Add ContextVarLike + ContextLike Protocols for stdlib-parity type contracts

[conradbzura]

Context

During PR #224's 20-agent multi-dimensional review, the C20 finding led to introducing a TokenLike Protocol (now wool.TokenLike) mirroring the stdlib contextvars.Token public surface — hiding the Wool-internal id / chain_id / used attributes behind the concrete Token class. The remediation plan deferred the analogous treatment of ContextVar and Context to a follow-up issue.

The follow-up

Extend the stdlib-parity narrowing C20 applied to Token to the other two core context types:

ContextVarLike[T]

Mirror contextvars.ContextVar (name, get, set, reset). Wool's concrete ContextVar already satisfies it structurally. Both should be public: wool.ContextVar stays the concrete user-instantiable class (carrying namespace and other Wool extras); wool.ContextVarLike is the narrow Protocol for users writing def use_var(var: ContextVarLike[int]) — "stdlib OR wool" type hints.

ContextLike

Mirror contextvars.Context (__getitem__, __contains__, __iter__, __len__, get, keys, values, items, run). Wool's concrete Context does not satisfy it today (snapshot dataclass — no dict-like methods, no run). Two sub-decisions for this issue:

• (a) Grow Wool's Context to satisfy ContextLike by adding dict-like methods + run(). Bigger change — run() interacts with mount/unmount and the chain-contention guard; needs careful design.
• (b) Define ContextLike for documentation/contract only; Wool's Context does not claim to satisfy it. Cheap; establishes vocabulary without forcing structural conformance.

Why this was deferred

Token's "Protocol replaces concrete" works because tokens are never user-instantiated; for ContextVar this asymmetry forces both Protocol and concrete to coexist, doubling the type-name surface. ContextLike (a) is a meaningful API expansion that deserves its own design pass and tests. None of this was required for the stdlib-parity goals PR #224 closed.

Reference

• REVIEW-PLAN-224 finding F1 in PR Reframe Wool's context model around stdlib contextvars — Closes #223, #229, #232 #224's review plan.