Summary

• overwrite persisted session runtime metadata when an active session explicitly switches models
• keep /insights aligned with the live provider/base URL instead of preserving stale first-write metadata forever
• add a regression test that reproduces the stale Gemini-vs-GLM provider report and asserts the corrected insights output

Testing

• ./scripts/run_tests.sh tests/run_agent/test_switch_model_context.py tests/run_agent/test_switch_model_fallback_prune.py -q
• git diff --check
• uv sync --frozen --extra all
• uv run --frozen ruff check .
• repo lint-diff semantics (ruff clean; ty advisory signal recorded in proof)
• clean env -i pytest attribution against latest origin/main (30 head failures, 27 reproduced on base, remaining 3 isolated and passed on retry/base)

Fixes #3988.