[robobun]

Problem

• In node:quic, the sender copies a queued body again for every write. One setBody(buffer) of 8/16/32/64 MiB costs 0.13/0.62/2.6/10.7 s of CPU behind a 16 KiB window.
• QuicStream::drain_outbound (src/runtime/node/quic/stream.rs:489) copies the whole unsent queue (a.to_vec()) before every lsquic_stream_write. lsquic takes a few KiB of each copy.

Fix

• drain_outbound gives both halves of the queue to lsquic_stream_writev in place. The same bodies cost 0.03/0.07/0.13/0.26 s.
• The queue is moved out of its JsCell for the call and put back after it. Every ingest path copies the body once (setBody() copied it twice).
• Outbound::clear drops the allocation, and drain_outbound calls it once the FIN or the trailers request is out. A finished stream no longer holds its body until the GC collects it. patches/lsquic/iovec-reader-size_t.patch makes lsquic's iovec reader keep its offset in a size_t: in an unsigned, an iovec of 4 GiB or more made it spin.
• Verified: test/js/node/quic/quic-stream.test.ts (main fails the CPU-time test, the three peak-RSS cases and the queue-release test), test/js/node/quic/, the node test-quic-* files. Self-reviewed: 26 concerns raised, 26 addressed (see Notes).

Background

• Outbound is a stream's queue of bytes not yet given to lsquic, a VecDeque<u8>. on_write, lsquic's callback for a writable stream, drains it.
• In one write lsquic takes what flow control, the congestion window and the pacer allow. It copies those bytes before it returns.
• JsCell is an UnsafeCell with no borrow check.
• Considered: a borrow held across writev (sound only while lsquic never calls back), lsquic_stream_writef (two new unsafe callbacks), a queue of owned chunks (a malloc and an lsquic call for each chunk).

Downsides

• lsquic's size query reads two iovec entries: 22 instructions against 18. drain_outbound itself runs as many instructions as on main (125 to 143 for a 1 KiB body).
• None found for the queue release and the lsquic patch. Checked the four clear callers (reset, abort, 0-RTT rejection, teardown), the FIN and trailers arms of drain_outbound, and both users of inner_reader_iovec in lsquic.

Notes

Where this came from. No user reported it, and no maintainer asked for it. An automated load test of node:quic found it: a server that answers with stream.setBody(buffer) stops serving other clients while it sends one large answer. Its report asked for a rebase of this PR onto main and for a test of the time, not only of the memory. The copy is in every release since 1.4.0. There is no Node column below: the released Node build at hand (v26.3.0) has no node:quic.

What the cost follows. Main copies what is queued, once for each write, so the cost is (bytes queued) x (number of writes).

• A body handed over in one piece pays most: setBody(buffer), the body option, one large writer.write*(). An array of 64 KiB chunks given to setBody() pays less (16 MiB behind a 16 KiB window: 0.28 to 0.31 s of CPU on main, 0.11 s with this PR). An async iterable of 64 KiB chunks pays nothing (0.10 s on both), because the queue stays at the high-water mark. That is the workaround on released builds.
• The peer steers it. lsquic cannot take more than the stream window that the peer advertises. A client with a stream window of 256 bytes costs the server 8.8 to 10.7 s of CPU for the first 512 KiB of a 64 MiB answer on main, and 0.10 to 0.11 s with this PR.
• A refused write copies too. An HTTP/3 body queued before its header block gets -1 from every write, and lsquic calls on_write again up to 1000 times in a pass. On main that takes 91 ms of CPU for 1 MiB queued and 412 to 481 ms for 4 MiB. With this PR it takes 1 ms and 3 ms. This PR makes each retry cheap. The retries stay with node:quic: reset the stream when lsquic_stream_write fails instead of retrying on every tick #42892.
• With default windows the number of writes depends on the congestion window and the pacer, and the cost of main varies a lot between runs. The load script below took 3.8 to 10.9 s for one answer of 32 MiB on main.

Not changed.

• The lsquic send window a write can fill, the congestion window and the pacer are lsquic's.
• QuicSession::events is drained with Vec::remove(0) (session.rs:898). It scales with the events of one tick, not with body bytes.
• The receive path copies each chunk (at most 16 KiB) twice (push_inbound, pull). It is linear.
• node:net has the same class of drain, open as socket: drain node:net's pending-write queue with a cursor #44219 on a contiguous cursor buffer. The ring stays here: a streaming writer needs no compaction, and a half-sent tail needs no second allocation.
• lsquic's iovec reader (inner_reader_iovec in lsquic_stream.c) kept its offset and copy length in an unsigned. For an iovec of 4 GiB + 10 bytes it copied 10 bytes, then computed a length of 0 and spun. Main handed the whole contiguous half to lsquic_stream_write, which uses the same reader. The patch makes both a size_t. The case needs a 4 GiB queue and is not tested.
• node:quic: reset the stream when lsquic_stream_write fails instead of retrying on every tick #42892 edits drain_outbound too. The refused write has its own arm here so that it can hook it. The PR that lands second rebases.

Measurements. linux x64. "main" is a release build of 0ffddcdc6d. "PR" is a release build of this change on that commit. The branch is on 017b2439a7 now. No commit between the two touches a quic file.

Sender CPU for one body, all of it delivered, against the same bytes in 64 KiB bodies. bun test/js/node/quic/outbound-body-cpu-fixture.ts N N: both ends in one process, receiver stream window 16 KiB, the clock starts when the body is queued, two invocations each.

Body	main, one body	PR, one body	PR, 64 KiB bodies
8 MiB	0.11 to 0.15 s	0.031 to 0.032 s	0.046 to 0.051 s
16 MiB	0.62 to 0.63 s	0.064 to 0.076 s	0.11 to 0.31 s
32 MiB	2.55 to 2.62 s	0.130 to 0.132 s	0.170 to 0.172 s
64 MiB	10.6 to 10.7 s	0.24 to 0.28 s	0.30 to 0.35 s

Per doubling: main x4.1 to x4.8, PR x1.9 to x2.2.

• Copies of 64 KiB or more for one body (LD_PRELOAD counter on memcpy and memmove, default windows): main 15 to 19 copies for 1 MiB (9.1x to 11.7x the payload) and 63 to 74 for 4 MiB (36.7x to 38.3x), PR 1 copy (1.00x) for both sizes, on each of the three ingest paths.
• drain_outbound for a 1 KiB body (gdb stepi, callees listed): main 125 to 143 instructions in the function plus 115 to 207 in malloc, memmove and free. PR 125 to 143 plus 0. A streaming write of 1 KiB: main 118 plus 112 to 115, PR 118 plus 0. A drain that only sends the FIN: 55 on both.
• lsquic's inner_reader_iovec_size: 18 instructions with one iovec entry, 22 with two. It is called once for a 1 KiB body and 17 times for a 16 KiB body, on both builds.
• Heap calls in drain_outbound for 10,000 x writer.writeSync(1 KiB) then endSync() (gdb call-site counts): main 10,000 malloc and 10,000 free, PR 0 and 0.
• Release text: 106,512,438 B on main, 106,510,902 B with this PR (1,536 B less). drain_outbound is 807 B (main 1,024 B), attachSource 288 B (389 B), and the per-element VecDeque::spec_extend (1,267 B) is gone. size_of::<Outbound>() is 40 B on both.
• bench/quic server bench (HTTP/3, 50 requests in flight, the same client build for both servers, runs in ABBA order): body 0: main 15,074 req/s and 1,380 ms of server CPU, PR 14,158 req/s and 1,400 ms. Body 1 KiB: main 13,288 req/s and 1,690 ms, PR 12,990 req/s and 1,730 ms (medians of 16 runs of 40,000 requests). These are equal within the noise of the bench: the same main binary twice gives 14,645 and 13,791 req/s. Body 64 KiB: both builds are bimodal in the same way, about 210 req/s or about 1,600 req/s (medians 216 and 213 of 8 runs of 10,000 requests, and the same main binary twice gives 1,221 and 330).
• The load script of the report. A second client counts its echo round trips while one answer of N MiB is sent. The script fails when they fall under a half.

Answer	main	PR
32 MiB, 3 runs	10.9 / 7.9 / 3.8 s, server CPU 6.6 / 5.8 / 2.2 s, round trips in 3 s fall from about 5100 to 2560 / 1810 / 1943: fails 2 of 3	0.6 / 3.1 / 1.7 s, server CPU 1.2 to 1.5 s, round trips stay at 4544 to 5152: passes 3 of 3
64 MiB, 1 run	35.6 s, server CPU 24.8 s, round trips fall from 4558 to 768: fails	4.8 s, server CPU 1.9 s, round trips 5005 to 4665: passes
32 MiB as 64 KiB answers, 1 run	0.8 s: passes	0.9 s: passes

Tests (test/js/node/quic/quic-stream.test.ts).

• costs the CPU time of the same bytes in 64 KiB bodies: the fixture queues 48 MiB behind a 16 KiB window and compares the CPU time until 16 MiB arrived (4 MiB on ASAN, 1 MiB on debug) with the same bytes in 64 KiB bodies. Bound 4. This PR: 0.73 to 1.08 on release (20 runs), 0.54 to 0.99 on release+ASAN (20 runs), 0.40 to 0.75 on debug+ASAN (10 runs). Main: 34.4 to 37.9 on release (7 runs), 98 to 133 on release+ASAN (4 runs), 8.7 to 13.0 on debug+ASAN (8 runs). With 12 fixture processes at once, 96 of 96 release runs of this PR stay under 4 (highest 1.22), and 144 of 144 release+ASAN runs (highest 1.12). With 6 at once, 24 of 24 debug+ASAN runs (highest 1.21). Main on release, 12 at once: 0 of 12 (lowest 37). The release+ASAN numbers of this PR are from its previous revision. That revision differs in one thing: it also freed the queue buffer when the send side ended. Skipped on Windows, where process.cpuUsage() advances in ticks of 15.6 ms.
• a queued body is buffered natively exactly once (3 cases): peak RSS of a fixture process that hands over 16 MiB, minus the peak of one that does not, over the body. Bound 1.5. This PR: 1.01 to 1.05 on release, 1.06 to 1.24 on debug+ASAN, 0.88 to 0.98 on release+ASAN (previous revision). Main: 1.98 to 2.02 on release, 1.79 to 1.89 on release+ASAN, 1.88 to 1.97 on debug+ASAN.
• a body written before the header block (1 MiB): the refused write. It passes on main's release build. On main's release+ASAN and debug+ASAN builds it does not finish in the default timeout of 5 s. Two mutants of this PR fail it: write_to without the sign check loses the body, and drain_outbound without the taken < 0 arm never reports the block.
• the queue of a finished stream is freed when its FIN goes out: outbound-body-release-fixture.ts keeps six finished streams of 8 MiB alive and reports the RSS growth after the first. Bound 35 MiB. Main: 49 to 54 MiB on release, 62 to 64 MiB on debug+ASAN. This PR: 7 to 20 MiB on debug+ASAN (8 runs). clear is also what the reset, abort, 0-RTT rejection and teardown paths call, so those free the buffer too.
• a body fed through a wrapped queue arrives intact: passes on main too. gdb on lsquic_stream_writev during this transfer: 30 calls, 12 of them with both halves of the ring in use.
• With main's src/: 5 of 13 fail on debug+ASAN and on release+ASAN (the CPU-time test, the three peak cases, and the refused-write case by timeout). 4 of 13 fail on release, where the refused-write case passes. With this PR: 13 pass on debug+ASAN and on release.
• The 235 node test-quic-* files on the debug+ASAN build: 228 pass with this PR and 228 with main's src/, four files at a time on a busy machine. On both builds, two files need node:stream/iter, which does not resolve, and test-quic-session-initial-rtt.mjs asserts an RTT bound that a debug build misses. The other failures are test-quic-callback-error-* files. They fail now and then on both builds, and not the same files each run. test-quic-callback-error-onstream.mjs alone, the builds in turn: 8 of 40 runs fail on main and 7 of 40 with this PR on debug+ASAN. On release, 0 of 25 fail on both. The lsquic log of a failing run shows the cause. The server drops the session without a close frame. The client still sends a packet before its 1 s idle timeout ends (a NEW_CONNECTION_ID frame on a timer of about 1.5 s from the start of the connection). The server answers with a stateless reset, and the client reports it as ERR_QUIC_TRANSPORT_ERROR. This diff does not touch that path.
• quic-stream.test.ts now measures CPU time and RSS, so it is taken out of the parallel batch of the test runner (test/parallel-allowlist.json, test/parallel-denylist.txt), like the other RSS tests (test: run harness-max-rss.test.ts and compile-rss.test.ts outside the parallel batch #45636). _meta.stats.excluded says 367 now, the length of excludeFiles. sql: consolidate the open Bun.sql, bun:sqlite and node:sqlite pull requests #45304 took two entries out and left the count at 368.

Self-review. 26 concerns, 16 of them "should fix". Code and tests: the buffer release taken out (8 concerns), the CPU clock moved after the handover and 4 MiB measured on ASAN (2), the peak-RSS helpers (1), the closed promises of the fixture wired to its result (1), the refused-write test (2). This text: the cost stated by bytes queued and number of writes with a table (3), the peer and the refused write as triggers (2), no user report and the workaround (3), the sites not changed (3), loaded pass counts (1). One recommendation inside a concern is not taken: an Outbound::abort() helper for the three sites that also reset end. The buffer release came back in 30a0c98 after review: it frees in clear, which every end-of-send-side path already calls, and the FIN and trailers paths call it too. A test covers it now.

The first version of this PR (6d0c309) held a borrow of the queue across lsquic_stream_writev, with the argument that lsquic never calls back from a write. That argument still holds by a reading of the vendored lsquic. The queue is now moved out for the call, so the code no longer depends on it.

---

no test proof · iteration 0 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/js/node/quic/quic-stream.test.ts

[coderabbitai]

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• src/lsquic_sys/lib.rs
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• src/runtime/node/quic/stream.rs
• test/js/node/quic/outbound-body-release-fixture.ts
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Walkthrough

The QUIC outbound path now uses vectored writes and a shared queue abstraction. Stream body attachment and queue lifecycle operations use that abstraction. New fixtures and tests cover body delivery, resource use, blocked writes, and queue wrap-around.

Changes

QUIC outbound buffering

Layer / File(s)	Summary
Vectored write and outbound queue src/lsquic_sys/lib.rs, src/runtime/node/quic/outbound.rs, src/runtime/node/quic/mod.rs	The lsquic binding uses lsquic_stream_writev. The new Outbound type stores queued bytes and pending end state, and writes the queue’s slices through Stream::writev.
Stream body attachment and queue lifecycle src/runtime/node/quic/stream.rs, src/runtime/node/quic/session.rs	QuicStream uses Outbound to attach bodies, append and drain bytes, measure pending data, and clear state. QuicSession::open_stream delegates ArrayBuffer body attachment to QuicStream.
Outbound stream validation test/js/node/quic/outbound-body-*-fixture.ts, test/js/node/quic/quic-stream.test.ts, test/parallel-allowlist.json, test/parallel-denylist.txt	New fixtures and tests measure body handoff resource use and check blocked writes, body delivery, and queue wrap-around. The test is added to the parallel-test exclusion lists.

Suggested reviewers: cirospaciari

Priority: ➖ Normal

Merge Risk: 🔵 Low · up to bbee5

The change makes QUIC outbound writes avoid copying the queue on every write, and no functional defect was found in review. The only open point is a test-timeout convention that the author has justified, so it is safe to merge once the maintainers accept that.

Pre-merge checks: 4

Check name	Status	Explanation
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Title check		The title clearly identifies the main change: writing the QUIC outbound queue to lsquic in place instead of copying it during each write.
Description check		The description is comprehensive and explains the problem, implementation, performance impact, verification results, tests, and known limitations. It uses different headings from the template, but it …

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[robobun]

^{Updated 5:06 AM PT - Oct 20th, 2026}

❌ @robobun, your commit 8699b18 has 1 failures in Build #129362 (All Failures):

• test/js/node/http/node-http-uaf.test.ts - code 1 on 🍎 any x64

---

🧪   To try this PR locally:

bunx bun-pr 37491

That installs a local version of the PR into your bun-37491 executable, so you can run:

bun-37491 --bun

[robobun]

Status

Reproduced on a release build of main (0ffddcdc6d) with the fixture of this PR, bun test/js/node/quic/outbound-body-cpu-fixture.ts N N: one setBody(buffer) of 8 / 16 / 32 / 64 MiB behind a 16 KiB stream window costs 0.13 / 0.62 / 2.6 / 10.7 s of CPU. With this branch it costs 0.03 / 0.07 / 0.13 / 0.26 s.

With main's src/ on a debug+ASAN build, bun bd test test/js/node/quic/quic-stream.test.ts fails 5 of 13 tests: the CPU-time test (ratio 8.7, bound 4), the three peak-RSS cases (1.93 to 1.94, bound 1.5), and the refused-write case by timeout. With this branch all 13 pass.

No user reported this. An automated load test of node:quic found it.

PR: #37491

[claude]

I reviewed this PR and didn't find any bugs. Because the core change holds a live borrow of the outbound VecDeque across an FFI call into lsquic (where the old code released it before calling), and JsCell is UnsafeCell-based with no runtime borrow check, the soundness now rests on lsquic_stream_writev never re-entering the stream callbacks — a human look at that claim would be worthwhile.

What was reviewed:

• drain_outbound bookkeeping (blocked/wrote_to_lsquic/BYTES_SENT/fin) matches the old loop for full, partial, zero, and -1 returns; the removed loop is subsumed by offering both deque halves in one writev.
• The iovec struct passed to lsquic_stream_writev is the one this crate already uses for us_nq_spec_iov, so its layout (incl. Windows) was already established.
• The three .extend(slice) sites and the attach_source restructure are semantically identical to the .iter().copied() / intermediate-Vec paths they replace.
• RSS test threshold (1.5×) is well below the unfixed floor (2.0×) and above the fixed ceiling (1.05×) on both release and debug+ASAN.

Extended reasoning...

Overview

The PR eliminates an O(body × ticks) copy in QuicStream::drain_outbound by handing lsquic the outbound VecDeque's two backing slices directly via lsquic_stream_writev, and replaces three per-byte .extend(.iter().copied()) sites with slice extend. bun_lsquic_sys::Stream::write (single caller) becomes writev. Two new tests cover RSS growth per ingest path and deque wrap-around correctness.

Security risks

None identified. This is a data-copy optimization on the send path; no parsing of untrusted input, no auth/crypto, no wire-format change.

Level of scrutiny

High. The change trades a defensive copy for an in-place borrow held across an FFI call into vendored C. The old code dropped the JsCell<Outbound> borrow before calling lsquic_stream_write, so it was structurally safe even if lsquic re-entered; the new code's soundness depends on lsquic_stream_writev not re-entering on_write/on_close/on_reset (which each touch self.outbound via with_mut). Since JsCell is a bare UnsafeCell wrapper with no runtime aliasing check, a re-entry would be silent UB rather than a panic. The PR description argues this convincingly (stream_write_to_packets only sets flags and queues the connection), but I couldn't verify against the vendored source in this checkout, and per the repo's review guidance native memory safety is the most-blocked category — a maintainer familiar with lsquic should confirm.

Other factors

The change itself reads correctly: the single writev call subsumes the old loop (both halves are offered at once, so a second iteration is never needed); usize::try_from(taken).unwrap_or(0) maps the -1 error case to the same note_write_blocked() path as before; .min(queued) is a defensive clamp. The .extend(slice) changes are pure perf with identical semantics. Tests are thorough — the RSS fixture covers all three ingest paths concurrently with a threshold well separated from both fixed and unfixed measurements, and the wrap-around test guards the new two-slice code path. The author also ran the 235 vendored node test-quic-* tests.

[robobun]

On the re-entrancy point: I did trace it through the vendored lsquic before making the borrow span the call, and have now put the trace in the PR body (Fix section) so it can be checked line by line. Short version: every stream_if->on_* invocation in lsquic_stream.c lives in the create/destroy/close/rst_in/stop_sending_in functions or in the read/write dispatch loops, and lsquic_full_conn_ietf.c only calls those from frame processing, process_streams_{read,write}_events and service_streams, all inside lsquic_engine_process_conns. lsquic_stream_writev bottoms out in stream_write_to_packets, whose only side effects beyond filling packets are marking the connection tickable and setting abort flags that the next tick acts on. So nothing touches outbound while the two slices are borrowed.

The function already depended on this, for a different reason: after the write returns it keeps using the lsquic stream handle (shutdown, want_write, flush), which a synchronous on_close from inside the write would have freed. This change adds the Rust borrow to the list of things resting on that property; it does not introduce the property.

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Inline comments:
Review comments at @test/js/node/quic/quic-stream.test.ts:
- Line 380: Remove the fixtureTimeout constant and its explicit timeout
arguments from the test.each and test.skipIf calls in the QUIC stream tests.
Keep the existing test cases and skip conditions unchanged.

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📒 Files selected for processing: 10

• src/lsquic_sys/lib.rs
• src/runtime/node/quic/mod.rs
• src/runtime/node/quic/outbound.rs
• src/runtime/node/quic/session.rs
• src/runtime/node/quic/stream.rs
• test/js/node/quic/outbound-body-cpu-fixture.ts
• test/js/node/quic/outbound-body-rss-fixture.ts
• test/js/node/quic/quic-stream.test.ts
• test/parallel-allowlist.json
• test/parallel-denylist.txt

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[claude]

Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.

Beyond the inline findings, I also checked two things on the new revision and ruled them out: the single-write drain_outbound keeps the old loop's observable behavior (a 0 or -1 return still reports blocked via taken < queued, and blocked_reported/wrote_to_lsquic/bytes-sent only move when bytes were taken), and moving the Outbound out of its JsCell across writev is sound here because JsCell::take/set go through the closure-scoped with_mut path and the cell holds a valid empty Outbound while lsquic runs, so no borrow is held across the FFI call.

Extended reasoning...

The change replaces the per-write queue copy in node:quic's send path with an in-place lsquic_stream_writev over both halves of the VecDeque, moves Outbound into its own module, and adds RSS, CPU-ratio, refused-write and wrap-around tests. It touches an unsafe FFI boundary (iovec construction in src/lsquic_sys/lib.rs) but no auth, crypto or input-parsing surface. Three inline findings are posted, so a human look is already signaled; this note only records the refactor-equivalence and cell-take checks that were examined and ruled out on the two new commits.

[claude]

I re-reviewed the two new commits and found no bugs; since this reworks the send path at the lsquic FFI boundary, a human look at src/runtime/node/quic/outbound.rs and Stream::writev would still be worthwhile.

What was reviewed:

• Outbound::write_queued moving the queue out of the JsCell for the writev call: the iovecs point into the moved VecDeque's heap buffer, which stays live until set() puts it back, and drain is clamped to self.data.len().
• drain_outbound against the old loop: blocked/partial/refused (-1) arms, the single bytes_sent stat add, and the FIN/trailers clear() sites give the same observable outcomes.
• Stream::writev iovec capping at u32::MAX and stopping after a capped buffer; an empty second half yields a zero-length iovec, which lsquic's reader skips.
• The new timing-ratio test (whole / pieces < 4, min of three interleaved runs) is the one assertion whose stability on loaded CI runners a maintainer may want to weigh.

Extended reasoning...

The change replaces the per-write copy in node:quic's outbound path with an in-place lsquic_stream_writev of both VecDeque halves, adds a new outbound.rs module, a shared attach_body helper used by set_body and session stream creation, and frees the queue allocation once the FIN or trailers request goes out; it touches no auth, crypto, or input-parsing surface, only the unsafe FFI write boundary. The two commits since the prior review addressed the earlier inline findings on releasing the allocation and the 4 GiB iovec cap. No new bugs were found, but the take/set-around-FFI pattern and the CPU-ratio test are judgment calls that a maintainer familiar with lsquic's callback model should confirm, so this is a defer rather than an approve.

[claude]

I reviewed the three follow-up commits and found no bugs; the earlier items (queue allocation freed with the FIN, the 4 GiB iovec) are addressed in the code. Because this moves the hot write path onto lsquic_stream_writev through a new unsafe binding and adds a vendor patch to lsquic, a human look is still worthwhile.

What was reviewed:

• Outbound::write_queued taking the queue out of its JsCell across the lsquic call: no borrow is held, and lsquic's write path does not invoke stream callbacks, so end/started are not lost to a re-entrant touch.
• Old drain_outbound loop vs the single writev: refused (-1), zero, partial and full writes report blocked/stats the same way; drain(..taken.min(len)) bounds lsquic's return.
• clear() on the FIN and trailers branches: both run only with an empty queue, and a later push still works on the fresh VecDeque.
• patches/lsquic/iovec-reader-size_t.patch: widens only the reader's two cursor variables; the vendored lsquic tree is not in this checkout, so the build applying it is the check. Note the PR description still says Stream::writev caps an iovec at u32::MAX; the last commit removed that cap in favour of the patch.

Extended reasoning...

The change touches src/lsquic_sys/lib.rs (new unsafe writev FFI binding replacing lsquic_stream_write), a new src/runtime/node/quic/outbound.rs that moves the send queue out of its JsCell for the duration of the lsquic call, the rewritten drain_outbound in stream.rs, an attach_body helper shared with session.rs, a new lsquic vendor patch registered in scripts/build/deps/lsquic.ts, and three spawned test fixtures plus ~219 lines of tests. It touches no auth, crypto or injection surface; the sensitive surface is unsafe Rust/FFI lifetime handling and size arithmetic on lsquic's return value, both of which check out. The bug hunt exited on dry_streak with no findings, my prior inline findings were addressed by subsequent commits, and no CODEOWNERS entry covers these paths. Defer rather than approve because the change rewrites a hot native send path with unsafe code and patches a vendored C library, which is beyond the simple/mechanical bar for an automated approval.