fix(api-io): serialize MultiCombo multi_select as object config

[Kosinkadink]

Summary

Fix MultiCombo.Input.as_dict() serialization so multi_select is emitted as an object config instead of a boolean, and fix validation so MultiCombo list values are accepted.

Based on #12662 by @Ni-zav with additional fixes:

• Remove dead if self.multiselect else None branch (MultiCombo always sets self.multiselect = True)
• Remove redundant top-level placeholder/chip keys (frontend reads them from multi_select object)
• Fix prompt validation to check each element of a MultiCombo list against options individually
• Fix custom node skip warning to mention comfy_entrypoint and remove nonexistent NODES_LIST
• Update tests to match simplified output

Why

Frontend expects multi_select to be an object (z.object({ placeholder, chip })). When serialized as a boolean, MultiCombo is not recognized as multiselect. Additionally, prompt validation rejected MultiCombo values because it compared the entire list against the options instead of checking each selected value individually.

Changes

• comfy_api/latest/_io.py: Emit multi_select: {} (or with placeholder/chip when provided)
• execution.py: Handle list values in combo validation for MultiCombo inputs
• nodes.py: Fix misleading skip warning message
• tests-unit/comfy_api_test/multicombo_serialization_test.py: Regression tests

Closes #12662

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📒 Files selected for processing (2)

• execution.py
• tests-unit/comfy_api_test/multicombo_serialization_test.py

🚧 Files skipped from review as they are similar to previous changes (2)

• execution.py
• tests-unit/comfy_api_test/multicombo_serialization_test.py

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📝 Walkthrough

Walkthrough

MultiCombo.Input.as_dict() now emits a nested multi_select object (containing optional placeholder and chip) while retaining the top-level boolean multiselect via Combo.Input.as_dict(); a stale TODO comment was removed. New unit tests were added to cover Combo and MultiCombo serialization and validation behavior. validate_inputs in execution.py was updated to accept multiselect values (treating inputs as lists when extra_info["multiselect"] is set) and to report invalid list elements individually. A log message in load_custom_node was edited to reference comfy_entrypoint.

🚥 Pre-merge checks | ✅ 3 | ❌ 2

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Out of Scope Changes check	⚠️ Warning	The changes in nodes.py (warning message update) are out of scope relative to #12662 but justified by the PR description as a related fix for misleading messaging.	The nodes.py change about comfy_entrypoint warning is not mentioned in issue #12662. Either move it to a separate PR or add it to the linked issue scope.
Docstring Coverage	⚠️ Warning	Docstring coverage is 25.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: fixing MultiCombo serialization to emit multi_select as an object config instead of a boolean.
Description check	✅ Passed	The description is well-related to the changeset, explaining the problem, why it matters, and what changes were made across multiple files.
Linked Issues check	✅ Passed	The PR fully addresses issue #12662 requirements: MultiCombo serialization now emits multi_select as an object config, backward compatibility is maintained, validation handles list values, and regression tests are included.

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@execution.py`:
- Around line 997-1002: The current validation treats any list-valued input
(val) as valid if all elements are in combo_options, which lets {"__value__":
["a","b"]} slip through for single-select combos; change the logic in the
MultiCombo validation to first check the combo's config/multi flag (e.g.,
combo_config.get("multi") or is_multi) and only perform per-element validation
when that flag is true—otherwise treat a list as an invalid whole value (use the
existing scalar-path check for non-multi combos). Ensure you update the branch
that computes invalid_vals (currently using val, combo_options, invalid_vals) to
enforce this multi-check so single-select combos reject list inputs.

🪄 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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• execution.py