CPython interns identifier-like string literals, so 'is' cannot
distinguish an import alias from a copy-pasted literal (verified:
two exec'd namespaces each defining the literal share one object).
The equality assertions three lines above are the full honest guard.
Also reword a comment: raw == is marker-SENSITIVE, not asymmetric.
Review-pass follow-up on the load-time durability stamp:
- hermes_state.py: import the marker from agent.context_compressor instead
of a third synced literal (hermes_state already imports agent.* at module
level; only run_agent is circular). Old comment claimed otherwise.
- agent/turn_finalizer.py: replace the raw "_db_persisted" string at the
fill-empty-tail pop site with the shared constant (was outside the drift
guard).
- agent/conversation_compression.py: the no-op progress check now falls back
to a marker-insensitive comparison (_strip_marker_for_comparison). Loaded
rows are stamped at materialization time while compress() output is
marker-swept, so a semantically-identical no-op copy on a cold-resumed
session would previously compare unequal and take the progress branch.
Raw == still runs first so engine-returned list subclasses keep their
__eq__ semantics.
- test_marker_constant_in_sync extended to turn_finalizer + identity
assertions; new test_noop_progress_check_is_marker_insensitive
(mutation-checked: fails when the helper is neutered).
Resumed sessions loaded message dicts from state.db WITHOUT the
_DB_PERSISTED_MARKER, so any flush that lost the identity boundary
(compression durable-snapshot adoption, incremental tool-call persists,
rotation preflight on cold resume) re-appended the ENTIRE loaded
transcript as new rows. Compression cycles then doubled the copies:
the incident session grew 998 -> 1995 -> 3990 -> 7981 rows across
three aborted rotations (15,962 active rows, only 472 distinct).
Fix at the architectural chokepoint: SessionDB._rows_to_conversation
(shared by get_messages_as_conversation and get_resume_conversations)
now stamps the marker at row materialization time - a dict built FROM
a durable row is persisted by construction, regardless of which caller
loads it or how the list is later handed to a flush.
Safety:
- Wire-safe: every transport strips underscore-prefixed keys before
the API request (chat_completion_helpers, anthropic_adapter), same
contract as the existing _row_id stamp in the same function.
- Rotation handoffs still write: compression's assembly copies strip
the marker (_fresh_compaction_message_copy + the terminal
_strip_persistence_markers sweep), so compacted transcripts still
flush to the child session (#57491 invariant preserved).
- Branch/seed copies unaffected: /branch and _persist_branch_seed
build fresh field-projected dicts and write via append_messages_batch
directly, not through the marker-gated flush.
Tests: new regression suite (marker sync, load stamping, 3-cycle
amplification repro, new-tail write guard, compaction-copy handoff);
updated the #68454 control test that asserted the old double-write
behavior and the ACP restore shape test.
Kshitij Kapoor