docs: correlate reply truncation with agent log screenshot

.project-docs/30-worklog/tasks/20260928-agent-reply-truncation-c812b59f.md

@@ -40,3 +40,11 @@
 ## Promotion Candidates
 
 - None. This read-only diagnosis adds evidence and a repair direction, not an accepted product behavior change.
+
+## Agent Log Screenshot Follow-up
+
+- Same-task start/status matched; reused unchanged project context and reviewed the new welcome-diagnosis/latest cleanup peer scope. Read-only gate passed; no product or live state edits.
+- User supplied an Agent log screenshot containing the visible prefix `{"reply":"它早就不是"刚搭好架子"那种阶段了——` followed by a substantial prose answer and legacy structure payload. The earlier client screenshot shows exactly the prose prefix 它早就不是, the legacy fallback notice, and the later tool payload in the raw-content box.
+- Independent reviewer replayed the visible prefix in memory against the old discussion parser and committed 9adab45 reply parser. Both cut at precisely the same quote. Together the screenshots locate the observed short-body symptom to malformed-format handling/recovery, strongly contradicting a stream that delivered only the first few characters.
+- Distinguish upstream malformed structured output from downstream unsafe recovery: model-produced internal quotes need valid encoding, and the client must not accept an ambiguous prefix as complete prose. This is parsing before rendering, rather than visual clipping.
+- Evidence remains screenshot-level, not a request-correlated byte capture. A log renderer could alter escape display, so do not claim the full transport was byte-for-byte audited or all possible transport issues were excluded. No corrective code has been applied.