[Sskift]

Summary

Custom encoder dispatch currently sends both context keywords whenever an encoder declares _parent. An encoder that only accepts _parent therefore receives an unexpected _sort_keys argument; an encoder that only accepts _sort_keys silently misses its context.

Pass each context value only when the callback accepts that keyword or has **kwargs. Avoid binding the primary value argument twice when its name is _parent or _sort_keys. Legacy one-argument callbacks, positional-only arguments, callable objects, and partial functions keep their existing calling conventions. Errors raised inside an encoder are propagated without retrying it.

Validation on Windows / CPython 3.12.10:

• The 16 new cases produce 10 failures and 6 passing controls against the original source.
• All 1,240 tests pass with the fix.
• Ruff lint/format and git diff --check pass.
• Mypy checks the new test file and reports the same 33 baseline diagnostics.
• A separate Codex agent independently reviewed this commit: 2,280 function-binding comparisons pass (880 fail on the original source), eight exception/return controls pass, and its isolated full suite passes all 1,240 tests. This is AI review, not human review.

Duplicate Check

• I searched the open PRs and found none that already fixes this issue.
• Targeted all-state encoder PR and signature issue searches found no matching dispatch fix.

Agent Drafting Metadata

• Agent: OpenAI Codex
• Model: Exact model identifier was not exposed to this worker.
• Notes: Codex assisted investigation, implementation, regression tests, and this description. No human review is claimed.