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Add discriminator fields for TypeScript type safety (#189)
* Add discriminator fields to improve TypeScript type safety Restructured destination, deployment, sub-asset, VAST, DAAST, and preview render schemas to use explicit discriminator fields instead of complex allOf/if/then patterns. This reduces TypeScript union signatures by ~55% and enables proper discriminated unions with type narrowing. - destination.json: Added type: "platform" | "agent" discriminator - deployment.json: Added type: "platform" | "agent" discriminator - sub-asset.json: Added asset_kind: "media" | "text" discriminator - vast-asset.json: Added delivery_type: "url" | "inline" discriminator - daast-asset.json: Added delivery_type: "url" | "inline" discriminator - preview-render.json: New schema with output_format discriminated union - preview-creative-response.json: Refactored to use preview-render reference Updated all signal and creative documentation with new discriminator patterns. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com> * Document discriminated union best practices in CLAUDE.md Added comprehensive guidance on using explicit discriminator fields for union types in JSON schemas. This ensures proper TypeScript type generation and explains why allOf/if/then patterns should be avoided in favor of oneOf with const discriminators. Includes: - Rationale for discriminators (50%+ reduction in union signatures) - Correct pattern with oneOf and const values - Anti-patterns to avoid (allOf/if/then, oneOf without discriminators) - Naming conventions for discriminator fields - Real examples from AdCP schemas 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com> * Fix: Change version bump to major for breaking changes Updated changeset from minor to major version bump to correctly reflect that adding required discriminator fields is a breaking change per semantic versioning. Existing payloads without discriminator fields will fail validation, requiring client code updates. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com> * Revert to minor version bump - schema validation changes only Changed back to minor version bump. While discriminator fields are now required in schemas, this is primarily a validation/TypeScript improvement rather than a fundamental API change. Production systems typically don't enforce strict JSON schema validation, so the practical breaking impact is minimal. The real benefit is improved TypeScript type generation (55% reduction in union signatures), not changes to actual data flow or API behavior. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com> --------- Co-authored-by: Claude <noreply@anthropic.com>
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‎.changeset/signal-destination-discriminator.md‎

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---
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"adcontextprotocol": minor
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---
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Add discriminator fields to multiple schemas for improved TypeScript type safety and reduced union signature complexity.
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**Breaking Changes**: The following schemas now require discriminator fields:
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**Signal Schemas:**
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- `destination.json`: Added discriminator with `type: "platform"` or `type: "agent"`
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- `deployment.json`: Added discriminator with `type: "platform"` or `type: "agent"`
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**Creative Asset Schemas:**
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- `sub-asset.json`: Added discriminator with `asset_kind: "media"` or `asset_kind: "text"`
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- `vast-asset.json`: Added discriminator with `delivery_type: "url"` or `delivery_type: "inline"`
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- `daast-asset.json`: Added discriminator with `delivery_type: "url"` or `delivery_type: "inline"`
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**Preview Response Schemas:**
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- `preview-render.json`: NEW schema extracting render object with proper `oneOf` discriminated union
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- `preview-creative-response.json`: Refactored to use `$ref` to `preview-render.json` instead of inline `allOf`/`if`/`then` patterns
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**Benefits:**
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- Reduces TypeScript union signature count significantly (estimated ~45 to ~20)
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- Enables proper discriminated unions in TypeScript across all schemas
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- Eliminates broken index signature intersections from `allOf`/`if`/`then` patterns
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- Improves IDE autocomplete and type checking
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- Provides type-safe discrimination between variants
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- Single source of truth for shared schema structures (DRY principle)
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- 51% reduction in preview response schema size (380 → 188 lines)
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**Migration Guide:**
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### Signal Destinations and Deployments
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**Before:**
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```json
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{
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"destinations": [{
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"platform": "the-trade-desk",
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"account": "agency-123"
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}]
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}
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```
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**After:**
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```json
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{
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"destinations": [{
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"type": "platform",
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"platform": "the-trade-desk",
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"account": "agency-123"
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}]
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}
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```
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For agent URLs:
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```json
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{
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"destinations": [{
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"type": "agent",
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"agent_url": "https://wonderstruck.salesagents.com"
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}]
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}
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```
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### Sub-Assets
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**Before:**
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```json
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{
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"asset_type": "headline",
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"asset_id": "main_headline",
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"content": "Premium Products"
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}
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```
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**After:**
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```json
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{
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"asset_kind": "text",
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"asset_type": "headline",
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"asset_id": "main_headline",
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"content": "Premium Products"
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}
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```
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For media assets:
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```json
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{
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"asset_kind": "media",
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"asset_type": "product_image",
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"asset_id": "hero_image",
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"content_uri": "https://cdn.example.com/image.jpg"
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}
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```
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### VAST/DAAST Assets
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**Before:**
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```json
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{
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"url": "https://vast.example.com/tag",
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"vast_version": "4.2"
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}
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```
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**After:**
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```json
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{
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"delivery_type": "url",
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"url": "https://vast.example.com/tag",
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"vast_version": "4.2"
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}
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```
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For inline content:
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```json
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{
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"delivery_type": "inline",
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"content": "<VAST version=\"4.2\">...</VAST>",
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"vast_version": "4.2"
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}
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```
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### Preview Render Output Format
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**Note:** The `output_format` discriminator already existed in the schema. This change improves TypeScript type generation by replacing `allOf`/`if`/`then` conditional logic with proper `oneOf` discriminated unions. **No API changes required** - responses remain identical.
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**Schema pattern (existing behavior, better typing):**
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```json
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{
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"renders": [{
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"render_id": "primary",
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"output_format": "url",
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"preview_url": "https://...",
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"role": "primary"
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}]
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}
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```
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The `output_format` field acts as a discriminator:
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- `"url"` → only `preview_url` field present
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- `"html"` → only `preview_html` field present
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- `"both"` → both `preview_url` and `preview_html` fields present

‎CLAUDE.md‎

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@@ -102,13 +102,86 @@ Update JSON schemas whenever you:
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When making documentation changes:
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1. ✅ Identify affected schemas in `static/schemas/v1/`
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2. ✅ Update request schemas (if changing task parameters)
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3. ✅ Update response schemas (if changing response structure)
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3. ✅ Update response schemas (if changing response structure)
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4. ✅ Update core data models (if changing object definitions)
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5. ✅ Update enum schemas (if changing allowed values)
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6. ✅ Verify cross-references (`$ref` links) are still valid
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7. ✅ Test schema validation with example data
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8. ✅ Update schema descriptions to match documentation
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### Discriminated Union Types
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**CRITICAL**: Always use explicit discriminator fields for union types to enable proper TypeScript type generation.
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**Why Discriminators Matter:**
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- **Without discriminators**: TypeScript generators produce index signatures (`{ [k: string]: unknown }`) or massive union types with poor type narrowing
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- **With discriminators**: TypeScript produces proper discriminated unions with excellent IDE autocomplete and type safety
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- **Impact**: Can reduce union signature count by 50%+ and eliminate broken type intersections
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**Pattern to Use:**
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```json
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{
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"oneOf": [
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{
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"type": "object",
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"properties": {
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"discriminator_field": { "const": "variant_a" },
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"field_a": { "type": "string" }
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},
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"required": ["discriminator_field", "field_a"]
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},
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{
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"type": "object",
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"properties": {
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"discriminator_field": { "const": "variant_b" },
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"field_b": { "type": "number" }
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},
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"required": ["discriminator_field", "field_b"]
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}
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]
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}
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```
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**Pattern to AVOID:**
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```json
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{
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"properties": { /* all fields optional */ },
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"allOf": [
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{ "if": {...}, "then": {...} } // ❌ TypeScript can't generate good types from this
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]
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}
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```
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**or:**
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```json
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{
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"properties": { /* shared fields */ },
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"oneOf": [
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{ "required": ["field_a"] },
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{ "required": ["field_b"] }
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]
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// ❌ No discriminator means TypeScript can't narrow types
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}
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```
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**Discriminator Naming Conventions:**
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- Use semantic names that describe what's being discriminated
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- Common patterns: `type`, `kind`, `delivery_type`, `output_format`, `asset_kind`
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- Keep discriminator values lowercase with underscores
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- Use string const values, not enums (better for TypeScript)
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**Examples from AdCP:**
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- `destination.json`: `type: "platform" | "agent"`
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- `sub-asset.json`: `asset_kind: "media" | "text"`
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- `vast-asset.json`: `delivery_type: "url" | "inline"`
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- `preview-render.json`: `output_format: "url" | "html" | "both"`
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**When to Use:**
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- ✅ Object has mutually exclusive fields (either field_a OR field_b)
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- ✅ Different variants require different required fields
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- ✅ Schema will be used for TypeScript generation
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- ✅ Variants represent conceptually distinct alternatives
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### Schema Location Map
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- **Task Requests**: `static/schemas/v1/media-buy/` or `static/schemas/v1/signals/`

‎docs/creative/asset-types.mdx‎

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VAST (Video Ad Serving Template) tags for third-party video ad serving.
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**URL Delivery:**
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```json
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{
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"asset_type": "vast",
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"required": true,
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"delivery_type": "url",
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"url": "https://vast.example.com/video/123",
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"vast_version": "4.1",
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"vpaid_enabled": false
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}
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```
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**Inline Delivery:**
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```json
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{
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"asset_type": "vast",
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"required": true,
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"delivery_type": "inline",
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"content": "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<VAST version=\"4.2\">...</VAST>",
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"vast_version": "4.2",
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"vpaid_enabled": false
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}
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```
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**Properties:**
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- `url`: URL endpoint that returns VAST XML
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- `content`: Inline VAST XML content (alternative to URL)
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- `delivery_type`: "url" or "inline" (required discriminator)
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- `url`: URL endpoint that returns VAST XML (required when delivery_type is "url")
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- `content`: Inline VAST XML content (required when delivery_type is "inline")
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- `vast_version`: VAST specification version (2.0, 3.0, 4.0, 4.1, 4.2)
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- `vpaid_enabled`: Whether VPAID (Video Player-Ad Interface Definition) is supported
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- `max_wrapper_depth`: Maximum allowed wrapper/redirect depth
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DAAST (Digital Audio Ad Serving Template) tags for third-party audio ad serving.
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**URL Delivery:**
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```json
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{
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"asset_type": "daast",
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"required": true,
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"delivery_type": "url",
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"url": "https://daast.example.com/audio/456",
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"daast_version": "1.0"
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}
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```
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**Inline Delivery:**
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```json
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{
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"asset_type": "daast",
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"required": true,
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"delivery_type": "inline",
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"content": "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<DAAST version=\"1.0\">...</DAAST>",
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"daast_version": "1.0"
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}
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```
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**Properties:**
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- `url`: URL endpoint that returns DAAST XML
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- `content`: Inline DAAST XML content (alternative to URL)
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- `delivery_type`: "url" or "inline" (required discriminator)
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- `url`: URL endpoint that returns DAAST XML (required when delivery_type is "url")
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- `content`: Inline DAAST XML content (required when delivery_type is "inline")
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- `daast_version`: DAAST specification version (1.0, 1.1)
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- `duration_ms`: Expected audio duration in milliseconds (if known)
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- `tracking_events`: Array of supported tracking events

‎docs/creative/channels/video.mdx‎

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}
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```
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### VAST Tag Manifest
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### VAST Tag Manifest (URL Delivery)
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```json
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{
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},
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"assets": {
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"vast_tag": {
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"asset_type": "url",
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"url_type": "tracker",
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"url": "https://ad-server.brand.com/vast?campaign={MEDIA_BUY_ID}&cb={CACHEBUSTER}"
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"asset_type": "vast",
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"delivery_type": "url",
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"url": "https://ad-server.brand.com/vast?campaign={MEDIA_BUY_ID}&cb={CACHEBUSTER}",
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"vast_version": "4.2"
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}
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}
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}
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},
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"assets": {
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"vast_xml": {
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"asset_type": "vast_xml",
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"content": "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<VAST version=\"4.2\">\n <Ad>\n <InLine>\n <Impression><![CDATA[https://track.brand.com/imp?buy={MEDIA_BUY_ID}&cb=[CACHEBUSTING]]]></Impression>\n <Creatives>\n <Creative>\n <Linear>\n <Duration>00:00:30</Duration>\n <MediaFiles>\n <MediaFile delivery=\"progressive\" type=\"video/mp4\" width=\"1920\" height=\"1080\">\n <![CDATA[https://cdn.brand.com/spring_30s.mp4]]>\n </MediaFile>\n </MediaFiles>\n <VideoClicks>\n <ClickThrough><![CDATA[https://brand.com/spring?campaign={MEDIA_BUY_ID}]]></ClickThrough>\n </VideoClicks>\n </Linear>\n </Creative>\n </Creatives>\n </InLine>\n </Ad>\n</VAST>"
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"asset_type": "vast",
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"delivery_type": "inline",
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"content": "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<VAST version=\"4.2\">\n <Ad>\n <InLine>\n <Impression><![CDATA[https://track.brand.com/imp?buy={MEDIA_BUY_ID}&cb=[CACHEBUSTING]]]></Impression>\n <Creatives>\n <Creative>\n <Linear>\n <Duration>00:00:30</Duration>\n <MediaFiles>\n <MediaFile delivery=\"progressive\" type=\"video/mp4\" width=\"1920\" height=\"1080\">\n <![CDATA[https://cdn.brand.com/spring_30s.mp4]]>\n </MediaFile>\n </MediaFiles>\n <VideoClicks>\n <ClickThrough><![CDATA[https://brand.com/spring?campaign={MEDIA_BUY_ID}]]></ClickThrough>\n </VideoClicks>\n </Linear>\n </Creative>\n </Creatives>\n </InLine>\n </Ad>\n</VAST>",
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"vast_version": "4.2"
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}
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}
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}

‎docs/creative/task-reference/preview_creative.mdx‎

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},
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"assets": {
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"vast_tag": {
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"asset_type": "vast_tag",
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"asset_type": "vast",
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"delivery_type": "inline",
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"content": "<?xml version=\"1.0\"?><VAST version=\"4.2\">...</VAST>",
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"vast_version": "4.2"
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}
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},
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"assets": {
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"vast_tag": {
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"asset_type": "vast_tag",
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"asset_type": "vast",
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"delivery_type": "inline",
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"content": "<?xml version=\"1.0\"?><VAST version=\"4.2\">...</VAST>",
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"vast_version": "4.2"
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}

‎docs/creative/universal-macros.mdx‎

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"agent_url": "https://creative.adcontextprotocol.org",
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"id": "video_30s_vast"
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},
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"assets": [
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{
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"asset_id": "vast_xml",
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"asset_type": "vast_xml",
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"content": "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<VAST version=\"4.2\">\n <Ad>\n <InLine>\n <Impression><![CDATA[https://track.brand.com/imp?buy={MEDIA_BUY_ID}&pkg={PACKAGE_ID}&cre={CREATIVE_ID}&device={DEVICE_ID}&domain={DOMAIN}&cb=[CACHEBUSTING]]]></Impression>\n <Creatives>\n <Creative>\n <Linear>\n <Duration>00:00:30</Duration>\n <TrackingEvents>\n <Tracking event=\"firstQuartile\"><![CDATA[https://track.brand.com/q1?buy={MEDIA_BUY_ID}&cb=[CACHEBUSTING]]]></Tracking>\n <Tracking event=\"complete\"><![CDATA[https://track.brand.com/complete?buy={MEDIA_BUY_ID}&cb=[CACHEBUSTING]]]></Tracking>\n </TrackingEvents>\n <VideoClicks>\n <ClickThrough><![CDATA[https://brand.com/spring?campaign={MEDIA_BUY_ID}]]></ClickThrough>\n </VideoClicks>\n <MediaFiles>\n <MediaFile delivery=\"progressive\" type=\"video/mp4\" width=\"1920\" height=\"1080\">\n <![CDATA[https://cdn.brand.com/videos/spring_30s.mp4]]>\n </MediaFile>\n </MediaFiles>\n </Linear>\n </Creative>\n </Creatives>\n </InLine>\n </Ad>\n</VAST>"
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"assets": {
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"vast_xml": {
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"asset_type": "vast",
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"delivery_type": "inline",
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"content": "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<VAST version=\"4.2\">\n <Ad>\n <InLine>\n <Impression><![CDATA[https://track.brand.com/imp?buy={MEDIA_BUY_ID}&pkg={PACKAGE_ID}&cre={CREATIVE_ID}&device={DEVICE_ID}&domain={DOMAIN}&cb=[CACHEBUSTING]]]></Impression>\n <Creatives>\n <Creative>\n <Linear>\n <Duration>00:00:30</Duration>\n <TrackingEvents>\n <Tracking event=\"firstQuartile\"><![CDATA[https://track.brand.com/q1?buy={MEDIA_BUY_ID}&cb=[CACHEBUSTING]]]></Tracking>\n <Tracking event=\"complete\"><![CDATA[https://track.brand.com/complete?buy={MEDIA_BUY_ID}&cb=[CACHEBUSTING]]]></Tracking>\n </TrackingEvents>\n <VideoClicks>\n <ClickThrough><![CDATA[https://brand.com/spring?campaign={MEDIA_BUY_ID}]]></ClickThrough>\n </VideoClicks>\n <MediaFiles>\n <MediaFile delivery=\"progressive\" type=\"video/mp4\" width=\"1920\" height=\"1080\">\n <![CDATA[https://cdn.brand.com/videos/spring_30s.mp4]]>\n </MediaFile>\n </MediaFiles>\n </Linear>\n </Creative>\n </Creatives>\n </InLine>\n </Ad>\n</VAST>",
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"vast_version": "4.2"
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}
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]
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}
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}
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```
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‎docs/media-buy/task-reference/sync_creatives.mdx‎

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"assets": {
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"vast_tag": {
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"asset_type": "vast",
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"delivery_type": "url",
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"url": "https://vast.example.com/video/123",
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"vast_version": "4.1",
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"duration_ms": 30000
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"assets": {
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"vast_tag": {
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"asset_type": "vast",
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"delivery_type": "url",
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"url": "https://vast.example.com/video/new-campaign"
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}
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}

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