation Impact

• This PR changes simulation-plane logic
  • No simulation implementation changes. This PR approves the specification only. Implementation will follow in a subsequent PR that references this approved spec.

Verification

• just ci (all checks pass)
• just ids (Constitution ID validation passes)
• just spec-lint (FS-0007 structure and ID references validated)
• Constitution docs changed: just ids-gen run and outputs committed (AC-0001 updates)

Risk / Notes

Spec Completeness: This spec underwent extensive review with multiple senior reviewers across 20+ refinement rounds. All P0 blockers closed:

• Wire schemas complete and consistent
• Validation rules unambiguous with single normative triggers
• Tie detection semantics explicitly defined (max_seq_tied evolution)
• Floor coherency byte-identical and testable
• Recovery under packet loss validated via T0.13a
• 20 Tier-0 gates enforce all critical requirements

Implementation Next Steps: Once merged, implementation work for AC-0001 can begin using this approved spec as the definitive requirements document.

Spec Length: 554 lines. Reviewer feedback noted this feels long due to Constitution material repetition. Post-v0 refactor tracked to move stable patterns into Constitution and shrink specs to deltas only. Not blocking for v0.

Checklist

• Trace block is complete and accurate
• This PR stays within Constitution invariants (no silent weakening)
• No new dependencies added
• Spec exists for non-trivial changes (FS-0007 approved)
• Gates defined per spec's Gate Plan (20 Tier-0 gates in FS-0007)