fix!: require unsafe loading for serialized Jinja filters

[sjrl]

Related Issues

• related to feat: add HAYSTACK_UNSAFE_DESERIALIZATION env var #12397
• Should fix https://github.com/deepset-ai/haystack-private/issues/551

Proposed Changes:

Require Pipeline.loads(..., unsafe=True) to load jinja2 custom filters since they allow for code execution at load time.

How did you test it?

New tests

Notes for the reviewer

Checklist

• I have read the contributors guidelines and the code of conduct.
• I have updated the related issue with new insights and changes.
• I have added unit tests and updated the docstrings.
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test: and added ! in case the PR includes breaking changes.
• I have documented my code.
• I have added a release note file, following the contributors guidelines.
• I have run pre-commit hooks and fixed any issue.

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
haystack-docs	Ignored	Preview	Aug 20, 2026 7:19am

[sjrl]

@julian-risch tagging you for review since we talked about this yesterday

[github-actions]

Coverage report

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
haystack/components/converters
output_adapter.py
haystack/components/routers
conditional_router.py
Project Total

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