Context compression today rewrites the message list AND rotates the
session id — it ends the session, forks a parent_session_id child, and
renumbers the title (name -> name #2). That moving identity key is the
root cause of a whole bug cluster: /goal lost (#33618), pending response
lost at the split (#14238), orphan sessions (#33907), TUI sid desync
(#36777), FTS search gaps + duplicate sidebar entries (#45117), null
continuation cwd (#42228), and title-rename dead-ends (#48989). It also
forced a large defensive apparatus (compression lock, contextvar/env/
logging triple-sync, orphan finalization, gateway SessionEntry
re-propagation, tip projection) whose only job is surviving a
mid-conversation id change.
Add a compression.in_place config flag (default False during rollout).
When True, compaction rewrites the transcript and rebuilds the system
prompt but keeps the SAME session_id: no end_session, no child row, no
title renumber, no contextvar/logging re-sync, no memory/context-engine
session-switch. The conversation keeps one durable id for life, like
Claude Code / Codex. Compaction is lossy by design — the pre-compaction
transcript is summarized away, not archived.
The rotation path is unchanged when the flag is off (moved verbatim into
an else branch). Staged rollout: this PR ships the option behind a
default-off flag for live validation; a follow-up flips the default and
deletes the now-redundant rotation machinery, superseding the 14 open
band-aid PRs in this area.
- hermes_cli/config.py: add compression.in_place (default False), documented
- agent/agent_init.py: resolve the flag -> agent.compression_in_place
- agent/conversation_compression.py: branch compress_context() on the flag
- tests/run_agent/test_in_place_compaction.py: in-place invariants +
rotation regression guard + config default
The pre-flush of current-turn messages (#47202) runs in BOTH modes, so no
boundary data loss. Prompt-cache invariant preserved: the system-prompt
rebuild is the same single sanctioned invalidation that already happens
during compaction — no NEW invalidation. Message alternation preserved.
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