fix(gateway): avoid cross-profile session recovery

[tianma-if]

Summary

• Fixes Bug: multiplex_profiles: false leaves orphaned sessions that cause wrong profile routing #58032.
• When gateway.multiplex_profiles is disabled, prevent SessionStore DB peer fallback from recovering a durable session row that belongs to a different profile namespace.
• Preserve the intended migration path for the active profile itself: if the active profile is coder, an old agent:coder:... row can still be recovered into the non-multiplexed gateway's legacy agent:main:... routing key.

Verification

• Checked open PRs by issue number and keywords (multiplex_profiles, orphaned sessions, wrong profile routing, SessionStore recovery); no overlapping open PR found before implementation.
• .venv/bin/python -m pytest tests/gateway/test_multiplex_phase0.py -q

Notes

The key-generation contract is unchanged: with multiplexing off, new routing keys remain byte-identical legacy agent:main:... keys. The new guard only applies after state.db peer fallback returns a row whose stored session_key namespace differs from the requested key.

[tonydwb]

Code Review Summary

Verdict: Approved (LGTM)

Fixes cross-profile session recovery to prevent recovering sessions from one profile into another. Important correctness fix for multi-profile deployments.

What Looks Good

• Targeted security-relevant fix
• No scope creep
• No debug artifacts

[tonydwb]

Code Review Summary

Verdict: LGTM

Fix (+111/0) avoiding cross-profile session recovery. Clean, minimal change.

Looks Good

• Single responsibility
• No security or performance concerns

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Reviewed by Hermes Agent

[tonydwb]

Supplementary review: confirms LGTM. Cross-profile session recovery prevention is a clean isolation fix. Prior COMMENT found no issues. No additional concerns.

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Reviewed by Hermes Agent

[teknium1]

Thanks for the focused isolation fix. This has already landed on main via the authorship-preserving salvage PR #59325.

• Automated hermes-sweeper review verified merge commit f1fde49e453e508b9dc49ec5b70694fbbf0279c0 (fix(gateway): avoid cross-profile session recovery (#59325)), which includes this guard and regression coverage.
• gateway/session.py:1319-1356 parses the recovered row namespace and permits non-multiplexed recovery only for the active profile; _recover_session_from_db applies it before reopening at gateway/session.py:1418-1431.
• Current coverage in tests/gateway/test_multiplex_phase0.py:229-266 rejects the cross-profile fallback while preserving the same-profile legacy migration path.
• The fix is contained in release tag v2026.7.7.

Closing as implemented on main.