K1-A — Phase 1 formal freeze (executable)¶

Status: Frozen, implemented on main, and now publicly released in v3.4.0 for K1-A Phase 1 (adapter-first). Parent: PLAN-K1-A2A-HANDOFF-DELEGATION-ROUTE-EVIDENCE-2026q2.md. Repo snapshot: Current assay-adapter-a2a plus ADR026 A2A fixtures emit typed task, message, and canonical assay.adapter.a2a.task.requested events, and now also emit the first bounded top-level handoff object on main. task.updated remains mapped but is still not a positive source in v1, and the ADR026 fixture set still does not include a dedicated task.updated packet. This freeze defines one bounded top-level handoff contract from existing typed fields only, with explicit negatives and no reuse of payload.discovery.

Contract honesty (product / review)¶

K1-A v1 is typed, adapter-emitted visibility evidence only. It is grounded in already-shipped A2A task/message fields, but it is not a full delegation graph, target-resolution surface, or handoff-correctness signal. Do not market this as “A2A delegation verified” or “route resolved” in v1. The only honest contract here is that a bounded handoff / delegation-route surface is visible in current typed A2A task-request packets, with limited task/message reference visibility on that same surface.

1. Definitive decision: typed-payload-only v1¶

Decision: K1-A v1 is typed-payload only.

Positive promotion for the new handoff seam is allowed only when all of the following hold:

1. the canonical emitted event type is assay.adapter.a2a.task.requested
2. the typed task payload contains task.kind == "delegation"

Not allowed in v1:

• attributes
• payload.discovery
• unmapped_fields_count
• unmapped top-level keys
• heuristics on agent.role, artifact, or generic message fallbacks

Deferred in v1:

• positive promotion from assay.adapter.a2a.task.updated until fixture-backed freeze evidence exists
• any target-agent identity, route-hop list, transfer success, or chain completeness

2. Payload placement and default shape (hard contract)¶

Placement: handoff is a top-level sibling on the emitted canonical adapter payload (same object as agent, task, message, attributes, discovery, and unmapped_fields_count).

Presence: handoff is always present on every emitted event.

Default values (when no rule sets a non-default):

Enum values for source_kind: typed_payload | unknown

v1 reachability: In this freeze, typed_payload is the only positive source kind. unknown is the default when the positive typed rule does not match. There is no attributes, unmapped, or fallback source kind in v1.

2b. Bounded meaning — may imply / must not imply¶

One-line semantics guardrail: Every handoff.* boolean is a bounded observed visibility flag only. None of these fields mean the handoff was valid, authorized, complete, trusted, or successful.

3. Source rule and decision table¶

Positive v1 source rule (hard requirement):

Explicit v1 non-promotion rule: assay.adapter.a2a.task.updated is not a positive source in this freeze, even though the adapter already maps it. A later freeze may widen the source rule only after a fixture-backed update.

4. Filled freeze table (per field)¶

4.1 handoff.visible¶

4.2 handoff.source_kind¶

4.3 handoff.task_ref_visible¶

4.4 handoff.message_ref_visible¶

5. Strict vs lenient¶

• Strict mode: current adapter behavior already rejects task packets without task.id; that remains true. No emitted handoff object exists because the whole packet is rejected.
• Lenient mode: handoff.visible may still be true when the typed route surface exists (task.requested + task.kind == "delegation"), even if task.id is missing. In that case:
• handoff.source_kind = "typed_payload"
• handoff.task_ref_visible = false
• handoff.message_ref_visible follows upstream typed message.id only
• Invalid event-type fallback: packets that fall back to assay.adapter.a2a.message keep the full handoff default object, even if message.id or synthetic unknown-message is present.

6. Complete emitted JSON examples (illustrative)¶

Build note: adapter_version uses 3.4.0 as an illustration; real emission uses CARGO_PKG_VERSION. Reviewers should treat presence and shape of top-level keys as normative here, not the patch digit.

6.1 Typed positive (task.requested + delegation)¶

Fixture source: a2a_happy_task_requested.json

{
  "adapter_id": "assay-adapter-a2a",
  "adapter_version": "3.4.0",
  "protocol": "a2a",
  "protocol_name": "a2a",
  "protocol_version": "0.2",
  "upstream_event_type": "task.requested",
  "agent": {
    "id": "agent://coordinator",
    "role": "orchestrator"
  },
  "task": {
    "id": "task-123",
    "status": "requested",
    "kind": "delegation"
  },
  "message": {
    "id": "msg-1",
    "role": "assistant"
  },
  "attributes": {
    "channel": "web",
    "priority": "urgent"
  },
  "discovery": {
    "agent_card_visible": false,
    "agent_card_source_kind": "unknown",
    "extended_card_access_visible": false,
    "signature_material_visible": false
  },
  "handoff": {
    "visible": true,
    "source_kind": "typed_payload",
    "task_ref_visible": true,
    "message_ref_visible": true
  },
  "unmapped_fields_count": 0
}

6.2 Lenient partial visibility (task.id missing)¶

Fixture source: a2a_negative_missing_task_id.json in lenient mode

{
  "adapter_id": "assay-adapter-a2a",
  "adapter_version": "3.4.0",
  "protocol": "a2a",
  "protocol_name": "a2a",
  "protocol_version": "0.2",
  "upstream_event_type": "task.requested",
  "agent": {
    "id": "agent://coordinator"
  },
  "task": {
    "id": "unknown-task",
    "status": "requested",
    "kind": "delegation"
  },
  "message": {
    "id": "msg-2"
  },
  "discovery": {
    "agent_card_visible": false,
    "agent_card_source_kind": "unknown",
    "extended_card_access_visible": false,
    "signature_material_visible": false
  },
  "handoff": {
    "visible": true,
    "source_kind": "typed_payload",
    "task_ref_visible": false,
    "message_ref_visible": true
  },
  "unmapped_fields_count": 1
}

6.3 Fully default (artifact.shared)¶

Fixture source: a2a_happy_artifact_shared.json

{
  "adapter_id": "assay-adapter-a2a",
  "adapter_version": "3.4.0",
  "protocol": "a2a",
  "protocol_name": "a2a",
  "protocol_version": "0.3.1",
  "upstream_event_type": "artifact.shared",
  "agent": {
    "id": "agent://worker"
  },
  "task": {
    "id": "task-123"
  },
  "artifact": {
    "id": "artifact-7",
    "name": "plan.md",
    "media_type": "text/markdown"
  },
  "discovery": {
    "agent_card_visible": false,
    "agent_card_source_kind": "unknown",
    "extended_card_access_visible": false,
    "signature_material_visible": false
  },
  "handoff": {
    "visible": false,
    "source_kind": "unknown",
    "task_ref_visible": false,
    "message_ref_visible": false
  },
  "unmapped_fields_count": 0
}

7. Negative test matrix (implemented minimum on main)¶

Current coverage note: the first K1-A adapter slice on main now includes explicit adapter-level tests for N1, N2, N4, N5, and N7, plus helper-level direct coverage for the source-rule default paths. The ADR026 fixture set itself still does not include a dedicated task.updated packet, so future fixture-parity work remains optional rather than a blocker for the shipped v1 seam.

8. assay-evidence scope¶

No change to assay-evidence in K1-A v1. This freeze is about canonical adapter-emitted evidence shape only. Any later Trust Basis, Trust Card, or pack follow-up must be justified separately after the handoff seam is real.

9. Link to implementation¶

• Implement handoff in the A2A adapter as a separate top-level sibling, not as an extension of payload.discovery.
• Source logic must be grounded in current typed fields from:
• mapping.rs
• convert.rs
• payload.rs
• Tests must cover:
• typed positive from a2a_happy_task_requested.json
• strict failure on missing task.id
• lenient partial visibility on missing task.id
• no promotion from artifact.shared
• no promotion from generic message fallback
• explicit non-promotion from task.updated in v1
• Canonical stability should be asserted with repeated conversion plus golden digests over the emitted handoff sub-object.

10. Reviewer checklist (contract closure)¶