RCA INTERIM — golden 34445961595 att1 @ a9e786b2. The run splits into TWO INDEPENDENT FINDINGS. One is SOLVED and is not a product defect. The other is the real one and is still open.

=== FINDING 2 (SOLVED, INFRA, NOT A PRODUCT RED): twohost-b was starved, not broken ===
Do not score twohost-b as a product failure. Proven timeline, all from job rows:
  07:18:59Z  golden "test" (Windows) completes FAILURE -> releases hfenduleam
  07:18:59Z  golden "twohost-a" enters queued
  07:19:01Z  PR run 34446095808 job "unit (self-hosted, Windows, hfenduleam)" STARTS  <-- seizes the runner 2s later, still in_progress
  07:19:02Z  golden "twohost-b" starts on kitsubito (free)
  07:36:16Z  twohost-b FAILS at 900.41s: "never converged on the rig: pairing: A rostered via the daemon-hosted responder"
Runner API at 07:43Z: hfenduleam online busy=true, kitsubito online busy=false. Exactly two runs live: golden (push, golden/crossnode-294) and ci (pull_request, assembly/v0.69.0, created 06:38:13Z).
MECHANISM: opening the golden PR fires ci.yml on pull_request against THE SAME SINGLE WINDOWS RUNNER the golden run needs. twohost needs BOTH boxes at once. The PR's Windows unit job took the runner two seconds after golden's test freed it, twohost-a has never left queued, and twohost-b on the free Linux box burned its full 900s window waiting for a partner that was never scheduled. GOLDEN'S OWN PR STARVES GOLDEN'S OWN TWOHOST PAIR. This is structural and it will recur on every golden run that has a PR open. INFRA-REGISTER entry, mine to file.
NOTE FOR DEPLOYAH: the 900s shape here is the SAME wall-clock signature as the banked "Windows runner firewall drops cold inbound / 900s peer unresponsive" hazard you flagged. It is NOT that hazard. Starvation and firewall-drop produce an identical 900s burn, and I would have accepted the firewall answer if I had stopped at the panel text. Worth banking that the two are indistinguishable from the panel alone.

=== FINDING 1 (OPEN, THE REAL ONE): Windows Phase A, 2 cells ===
  contract_e2e live_agent_lifecycle_e2e      30s poll window burned (35.82s wall)  vs Linux PASS 4.424s
  spt-daemon::sync two_tier_sync_lands_...   58.77s "sync stream never appeared"    vs Linux PASS 1.467s
Both deadline-burn shapes. Both on source THIS MILESTONE CHANGED: livehost.rs (+107/-17, 5 hunks) and sync.rs (+3/-1); brain.rs also touched, and the e2e polls the brain pulse. contract_e2e.rs itself is BYTE-UNTOUCHED across de5a44bc..a9e786b2.
NOT CONTENTION-CONTAMINATED: the Windows test job held the runner EXCLUSIVELY 06:44:27-07:18:59; the PR's Windows unit did not start until 07:19:01. So Finding 2 does not explain Finding 1, and I am not letting it.
STILL UNRESOLVED, and I will not guess: Windows-only regression in the changed code, vs Windows-only timing loss. Linux green does not settle it (hertz's boundary, which I accept).

=== COVERAGE HOLE, CASHED ===
My head gate ran kind(lib)+kind(bin) -> excludes e2e binaries. hertz's e2e proof covered the three TOUCHED test binaries. contract_e2e is untouched, so it was in NEITHER selection. Nobody ran this cell at this tree before golden. That is IR-10 verbatim: run the CONSUMERS of any predicate you change. We gated the changed FILES instead of the changed PREDICATE's consumers. That is my gating defect, not hertz's and not todlando's.

=== NEXT, AND WHAT I NEED ===
Decisive experiment: run live_agent_lifecycle_e2e + two_tier_sync on WINDOWS at main de5a44bc (pre-milestone), then at a9e786b2. Green-then-red = regression, red-then-red = pre-existing Windows weakness this milestone merely exposed.
BLOCKED ON THE BOX: hfenduleam is busy with the PR's unit job. A local run now contaminates it and manufactures exactly the class of red I am trying to classify (IR-76). NOBODY runs anything on HFENDULEAM until that job clears.
DEPLOYAH — one decision is yours, not mine: the PR ci run 34446095808 is duplicating coverage golden already provides and is holding the Windows runner. Cancelling it frees the box, lets twohost-a finally run, and unblocks my experiment. I am recommending it, not doing it; it is your PR and your run.
VERDICT UNCHANGED: RED. Release held. No rerun request from me, and a rerun would hit the same starvation.