## 1. Artifact Transfer Contracts

- [x] 1.1 Add typed run artifact transfer protocol payloads in `run/protocol` for open, chunk upload, status/resume, completion, and acknowledgements.
- [x] 1.2 Add matching platform DTO/domain contracts and conversion helpers for artifact transfer requests and responses.
- [x] 1.3 Add validation rules for active upload direction, owner scope, bounded chunk size, byte ranges, chunk checksums, final checksums, and completion state.

## 2. Platform Artifact Transfer

- [x] 2.1 Extend platform service behavior to open upload transfers, accept idempotent chunks, reject conflicting chunks, report resume status, and mark artifacts available only after verified completion.
- [x] 2.2 Implement platform artifact transfer HTTP routes using named DTOs and service methods.
- [x] 2.3 Add platform service/API tests for successful upload, resume status, duplicate ack, checksum mismatch, invalid owner/session, and missing-chunk completion rejection.

## 3. Run Artifact Queue And Client

- [x] 3.1 Implement a run-side local artifact queue that writes pending chunk requests to disk, lists them for retry, and removes acknowledged chunks.
- [x] 3.2 Extend `run/api.PlatformClient` with typed artifact transfer methods.
- [x] 3.3 Add run queue/client tests for retry retention, acknowledgement cleanup, request paths, JSON payloads, response decoding, and platform error handling.

## 4. Documentation

- [x] 4.1 Update run and platform protocol/route documentation to mark artifact open/chunk/status/complete implemented and keep control/job/log/game-client channels separate.

## 5. Verification

- [x] 5.1 Run `go test ./...` from `platform/` and record evidence.
- [x] 5.2 Run `go test ./...` from `run/` and record evidence.
- [x] 5.3 Run `scripts/check-structure.sh` and record evidence.
- [x] 5.4 Run `openspec validate implement-artifact-transfer-channel --strict` and record evidence.

## Evidence

- 2026-07-03: `go test ./...` from `platform/` passed.
- 2026-07-03: `go test ./...` from `run/` passed.
- 2026-07-03: `scripts/check-structure.sh` passed with `structure check passed`.
- 2026-07-03: `openspec validate implement-artifact-transfer-channel --strict` passed with `Change 'implement-artifact-transfer-channel' is valid`.