fix(agent): guard multimodal tool content behind provider profile flag

[zccyman]

Summary

When computer_use captures a screenshot and returns _multimodal content (list of text + image_url parts), _tool_result_content_for_active_model currently only checks _model_supports_vision() before passing through the multimodal content list.

However, many providers (e.g. Xiaomi MiMo) support images in user messages but require content to be a string in role: "tool" messages. Sending a list causes a 400 error.

Changes

• providers/base.py: Add supports_multimodal_tool_content: bool = False to ProviderProfile
• run_agent.py:
  • New method _provider_supports_multimodal_tool_content() that checks the profile flag
  • Guard _tool_result_content_for_active_model() to also check this flag before passing multimodal content through
• Provider profiles: Enable for Anthropic, OpenAI Codex, OpenRouter, xAI (known to support multimodal tool content)
• Tests: Add regression test for [Bug] computer_use multimodal tool message causes 400 error on providers that don't support multimodal tool content (e.g. Xiaomi MiMo) #27344 — vision model without multimodal tool support gets downgraded content

Approach

Option 2 from the issue — conservative default. Only providers explicitly marked with supports_multimodal_tool_content=True receive multimodal tool content. All others (including new/unrecognized providers) get the text summary fallback.

This is safe because:

• Default False means no existing provider behavior changes unless explicitly enabled
• Providers that don't support it already fail at the API layer — this just prevents the failure
• The fallback path (text summary) already exists and is well-tested

Fixes #27344

[alt-glitch]

Duplicate of #27351 — both PRs fix #27344 with the same approach (provider profile flag for multimodal tool content support).

[BoardJames-Bot]

CI triage note from rock-turning: this PR is already called out above as a duplicate of #27351. Its current blocking check is not a code failure; the test job was cancelled in run 26002320915 while e2e and the rest of the checks had passed. I attempted gh run rerun 26002320915 --failed, but rerun is blocked for this account by repo admin permission (Must have admin rights to Repository). Next owner: repo maintainer should either close this as duplicate of #27351 or rerun the cancelled test job if keeping this PR open.

[zccyman]

Closing as duplicate of #27351 (confirmed by alt-glitch). Both PRs implement the same provider profile flag approach for multimodal tool content support.