fix: check is_available() before creating Spout/unavailable sinks and sources (#688)

[livepeer-tessa]

Summary

Fixes #688 — same availability-guard pattern as #644 (NDI), now applied to output sinks generally and the input source path.

Changes

src/scope/server/frame_processor.py

_update_output_sink() — add is_available() guard before attempting to create:

if not sink_class.is_available():
    logger.warning(
        "Output sink '%s' is not available on this platform, skipping",
        sink_type,
    )
    return

_create_and_connect_input_source() — downgrade existing is_available() failure from ERROR to WARNING for consistency.

Why

SpoutGL is a Windows-only DirectX texture sharing library. On Linux fal.ai workers, enabling the Spout sink/source produced ERROR-level log noise even though the outcome was benign. This cluttered the error monitoring dashboard alongside real errors.

Test

• On Linux: enabling Spout output sink/input source should produce a WARNING and no further errors (no create() attempt)
• On Windows: no behaviour change — is_available() returns True, sink creates as normal

Related

• NDI output sink logs ERROR on fal.ai where NDI is unavailable — should check is_available() first #644 — identical fix for NDI output sink (the template for this change)

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🚀 fal.ai Preview Deployment

App ID	daydream/scope-pr-690--preview
WebSocket	wss://fal.run/daydream/scope-pr-690--preview/ws
Commit	ae74127

Testing

Connect to this preview deployment by running this on your branch:

uv run build && SCOPE_CLOUD_APP_ID="daydream/scope-pr-690--preview/ws" uv run daydream-scope

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