Two bugs prevented the usage block from ever reaching the wire:
1. CallLLM read turnStateFromContext(ctx), but the raw ctx is not seeded
with the turn state (only turnCtx is), so SetLastUsage/SetLastFinishReason
were dropped — GetLastUsage() returned nil at finalize. Set them on the
ts parameter directly, which is also what the streaming publisher reads.
2. The manager wraps the channel streamer in finalizeHookStreamer /
splitMarkerStreamer, neither of which forwarded SetTurnUsage (it is not
part of the bus.Streamer interface), so the type assertion in the
publisher's Finalize failed silently. Mirror the existing SetModelName
forwarding: add a turnUsageStreamer interface + setStreamerTurnUsage
helper and SetTurnUsage methods on both wrappers (splitMarker also stores
and re-applies usage to each freshly-begun part streamer).
Adds regression tests asserting both wrappers forward SetTurnUsage.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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