fix: Bump decommissioned Snowflake Python UDF runtime from 3.9 to 3.10 (#6606)

[zerafachris]

Fixes #6606

Snowflake decommissioned the Python 3.9 UDF runtime environment as of
April 30, 2026, so any feast apply against a Snowflake offline store
that deploys Feast's materialization UDFs now fails with:
Python runtime version 3.9 is decommissioned. Please update your code to Python runtime version 3.10 or later.

What changed

RUNTIME_VERSION = '3.9' was hardcoded 16 times in
snowflake_python_udfs_creation.sql (the SQL template actually executed
against Snowflake by SnowflakeComputeEngine.deploy_infra) and mirrored
in the reference docstrings of snowflake_udfs.py. Both are bumped to
'3.10', matching Feast's own minimum supported Python version
(requires-python = ">=3.10.0" in pyproject.toml) and a runtime
Snowflake still supports.

Test evidence

Added sdk/python/tests/unit/infra/utils/snowflake/test_snowflake_udfs.py,
which statically asserts neither file references the decommissioned
runtime version.

Before fix:

test_udf_creation_sql_does_not_use_decommissioned_runtime_version FAILED
test_udf_module_docstrings_do_not_reference_decommissioned_runtime_version FAILED
(AssertionError: ... still requests the decommissioned Snowflake Python runtime '3.9')

After fix:

test_udf_creation_sql_does_not_use_decommissioned_runtime_version PASSED
test_udf_module_docstrings_do_not_reference_decommissioned_runtime_version PASSED

Full snowflake unit suite: 28 passed. Broader sdk/python/tests/unit/infra
suite: 397 passed (1 pre-existing, unrelated environment failure due to
missing pip in the test venv). ruff check/format and mypy clean on
touched files.

Prepared with AI assistance (Claude, agent: claude-sonnet-5), reviewed for correctness before submission.

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 45.86%. Comparing base (f487b37) to head (0a3db47).
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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6608      +/-   ##
==========================================
+ Coverage   45.64%   45.86%   +0.22%     
==========================================
  Files         412      412              
  Lines       48761    48763       +2     
  Branches     6913     6913              
==========================================
+ Hits        22256    22367     +111     
+ Misses      24957    24849     -108     
+ Partials     1548     1547       -1     

Flag	Coverage Δ
go-feature-server	30.58% <ø> (ø)
python-unit	47.16% <100.00%> (+0.24%)	⬆️

Files with missing lines	Coverage Δ
...nfra/compute_engines/snowflake/snowflake_engine.py	46.47% <100.00%> (+46.47%)	⬆️
...t/infra/utils/snowflake/snowpark/snowflake_udfs.py	0.00% <ø> (ø)

... and 2 files with indirect coverage changes

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[ntkathole]

@zerafachris is it possible to make it user configurable ?

[zerafachris]

@ntkathole Good call — done. Pushed a follow-up commit (c5ae39b) that makes the Python UDF runtime version user-configurable instead of hardcoded.

Added a new field python_udf_runtime_version to SnowflakeComputeEngineConfig (the batch_engine config, alongside account, warehouse, database, etc.):

batch_engine:
  type: snowflake.engine
  ...
  python_udf_runtime_version: "3.10"  # optional, defaults to "3.10"

• Defaults to "3.10" (matching Feast's own requires-python = ">=3.10.0" floor), so no config change is needed for existing users picking up this PR.
• Validated as a Python version string (e.g. "3.10" or "3.11.2") — an invalid value raises a clear ValidationError instead of failing later as an opaque Snowflake SQL error.
• Plumbed through to the executed SQL the same way PROJECT_NAME/STAGE_HOLDER already are: snowflake_python_udfs_creation.sql now uses a RUNTIME_VERSION_HOLDER placeholder, which SnowflakeComputeEngine.update() fills in from python_udf_runtime_version at deploy time.

So the next time Snowflake decommissions a runtime, it's a one-line config change (e.g. python_udf_runtime_version: "3.11") rather than another hardcoded-value PR. Also documented in docs/reference/compute-engine/snowflake.md, and added tests covering the default, a custom override, invalid-value validation, and the rendered SQL template.