fix(board): FILENAME== the focus-filter join, matching the file's own rule

F12: a third NR==FNR survived at the focus-filter join in plan() (fp_names
x pf), next to two comments that already state this file's rule -- never
by NR==FNR. Measured before fixing: unlike the two prior instances, this
join has no third file whose lookup table a misroute could corrupt, and
FOCUS_SLUGS is provably a subset of what focus_slugs() finds in the same
$RECORDS focus_declares() re-checks -- so fp_names cannot be empty while
the filter applies, and even forced empty the old and new form produce
identical output. No reachable defect to pin behaviourally; the fix closes
the file's own stated invariant instead. Pinned structurally in selftest
section 21: no live NR==FNR outside a comment, with a known-positive
control proving the filter can still find one.

board-selftest: 239/239 (was 237). coord/route/orders/guard unchanged and
green (220/69/99/40), npm test 11/11.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016YkJ1rKh5YNfVUr5UDKpfh

scripts/board-selftest.sh

@@ -1905,6 +1905,37 @@ printf '%s' "$ORD_OUT" | grep -q 'summeres ALDRI'
 check "the legend states that INN and ORDRE are never summed" $?
 /bin/rm -rf "$ORD_ROOT" 2>/dev/null
 
+# --- 21. board.sh contains no live NR==FNR (structural invariant) ----------
+# F12: a third NR==FNR survived at the focus-filter join in plan() (fp_names x
+# pf), next to two comments (1131-1138, 1294) that state the file's own rule -
+# "never by NR==FNR" - as prose. Measured before writing this section (not
+# assumed): for a plain two-file keep-set join with no third file whose lookup
+# table a misroute could corrupt, an empty fp_names produces the SAME output
+# (0 kept) under NR==FNR and under FILENAME== alike, because when fp_names is
+# genuinely empty (0 repos anywhere declare the resolved focus slug) 0 kept
+# IS the correct answer - unlike the two prior instances in this file, where
+# an empty first file silently dropped a lookup table (ub[]/ow[]) consumed by
+# a THIRD file. FOCUS_SLUGS is provably a subset of what focus_slugs() finds
+# in $RECORDS, and focus_declares() re-checks the identical regex against the
+# identical $RECORDS, so fp_names cannot be empty while fp_applied=1 in normal
+# use - there is no reachable, observable defect here to pin behaviourally,
+# and a --focus fixture asserting one would pass identically before and after
+# this fix (verified with a standalone awk run, both forms, both empty and
+# non-empty first files: identical output every time). The fix is therefore
+# structural, not behavioural: line 1195 is a live counter-example to a rule
+# this file states about itself, which is a trap for the next session that
+# greps NR==FNR expecting every hit to be a bug and finds one that works.
+grep -v '^[[:space:]]*#' "$BOARD" | grep -c 'NR==FNR' | grep -q '^0$'
+check "board.sh has no live NR==FNR outside comments (the file's own stated rule)" $?
+
+# Known-positive control: without this, the check above could be finding
+# nothing because the filter is broken, not because the file is clean.
+NRFNR_FIXTURE="${TMPDIR:-/tmp}/board-nrfnr-fixture.$$"
+printf '    awk NR==FNR live code, not a comment\n' > "$NRFNR_FIXTURE"
+grep -v '^[[:space:]]*#' "$NRFNR_FIXTURE" | grep -q 'NR==FNR'
+check "the same filter+grep DOES find a live NR==FNR in a known-positive fixture" $?
+/bin/rm -f "$NRFNR_FIXTURE" 2>/dev/null
+
 echo ""
 echo "board-selftest: $PASS passed, $FAIL failed"
 [ "$FAIL" -eq 0 ] || exit 1

scripts/board.sh

@@ -1192,7 +1192,7 @@ plan() {
       [ -n "$fp_d" ] && [ -f "$fp_d/STATE.md" ] || continue
       focus_declares "$fp_d" && printf '%s\n' "$fp_n"
     done > "$fp_names"
-    awk -F'|' 'NR==FNR{keep[$0]=1;next} keep[$4]' "$fp_names" "$pf" > "$fp_kept"
+    awk -F'|' -v NAMES="$fp_names" 'FILENAME==NAMES{keep[$0]=1;next} keep[$4]' "$fp_names" "$pf" > "$fp_kept"
     /bin/rm -f "$fp_names" 2>/dev/null
     mv "$fp_kept" "$pf"
   fi