RFC: Registry sandbox for engram/impulse I/O validation and compatibility badges

[lanycrost]

Context

During integration testing of the realtime examples (livekit-chat, livekit-translation, livekit-voice), we discovered multiple issues caused by incompatible I/O between engrams:

• Output schema mismatches that kill hub streams (bobravoz-grpc#63, livekit-bridge-engram#18)
• Payload field leakage between steps (bobravoz-grpc#60, chore(main): release 0.1.2 #62)
• Silent template resolution failures when packet.* fields do not exist (bobravoz-grpc#64)
• The shouldEncodeStructuredStreamPayload MimeType trap (bubu-sdk-go#74 comment)

All of these boil down to: engram I/O contracts are implicit and untested. You only discover incompatibilities at runtime in a full Kubernetes deployment.

Proposal

Add a registry validation layer that tests engram I/O compatibility outside Kubernetes in a lightweight sandbox:

What it validates

1. Output schema conformance — feed sample inputs to an engram, verify outputs match the EngramTemplate outputSchema
2. Pairwise compatibility — given engram A output schema and engram B input schema, verify they are compatible without deploying
3. Runtime template resolution — verify that packet.* and steps.* references in story templates can actually resolve given the upstream engram output structure
4. Payload isolation — verify that a step output contains ONLY the declared fields, not leaked upstream config

How it works

• Runs in a sandbox (Docker container or local process), not in Kubernetes
• Uses the engram container image directly with mock transport
• Feeds predefined test fixtures (sample audio, sample chat messages, sample webhook events)
• Validates outputs against the declared schema
• Produces a compatibility matrix

Registry integration

• Engrams in the registry show their validated input/output schemas
• Pairwise compatibility is displayed: works with openai-stt, conversation-memory, openai-tts
• Engrams that pass validation get a tested badge
• Engrams that pass pairwise tests with specific partners get a compatible badge

Relationship to existing RFCs

• RFC RFC: Typed transport/config ABI as a prerequisite for multi-language SDKs #75 (Typed ABI) — the sandbox validates against the typed ABI once defined
• RFC RFC: Canonical streaming ABI across tractatus, Bobravoz, and the Go SDK #77 (Canonical streaming ABI) — the sandbox enforces the canonical ABI at test time
• bobravoz-grpc#67 — per-engram image overrides enable testing candidate versions in the sandbox before promoting

Why this matters

Right now, the only way to test engram compatibility is to deploy a full story on a Kubernetes cluster and read pod logs. This does not scale. A sandbox validator would catch I/O mismatches before deployment, enable CI/CD pipelines for engram development, and reduce the debugging cycle from reading 8 pod logs to running one test command.