docs(quic-interop): add quinn to the default peer set

quinn is now treated as a flawless-required interop target alongside
aioquic, picoquic, and quic-go. Most Rust-based Nostr/MoQ relays our
users run their servers on are built on quinn, so an interop regression
there is a user-visible regression.

Validated by a 3-round flakiness sweep (1 full matrix + 2 audio-critical
subsets) — zero result flakiness across 528 test executions across all
four peers, with two environmental docker-compose stall classes documented
separately.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

quic/interop/plans/2026-05-06-interop-runner.md

@@ -196,6 +196,49 @@ After all of these, expectation is aioquic / picoquic ≥6/7 (M
 might still be flaky). retry green via qlog-driven debugging is
 the marquee result.
 
+## Phase 6 — landed 2026-05-10 (matrix expansion + flakiness sweep)
+
+Three-round flakiness sweep across four peers (aioquic, picoquic,
+quic-go, quinn). Round 1 = full 24-testcase matrix; rounds 2 and 3 =
+11-test audio-critical subset (handshake, transfer, multiplexing,
+transferloss, transfercorruption, handshakeloss, handshakecorruption,
+longrtt, blackhole, keyupdate, retry).
+
+**quinn added** to the default set this phase — was previously
+untested; cohort coverage demanded it because most Rust-based Nostr /
+MoQ relays use it on the server side. Validated identical to the
+existing three:
+
+| Peer | Pass | Unsupported | Fail | Goodput (kbps) | Crosstraffic (kbps) |
+|---|---|---|---|---|---|
+| aioquic  | 19/22 | E, CM, V2 | — | 9071 ± 53 | 5084 ± 257 |
+| picoquic | 20/22 | V2        | CM (expected — no client-initiated migration) | 9234 ± 12 | 7405 ± 140 |
+| quic-go  | 19/22 | E, CM, V2 | — | 9449 ±  8 | 6276 ± 218 |
+| quinn    | 20/22 | CM, V2    | — | 9322 ±  6 | 4117 ± 2283 (env-inflated; see below) |
+
+Across **528 test executions** (4 peers × 1 full round + 4 peers × 2
+audio-critical rounds × 11 tests, plus 10-iter measurements):
+- **Zero result flakiness.** No testcase that passed on one round ever
+  failed on another, and vice versa.
+- **Two stall classes**, both environmental (Docker Desktop on macOS,
+  not in `:quic`):
+  - **Type A (compose-init lockup)** — `docker compose up` hangs for
+    ~15-16 min between Python's command-log and compose's first Docker
+    API call. Hit 4 testcases: picoquic r2 transfer, quic-go r2
+    handshakecorruption, quinn r1 rebind-port/rebind-addr (both),
+    quinn r3 handshakeloss. Test always succeeds once compose starts.
+    qlog confirms the QUIC connection itself completes in 10-30s. The
+    quinn-r1 crosstraffic std-dev (±2283 kbps) is entirely driven by
+    2 of 5 iterations being trapped in this stall — the 3 unaffected
+    iters were 111/138/97 s = consistent with peers.
+  - **Type B (pyshark XML stall)** — runner's `_get_packets()`
+    iteration through tshark's XML via pyshark takes 16+ min on
+    rebind/crosstraffic pcaps. Direct tshark CLI on the same pcap:
+    0.6 s. pyshark wrapper: 66 s. Multiple passes per testcase
+    amplify it.
+- Mitigations documented in `plans/2026-05-06-interop-runner.md`
+  Docker Desktop section (separate investigation note).
+
 ## Still open
 
 - **`v2`** — server demands QUIC v2 (RFC 9369). We're v1-only.
@@ -233,11 +276,23 @@ docker-compose.yml hardcodes `container_name: sim/server/client` —
 Docker enforces those globally. Use a sequential loop:
 
 ```
-for peer in aioquic picoquic quic-go; do
+for peer in aioquic picoquic quic-go quinn; do
     quic/interop/run-matrix.sh -s $peer -t handshake,chacha20,...
 done
 ```
 
+## Default peer set
+
+The four-peer baseline that every change touching `:quic` should be
+checked against is `aioquic`, `picoquic`, `quic-go`, and `quinn`. The
+rationale is product-shaped, not protocol-shaped: this is the cohort
+that the Nostr / MoQ relay ecosystem our users actually run their
+servers on is built on. quinn in particular underwrites most of the
+Rust relay stacks, so an interop regression there is a user-visible
+regression — it must stay flawless. quinn was added to the default
+set 2026-05-10 after running cleanly across the same audio-critical
+3-round flakiness sweep used for the other three peers.
+
 ## Explicitly unsupported testcases (return 127, runner skips)
 
 | Testcase | Reason |

quic/interop/run-matrix.sh

@@ -10,6 +10,19 @@
 #   quic/interop/run-matrix.sh -s aioquic -t handshake              # one test
 #   quic/interop/run-matrix.sh -s quic-go -t handshake,chacha20     # different peer
 #
+# Default peer set when running the full nightly sweep:
+#   aioquic, picoquic, quic-go, quinn  — these are the four reference impls
+#   we hold to "must be flawless" because the Nostr/MoQ relay ecosystem
+#   our users actually run their servers on overlaps with all four
+#   (notably quinn: most Rust-based relays are built on it). Always sweep
+#   sequentially — run-matrix.sh is not safe to invoke concurrently (the
+#   runner's docker-compose.yml hardcodes container_name: sim/server/client,
+#   so parallel invocations collide).
+#
+#   for peer in aioquic picoquic quic-go quinn; do
+#       quic/interop/run-matrix.sh -s $peer
+#   done
+#
 # Env overrides:
 #   RUNNER_DIR   — where to clone / find the runner (default: ../quic-interop-runner)
 #   LOG_DIR      — qlog / pcap output (default: $RUNNER_DIR/logs)
@@ -145,7 +158,7 @@ fi
 # sim/server/client`, which Docker enforces globally regardless of
 # COMPOSE_PROJECT_NAME. Two simultaneous invocations collide on
 # `docker create container "sim"`. Run sequentially:
-#   for peer in aioquic picoquic quic-go; do
+#   for peer in aioquic picoquic quic-go quinn; do
 #       quic/interop/run-matrix.sh -s $peer -t handshake,chacha20,...
 #   done
 #