[CI/Bug]Fix multimodal encoder budget KeyError for shared audio placeholders

[pacoxu]

Purpose

fix a keyerror in CI https://buildkite.com/vllm/ci/builds/49647/steps/canvas?jid=019c205f-dc84-45ec-949c-ea4fc62d9a54

• the CI is a main branch CI failure.

[2026-02-02T22:40:50Z] /usr/local/lib/python3.12/dist-packages/vllm/v1/engine/input_processor.py:79: in __init__
--
[2026-02-02T22:40:50Z]     mm_budget = MultiModalBudget(vllm_config, mm_registry)
[2026-02-02T22:40:50Z] _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
[2026-02-02T22:40:50Z]
[2026-02-02T22:40:50Z] >       modality: all_mm_max_toks_per_item[modality]
[2026-02-02T22:40:50Z]         for modality in active_modalities
[2026-02-02T22:40:50Z]     }
[2026-02-02T22:40:50Z] E   KeyError: 'audio'
[2026-02-02T22:40:50Z]
[2026-02-02T22:40:50Z] /usr/local/lib/python3.12/dist-packages/vllm/multimodal/budget.py:76: KeyError

Test Plan

Test Result

---

Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.
• (Optional) Release notes update. If your change is user facing, please update the release notes draft in the Google Doc.

[gemini-code-assist]

Code Review

This pull request addresses a KeyError that occurred during the multimodal encoder budget calculation. The fix correctly replaces a direct dictionary access with a safer .get() call, using an assignment expression to avoid a second lookup. This change not only resolves the KeyError but also improves robustness by filtering out None values, which could lead to a TypeError in downstream processing. The change is concise, correct, and improves the overall reliability of the code.

[DarkLight1337]

It has been fixed by #33634 already.

[pacoxu]

It has been fixed by #33634 already.

thanks.