Assistant-role compaction summaries were treated as the last visible assistant reply after head protection decayed. That pulled the tail boundary back to the summary itself and left zero new turns to summarize.
Exclude internal context summaries from both the visible-reply search and the assistant fallback, mirroring the existing user-role summary exclusion.
Follow-up to the END-MARKER reorder: moving the summary prefix after the
[PRIOR CONTEXT] wrapper meant _is_context_summary_content (prefix-at-start)
no longer recognized a merged-tail summary. That silently broke three
consumers — the last-real-user anchor (would pick the merged summary as a
real user turn, causing active-task loss), the carry-forward summary find,
and the auto-focus skip. _strip_summary_prefix would also carry the wrapper
+ stale tail content forward as the next summary body.
Extract the two delimiter strings into _MERGED_PRIOR_CONTEXT_HEADER /
_MERGED_SUMMARY_DELIMITER constants (writer + detector stay in sync), teach
_is_context_summary_content and _strip_summary_prefix to look past the
delimiter, and add a regression test. Standalone summaries unchanged.
A context-compaction handoff banner is inserted with role="user" when the
protected head ends in an assistant/tool message. On a resumed or
multi-compaction session, _find_last_user_message_idx would return that
banner as the latest user turn, so _ensure_last_user_message_in_tail anchored
the tail to the summary and rolled the genuine last user message into the
next compaction — the exact active-task loss the anchor exists to prevent
(#10896/#22523).
Reuse the existing _is_context_summary_content helper to skip summary banners
when locating the last real user message.
Salvaged from #36626 by Frank Song (issue #36624). The PR's other two changes
(demoting completed tool results inside the protected tail; a preflight
compression_exhausted result) are superseded on current main by the min_tail
floor (#39170), the no-op compression counting (#40803), and the existing
413/disabled terminal-error paths.
21 cases pinning the new ``_ensure_last_assistant_message_in_tail``
anchor and its interaction with the existing tail-cut path:
* ``TestFindLastAssistantMessageIdx`` — helper contract: prefers a
content-bearing assistant message, skips ``tool_calls``-only
stubs, multimodal text-block content counts, falls back to
"any assistant" when no content-bearing reply exists, honours
``head_end``, returns -1 when there's none.
* ``TestEnsureLastAssistantMessageInTail`` — direct: no-op when
already in the tail, walks ``cut_idx`` back when the reply is
in the compressed middle, never crosses into the head region,
re-aligns through a preceding ``tool_call`` / ``tool_result``
group instead of orphaning it.
* ``TestFindTailCutByTokensAnchorsAssistant`` — integration:
reporter repro (long tool-output run after the visible reply)
now preserves the reply; user and assistant anchors compose
in a single tail-cut call; a soft-ceiling-overrunning oversized
tool result no longer strands the prior reply.
* ``TestCompactionRollupReproduction`` — end-to-end through
``compress()`` with a stubbed ``_generate_summary``: the
visible reply text survives either as its own standalone
assistant message (normal path) or concatenated onto the
merged summary tail (double-collision path the WebUI then
re-splits). The standalone-summary case is asserted strictly
(exactly one summary row, exactly one separate assistant
row carrying the reply) — that's the dominant path and any
drift there reintroduces the original bug.
* ``TestSourceGuardrail`` — static asserts on
``agent/context_compressor.py``: the helper exists, the
anchor is wired into ``_find_tail_cut_by_tokens`` AFTER the
user-message anchor (so chaining is monotonic), the
content-bearing preference is preserved, and the issue
number is referenced so future bisects can find this fix.
Teknium
McHermes
kshitijk4poor
Frank Song
xxxigm