Codex reproduced an Oracle failure when purging and reinstalling an extension
on phpBB 4.0. The Doctrine-backed DB tools drop the extension's table but leave
its identity sequence behind. Recreating the table then fails with
`ORA-00955: name is already used by an existing object`.

Reproduction:

1. On phpBB 4.0 with Oracle, create a table through DB tools with a single
integer primary key using `auto_increment`.
2. Drop it through `sql_table_drop()` or an extension's schema-revert migration.
3. Recreate the same table through DB tools.
4. Observe ORA-00955 because the existing table identity sequence was not removed.

Expected: dropping the table removes its identity sequence so that the table
can be recreated. Unrelated sequences must remain intact.

Oracle introspection returns uppercase identifiers and does not mark the
trigger-backed identity column as autoincrement. Cleanup therefore needs to
recognize the matching sequence under those conditions as well as remove it
from the schema before generating the drop statements.

Codex added two focused schema regression cases that preserve an unrelated
sequence. Both passed. On a disposable phpBB 4.0.0-a3-dev board with PHP 8.4.26
and Oracle AI Database 26ai Free release 23.26.3, Codex reproduced the original
purge/reinstall failure, then verified disable/re-enable preservation, purge,
and clean reinstall after applying the correction.

Patch and regression tests: https://github.com/bonelifer/phpbb/pull/3

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Investigated and written by [Codex](https://openai.com/codex/) on behalf of William Jacoby ([bonelifer](https://github.com/bonelifer)).