fix: preserve ACP multimodal content during persistence

[Rivuza]

Summary

• Keep text-only persist_user_message overrides from replacing multimodal current-turn user content
• Preserve ACP image/image_url blocks through early crash-resilience persistence so they can reach the provider request
• Add regression coverage for text override behavior and multimodal preservation

Test Plan

• /home/rivuza/hermes-agent/.venv/bin/python -m pytest tests/run_agent/test_run_agent.py::test_persist_user_message_override_rewrites_text_turns tests/run_agent/test_run_agent.py::test_persist_user_message_override_preserves_multimodal_turns -q
• /home/rivuza/hermes-agent/.venv/bin/python -m pytest tests/run_agent/test_run_agent.py -q

Closes #44242

[liuhao1024]

Verification review — reviewed the diff and tests; no issues found.

The guard if isinstance(msg.get("content"), list): return correctly prevents the text-only persistence override from clobbering multimodal content-part lists. The unit tests directly exercise _apply_persist_user_message_override for both text-rewriting and multimodal-skip paths.

Note: #44248 addresses the same issue (#44242) with an equivalent guard. Its test is more end-to-end — it drives _persist_session and verifies that (a) the API-bound message keeps the image part and (b) the DB persistence still redacts to "[screenshot]". Both PRs are clean; the maintainer can pick either. If this one lands first, #44248 can be closed (and vice versa).

[alt-glitch]

Duplicate of #44247 — same approach (isinstance(content, list) guard in _apply_persist_user_message_override to skip the text-only override for multimodal turns), both fixing #44242. #44247 is the earliest open PR of the trio (#44248 is the other dup).

[teknium1]

Salvaged and merged via #47907 (commit 3d21666) — your fix landed on main with your authorship preserved via rebase-merge. I adapted the guard slightly so it keeps the message-timestamp metadata write that landed after you filed this. Thanks for the clean fix and the regression test! Closes #44242.