WebSub: Version-aware deployment transform for 0.5 gateways (Platform API remains 0.6-only)

Summary

• Platform API will accept only WebSub 0.6 payloads (allChannels + per-event wrapper). Deployments must remain compatible with 0.5 gateways.

Context

• See PR #1948 for the schema refactor to 0.6-only. As noted in the referenced comment, we should not accept 0.5 payloads at the Platform API layer; backward compatibility must be handled only in the deployment path.

Problem

• The current WebSub deployment YAML builder emits the 0.6 structure. 0.5 gateways expect the legacy 0.5 shape, so deployments targeting 0.5 gateways must receive a compatible manifest.

Goal

• Add a version-aware transformation in the deployment path so that:
  • When the target gateway is 0.5.x, the emitted manifest uses the legacy top-level and per-event array shapes expected by 0.5 (and omits 0.6-only sections where unsupported).
  • When the target gateway is 0.6.0+, emit the 0.6 event-policy structure.

Acceptance criteria

• Detect target gateway version during deployment and select the appropriate manifest shape.
• Unit tests assert both shapes (0.5 vs 0.6) for representative cases (global/all-channels and per-channel event policies).
• No changes to the Platform API OpenAPI are required; it remains 0.6-only.
• Add a brief note in code/docs describing the version-aware behavior.

Backlinks

• PR: https://github.com/wso2/api-platform/pull/1948
• Comment: https://github.com/wso2/api-platform/pull/1948#discussion_r3234750942

Requested by @tharindu1st on 2026-05-13.