The cherry-picked guard sat inside the codex-items block, which (a) is
skipped entirely in codex_responses mode (conversation_loop passes
drop_codex_reasoning_items=False there) and (b) is unreachable for
carriers whose adapter-joined commentary populates msg['reasoning'] —
the string-reasoning branch returns True first. Hoist the checkpoint
check above every reasoning branch so no carrier shape can be dropped,
in any api_mode. Adds the two carrier-shape tests that pin exactly this
(both fail with the guard in its original position).
A type="compaction" item is the server-side stand-in for history that has
already been pruned, and it rides the same codex_reasoning_items sidecar as
per-turn reasoning. e00965a7e taught compaction pruning to filter that
sidecar instead of popping it so checkpoints survive on every retained
message.
The thinking-only sanitizer reaches the same sidecar from the other
direction and asks a coarser question: does any item have type ==
"reasoning"? A commentary turn carrying both a reasoning item and a
checkpoint answers yes, so the whole message is dropped from the wire copy
and the only copy of the checkpoint goes with it. The request then carries
neither the compacted history nor the checkpoint standing in for it.
Extract has_compaction_checkpoint() into agent/native_compaction.py — the
module that owns the concept, and where merge_interim_reasoning_items()
already spelled the same predicate inline — and consult it before the
thinking-only verdict. A reasoning-only carrier is still dropped.
Adds a pre-call sanitizer that detects assistant messages containing only
reasoning (reasoning / reasoning_content, no visible content, no
tool_calls) and drops them from the API copy. Adjacent user messages
left behind are merged so role alternation is preserved for the
provider.
Mirrors Claude Code's approach in src/utils/messages.ts
(filterOrphanedThinkingOnlyMessages + mergeAdjacentUserMessages). We
drop the whole turn rather than fabricate stub text (the '.' /
'(continued)' pattern from contributor PRs #11098, #13010, #16842 that
were rejected because they put words in the model's mouth).
The stored conversation history (self.messages) is never mutated — only
the per-call api_messages copy. Users still see the reasoning block in
the CLI/gateway transcript; only the wire copy is cleaned. Session
persistence keeps the full trace.
Two call sites covered:
- Main agent loop, after _sanitize_api_messages (catches every turn).
- Iteration-limit-summary fallback path.
Tests: tests/run_agent/test_thinking_only_sanitizer.py — 25 cases
covering detection (string/list content, whitespace-only, tool_calls,
reasoning_details list form), drop behavior, adjacent-user merge
(string+string, list+list, mixed), non-mutation of input dicts, and
system-message handling.
E2E live-tested against 5 providers with a poisoned history (empty
assistant message + reasoning_content): OpenRouter→Anthropic/OpenAI/
DeepSeek-R1/Qwen, native Gemini. All 5 accepted the cleaned request.
Happy-path regression (5/5) confirms the sanitizer is a noop when no
thinking-only turn exists.
Related: #16823 (wontfix — stub-text approach rejected).
Co-authored-by: teknium1 <teknium@users.noreply.github.com>
Teknium
Drexuxux
Jefftree
briandevans