Post-fork `_runtime_vars` reset in `subint_forkserver_proc`
was previously done via direct mutation of
`_state._runtime_vars` from an external module + an inline
default dict duplicating the `_state.py`-internal defaults.
Split the access surface into a pure getter + explicit
setter so the reset call site becomes a one-liner
composition.
Deats `tractor/runtime/_state.py`,
- extract initial values into a module-level
`_RUNTIME_VARS_DEFAULTS: dict[str, Any]` constant; the
live `_runtime_vars` is now initialised from
`dict(_RUNTIME_VARS_DEFAULTS)`
- `get_runtime_vars()` grows a `clear_values: bool = False`
kwarg. When True, returns a fresh copy of
`_RUNTIME_VARS_DEFAULTS` instead of the live dict —
still a **pure read**, never mutates anything
- new `set_runtime_vars(rtvars: dict | RuntimeVars)` —
atomic replacement of the live dict's contents via
`.clear()` + `.update()`, so existing references to the
same dict object remain valid. Accepts either the
historical dict form or the `RuntimeVars` struct
Deats `tractor/spawn/_subint_forkserver.py`,
- collapse the prior ad-hoc `.update({...})` block into
`set_runtime_vars(get_runtime_vars(clear_values=True))`
- drop the `_state._current_actor = None` line —
`_trio_main` unconditionally overwrites it downstream,
so no explicit reset needed (noted in the XXX comment)
(this commit msg was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
Gud Boi
27cc02e83d