[Partner Nodes] fix: add runtime check for SeeDance2 image inputs

[bigcat88]

PR adds runtime input validation for the Seedance 2.0 first-last-frame and reference nodes - so users no longer hit opaque server-side InvalidParameter errors at upload.
ReferenceNode's existing auto_downscale widget continues to control reference-video downscaling only and now defaults to True

API Node PR Checklist

Scope

• Is API Node Change

Pricing & Billing

• Need pricing update
• No pricing update

If Need pricing update:

• Metronome rate cards updated
• Auto‑billing tests updated and passing

QA

• QA done
• QA not required

Comms

• Informed Kosinkadink

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR adds input validation and downscaling for Seedance image processing in two ByteDance nodes. It imports a downscaling utility, introduces a _prepare_seedance_image() helper that enforces aspect ratio and dimension constraints by downscaling images to a 6000-pixel max side, then applies this preprocessing to ByteDance2FirstLastFrameNode and ByteDance2ReferenceNode before their respective asset operations. The auto_downscale default for the reference node changes from False to True.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically describes the main change: adding runtime validation for SeeDance2 image inputs to prevent server-side errors.
Description check	✅ Passed	The description is directly related to the changeset, explaining the runtime validation additions for SeeDance nodes and the auto_downscale default change.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@comfy_api_nodes/nodes_bytedance.py`:
- Around line 1793-1797: The synchronous call to _prepare_seedance_image inside
the async def execute is blocking the event loop; change those direct calls (the
ones for first_frame and last_frame and the per-key calls against
reference_images[key]) to run in a threadpool by awaiting
asyncio.to_thread(_prepare_seedance_image, ...) or using loop.run_in_executor,
and for multiple reference images use asyncio.gather over to_thread tasks so all
image preparations run off the event loop; update the execute function to await
these offloaded tasks where first_frame, last_frame and reference_images are
assigned.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

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Run ID: 1e0040cd-7c12-4dfd-8561-ff888694fc1f

📥 Commits

Reviewing files that changed from the base of the PR and between be06873 and e69e4a5.

📒 Files selected for processing (1)

• comfy_api_nodes/nodes_bytedance.py