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.

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`