Drop the Responses-API native compaction path and its opt-in umbrella
flag from the salvaged feature. On the Codex OAuth chat route Hermes
owns the message list and the summary compressor works (and stays
provider-portable — encrypted compaction items would lock the session
history to chatgpt.com and break /model switches and provider
fallback). On the app-server runtime (codex CLI/agent) the codex agent
owns the real thread context, so thread/compact/start is the only
mechanism that can actually shrink it (#36801) — that path is now the
default behavior for codex_app_server sessions, controlled by
compression.codex_app_server_auto (native|hermes|off), no umbrella
flag.
Removed: responses.compact() call path, codex_compaction_items replay/
persistence plumbing, codex_native_compaction + codex_responses_threshold
config keys, desktop settings fields, and their tests. Kept: everything
app-server (compact_thread(), compaction notifications, bookkeeping,
docs, tests) plus cache-busting keys for the surviving knobs.
