[vistart]

Description

Implements the backend half of the portable seconds_between expression added in
rhosocial/python-activerecord#129: format_seconds_between_expression() renders
end - start in signed, fractional seconds. The formatter renders DATEDIFF_BIG(MILLISECOND, start, end) / 1000.0, which avoids the DATEDIFF overflow; below SQL Server 2016, where DATEDIFF_BIG does not exist, it refuses with UnsupportedFeatureError.

The core raises UnsupportedFeatureError until a dialect adapts the hook, so this
change is what makes the expression usable on this engine. The implementation lives in
src/rhosocial/activerecord/backend/impl/sqlserver/mixins/datetime.py (plus the version floor in .../sqlserver/dialect.py).

Type of change

• feat: A new feature
• docs: Documentation for the new capability
• test: Tests for the new capability
• chore: CI installs the core from the feature branch (see below)
• perf / ci / build / revert: not applicable

Breaking Change

• Yes, for end-users (backward-incompatible API changes)
• Yes, for backend developers (internal architectural changes that may affect custom implementations)
• No breaking changes

Impact on End-Users:
No backward-incompatible changes are expected: the expression is new, and nothing
existing changes shape.

Impact on Backend Developers (Custom Implementations):
None. The dialect hook is additive; implementations that do not override it keep
inheriting the core refusal.

Related Repositories/Packages

Requires rhosocial/python-activerecord#129 (branch feature/extract-epoch).

.github/workflows/test.yml now installs the core from feature/extract-epoch
instead of release/v1.0.0.dev30, so CI exercises the core change and this backend
together (see the chore(ci) commit on this branch). That pin is temporary: it should
go back to the release branch once the core PR merges.

Testing

• I have added new tests to cover my changes.
• I have updated existing tests to reflect my changes.
• All existing tests pass.
• This change has been tested on the target engine.

Test Plan:

• tests/rhosocial/activerecord_sqlserver_test/feature/backend/expression/test_seconds_between.py

Checklist

• My code follows the project's code style guidelines.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation (Docstrings, README.md, etc.).
• My changes generate no new warnings.
• I have added a Changelog fragment (added in a follow-up commit, once the PR number is known).
• I have verified that my changes do not introduce SQL injection vulnerabilities.
• I have checked for potential performance regressions.

Additional Notes

The changelog fragment is intentionally deferred until the PR number exists; it is
added as changelog.d/<pr_number>.added.md right after the PR opens.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.32%. Comparing base (ce1db88) to head (63a4e9d).
⚠️ Report is 1 commits behind head on release/v1.0.0.dev3.

Additional details and impacted files

@@                   Coverage Diff                   @@
##           release/v1.0.0.dev3      #11      +/-   ##
=======================================================
+ Coverage                77.87%   78.32%   +0.45%     
=======================================================
  Files                      144      144              
  Lines                     8306     8522     +216     
  Branches                  1289     1325      +36     
=======================================================
+ Hits                      6468     6675     +207     
+ Misses                    1408     1375      -33     
- Partials                   430      472      +42     

Flag	Coverage Δ
python-3.14	78.32% <100.00%> (+0.45%)	⬆️
sqlserver-2025	78.32% <100.00%> (+0.45%)	⬆️
unittests	78.32% <100.00%> (+0.45%)	⬆️

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[sonarqubecloud]

Quality Gate failed

Failed conditions
C Security Rating on New Code (required ≥ A)

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