Stop a node whose logs cannot be read from counting as a clean node

count_log_pattern summed a per-node `docker logs | grep -c ... || true`, so a
node the harness could not read contributed zero. The six assert_zero_count
callers are negative health assertions -- no panics, no ERROR lines, no AEAD
decrypt failures, no rekey msg2 failures -- and a contributed zero reads as
clean, so one unreadable node silently weakened the assertion and all of them
voided it. This is the family the harness-fallback issue was raised to high
priority for, and it is the one remaining audit residual that can make a green
rekey run lie about protocol code.

The read now fails the count rather than degrading it, printing a sentinel that
names the container. Both callers split the declaration from the assignment,
because `local c=$(fn)` takes local's exit status and discards the function's --
which is how the original defect stayed invisible.

Validated by breaking what it guards rather than by observing green: against
absent containers the old reader returns 0 and assert_zero_count passes
vacuously, while the new one returns rc=1 and reports a failure. Checked the
other direction too, since a fix that reds a legitimately clean run is no use: a
genuine zero across readable nodes still returns 0, and the sum is unchanged at
2+1+0 for a shimmed three-node read.

testing/static/scripts/rekey-test.sh

@@ -285,15 +285,31 @@ phase_result() {
     fi
 }
 
-# Count occurrences of a pattern across all node logs
+# Count occurrences of a pattern across all node logs.
+#
+# A node whose logs cannot be read makes the whole count unusable rather than
+# contributing 0. The previous form ended each read `| grep -c "$pat" || true`,
+# so a failed `docker logs` yielded 0 for that node and the six assert_zero_count
+# callers below read a clean result from a node that was never consulted — one
+# unreadable node silently weakened the assertion instead of voiding it.
+#
+# Returns non-zero and prints a sentinel naming the container. Every caller must
+# split the declaration from the assignment (`local c` then `c=$(...)`), because
+# `local c=$(...)` takes `local`'s exit status and discards this one.
 count_log_pattern() {
     local pattern="$1"
     local total=0
+    local node logs count
     for node in $NODES; do
-        local count=$(docker logs "fips-node-${node}${FIPS_CI_NAME_SUFFIX:-}" 2>&1 | grep -c "$pattern" || true)
+        if ! logs=$(docker logs "fips-node-${node}${FIPS_CI_NAME_SUFFIX:-}" 2>&1); then
+            echo "unreadable:fips-node-${node}${FIPS_CI_NAME_SUFFIX:-}"
+            return 1
+        fi
+        count=$(grep -c "$pattern" <<<"$logs" || true)
         total=$((total + count))
     done
     echo "$total"
+    return 0
 }
 
 wait_for_log_pattern_count() {
@@ -325,7 +341,12 @@ assert_min_count() {
     local pattern="$1"
     local min_count="$2"
     local description="$3"
-    local count=$(count_log_pattern "$pattern")
+    local count
+    count=$(count_log_pattern "$pattern") || {
+        echo "  ✗ $description: node logs unreadable ($count), count not established"
+        FAILED=$((FAILED + 1))
+        return
+    }
     if [ "$count" -ge "$min_count" ]; then
         echo "  ✓ $description: $count (>= $min_count)"
         PASSED=$((PASSED + 1))
@@ -339,7 +360,12 @@ assert_min_count() {
 assert_zero_count() {
     local pattern="$1"
     local description="$2"
-    local count=$(count_log_pattern "$pattern")
+    local count
+    count=$(count_log_pattern "$pattern") || {
+        echo "  ✗ $description: node logs unreadable ($count), zero not established"
+        FAILED=$((FAILED + 1))
+        return
+    }
     if [ "$count" -eq 0 ]; then
         echo "  ✓ $description: 0"
         PASSED=$((PASSED + 1))