fix: rebuild namedtuples in _deepcopy_with_exceptions

[chuenchen309]

What

_deepcopy_with_exceptions (used when Haystack copies component inputs/params) is designed to degrade gracefully: if an object cannot be deep-copied it returns the original and logs. But its container branch crashes on a namedtuple:

if isinstance(obj, (list, tuple, set)):
    return type(obj)(_deepcopy_with_exceptions(v) for v in obj)

A namedtuple is a tuple subclass, so it takes this branch — but type(obj)(<generator>) calls the namedtuple's __new__ with a single iterable, whereas its __new__ expects the fields as positional arguments. The result is an uncaught TypeError, which propagates out of the copy (also through any dict/list that contains the namedtuple), defeating the function's own graceful-fallback contract.

Reproduction:

from collections import namedtuple
from haystack.core.pipeline.utils import _deepcopy_with_exceptions

Point = namedtuple("Point", ["x", "y"])
_deepcopy_with_exceptions({"pt": Point(1, 2)})
# TypeError: Point.__new__() missing 1 required positional argument: 'y'

Fix

Handle namedtuples explicitly (detected via the _fields attribute) before the generic list/tuple/set branch, rebuilding them by unpacking their deep-copied fields. Plain tuples/lists/sets are unaffected.

Test

Added TestDeepcopyWithFallback::test_deepcopy_with_fallback_namedtuple, which fails before the change (the TypeError above) and passes after, verifying the namedtuple is reconstructed as its own type with deep-copied contents.

Verified locally: the full test/core/pipeline/test_utils.py suite passes (27 passed). ruff check and ruff format --check are clean. Added a release note.

---

Authored with AI assistance (Claude Code); the change and tests were reviewed and verified locally by me.

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Coverage report

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File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
haystack/core/pipeline
utils.py
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