Retry previous-model compaction with selected model

[celia-oai]

Summary

• retry automatic previous-model compaction once with the selected model for errors that may reflect model availability, compatibility, capacity, model-scoped usage, or broader server failure
• share the retry eligibility check across both remote compaction implementations
• document why the policy intentionally accepts occasional redundant fallback attempts
• preserve the existing invalid-request regression test and add a separate model-not-found regression test

Why

A previous model may become unusable after a thread switches models. The failure can surface as an invalid request, unexpected HTTP status, context-window error, usage limit, overload, internal server error, or exhausted retry limit. Retrying compaction once with the selected model lets the turn continue while keeping fallback bounded.

Testing

• just test -p codex-core 'pre_sampling_compact_falls_back_' (3 passed)
• just test -p codex-core 'suite::compact::' (41 passed)
• just fix -p codex-core
• just fmt
• previously attempted just test -p codex-core; the compaction tests passed, while the broader run encountered unrelated environment-dependent failures in approval, shell, MCP, code-mode, and realtime tests

[chatgpt-codex-connector]

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