[AZ-220] Add shared runtime contract models

Implement the shared DTO contract surface with validation so runtime components consume one public model set instead of duplicating shapes.

Co-authored-by: Cursor <cursoragent@cursor.com>

_docs/02_tasks/done/AZ-220_shared_runtime_contracts.md

@@ -0,0 +1,78 @@
+# Shared Runtime Contracts
+
+**Task**: AZ-220_shared_runtime_contracts
+**Name**: Shared Runtime Contracts
+**Description**: Define the shared DTO and event contract surface used across the onboard runtime.
+**Complexity**: 3 points
+**Dependencies**: AZ-219_initial_structure
+**Component**: Bootstrap / Shared Contracts
+**Tracker**: AZ-220
+**Epic**: AZ-206
+
+## Problem
+
+Runtime components need common shapes for frames, telemetry, VIO state, position estimates, candidates, anchors, cache tiles, and FDR events.
+
+## Outcome
+
+- Components consume one documented shared contract surface.
+- Cross-component DTO drift is prevented before implementation begins.
+
+## Scope
+
+### Included
+- Shared runtime DTO names, fields, invariants, versioning rules, and contract tests.
+- Public contract document for consumers.
+
+### Excluded
+- Component-specific algorithms.
+- E2E runner-only report schemas.
+
+## Acceptance Criteria
+
+**AC-1: Shared contract exists**
+Given runtime components need common DTOs
+When the shared contracts are implemented
+Then each runtime component can import or reference the same contract surface.
+
+**AC-2: Contract validation exists**
+Given a malformed shared DTO
+When validation runs
+Then the input is rejected with a structured error.
+
+## Non-Functional Requirements
+
+**Compatibility**
+- Contract changes follow documented versioning rules.
+
+**Reliability**
+- Invalid or missing required fields are not silently ignored.
+
+## Unit Tests
+
+| AC Ref | What to Test | Required Outcome |
+|--------|--------------|------------------|
+| AC-1 | DTO construction for valid minimal values | Accepted |
+| AC-2 | Missing required timestamp or ID | Rejected with structured error |
+
+## Blackbox Tests
+
+| AC Ref | Initial Data/Conditions | What to Test | Expected Behavior | NFR References |
+|--------|-------------------------|--------------|-------------------|----------------|
+| AC-1 | Runtime started with contract consumers | Public interfaces exchange typed records | No component-specific duplicate shape required | Compatibility |
+
+## Constraints
+
+- Contracts are shared API surface and must be consumed through documented public modules.
+- Raw frame payloads are referenced, not retained in shared DTOs.
+
+## Risks & Mitigation
+
+**Risk 1: Contract drift**
+- *Risk*: Consumers create local incompatible DTOs.
+- *Mitigation*: Contract file is required dependency for consuming tasks.
+
+## Contract
+
+This task produces/implements the contract at `_docs/02_document/contracts/shared/runtime_contracts.md`.
+Consumers MUST read that file — not this task spec — to discover the interface.