quest: JS lite fetch waits for the publisher's answer

quest/m1/README.md

@@ -19,6 +19,7 @@ transport, benchmark tooling); worktrees isolate commits, not semantics.
 
 - [Play harness](/quest/m1/play-harness.md) - moq play's tune-in, rendition-switch, and drain logic runs in per-PR CI without a device
 - [Missing fetch group](/quest/m1/fetch-missing-group.md) - HTTP /fetch answers 404 and `moq fetch` fails cleanly for a group the track lacks
+- [JS fetch answer](/quest/m1/js-fetch-answer.md) - js/net's lite fetch settles on the publisher's answer, and a JS publisher's miss resets with NotFound
 - [libmoq hidden opt-in](/quest/m1/libmoq-hidden.md) - `moq_origin_announced` takes a `hidden` flag so C callers can list `.`-named broadcasts
 - [lite-07 stream count](/quest/m1/lite-stream-count.md) - moq-lite-07 replaces SUBSCRIBE_DROP with a group-stream count in SUBSCRIBE_END, like moq-transport
 - [Announce compression](/quest/m1/announce-compression.md) - a lite-07 announce reuses the path head and hop-chain tail of a live announcement on its stream instead of resending them

quest/m1/js-fetch-answer.md

@@ -0,0 +1,32 @@
+# [S] JS lite fetch waits for the publisher's answer
+
+## Goal
+
+`js/net`'s lite `fetchGroup` resolves only once the publisher has answered:
+the first response byte, or a FIN for an empty group. A missing group rejects
+the fetch itself, and every coalesced caller sees the same rejection, instead
+of receiving a group whose first `readFrame()` fails. A JS publisher that
+cannot serve a group resets the stream with `NotFound`, not a generic error,
+so a Rust or JS subscriber can tell a miss from a failure.
+
+## Plan
+
+- Rust already behaves this way since #4164, which waits in the lite
+  subscriber before accepting and rejects on reset. Mirror it: resolve after
+  the first response byte or an empty-group FIN, and reject on reset. Today
+  the fetch path returns its mirror before the response arrives; the stream
+  reader can already block until data or FIN and throw on reset.
+- The publisher side throws a plain error for a local miss, which reaches the
+  wire as a generic reset code. Give it the `NotFound` code the Rust side uses.
+- The IETF JS path refuses `fetchGroup` outright and is out of scope.
+- Tests in the lite integration suite: a missing group rejects the fetch, a
+  coalesced second caller rejects too, an existing group is unchanged, and a
+  JS publisher's miss reaches a subscriber as `NotFound`.
+
+Public API: none; a behavior change in when `fetchGroup` settles. Wire: no
+format change; a miss resets with the existing `NotFound` code instead of a
+generic one.
+
+## Related
+
+- [#4164](https://github.com/moq-dev/moq/pull/4164) - the same fix in Rust