fix(moq-tokio): finite default connection receive window (backport #4605)

[kixelated]

Backport of #4605 onto release. Quest: quest/m0/branch-flip.md (the remaining item only; the branch flip itself already landed).

Problem

release still leaves the connection receive window at the transport default, which is unlimited (VarInt::MAX). One peer can make the relay buffer about 12.5 GB per connection (max_streams 10k times the 1.25 MB stream window). main already applies 64 MiB when quic.receive_window is unset (#4605, 275af93).

Approach

Cherry-pick the moq-tokio and docs changes from 275af93. noq and iroh call receive_window with the configured value, or DEFAULT_RECEIVE_WINDOW (64 MiB) when it is unset. An explicit value still wins. Resolved.receive_window stays None when unset, so the io_uring workers can keep refusing an explicit window.

The quest-file hunks in that commit (quest/m0/README.md, quest/m0/noq-reassembly-cap.md, quest/m1/quic/fork/README.md) are not in this PR. They already landed on main with #4605, and they do not apply cleanly onto release.

Impact

• Public API: none. quic::Config::receive_window and quic::Resolved::receive_window stay Option<u64>. The new DEFAULT_RECEIVE_WINDOW constant is pub(crate).
• Behavior: noq and iroh connections advertise a 64 MiB initial MAX_DATA instead of 2^62 - 1 when the knob is unset. A peer can have at most 64 MiB of unread data across all of its streams.
• Wire: no MoQ format change.

Alternatives

• Resolving the default inside Config::resolve so Resolved shows 64 MiB. That makes the io_uring workers refuse every config, because they reject any Some window.
• Leaving release unlimited until the next cut. The cut is not happening yet, and this is the urgent bound the quest still calls for.

Follow-ups

• On main, delete quest/m0/branch-flip.md and its link in quest/m0/README.md once this backport merges. That edit does not belong on release.
• The iroh build's upstream noq-proto 1.3.0 is still uncapped until n0 releases fix(proto): bound assembler chunk count (port of quinn RUSTSEC-2026-0185 fixes) n0-computer/noq#828 (quest/m0/noq-reassembly-cap.md on main).

(Written by Grok 4.7)

[kixelated]

Took over the stale claim at f25cfbd (empty "quest: claim branch-flip", no open PR) with --force-with-lease onto a branch based on origin/release.

Cherry-picked 275af93 without the quest-tree hunks. just check origin/release passed locally. Left as a draft. Deleting quest/m0/branch-flip.md belongs on main after this merges, not in this PR.

(Written by Grok 4.7)

[kixelated]

@codex review

(Written by Grok 4.7)

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-06T06:26:49.701138Z	2645bcc	Manual request

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[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Delightful!

Reviewed commit: 2645bcc342

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[kixelated]

Backport of #4605 onto release. When quic.receive_window is unset, noq and iroh advertise a 64 MiB connection window instead of the unlimited transport default. An explicit value still wins, and Resolved.receive_window stays unset so the io_uring workers can keep refusing an explicit window. Public API is unchanged. Wire: an unset session's initial MAX_DATA is 64 MiB, not 2^62-1.

Confirmed: do not delete quest/m0/branch-flip.md here. That file lives on main and comes out in a follow-up after this lands. Codex reviewed 2645bcc342ee77c49308b6367f467573866bf3c9 and found no issues. Check and Test are green.

(Written by Grok 4.7)