fix(guardrails): support array-type content in Presidio pre-call hook

[tjtanjin]

Title

fix(guardrails): support array-type content in Presidio pre-call hook

Description

Previously, the async_pre_call_hook in Presidio PII masking only handled messages with content as strings, and ignored messages where content was structured as a list of text blocks.

This caused PII in messages like the following to go unmasked:

{
  "messages": [
    {
      "role": "user",
      "content": [
        {"type": "text", "text": "My credit card is 4111-1111-1111-1111."},
        {"type": "text", "text": "My email is [email protected]."}
      ]
    }
  ]
}

Only messages with a simple string like this were being processed correctly:

{
  "messages": [
    {
      "role": "user",
      "content": "My credit card is 4111-1111-1111-1111."
    }
  ]
}

This PR adds proper handling for list-type content, ensuring PII detection and anonymization works consistently for both string and list message formats.

Pre-Submission checklist

• I have Added testing in the [tests/litellm/](https://github.com/BerriAI/litellm/tree/main/tests/litellm) directory
• I have added a screenshot of my new test passing locally
• My PR passes all unit tests on [make test-unit](https://docs.litellm.ai/docs/extras/contributing_code)
• My PR's scope is as isolated as possible, it only solves 1 specific problem

Type

🐛 Bug Fix

Changes

• Updated async_pre_call_hook in _OPTIONAL_PresidioPIIMasking to handle messages where content can be a list of text blocks instead of just a string.

• Introduced minimal targets tracking to ensure PII-masked text is written back to the correct location.

• Added new unit tests covering:

  • single text block inside a list
  • mixed string and list messages to verify target alignment

• No changes to existing behavior for string-only messages.

[vercel]

@tjtanjin is attempting to deploy a commit to the CLERKIEAI Team on Vercel.

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[krrishdholakia]

We do handle content list text blocks in presidio now -

litellm/litellm/proxy/guardrails/guardrail_hooks/presidio.py

Line 421 in 5ad108b

elif isinstance(content, list):

[krrishdholakia]

Let me know if I missed anything!