provider-tangle: a session-bound environment.stream() refuses OpenCode's live raw frames, whose sessionID is the harness-native session

[drewstone]

Observation

environment.stream({ prompt, sessionId }) fails on the first OpenCode raw frame of a live run stream with Tangle exact session event identified a different sessionId.

The sidecar writes a live raw frame's data as the harness event itself (agent-dev-container apps/sidecar/src/routes/agents-stream.ts:1103-1113 on 9bb408e9f7).
OpenCode's events carry their own session id at the top level, for example { type: "step_start", timestamp, sessionID: "ses_f67f4b273ffeq38073UGm8RzAK", part }.
sandboxEventIdentity reads data.sessionID as the run-frame session position (packages/agent-provider-tangle/src/tangle-events.ts), and environmentEventFromSandboxEvent exempts that position only for session.updated.
The replay lane is unaffected: it sends the buffered { type: "raw", backend: "opencode", event } envelope, where the native id sits under event.

Reproduction

Frames recorded from production execution s19 of run mech-interp-foundations-astra-b-20260912a (the fixture added in #327), streamed through environment.stream({ prompt, sessionId: <runtime session id> }) on the #327 branch:

frame shape	result
replay envelope, as recorded	63 events delivered
live shape (data = the inner OpenCode event plus sandboxId)	throws after 8 events, on the first step_start

The live shape is reconstructed from the sidecar and SDK source; no live session-bound OpenCode stream was captured.

Ask

Treat the run-frame session position of a raw frame as backend content, as the adapter already does for session.updated on a stream-bound iterator and for properties.part on unshaped frames.
Keep comparing the envelope positions the sidecar rewrites.