Replace the manual `_quote_streams` raw-channel registry with a
symbol-keyed `maybe_open_context()` resource whose lifetime extends to
the final quote consumer.
Give every `open_aio_quote_stream()` caller a lexical child from the
cached `LinkedTaskChannel` broadcaster so concurrent users receive the
same quotes and close independently.
Prompt-IO: ai/prompt-io/opencode/20260813T230744Z_ddac3553_prompt_io.md
(this patch was generated in some part by `opencode` using `gpt-5.6-sol` (`openai`))
Gud Boi