testing: convert remaining fixed-sleep settles to progress-aware polling

Replace the fixed post-first-rekey and post-second-rekey settle sleeps in
the rekey integration test, and the fixed-deadline baseline wait in the
interop test, with the deterministic wait_until_connected progress-aware
polling helper already used for the initial baseline convergence.

Each converted site fails fast with structured diagnostics when the mesh
is stuck and extends its deadline only while pairwise reachability is
still climbing, removing the wall-clock settle windows that produced
intermittent connectivity failures after a rekey.

testing/interop/interop-test.sh

@@ -162,6 +162,13 @@ REKEY_SETTLE=12                 # FSP-cutover settle budget (Phase 6)
 # strict assertion sweep runs. A genuinely stuck pair still fails — the
 # poll times out and the recording sweep captures it.
 POST_REKEY_TIMEOUT=45
+# Progress-aware stall budget for the convergence detector
+# (wait_for_full_baseline → wait_until_connected). If no additional pair
+# becomes reachable for this long while more than the near-converged
+# slack of pairs is still down, the detector gives up early instead of
+# burning the whole convergence/post-rekey window; any progress resets
+# the clock, so a slow-but-converging mesh under netem keeps polling.
+RECONVERGE_STALL=15
 LOG_POLL_INTERVAL=2
 
 # Data-plane continuity stream (control-differential). Streams run a
@@ -434,25 +441,27 @@ ping_all_pairs() {
     done
 }
 
+# Convergence detector probe: one full all-pairs ping sweep in the
+# "convergence" context (which ping_all_pairs deliberately does NOT
+# record as a failure), setting PASSED/FAILED for wait_until_connected.
+_baseline_probe() {
+    ping_all_pairs quiet 1 "convergence"
+}
+
 # Poll until every directed pair pings clean, or until timeout. This is a
 # convergence DETECTOR — used at establishment (Phase 1) and after each
 # rekey (Phases 3/5). It pings with the "convergence" context, which
 # ping_all_pairs deliberately does not record as a failure; the caller
 # runs a separate strict assertion sweep afterwards.
+#
+# Delegates to the shared progress-aware wait_until_connected so the
+# deadline extends while more pairs are still coming up and gives up fast
+# on a genuine stall, instead of the prior fixed-deadline poll that could
+# false-time-out under heavy CI contention even while still converging.
+# Returns 0 once every pair is reachable, 1 on stall/timeout.
 wait_for_full_baseline() {
     local timeout="$1"
-    local start=$SECONDS
-    local best_passed=0 best_failed="$NUM_DIRECTED"
-    while (( SECONDS - start < timeout )); do
-        ping_all_pairs quiet 1 "convergence"
-        if [ "$PASSED" -gt "$best_passed" ]; then
-            best_passed="$PASSED"; best_failed="$FAILED"
-        fi
-        [ "$FAILED" -eq 0 ] && return 0
-        sleep 1
-    done
-    PASSED="$best_passed"; FAILED="$best_failed"
-    return 1
+    wait_until_connected _baseline_probe "$timeout" "$RECONVERGE_STALL"
 }
 
 phase_result() {
@@ -759,8 +768,15 @@ echo ""
 
 # ── Phase 4: second rekey cycle ──────────────────────────────────────
 
-echo "Phase 4: Second rekey cycle (waiting ${SECOND_REKEY_WAIT}s)"
-sleep "$SECOND_REKEY_WAIT"
+echo "Phase 4: Second rekey cycle (waiting up to ${SECOND_REKEY_WAIT}s for the next cutover)"
+# Poll for the next FMP cutover beyond what Phases 2/3 already saw, using
+# the same pre/post cutover-count delta convention as the control window
+# (Phase 1b), instead of a blind sleep. Bounded by SECOND_REKEY_WAIT so a
+# stalled rekey falls through to the strict Phase 5/6 assertions.
+fmp_cutovers_before="$(count_log_pattern 'Rekey cutover complete \(initiator\), K-bit flipped')"
+wait_for_log_pattern_count \
+    "Rekey cutover complete \(initiator\), K-bit flipped" \
+    "$((fmp_cutovers_before + 1))" "$SECOND_REKEY_WAIT" || true
 echo ""
 
 echo "Phase 5: Post-second-rekey connectivity (reconverge within ${POST_REKEY_TIMEOUT}s)"