Each mid-session `/model` switch appended a `[System: The active model for
this chat has changed to …]` user-role marker to the live conversation history
and never removed the prior one. N switches left N stale markers, all re-sent
to the provider on every subsequent turn — the issue measured ~80-120 tokens
each (Chinese+English), so 5 MoA-preset switches burned ~400-600 context
tokens per API call, permanently. Only the newest marker is meaningful (it
names the currently-active model); the rest are pure waste. Fixes#65891.
`_append_model_switch_marker` now strips any earlier markers from
`session["history"]` (in place, under the existing history_lock) before
appending the new one, so the live payload carries exactly one marker. This is
the payload re-sent each turn, and it's self-healing across resumes: whatever
markers a history reload brings back, the next switch collapses to one.
A stable `_MODEL_SWITCH_MARKER_PREFIX` constant is shared by the builder and
the `_is_model_switch_marker` predicate so the two can't drift; the marker
string itself is byte-for-byte unchanged. Existing behavior (role='user' per
the single db.append_message persistence) is preserved.
Scope note: this dedups the in-memory history (the per-turn cost the issue
quantifies). The DB still persists one row per switch for audit/resume; I did
NOT soft-archive prior marker rows because `active=0, compacted=0` is the
repo's rewind/undo sentinel (hermes_state.py get_messages docs), so
deactivating a marker naively would make it look rewound — a follow-up that
needs its own archive semantics.
Tests (tests/tui_gateway/test_model_switch_marker_role.py, +5): second switch
replaces (not stacks) the marker; the issue's exact 5-MoA-switch sequence
leaves one marker naming the last model; real conversation turns are preserved
in order; a stale marker sitting between turns is stripped; history_version
increments once per switch. `pytest test_model_switch_marker_role.py` → 13
passed (8 existing unchanged). Authored on Windows.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013b1XyXitAxV7phGmKWigJX
hans
f09c56c003