fix(gateway): batch SSH session cleanup writes

[drew]

Summary

Batch SSH-session persistence cleanup into bounded set-based deletes so sandbox teardown and the session reaper do not issue one database write per session. This addresses the gateway-side contention risk reported in #2999 without changing SQLite journal settings, timeouts, or session ownership schema.

Related Issue

Part of #2999.

This is PR 1 of 2. The issue does not currently carry an accepted-state label; the direct implementation and ready-for-review request authorized this submission, while maintainers retain the acceptance and merge decision.

Changes

• add a backend-neutral delete_many store operation with fixed 128-ID chunks for SQLite and Postgres
• paginate SSH-session discovery before mutation and batch sandbox-owned cleanup writes
• batch expired/revoked session reaping and replace token-bearing per-session errors with aggregate telemetry
• add persistence, pagination, type-isolation, reaper, and file-backed SQLite concurrency coverage
• document the bounded owned-record cleanup invariant

Testing

• mise run pre-commit
• mise run test (review rerun: 1,443 server tests passed)
• focused persistence, compute cleanup, and reaper regression tests
• exact OpenClaw fixture reproduced on main, then passed on this PR and the combined branches
• mise run e2e:docker
• mise run ci passes locally — all Rust, Python, TypeScript, lint, compile, and policy checks passed; three unrelated Go gateway fixture tests fail because this workstation's hard-coded /etc/openshell/gateways/default is included as an unexpected system fixture

Review

A full line-by-line review covered both persistence backends, chunk bounds, empty/duplicate/missing IDs, object-type isolation, pagination before mutation, partial-chunk idempotency, cleanup/reaper telemetry, secret-safe logging, tests, and architecture documentation. No actionable findings remained.

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture docs updated (if applicable)

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[drew]

🏗️ build-from-issue-agent

Issue fixture verification

Verified commit 36e598574fcef3b122e7fa09037dc42e21e94ca2 with the exact OpenClaw fixture referenced by #2999.

• Untouched main: fixture failed 1 of 5 tests; gateway emitted 1,151 individual SSH-session DELETE statements. The largest 568-session cleanup took about 8.49 seconds.
• This PR: fixture passed all 5 tests; the same cleanup load used 13 bounded statements and zero individual SSH-session DELETE statements. The 568-session cleanup used 5 batches and took about 51 ms.
• Temporary combined build with fix(cli): wait for terminal sandbox deletion #3001: all 5 tests passed with the same bounded cleanup shape.
• No SQLite read failure occurred locally on baseline or PR, so this attests removal of the reproduced serial-write contention mechanism rather than claiming the intermittent INTERNAL symptom was observed.

Full evidence: #2999 (comment)

[drew]

Full code review completed.

• Reviewed both persistence backends, bounded query construction, type isolation, pagination-before-mutation, cleanup/reaper idempotency and telemetry, log safety, tests, and architecture docs.
• No actionable findings remained.
• Review validation passed: mise run pre-commit, the full mise run test suite (including 1,443 server tests), focused bulk-delete/cleanup/reaper tests, Docker E2E, and the exact Control-plane read failures during sandbox SSH-session cleanup; delete acknowledgment can precede durable cleanup #2999 OpenClaw fixture.
• The exact fixture changed the SSH cleanup from 1,151 individual writes on main to 13 bounded deletes here; the largest 568-session cleanup completed in about 51 ms.

Ready for maintainer review.