sqlite_sql_translate.py: 20 surviving mutants in _translate_sql / _returning_was_stripped

[cdeust]

What

A scoped mutation run (mutmut 3.x, rules/coding-standards.md §12) against
mcp_server/infrastructure/sqlite_sql_translate.py — the SQL-dialect
translation module extracted from sqlite_compat.py in #260 to bring that
file under the project's 300-line cap — surfaces 20 surviving mutants:

mcp_server.infrastructure.sqlite_sql_translate.x__returning_was_stripped__mutmut_8: survived
mcp_server.infrastructure.sqlite_sql_translate.x__returning_was_stripped__mutmut_10: survived
mcp_server.infrastructure.sqlite_sql_translate.x__translate_sql__mutmut_38: survived
mcp_server.infrastructure.sqlite_sql_translate.x__translate_sql__mutmut_51: survived
mcp_server.infrastructure.sqlite_sql_translate.x__translate_sql__mutmut_62: survived
mcp_server.infrastructure.sqlite_sql_translate.x__translate_sql__mutmut_64: survived
mcp_server.infrastructure.sqlite_sql_translate.x__translate_sql__mutmut_78: survived
mcp_server.infrastructure.sqlite_sql_translate.x__translate_sql__mutmut_92: survived
mcp_server.infrastructure.sqlite_sql_translate.x__translate_sql__mutmut_105: survived
mcp_server.infrastructure.sqlite_sql_translate.x__translate_sql__mutmut_117: survived
mcp_server.infrastructure.sqlite_sql_translate.x__translate_sql__mutmut_119: survived
mcp_server.infrastructure.sqlite_sql_translate.x__translate_sql__mutmut_134: survived
mcp_server.infrastructure.sqlite_sql_translate.x__translate_sql__mutmut_136: survived
mcp_server.infrastructure.sqlite_sql_translate.x__translate_sql__mutmut_137: survived
mcp_server.infrastructure.sqlite_sql_translate.x__translate_sql__mutmut_149: survived
mcp_server.infrastructure.sqlite_sql_translate.x__translate_sql__mutmut_161: survived
mcp_server.infrastructure.sqlite_sql_translate.x__translate_sql__mutmut_163: survived
mcp_server.infrastructure.sqlite_sql_translate.x__translate_sql__mutmut_175: survived
mcp_server.infrastructure.sqlite_sql_translate.x__translate_sql__mutmut_186: survived
mcp_server.infrastructure.sqlite_sql_translate.x__translate_sql__mutmut_188: survived

Reproduce (from a clean checkout, UV_NO_SYNC=1 to avoid a lockfile sync):

$ cp pyproject.toml /tmp/p.bak
$ python3 -c "
import re
s = open('pyproject.toml').read()
s = s.replace('only_mutate = [\"mcp_server/shared/json_native.py\"]',
              'only_mutate = [\"mcp_server/infrastructure/sqlite_sql_translate.py\"]')
s = s.replace('pytest_add_cli_args_test_selection = [\"tests_py/shared/test_json_native.py\"]',
              'pytest_add_cli_args_test_selection = [\"tests_py/handlers/test_wiki_pipeline_sqlite.py\", \"tests_py/infrastructure/test_sqlite_parity_197.py\"]')
open('pyproject.toml', 'w').write(s)
"
$ rm -rf mutants .mutmut-cache
$ UV_NO_SYNC=1 uv run mutmut run
$ UV_NO_SYNC=1 uv run mutmut results | grep survived
$ cp /tmp/p.bak pyproject.toml && rm -rf mutants .mutmut-cache

Why this is not new debt from #260

_translate_sql/_returning_was_stripped/_SUPPORTS_RETURNING were moved
byte-for-byte from sqlite_compat.py into the new
sqlite_sql_translate.py module — no logic changed, same tests run
against them before and after. The project's own test suite already
documents partial awareness of this class of gap:
tests_py/handlers/test_wiki_pipeline_sqlite.py::test_translate_sql_handles_postgres_constructs
says "a scoped mutation run over _translate_sql left 47 mutants alive
against fragment matching" and switched those parametrized cases to
exact-string comparison as a mitigation — which reduced, but by this
run's count did not eliminate, the survivor set. This run's 20 survivors
predate #260; they were simply never previously counted in isolation
because _translate_sql lived inside the larger, already-partially-tested
sqlite_compat.py.

Acceptance criteria

1. For each of the 20 mutant ids above, mutmut show <id> names the exact
   line/branch a test does not pin.
2. Each is either killed by a new or strengthened test (prefer exact-string
   assertions, per the existing file's own documented lesson), or
   documented as a provable equivalent mutant with a written rationale
   (coding-standards §12.1(b)) — e.g. a mutation inside a regex character
   class that cannot change matched input for any reachable SQL shape.
3. Re-running the reproduction above reports 0 unaccounted-for survivors.

Provenance

Surfaced 2026-07-29 while fixing #260 (the sqlite_compat.py datetime
adapter). Outside that fix's blast radius — the datetime-adapter change
touches only the module docstring, the import block, and the new
_adapt_datetime_iso function/registration in sqlite_compat.py; it does
not modify _translate_sql/_returning_was_stripped at all — so deferred
here per coding-standards.md §14.3 rather than folded into that PR.