Keep provider root streams private to the cached `Feed` and give every
`maybe_open_feed()` caller, including the first owner, a local
subscription view with copied `Flume` descriptors.
Also,
- key cached resources by the normalized full symbol set and stream
policy instead of only the first FQME.
- subscribe each `Feed.open_multi_stream()` provider relay and wait for
all relays to start before yielding the merged channel.
- give each provider relay an independent send-channel clone so one
provider EOC cannot terminate its siblings.
- document `Feed.pause()` and `Feed.resume()` as shared remote-provider
controls rather than caller-local cursor operations.
- cover miss/hit ownership, multi-market provider mapping, relay
fan-out, lexical teardown and cache-key separation.
Prompt-IO: ai/prompt-io/opencode/20260813T202402Z_12b0d66e_prompt_io.md
(this patch was generated in some part by `opencode` using `gpt-5.6-sol` (`openai`))
Gud Boi