[AI-stack] usage/cost rollups + message feedback (product analytics) — track only

[rickylabs]

Summary

Track (do not implement yet) a usage/cost rollups + message-feedback capability for the NetScript AI stack — the product-analytics counterpart to the tracing usage-capture in E9 (#248).

This came in as a complementary candidate on the epic (eis-chat POC #45, flagged [PRODUCT SIGN-OFF]). Fable's rev.5 scope ruling: reject as a framework slice, defer to product. The user has now made the product call:

No implementation for now — keep an open issue for tracking.

Scope decision (v1)

• No billing/analytics sink and no fork-seam is built into E9 for v1. E9's usage-capture stays tracing-only (the OTel GenAI usage chunk from the TanStack finish event — real token counts, not chars/4). It does not grow a second capture path or a rollup sink.
• This issue is the durable tracking home for the rollups/feedback feature so it isn't lost. Revisit as a product initiative, not a framework-scope call.

What the feature would be (for when it's revisited)

• Usage/cost rollups — per-user / per-session / per-model aggregation of token + cost, built on the same usage events E9 captures for tracing (design the capture once so an app-owned rollup sink could consume it — but that seam is deferred with this issue, not shipped in v1).
• Message feedback — thumbs/rating + free-text on assistant messages, persisted app-side, joinable to the usage/trace record.
• Billing-grade accounting stays app-owned; the framework's only possible future contribution is making E9's usage event forkable — explicitly out of v1 per this decision.

References

• Epic: epic: NetScript AI Stack — first-class AI runtime, chat & plugin seams (anchor #219) #238 (AI plugin stack) · anchor [AI-stack anchor] streams: no durable-CHAT integration — @netscript/fresh/ai seam (StreamDB shapes → Electric "Decoding failed") #219
• E9 tracing slice: [AI-stack E9] @netscript/ai: OTel GenAI/MCP semconv telemetry adapter (./otel) #248 (usage-capture stays tracing-only per this decision)
• POC: eis-chat [WIP] Copilot Request #45 ([PRODUCT SIGN-OFF])
• Fable rev.5 ruling: reject-as-framework → defer-to-product; product decision = track-only, no impl.

Part of #238