* feat(guardrails): add pre_mcp_call support to Content Filter
* test(guardrails): cover canonical MCP key gate under pre_mcp_call mode
* fix(guardrails): scan MCP arguments per value and gate mixed-mode scans by call type
* fix(guardrails): cap MCP argument scan depth and register the walker with the recursion detector
* test(guardrails): update LIT-4226 UI settings tests for content filter pre_mcp_call support
* fix(guardrails): use builtin generics in MCP scan annotations to satisfy strict-rule budget
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Co-authored-by: Claude Fable 5 <noreply@anthropic.com>