ci(nests): defer cross-stack interop CI; document manual run

Removes the `hang-interop` + `browser-interop` jobs from
`build.yml` (added in commit `21947bc5` after a 10/10 stability
sweep × 22 tests = 220/220 hard-pass). Cold-cache cost is
~10 min hang + ~13 min browser; warm-cache critical-path add
is ~6 min via the parallel browser job. Most PRs don't touch
audio / MoQ / QUIC, so paying that cost on every PR is
net-negative for the change-pattern the repo sees.

Adds `nestsClient/tests/README.md` covering:
- when to run (changes to nip53 / moq-lite session / audio
  pipeline / MoqLiteNests* / ReconnectingNests* / :quic /
  the sidecars themselves);
- quick-start gradle commands for hang-only, browser-only,
  combined;
- prerequisites + first-run cache costs;
- all the configuration knobs (incl. the
  `-DnestsHangInteropTraceRelay=true` trace-capture switch
  added during the routing investigation);
- known limitations (hot-swap browser soft-pass,
  framesPerGroup pin-vs-prod gap, I7 cycle 2 truncation);
- a 4-step debug recipe for triaging a flaking scenario.

Plan updates:
- `2026-05-07-t16-closure-roadmap.md` — Priority 3 marked
  ⏸ DEFERRED instead of ✅ CLOSED, pointing at the new README.
- `2026-05-07-cross-stack-interop-ci-gating.md` — status
  changed to ⏸ DEFERRED; YAML shape preserved verbatim in the
  plan for the next revisit.
- `2026-05-06-cross-stack-interop-test-results.md`,
  `2026-05-06-cross-stack-interop-test-gap-matrix.md` — CI
  integration § rewritten to "manual-run only" + README link.

The trace-capture instrumentation in `NativeMoqRelayHarness`
stays in place; it's useful for future flake triage even
without CI.

.github/workflows/build.yml

@@ -174,164 +174,6 @@ jobs:
           name: ${{ matrix.desktop-artifact-name }}
           path: ${{ matrix.desktop-artifact-path }}
 
-  # Cross-stack interop tests (T16). Builds the Rust hang-listen +
-  # hang-publish sidecars (nestsClient/tests/hang-interop/), `cargo install`s
-  # moq-relay + moq-token-cli at the version pinned in
-  # `nestsClient/tests/hang-interop/REV`, then runs `:nestsClient:jvmTest
-  # -DnestsHangInterop=true`. See
-  # `nestsClient/plans/2026-05-06-cross-stack-interop-test.md` and the
-  # closure roadmap at
-  # `nestsClient/plans/2026-05-07-t16-closure-roadmap.md`.
-  #
-  # Linux-only: the cargo install of `moq-relay` 0.10.x has nontrivial
-  # native deps (aws-lc-sys, ring) that take 5+ min cold; we cache
-  # both ~/.cargo and the nestsClient/tests/hang-interop/target tree so the warm
-  # path is a few seconds. macOS / Windows runs would double the
-  # matrix cost without catching anything Linux doesn't catch — the
-  # protocol logic is platform-agnostic and the JNA libopus natives
-  # are already exercised by the unit-level JvmOpusRoundTripTest on
-  # the Android job.
-  hang-interop:
-    needs: lint
-    runs-on: ubuntu-latest
-    timeout-minutes: 30
-    steps:
-      - name: Checkout code
-        uses: actions/checkout@v6
-
-      - name: Set up JDK 21
-        uses: actions/setup-java@v5
-        with:
-          distribution: 'zulu'
-          java-version: 21
-
-      - name: Set up Gradle
-        uses: gradle/actions/setup-gradle@v4
-        with:
-          cache-read-only: ${{ github.ref != 'refs/heads/main' }}
-
-      # Pin Rust to ≥ 1.95 — moq-relay 0.10.25's transitive dep
-      # `constant_time_eq 0.4.3` requires it, and ubuntu-latest's
-      # default Rust version drifts.
-      - name: Set up Rust
-        uses: dtolnay/rust-toolchain@stable
-
-      # Cache cargo registry + the sidecar workspace's target/.
-      # First cold run takes ~6 min for the moq-relay install;
-      # cached runs ~30 s.
-      - name: Cache cargo
-        uses: actions/cache@v4
-        with:
-          path: |
-            ~/.cargo/registry
-            ~/.cargo/git
-            nestsClient/tests/hang-interop/target
-            ~/.cache/amethyst-nests-interop/hang-interop-cargo
-          key: ${{ runner.os }}-cargo-${{ hashFiles('nestsClient/tests/hang-interop/Cargo.lock', 'nestsClient/tests/hang-interop/REV') }}
-          restore-keys: |
-            ${{ runner.os }}-cargo-
-
-      - name: Run cross-stack interop suite
-        run: ./gradlew :nestsClient:jvmTest --tests "com.vitorpamplona.nestsclient.interop.native.HangInteropTest" -DnestsHangInterop=true
-
-      - name: Upload interop test report
-        uses: actions/upload-artifact@v7
-        if: failure()
-        with:
-          name: Hang Interop Test Reports
-          path: nestsClient/build/reports/tests/jvmTest/
-
-  # Phase 4 of T16: browser-side cross-stack interop. Drives a headless
-  # Chromium (via Playwright) running @moq/lite + @moq/hang against
-  # the same moq-relay subprocess the hang-interop job uses. Linux-only:
-  # Chromium QUIC behaviour is consistent across platforms in the
-  # scenarios we care about, and macOS/Windows would double the matrix
-  # cost without catching new defects.
-  #
-  # Inherits the cargo cache from `hang-interop` because the browser
-  # path still needs `moq-relay` + `hang-listen` built (the harness
-  # boots the same Rust subprocess). Adds bun + node_modules + Playwright
-  # browser caches. See:
-  #   nestsClient/plans/2026-05-06-phase4-browser-harness.md
-  browser-interop:
-    needs: lint
-    runs-on: ubuntu-latest
-    timeout-minutes: 30
-    steps:
-      - name: Checkout code
-        uses: actions/checkout@v6
-
-      - name: Set up JDK 21
-        uses: actions/setup-java@v5
-        with:
-          distribution: 'zulu'
-          java-version: 21
-
-      - name: Set up Gradle
-        uses: gradle/actions/setup-gradle@v4
-        with:
-          cache-read-only: ${{ github.ref != 'refs/heads/main' }}
-
-      - name: Set up Rust
-        uses: dtolnay/rust-toolchain@stable
-
-      - name: Cache cargo
-        uses: actions/cache@v4
-        with:
-          path: |
-            ~/.cargo/registry
-            ~/.cargo/git
-            nestsClient/tests/hang-interop/target
-            ~/.cache/amethyst-nests-interop/hang-interop-cargo
-          key: ${{ runner.os }}-cargo-${{ hashFiles('nestsClient/tests/hang-interop/Cargo.lock', 'nestsClient/tests/hang-interop/REV') }}
-          restore-keys: |
-            ${{ runner.os }}-cargo-
-
-      # bun is a separate install — Playwright + the bun harness build
-      # both go through it. Pin the version that matches the local agent
-      # tooling so a CI/local skew can't surface a wire-format change
-      # in `bun build` output.
-      - name: Set up bun
-        uses: oven-sh/setup-bun@v2
-        with:
-          bun-version: 1.3.11
-
-      # Cache bun-installed node_modules for the browser harness.
-      # Keyed on package.json + bun.lock so a dep bump invalidates.
-      - name: Cache node_modules
-        uses: actions/cache@v4
-        with:
-          path: |
-            nestsClient/tests/browser-interop/node_modules
-            nestsClient/tests/browser-interop/dist
-          key: ${{ runner.os }}-bun-${{ hashFiles('nestsClient/tests/browser-interop/package.json', 'nestsClient/tests/browser-interop/bun.lock') }}
-
-      # Cache Playwright's browser cache (~/.cache/ms-playwright/chromium-*).
-      # The cold install of Chromium is ~200 MB and 30–60 s; cached runs
-      # are essentially instant.
-      - name: Cache Playwright browsers
-        uses: actions/cache@v4
-        with:
-          path: ~/.cache/ms-playwright
-          key: ${{ runner.os }}-playwright-${{ hashFiles('nestsClient/tests/browser-interop/package.json') }}
-
-      - name: Run browser cross-stack interop suite
-        run: |
-          ./gradlew :nestsClient:jvmTest \
-              --tests "com.vitorpamplona.nestsclient.interop.native.BrowserInteropTest" \
-              -DnestsHangInterop=true \
-              -DnestsBrowserInterop=true
-
-      - name: Upload browser interop test report
-        uses: actions/upload-artifact@v7
-        if: failure()
-        with:
-          name: Browser Interop Test Reports
-          path: |
-            nestsClient/build/reports/tests/jvmTest/
-            nestsClient/tests/browser-interop/test-results/
-            nestsClient/tests/browser-interop/playwright-report/
-
   test-and-build-android:
     needs: lint
     runs-on: ubuntu-latest

nestsClient/plans/2026-05-06-cross-stack-interop-test-gap-matrix.md

@@ -92,9 +92,13 @@ DoD #5 (gap matrix coverage) closed.
   tier — Chromium's `@moq/lite` 0.2.x re-attach across
   `Active::Ended → Active` is unreliable; T12 protection is
   asserted by the hang-tier counterpart.
-- CI gating wired in
-  `2026-05-07-cross-stack-interop-ci-gating.md` after a 10/10
-  sweep × 22 tests = 220/220 pass stability bar.
+- CI gating reached green-on-the-rig (10/10 × 22 = 220/220)
+  in commit `21947bc5`, then was deferred on cost grounds —
+  both suites run manually now per
+  [`nestsClient/tests/README.md`](../tests/README.md). YAML
+  shape preserved in
+  `2026-05-07-cross-stack-interop-ci-gating.md` for the next
+  revisit.
 
 ## Files referenced
 

nestsClient/plans/2026-05-06-cross-stack-interop-test-results.md

@@ -440,25 +440,30 @@ relay-side timing under load.
 
 ## CI integration
 
-**Wired** as of 2026-05-07 (commit `21947bc5`). Both
-`hang-interop` and `browser-interop` jobs in
-`.github/workflows/build.yml`, gated on `lint`, `ubuntu-latest`,
-30 min timeout each, with cached cargo + bun + Playwright Chromium.
+**Manual-run only** (deferred from CI on cost grounds). Both
+suites are kept green and locally invokable; developer-facing
+docs at [`nestsClient/tests/README.md`](../tests/README.md)
+cover when/how/prerequisites.
 
-Stability bar that unblocked CI: **10/10 BUILD SUCCESSFUL × 22
-tests = 220/220 pass** on the merged branch (~5m 28s per sweep,
-steady state). The earlier `late_join_listener_still_decodes_tail`
-flake was a `:quic` post-handshake bidi-acceptance bug, not a
-moq-relay routing race; the QUIC team's recent main work
-(commits `2a4c07ae`, `d5c854be`, `b622d0c9`, `86a4727e`,
-`31d19258`) closed it. See
-`2026-05-07-moq-relay-routing-investigation.md` § Closure for
-the trace evidence and
-`2026-05-07-t16-closure-roadmap.md` for the rolled-up status.
+Brief history:
 
-The 2-week post-merge CI green-rate watch is on the maintainer
-who lands this: ≥ 95 % required per the plan's stability gate;
-otherwise pull both jobs and reopen the routing investigation.
+- 2026-05-07: 10/10 sweep × 22 tests = 220/220 hard-pass
+  established a working stability bar after the `:quic`
+  post-handshake bidi-drop fix landed via `origin/main` (commits
+  `2a4c07ae`, `d5c854be`, `b622d0c9`, `86a4727e`, `31d19258`).
+- Commit `21947bc5` re-added the `hang-interop` +
+  `browser-interop` jobs to `.github/workflows/build.yml`.
+- Maintainer review then deferred CI gating on cost grounds
+  (cold cache ~10 min hang, ~13 min browser; most PRs don't
+  touch audio / MoQ / QUIC). Both jobs were removed; the YAML
+  shape stays preserved in the closed-but-deferred plan
+  [`2026-05-07-cross-stack-interop-ci-gating.md`](2026-05-07-cross-stack-interop-ci-gating.md)
+  for re-evaluation if the cost calculus changes.
+
+The trace-capture instrumentation
+(`-DnestsHangInteropTraceRelay=true`) added during the routing
+investigation stays in place — useful when triaging a future
+flake.
 
 ## Pending follow-ups
 

nestsClient/plans/2026-05-07-cross-stack-interop-ci-gating.md

@@ -1,19 +1,26 @@
 # Plan: wire CI gating for the cross-stack interop suite
 
-**Status:** ✅ CLOSED 2026-05-07. Both jobs wired in commit
-`21947bc5` (path-tweaked from the original removed shape per
-the `nestsClient/tests/browser-interop/` move). Stability-bar
-sweep: **10/10 BUILD SUCCESSFUL × 22 tests = 220/220 pass.**
-Acceptance bar from the roadmap met.
+**Status:** ⏸ DEFERRED 2026-05-07.
+The infrastructure to wire CI is ready — both jobs landed in
+commit `21947bc5` and a 10/10 stability sweep × 22 tests =
+220/220 passed on the agent rig. A maintainer review then
+judged the wallclock cost too high for the change-pattern and
+removed the jobs (cold cache: ~10 min hang, ~13 min browser;
+most PRs don't touch audio / MoQ / QUIC).
+
+The suites are now run manually before merging changes that
+touch the relevant code paths. Developer-facing docs:
+[`../tests/README.md`](../tests/README.md). This plan stays
+in the tree for the next time someone wants to revisit CI
+gating — the YAML shapes below are the exact reverse-merge
+target, and the stability bar (10/10 sweep) has already been
+demonstrated on this branch.
 
 **Depended on:**
 - `2026-05-07-moq-relay-routing-investigation.md` closed (✅)
 - `2026-05-07-tighten-cross-stack-assertions.md` closed (✅)
 - 10/10 sweep stability verified (✅)
 
-This is the FINAL step of the T16 closure. With stable hard-pass
-suites, CI gating becomes safe and meaningful.
-
 ## What's needed
 
 ### A) `.github/workflows/build.yml` — the hang-interop job

nestsClient/plans/2026-05-07-t16-closure-roadmap.md

@@ -67,22 +67,23 @@ HangInteropTest with their current soft-pass assertions intact.
 
 **Acceptance bar met.** 5/5 sweep with hard assertions.
 
-## Priority 3 — `2026-05-07-cross-stack-interop-ci-gating.md` ✅ CLOSED
+## Priority 3 — `2026-05-07-cross-stack-interop-ci-gating.md` ⏸ DEFERRED (manual run only)
 
-> **Closed 2026-05-07** by commit `21947bc5`. Both
-> `hang-interop` and `browser-interop` jobs landed in
-> `.github/workflows/build.yml`, gated on `lint`,
-> `ubuntu-latest`, 30 min timeout, with cached cargo + bun +
-> Playwright Chromium. Path-tweaked from the original removed
-> shape because the browser harness moved from
-> `nestsClient-browser-interop/` to
-> `nestsClient/tests/browser-interop/` (commit `bd7b166f`).
-
-**Acceptance bar met.** 10/10 sweep BUILD SUCCESSFUL × 22 tests
-= **220/220 pass** (~5m 28s steady state per sweep on the agent
-rig). The first 2 weeks of post-merge CI runs still need a
-maintainer to monitor flake rate (per the plan's "≥ 95% green
-rate" gate); pull the jobs again if it falls below.
+> **Briefly wired then reverted, 2026-05-07.** Commit `21947bc5`
+> re-added both jobs to `build.yml`; verification gave 10/10
+> sweep × 22 tests = 220/220 hard-pass on the agent rig. A
+> subsequent maintainer review judged the cold-cache cost
+> (~10 min hang, ~13 min browser) too high for the change-pattern
+> (most PRs don't touch audio / MoQ / QUIC) and removed the jobs.
+>
+> The suites stay green locally and are intended to run before
+> merging any change that touches the audio / moq-lite / `:quic`
+> stack. Documentation: [`nestsClient/tests/README.md`](../tests/README.md)
+> covers when/how/prerequisites/debugging.
+>
+> The CI-gating plan is kept around in case the wallclock cost
+> calculus changes (e.g., a much faster runner, or a smaller
+> opt-in subset of the suite that runs in <2 min).
 
 ## Independent track — `2026-05-07-framespergroup-production-rerun.md`
 

nestsClient/tests/README.md

@@ -0,0 +1,186 @@
+# Cross-stack interop tests
+
+> Manually invoked. Not part of `build.yml` — see "Why not in CI" below.
+
+Two suites that drive the production Amethyst Kotlin nests stack against
+external reference implementations of moq-lite-03:
+
+| Suite | Path | Runs | What it asserts |
+|---|---|---|---|
+| **`HangInteropTest`** | `nestsClient/tests/hang-interop/` | Rust `hang-listen` / `hang-publish` (kixelated reference) ↔ Amethyst Kotlin via a real `moq-relay` 0.10.x subprocess | Wire-byte capture, FFT peaks on decoded PCM, sample-count floors, mute / hot-swap / packet-loss / late-join / 60 s long broadcast / multi-listener fan-out. |
+| **`BrowserInteropTest`** | `nestsClient/tests/browser-interop/` | Headless Chromium running `@moq/lite` + `@moq/hang` via Playwright ↔ Amethyst Kotlin (forward + reverse) | Same scenario family as hang-interop, plus WebCodecs `AudioDecoder` / `AudioEncoder` correctness, ALPN negotiation, browser-side reconnect. |
+
+Coverage matrix: [`nestsClient/plans/2026-05-06-cross-stack-interop-test-gap-matrix.md`][gap]
+
+[gap]: ../plans/2026-05-06-cross-stack-interop-test-gap-matrix.md
+
+## When to run
+
+Run **both suites locally before merging** any change that touches:
+
+- `quartz/.../nip53` (audio rooms event types, catalog wire format)
+- `nestsClient/src/.../moq/lite/` (moq-lite session, publisher/subscriber, codec)
+- `nestsClient/src/.../audio/` (capture, encoder/decoder, broadcaster, player)
+- `nestsClient/src/.../MoqLiteNestsSpeaker.kt` / `MoqLiteNestsListener.kt`
+- `nestsClient/src/.../ReconnectingNests*.kt`
+- `:quic` (WebTransport, packet header protection, key updates, stream demux)
+- The hang/browser sidecars themselves
+
+Skip if the change is documentation, UI-only, build-script-only, or otherwise
+can't affect wire bytes / decoded audio.
+
+## Quick start
+
+```bash
+# Hang-tier (Rust ↔ Kotlin via real moq-relay subprocess)
+./gradlew :nestsClient:jvmTest \
+    --tests "com.vitorpamplona.nestsclient.interop.native.HangInteropTest" \
+    -DnestsHangInterop=true
+
+# Browser-tier (Chromium ↔ Kotlin) — also boots the moq-relay
+./gradlew :nestsClient:jvmTest \
+    --tests "com.vitorpamplona.nestsclient.interop.native.BrowserInteropTest" \
+    -DnestsHangInterop=true \
+    -DnestsBrowserInterop=true
+
+# Both together
+./gradlew :nestsClient:jvmTest \
+    --tests "com.vitorpamplona.nestsclient.interop.native.HangInteropTest" \
+    --tests "com.vitorpamplona.nestsclient.interop.native.BrowserInteropTest" \
+    -DnestsHangInterop=true -DnestsBrowserInterop=true
+```
+
+The opt-in flags (`-DnestsHangInterop=true` / `-DnestsBrowserInterop=true`)
+also act as JUnit `Assume` gates — without them, the suites mark every
+scenario `skipped` rather than failing on missing prerequisites.
+
+## Prerequisites
+
+| Tool | Why | Install |
+|---|---|---|
+| **Rust ≥ 1.95** | `moq-relay` 0.10.25's transitive dep `constant_time_eq 0.4.3` requires it | `rustup install 1.95 && rustup default 1.95` |
+| **`cargo`** on PATH | Builds the hang-interop sidecars + `cargo install`s `moq-relay`, `moq-token-cli` | Comes with rustup |
+| **`bun` ≥ 1.3.x** (browser only) | Bundles the Chromium harness + drives Playwright | `curl -fsSL https://bun.sh/install \| bash` |
+| **Playwright Chromium** (browser only) | Headless Chromium for `@moq/lite` + `@moq/hang` | Auto-installed by `interopInstallPlaywrightChromium` Gradle task |
+
+The Gradle build automates everything from there. First run installs and
+caches:
+
+- `moq-relay` 0.10.25 + `moq-token-cli` 0.5.23 → `~/.cache/amethyst-nests-interop/hang-interop-cargo/bin/`
+- Sidecar release binaries → `nestsClient/tests/hang-interop/target/release/`
+- bun's `node_modules` + `dist/` → `nestsClient/tests/browser-interop/`
+- Playwright Chromium → `~/.cache/ms-playwright/`
+
+Cold first run: ~10 min hang, ~13 min browser. Cached: ~3-4 min hang,
+~5-7 min browser.
+
+## Configuration knobs
+
+| Flag | Default | Purpose |
+|---|---|---|
+| `-DnestsHangInterop=true` | unset (skip) | Enable HangInteropTest. |
+| `-DnestsBrowserInterop=true` | unset (skip) | Enable BrowserInteropTest. Implies `nestsHangInterop` (the browser harness boots the same `moq-relay` subprocess). |
+| `-DnestsHangInteropTraceRelay=true` | unset | Per-test moq-relay trace capture. Writes the relay subprocess's combined stdout/stderr (with `RUST_LOG=info,moq_relay=trace,moq_lite=trace,moq_native=debug`) to `nestsClient/build/relay-logs/<methodName>-<seq>-<ts>.log`. Use for debugging suite flakes. |
+| `-DnestsHangInteropDiagnostic=true` | unset | Runs the Kotlin↔Kotlin variant gated separately (`KotlinSpeakerKotlinListenerThroughNativeRelayTest`) — useful to bisect wire-format bugs without involving Rust or Chromium. |
+| `BUN_BIN`, `NPX_BIN` (env) | autodetected | Override the bun / npx binary path if your install lives outside the agent default (`/root/.bun/bin/bun`). |
+
+## Known limitations
+
+- **`chromium_listener_speaker_hot_swap_does_not_crash`** soft-passes its
+  PCM assertion — Chromium's `@moq/lite` 0.2.x doesn't re-attach across
+  `Active::Ended → Active`, so the browser captures only ~100 ms post-swap.
+  T12 (group sequence carry across hot-swaps) is hard-asserted by the
+  hang-tier counterpart.
+- **`framesPerGroup`** is pinned to `5` in the test scenarios. Production
+  defaults to `50`. The two haven't been reconciled against a single
+  multi-rig benchmark — see
+  [`framespergroup-reconciliation`](../plans/2026-05-07-framespergroup-reconciliation.md).
+- **I7 cycle 2 truncation**: `moq-relay` 0.10.x truncates the second
+  cycle of a publisher reconnect at ~1.0 s out of ~2.5 s. Tests assert
+  `≥ 2.5 s` floor which the truncated cycle still clears; a future
+  upstream fix may let us tighten further.
+- **I12 GOAWAY**: not applicable to moq-lite-03; only the IETF
+  moq-transport target (currently disabled) would exercise it.
+
+Full open-issues list:
+[`2026-05-06-cross-stack-interop-test-results.md` § Pending follow-ups][results].
+
+[results]: ../plans/2026-05-06-cross-stack-interop-test-results.md
+
+## Debugging a flaking scenario
+
+1. Re-run the failing scenario in isolation (no `--tests` filter races):
+   ```bash
+   ./gradlew :nestsClient:jvmTest \
+       --tests "*HangInteropTest.late_join_listener_still_decodes_tail" \
+       -DnestsHangInterop=true \
+       -DnestsHangInteropTraceRelay=true \
+       --rerun-tasks
+   ```
+2. Inspect `nestsClient/build/relay-logs/<methodName>-*.log` for
+   `subscribed started` / `encoding self=Subscribe` /
+   `decoded result=SubscribeOk` / `subscribed cancelled` events.
+3. Cross-reference with the speaker-side `Log.d("NestTx")` lines
+   captured in JUnit XML's `<system-err>`
+   (`nestsClient/build/test-results/jvmTest/TEST-*.xml`) by timestamp.
+4. The fastest diagnostic loop bypasses Browser/Chromium entirely — use
+   the diagnostic test:
+   ```bash
+   ./gradlew :nestsClient:jvmTest \
+       --tests "*KotlinSpeakerKotlinListenerThroughNativeRelayTest" \
+       -DnestsHangInteropDiagnostic=true
+   ```
+
+Sample pre/post-merge trace pair for the previously-flaking late-join
+scenario lives at
+[`plans/artefacts/2026-05-07-routing-race-disproven/`](../plans/artefacts/2026-05-07-routing-race-disproven/)
++ [`plans/artefacts/2026-05-07-routing-race-closed-by-merge/`](../plans/artefacts/2026-05-07-routing-race-closed-by-merge/).
+
+## Why not in CI
+
+Both suites are slow on a cold cache (~10–13 min each), and even on a
+warm cache the browser tier dominates the critical path at ~5-7 min.
+Running them on every PR doubles CI time for changes that don't touch
+audio / MoQ / QUIC.
+
+History:
+
+- `21947bc5` re-added both jobs after the T16 closure roadmap closed
+  Priority 1 (`:quic` post-handshake bidi-drop fixed via `origin/main`
+  merge) and Priority 2 (assertion hardening). 10/10 sweep × 22 tests
+  = 220/220 hard-pass on the merged branch.
+- A subsequent maintainer review judged the wallclock cost too high
+  for the change-pattern (most PRs don't touch the relevant code) and
+  removed the jobs.
+
+The suites still run locally per the rules above. If a PR DOES touch
+audio / MoQ / QUIC code paths and the author hasn't run them, ask in
+review.
+
+## Files
+
+- `hang-interop/REV` — pinned upstream versions (`MOQ_RELAY_VERSION`,
+  `MOQ_TOKEN_CLI_VERSION`, `HANG_VERSION`, `MOQ_LITE_VERSION`,
+  `MOQ_NATIVE_VERSION`). Bump deliberately.
+- `hang-interop/Cargo.toml` + `hang-{listen,publish}/`,
+  `udp-loss-shim/` — Rust sidecar workspace.
+- `browser-interop/package.json` + `src/` + `playwright.config.ts` —
+  bun + Playwright harness.
+- `nestsClient/src/jvmTest/kotlin/.../interop/native/`:
+  - `NativeMoqRelayHarness.kt` — boots the relay subprocess + captures
+    per-test trace.
+  - `HangInteropTest.kt`, `HangInteropReverseTest.kt`,
+    `HangInteropMultiListenerTest.kt`,
+    `KotlinSpeakerKotlinListenerThroughNativeRelayTest.kt` —
+    hang-tier scenarios.
+  - `BrowserInteropTest.kt`, `PlaywrightDriver.kt` — browser-tier.
+
+## See also
+
+- [`2026-05-06-cross-stack-interop-test.md`](../plans/2026-05-06-cross-stack-interop-test.md)
+  — original spec / Definition of Done.
+- [`2026-05-07-t16-closure-roadmap.md`](../plans/2026-05-07-t16-closure-roadmap.md)
+  — closure roadmap (Priorities 1, 2 closed; Priority 3 deferred).
+- [`2026-05-07-cross-stack-interop-ci-gating.md`](../plans/2026-05-07-cross-stack-interop-ci-gating.md)
+  — the deferred CI-gating plan (kept around in case the wallclock
+  cost calculus changes).