[dashboard DDX-23] seam-event flow plane: unified envelope + HTTP boundary events (S13 co-req)

[rickylabs]

feat(telemetry): seam-event flow plane — unified envelope + HTTP boundary events

Summary

Emit a uniform seam event at each framework boundary a request crosses — HTTP ingress/egress, contract procedure invoke/return, job enqueue/complete, saga transition, stream publish/delivery — onto an owned in-process bus exposed at /_netscript/flows/subscribe (SSE), keyed by the stamped traceparent.

Scope

• Envelope (contract-first): { flowId (traceparent), seam, primitive, name, phase: start|end|error, payloadRef, attempt?, ts } — reuses the [telemetry T1] Framework telemetry convention (TC-1..14) + attribute-namespacing law #402 TC-1..14 attribute vocabulary; no parallel naming.
• Emitters piggyback on the existing lifecycle event points (execution events, saga history, trigger events, stream deliveries) + new HTTP boundary hooks at the router seam.
• Replaces the beta.6 join-layer in /_netscript/flows ([dashboard DDX-13] Introspection endpoint (/_netscript/*) #423) transparently — same SSE shape, higher fidelity.

Non-goals

• Not OTLP; not an exporter; never proxied from /api/telemetry/* ([dashboard DDX-3] TelemetryQueryPort + aspire-otlp-http adapter #413 stays correlation-only). No UI (that's S13/[dashboard DDX-8] S13: Live Flow — request journey across framework seams #418). No durable storage beyond a bounded ring buffer (dev-time surface).

Acceptance criteria

• One scaffold-app HTTP request yields a complete ordered seam-event chain incl. the HTTP boundary; S13 renders it with zero join heuristics.
• deno check --unstable-kv green; TC vocabulary lint clean.

Dependencies

#408 (traceparent stamping), #423 (mount), feeds #418/S13. Co-lands sensibly with epic:telemetry-revamp.