fix(agent): tolerate content-parts lists in interim visible text

[null-runner]

Bug

AIAgent._interim_assistant_visible_text (run_agent.py:4823-4824) reads the assistant message content and passes it straight into the think-block stripper:

content = assistant_msg.get("content")
return self._strip_think_blocks(content or "").strip()

_strip_think_blocks (run_agent.py:1513) forwards to strip_think_blocks in agent/agent_runtime_helpers.py, which runs re.sub(...) on that value (agent_runtime_helpers.py:678). When content is a list of parts rather than a string, re.sub raises:

TypeError: expected string or bytes-like object, got 'list'

The exception propagates out of _interim_assistant_visible_text and then out of every subsequent API call in the turn, so the conversation appears frozen to the user (observed in practice with several back-to-back API calls in one turn all dying the same way).

When is content a list?

An assistant message's content is a parts list (not a string) after context compaction, and with multimodal providers, e.g.:

[{"type": "text", "text": "..."}, {"type": "image_url", "image_url": {...}}]

The helper only ever handled string content, so this path was unguarded.

Fix

Join the textual parts before stripping think-blocks; non-text parts (images) are ignored, and plain-string content is unchanged. 8 lines in run_agent.py.

Tests

New tests/run_agent/test_interim_visible_list_content.py — 3 cases: a mixed text/image parts list, an image-only list, and a plain string.

• Failing-first verified: against the unfixed run_agent.py, test_interim_visible_text_handles_content_parts_list fails with TypeError: expected string or bytes-like object, got 'list'.
• With the fix: tests/run_agent/test_interim_visible_list_content.py 3/3 pass; tests/run_agent/test_run_agent_codex_responses.py 104/104 pass (107 total).

[alt-glitch]

This was generated by AI during triage.

Related to #66218: both prevent the multimodal content-list regex crash. This PR guards the interim-visible path, while #66218 applies coercion in the shared stripping helper.

[tonydwb]

Code Review Summary

Verdict: Approved

Fix for content-parts lists in interim visible text. The change handles a real edge case where compaction or multimodal providers leave content as a list instead of a string. The implementation correctly joins only textual parts and ignores non-text entries. New tests cover the key scenarios.

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Reviewed by Hermes Agent

[tonydwb]

Code Review Summary

Verdict: Approved (LGTM)

Overview

Tolerates content-parts lists in interim visible text for agent. +53/0.

Security

• No hardcoded secrets or credentials

Code Quality

• Clean multimodal content handling

Looks Good

• Proper edge case handling

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Reviewed by Hermes Agent

[null-runner]

Closing: main now fixes this at the shared helper level — 296494d hardens strip_think_blocks to flatten list/dict content for every caller (including _interim_assistant_visible_text, the path this PR patched), which supersedes the caller-side guard here. Verified the merged fix covers our production repro (post-compaction list content no longer raises).

[kshitijk4poor]

Merged via commit 296494d — Teknium's fix at the shared chokepoint (strip_think_blocks) covers the same bug class this PR addresses. The fix coerces list/dict content to visible text before any regex runs, protecting all callers including _interim_assistant_visible_text.

Your contribution is appreciated — narrow fix in _interim_assistant_visible_text only. Credit preserved in the commit message investigation. Thanks for the report and fix!

For the remaining gap (build_assistant_message defense-in-depth + error classifier concept), we're tracking in a follow-up issue.