fix(dataframes): generated filter code should match the widget for the literal contains operator - #10617

…e literal `contains` operator (marimo-team#10617)

**This pull request was authored by a coding agent.**

## 📝 Summary

The dataframe transform code printer emits an unflagged
`.str.contains(value)` for the literal `contains` filter operator, so
the code marimo shows (and that the user copies out of the notebook)
evaluates the search string as a **regex**, while the handler that
actually filters the displayed table passes `literal=True`.

The result is that the generated code silently returns different rows
than the widget displays, and raises outright on an unbalanced
metacharacter.

**This does not affect the widget's own filtering** —
`NarwhalsTransformHandler._evaluate_condition` (`handlers.py:268-270`)
is correct. The defect is purely printed-code vs. handler divergence.

Two sites, fixed together:

| Backend | Line | Emitted before | Default | Now |
| --- | --- | --- | --- | --- |
| pandas | `print_code.py:52` | `df[col].str.contains(value)` |
`Series.str.contains` defaults `regex=True` | `regex=False` |
| polars | `print_code.py:320` | `pl.col(c).str.contains(value)` |
`Expr.str.contains` defaults `literal=False` | `literal=True` |

**Reproduction** (rows `["abc", "a.c", "f(x)", "zzz"]`):

- value `a.c` — handler keeps `["a.c"]`; the printed pandas/polars code
keeps `["abc", "a.c"]`.
- value `(` — handler keeps `["f(x)"]`; the printed pandas code raises
`pyarrow.lib.ArrowInvalid: Invalid regular expression: missing )`, and
the printed polars code raises `ComputeError: regex parse error ...
unclosed group`.

**Why literal is the intended behavior here** (not a judgement call):

1. The `regex` operator immediately below each of these two branches
already passes the flag explicitly — `regex=True` for pandas (line 54),
`literal=False` for polars (line 322). `contains` and `regex` are
separate operators precisely so that one is literal and one is not.
2. The ibis printer at `print_code.py:557` emits `.contains(value)`,
which is literal in ibis and therefore already agrees with the handler.

**Why the existing tests missed it:**
`test_print_code_result_matches_actual_transform_pandas` and
`..._polars` already assert printed-code result == handler result, but
they share `create_transform_strategy`, whose string filter value
strategy is `st.text(alphabet=string.ascii_letters + string.digits)` —
an alphabet that can never emit a regex metacharacter, so `contains` and
`regex` are indistinguishable under it. The two new tests are therefore
explicit rather than generated, and use values that *are* regexes
(`a.c`, `(`); an alphanumeric value would pass both before and after
this change.

**Deliberately left alone:** the superficially similar
`str.contains(f"(?i){query}")` calls in
`tables/narwhals_table.py:359,373` and `tables/polars_table.py:262,274`.
Those are intended regex search and are locked by
`tests/_plugins/ui/_impl/tables/test_narwhals.py::test_search_with_regex`.
`print_code.py:557` (ibis) is already correct and is untouched.

**Testing:** `tests/_plugins/ui/_impl/dataframes/test_print_code.py`
goes 13 → 17 passed; the new cases fail on `main` for the reasons above.
`tests/_plugins/ui/_impl/tables/` +
`tests/_plugins/ui/_impl/dataframes/` together: 862 passed, 0 failed.
`ruff check`, `ruff format --check`, and `mypy` are clean.

## 📋 Pre-Review Checklist

- [ ] For large changes, or changes that affect the public API: this
change was discussed or approved through an issue, on Discord, or the
community discussions. <!-- not applicable: two-line behavioral fix to
an internal code printer, no public API change -->
- [x] Any AI generated code has been reviewed line-by-line by the human
PR author, who stands by it.
- [ ] Video or media evidence is provided for any visual changes
(optional).

## ✅ Merge Checklist

- [x] I have read the [contributor
guidelines](https://github.com/marimo-team/marimo/blob/main/CONTRIBUTING.md).
- [x] Documentation has been updated where applicable, including
docstrings for API changes.
- [x] Tests have been added for the changes made.

---------

Co-authored-by: Kiran Gadhave <[email protected]>