IB history frames omit the derived `index` and append `count`.
Normalize provider data to durable names, order, and dtypes before
merge, and reject fractional epoch truncation.
Also,
- map canonical storage fields into provider-specific SHM on reload
- select Polars columns by name instead of position
- exercise first-start and restart through actor, SHM, and Parquet
Prompt-IO: ai/prompt-io/opencode/20260727T212454Z_689df816_prompt_io.md
(this patch was generated in some part by `opencode` using `gpt-5.6-sol` (`openai`))
