After context compression, the agent re-sent an already-delivered
generated image on every subsequent turn (#46627). The auto-append
fallback rescans full history when the message list shrinks (compression-
safe path), deduping against _history_media_paths — but that set was built
by scanning ONLY MEDIA: text tags in tool results. image_generate returns
its path in a JSON payload field (host_image/image/agent_visible_image),
never a MEDIA: tag, so generated-image paths never entered the dedup set
and were re-emitted after the boundary.
Extract the history-path collection into _collect_history_media_paths(),
which now covers BOTH delivery shapes: MEDIA: text tags AND image_generate
JSON-payload paths (mirroring what _collect_auto_append_media_tags
extracts). The inline block in _handle_message is replaced with a call to
the helper.
Co-authored-by: liuhao1024 <sunsky.lau@gmail.com>
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