feat(langchain): preserve owned-client authentication and Store cleanup - #7039

Description

Owned adapter clients cannot select API-key authentication independently of ambient LDAP/OIDC settings. Store cleanup can also return while a cancelled initialization or safe-read retry later opens an owned transport. This change forwards an explicit auth_mode through owned sync/async clients, copies and safe-read recovery, and drains active Store requests during cleanup.

An API-key-only client keeps its configured mode after recovery. Store cleanup rejects new backend requests, drains active requests, and releases only owned transports. Cancelled initialization and safe-read recovery cannot leave a replacement transport open after context exit. Concurrent Store reads remain concurrent; injected clients remain caller-owned.

Cherry-picks #6614 with its original author identity, date and source SHA retained. The Store lifecycle API from #6968 has already merged into main as 02611de; its duplicate cherry-pick was dropped during rebase. The cancellation/drain repair and its two deterministic SDK regression cases remain a separate commit. Unset auth_mode retains existing SDK defaults. The SDK minimum is 0.1.7, the first version exposing the explicit mode.

Related to #6612 and #6964. Follows up merged #6968.

Validation against upstream f7b726f: 820 passed on Python 3.12/current frameworks; 818 passed with 2 expected skips on Python 3.10/framework 1.0.0. The combined three-branch candidate passes 916 tests on Python 3.12 and 914 with 2 skips on Python 3.10. Ruff lint/format, mypy on 15 source modules, git diff --check, wheel/sdist builds and Twine checks pass. The combined package and SDK source remain byte-identical to the prior candidate that passed clean installed-wheel checks with published SDKs 0.1.7 and 0.1.18.

Companion drafts: #7038 (Store contracts) and #7040 (archive queries). The combined candidate retains both the Store contract fixes and cleanup draining.

Cleanup drains active backend requests; a multi-request Store operation can be interrupted between requests. It adds no transaction or rollback mechanism.

Contributors: Xinmin Zeng for the auth-mode change and stefanielizeth73-art for the already merged Store lifecycle proposal. The #6614 commit keeps its original author identity and date. Hao Zhe authored the separate cleanup repair and is the committer of the cherry-pick.

Landing: preserve these commits through a merge/rebase merge. If squashing is required, retain all contributor credit explicitly in the squash commit. Original PRs should be marked covered after the accepted consolidated change lands.

Human Involvement

• A human participated in the implementation or review loop
• This PR was generated entirely by AI agents without human participation in the loop

Type of Change

• Bug fix
• New feature
• Test update
• Documentation update

Checklist

• Final diff reviewed
• New and existing local tests pass
• Package build and installed-wheel checks pass