fix(gateway): preserve media dedup after streamed replies

[TheEpTic]

what does this PR do?

Fixes a gateway crash in the post-stream delivery path. When a streamed agent result has already_sent=True and a non-empty final response, _handle_message_with_agent passed _history_media_paths, which is only bound inside _run_agent_inner's nested run_sync function. The outer handler therefore raises NameError after the model request succeeds, turning an otherwise-complete reply into a generic platform error.

This happens for ordinary streamed text replies as well as responses containing MEDIA: directives, because the post-stream attachment-delivery helper is invoked for any non-empty response.

The fix derives the existing history-media dedup set from the handler's loaded transcript. This resolves the crash without disabling cross-turn MEDIA deduplication.

This is deliberately limited to the gateway fix and its regression coverage. The related open #72228 also modifies unrelated desktop performance/debug files; its fallback-to-empty-set guard avoids the exception but drops the existing dedup context.

related issue

No filed issue. Related PR: #72228.

type of change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✅ Tests (adding or improving test coverage)

changes made

• gateway/run.py: derive prior delivered MEDIA paths from the transcript before post-stream delivery.
• tests/gateway/test_42039_duplicate_user_message.py: exercise the real already_sent branch with an ordinary text reply and assert prior MEDIA paths reach the delivery helper.

how to test

1. On unpatched main, drive _handle_message_with_agent with already_sent=True, any non-empty response, and a platform adapter. It raises NameError: name '_history_media_paths' is not defined after the streamed response completes.
2. Apply this patch and repeat. The post-stream helper receives the prior assistant MEDIA path and the reply completes normally.
3. Run:

   scripts/run_tests.sh tests/gateway/test_42039_duplicate_user_message.py tests/gateway/test_post_stream_media_delivery.py tests/gateway/test_tts_media_routing.py

   Result: 17 passed.

checklist

• I've read the Contributing Guide.
• My commit message follows Conventional Commits.
• I searched existing PRs; fix(gateway): handle undefined _history_media_paths in auto-resume path #72228 is the only exact open overlap and this PR does not duplicate its unrelated desktop changes.
• My PR contains only changes related to this bug fix.
• I've run pytest tests/ -q and all tests pass. Full hermetic scripts/run_tests.sh is running separately; the targeted canonical suite above passed.
• I've added a regression test for this bug fix.
• I've tested on Linux (Arch).
• Documentation/config/tool-schema changes: N/A.
• Cross-platform impact considered: pure in-memory history parsing, no platform-specific I/O or process behavior.

[Tornado-Truxton]

Independent production confirmation from a Fedora 44 Telegram gateway:

• Current upstream main raised NameError: name _history_media_paths is not defined from _handle_message_with_agent on the already-streamed MEDIA-delivery path, yielding Telegram’s generic unexpected-error reply.
• We applied the same pre-turn transcript approach locally: _collect_history_media_paths(history) immediately after loading the handler history, then restarted the gateway.
• A fresh Telegram session subsequently completed a status request normally, and the gateway has logged no further NameError / agent-handler errors.

This preserves prior-turn MEDIA deduplication, so it is preferable to an empty-set fallback. Thanks for including real branch coverage here.

[hanzckernel]

Independent macOS/Telegram confirmation: an ordinary text-only streamed reply completed successfully with finish_reason=stop and was fully delivered, after which _handle_message_with_agent raised NameError: name '_history_media_paths' is not defined and the gateway emitted its generic unexpected-error message.

No attachment directive was required to trigger the failure, so this affects ordinary streamed text replies as well as MEDIA-bearing replies. The model/provider request had already succeeded. Latest main still contains the undefined outer-scope reference.

#72321’s history-derived fix preserves the existing cross-turn deduplication contract and is preferable to an empty-set fallback.

[teknium1]

Merged via PR #72341 — your commit was cherry-picked onto current main with your authorship preserved in git log (c2ee503). Thanks for the clean fix and the real branch coverage!