RFC: Tracker execution contracts and preview observation

[bokelley]

Summary

Proposes a coherent AdCP 3.3 design for two related but distinct surfaces:

• a format-option-scoped production contract for buyer tracker acceptance and
  initiation, advancing RFC: Measurement capability declaration (tracking_capabilities, attribution methodologies, TMP exposure data) #6207 without a product-wide union; and
• an opt-in creative-preview observation session for macro processing,
  interactions, creative events, and safely intercepted outbound actions.

The RFC keeps three claims separate: a seller's production commitment, the
exact macro semantics introduced by #6767, and evidence from one controlled
preview execution. None is allowed to imply either of the others.

Key decisions proposed

• Tracker execution commitments live on the selected product format option,
  not as a product-wide union.
• Package state retains an immutable, placement-bound selected-format snapshot
  and digests; later discovery changes do not mutate the serving contract.
• An exact event selector promises one initiation in total; client/server are
  possible execution paths, not permission to double-fire.
• Macro handling reuses feat(creative): define delivery representations and macro resolution #6767's dialect, semantic, actor, context, and encoding
  tuples rather than introducing a second macro vocabulary.
• Interactive preview observation is a provider-side isolated session with an
  ordered trace. Consumer preview renders remain inert.
• Tracker/navigation egress is intercepted before dispatch. The trace reports
  intercepted or blocked, never falsely claims delivery.
• DR-0005 is narrowed only for an explicitly requested Live Integration
  observation session; ordinary serve-time substitution remains outside wire
  observation.
• Impression-ID source, delivery exports, TMPX log joins, attribution methods,
  and portable scripted scenarios are split into correctly owned follow-on
  work.

Scope

This PR is the working-group RFC only. It intentionally does not add normative
schemas before the needs-wg-review decisions on #6207 are ratified. The RFC
now lists explicit ratification gates for the 3.3 version line, immutable event
registries, per-version VAST/DAAST matrices, DAAST plural acceptance, package
snapshots, authority projections, and digest preimages.

Once the shape is accepted, implementation should land as two reviewable
protocol PRs:

1. the production tracker execution contract; and
2. preview observation capabilities, tasks, session schemas, and Live
   Integration vectors.

Validation

• All 16 JSON examples parse.
• Reviewed against the existing preview request/response and reference
  renderer behavior.
• Reviewed against feat(creative): define delivery representations and macro resolution #6767 macro ownership and translation semantics.
• Reviewed against current VAST/DAAST tracker asset coverage and the dormant
  substitution-observer test kit.
• Uses fictional entities only.

Advances #6207; it does not close the issue or claim implementation.
Related: #3832, #6767.

[aao-secretariat]

Ladon verdict: Approve

Approve — single-file nonnormative RFC with no blocking or medium findings.

Checked:

• Scope: only specs/tracker-execution-preview-observation.md (1518 additions). No changes under static/schemas/source/**, docs/reference/**, dist/**, or task schemas — so no schema↔docs drift, oneOf regression, or artifact-immutability exposure.
• Changeset: correctly absent — specs/ is outside PROTOCOL_SCOPED_PATHS (verified against scripts/check-changeset-protocol-scope.cjs), and L1522-1524 documents the rationale.
• Governance: DR-0005 cited by ID and handled correctly (supersession only upon human ratification; declines to write a decision record). All changes additive and gated behind explicit ratification gates — no Breaking-class change auto-approved here.
• Naming/conventions: AdCP throughout; no AAO/ADCP/Alliance; fictional entities only.
• Coherence: wire-compat floor (L36-38) consistent with DR-0009; exactly-once model (L1281-1284) coherent with summary states (L1362-1371).

No Critical/High/Medium findings. gated_paths is false and no author-team gate applies, so despite review_decision=REVIEW_REQUIRED the PR falls through to row 9.