Carry conversation history as list[{"role", "content"}] from the chat talent's pre-hook through _execute_generate into each provider SDK's native turn array. List-of-strings callers continue unchanged - no dual runtime, no feature flag. Google gets a new types.Content/Part mapper (assistant -> "model"). chat.md drops $chat_stream_tail; the tail is now a first-class structured list on the pre-hook return. Decisions (req_h5iyql3s): - messages key on pre-hook return dict; plain list[dict[str, str]] with role in {"user","assistant"} - owner_message trigger: triggering owner turn already persisted in the chat stream; for talent_finished / talent_errored synthesize a final user turn "[talent <name> finished: <summary>]" / "[talent <name> errored: <reason>]" - drop $chat_stream_tail from chat.md; tests/baselines/api/sol/preview.json regenerated to match - drop in-tail talent_* markers from the structured history (the system prompt $active_talents block still carries in-flight exec context) - per-provider mapping lives in its own module; no shared/abstract messages type; system instruction stays in each provider's native field Test plan: - make test-only TEST=tests/test_chat_context.py (passed) - make test-only TEST=tests/test_anthropic.py (passed, including structured+schema) - make test-only TEST=tests/test_openai.py (passed) - make test-only TEST=tests/test_ollama.py (passed) - make test-only TEST=tests/test_google.py (passed, sync+async Content/Part mapping) - make test-only TEST=tests/test_talent_fallback.py (passed, _execute_generate regression locks) - PYTEST_ADDOPTS="--basetemp=$(mktemp -d /tmp/pytest-qufbiyo2.XXXXXX)" make ci (passed - isolated tempdir to avoid a concurrent-worktree /var/tmp/pytest-of-jer collision) - make review: browser verify 19/19 pass; API verify hit one pre-existing drift on sol/badge-count (expected {"count": 1}, got {"count": 0}) that reproduces on a clean tree with this diff stashed - unrelated to structured messages, filed as separate follow-up. Manual chat-tail sandbox spot-check was skipped since the 19/19 browser verify exercises the chat UI path. Co-Authored-By: OpenAI Codex <codex@openai.com>