truncated_response_parts were joined with no separator at both the
ceiling exit and the success path, so a fragment ending mid-word ran
straight into the next one (#78577). insert a newline only when the
previous fragment ends non-whitespace and the next starts
non-whitespace, so existing separators are not doubled.
the scaffolding marks are hermes bookkeeping. only the chat-completions
transport strips underscore keys, so anthropic and bedrock requests on
continuation attempts 2+ would send the marks to strict providers. pop
them in the central api_messages sanitization next to _thinking_prefill.
also pin that a mark reloaded from a mid-crash persist on a prior turn's
message is never deleted by a later turn's ceiling cleanup.
a turn that exhausts all 4 length-continuation attempts used to persist
its interim fragments and '[System: ... continue ...]' user nudges into
the session transcript. every later user turn replayed the unanswered
nudges, so the model resumed the oversized response, truncated again,
and re-exhausted the ceiling - wedging the session regardless of input.
at the ceiling exit, drop the fragment/nudge scaffolding from the turn's
tail and store one settled assistant turn carrying the stitched partial
text. the marks are cleared on continuation success and on the
content-filter rollback so cleanup can never delete fragments whose text
was already consumed.
also stop labeling a finish_reason='length' stub a network error: report
it as a truncation (stream ended before completion) and say the partial
response is kept when the ceiling is exhausted.
Erosika