docs(nests): refresh all T16 + cliff plans to current state

8 plan files updated to reflect what's actually shipped vs. what
each doc said before:

- 2026-05-06-cross-stack-interop-test.md: 'Spec — ready to
  implement' → 'Implemented and merged' with pointers to results,
  gap matrix, and closure roadmap.

- 2026-05-06-cross-stack-interop-test-results.md: scenario
  inventory updated to show all branches merged into
  claude/cross-stack-interop-test-XAbYB; suite-flake caveats
  flagged with cross-refs to the routing investigation; file
  inventory now lists BrowserInteropTest + PlaywrightDriver +
  the moved nestsClient/tests/browser-interop/ tree (no more 'in
  sister branches not yet merged' section).

- 2026-05-06-cross-stack-interop-test-gap-matrix.md: T8/T10/T11/
  T12/T13 all show hang ✅ + browser ✅; I13/I14 'NOT YET LANDED'
  callouts removed; the 'in sister branch' qualifier on T13 / I7
  / I6 dropped; coverage-holes section replaced with caveat
  pointers to the routing investigation.

- 2026-05-06-i4-stereo-cross-stack-scenario.md: 'Spec — ready for
  implementation' → 'Landed' with PR #2755 + the three test
  scenarios that ship the assertion.

- 2026-05-06-phase4-browser-harness.md: 'Spec — ready for
  implementation' → 'Landed', with notes on how the implementation
  diverged (used Container.Legacy.Consumer not @moq/watch; cert
  pinning via serverCertificateHashes; I2/I3/I4/I13/I14 originally
  deferred but later landed).

- 2026-05-06-phase4-browser-harness-results.md: status updated to
  reflect 4.D CI removed per maintainer ask; layout note for
  the nestsClient/tests/browser-interop/ relocation; full
  scenario list reconciled with results doc.

- 2026-05-07-late-join-catalog-flake-investigation.md: status
  updated to mention 00f6cba31 + 207057374 were reverted, and
  link to 2026-05-07-moq-relay-routing-investigation.md as the
  action plan. Adds note that the flake also affects four
  browser-tier scenarios after Browser I7 landed.

- 2026-05-01-quic-stream-cliff-investigation.md: adds an HCgOY-
  override banner — recommendation 2 (framesPerGroup = 5) was
  superseded 4 days later by HCgOY field tests landing the prod
  default at 50. Cross-refs the reconciliation + production-
  rerun plans. Open follow-up #3 ('reset to 1') updated with
  the same context.

No code or test changes.

nestsClient/plans/2026-05-06-phase4-browser-harness-results.md

@@ -1,8 +1,25 @@
 # Plan: Phase 4 (browser harness) — landed results
 
-**Status:** 4.A scaffold + 4.B Playwright driver + first Kotlin
-test green; 4.C ships I15; 4.D ships the CI workflow job. Tracks
-the spec at `nestsClient/plans/2026-05-06-phase4-browser-harness.md`.
+**Status:** ✅ Phase 4.A (scaffold) + 4.B (Playwright driver) +
+4.C (full scenario coverage) all landed. Phase 4.D (CI workflow
+job) was originally added in commit `c79a3ffa8` but later removed
+per maintainer ask in commit `b94737de7` ("don't add these tests
+to the build.yml for now"); see
+`2026-05-07-cross-stack-interop-ci-gating.md` for the path to
+re-wiring.
+
+**Browser harness location:** `nestsClient/tests/browser-interop/`
+(was originally `nestsClient-browser-interop/` at repo root;
+moved to mirror `nestsClient/tests/hang-interop/` layout).
+
+**Final scenario coverage:** I1, I2, I3, I4 (stereo), I5
+(hot-swap), I7 (Chromium publisher reconnect), I9 (packet loss),
+I13 (long broadcast), I14 (WebCodecs warmup × CSD), I15 (ALPN).
+See `2026-05-06-cross-stack-interop-test-results.md` for the
+full inventory.
+
+Tracks the spec at
+`nestsClient/plans/2026-05-06-phase4-browser-harness.md`.
 
 ## Where it landed