Orchestrator can express and enforce limits for A2UI layouts

Ability for Orchestrator to express and enforce limits for A2UI layouts e.g. define max depth, tree structure requirements as requested by internal Google customers and Search.

The issue mentions adding limits for A2UI layouts in the Orchestrator, likely in the layout definition or validation logic. Look for files related to layout parsing, tree structure validation, or configuration limits in the orchestrator module. Start by understanding the existing layout structure and where constraints could be enforced. Check for any existing tests on layout validation to see the current behavior.

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