## Stack
Stacked on #29417. Review and land that PR first.
## Summary
- reject HTTP(S) image URLs in the handlers for `turn/start` and
`turn/steer`
- validate `thread/inject_items` after its existing
JSON-to-`ResponseItem` conversion, so each item is deserialized once
- turn invalid dynamic-tool image responses into the existing
unsuccessful text fallback; the model receives the validation message as
the function output
- leave `thread/resume.history` compatible with legacy history; #29417
replaces remote images before model input
- continue accepting inline data URLs and `localImage` inputs
- keep this policy in app-server; this PR does not add a shared protocol
API or change core image preparation
## Test plan
- `just test -p codex-app-server -E
'test(/request_handlers_reject_remote_image_urls|dynamic_tool_remote_image_response_becomes_model_visible_error|dynamic_tool_call_round_trip_sends_content_items_to_model|turn_start_tracks_turn_event_analytics|standalone_image_edit_uses_recent_pathless_image/)'`
(5 passed)
- `just fix -p codex-app-server`
- `just fmt`
rka-oai