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

CLAUDE.md

@@ -564,6 +564,35 @@ marketplace plugin. Three components, one boundary:
   known-positive controls that a genuinely absent board line still reads `?`
   and a genuinely valid route line still derives a real command.
 
+  **F12 (2026-08-17): a third `NR==FNR` survived at the focus-filter join in
+  `plan()` (`fp_names` x `pf`), next to two comments (the block above and the
+  one on `--brief`'s OWED join) that already state the file's own rule -
+  "never by `NR==FNR`" - as prose. Measured, not assumed, before touching
+  it: 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 - run
+  standalone with both forms against both an empty and a non-empty first
+  file, output was identical every time. That is 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 corrupted a lookup table (`ub[]`/`ow[]`) consumed by a
+  THIRD file and silently dropped repos that should have stayed. Stronger
+  than that: `FOCUS_SLUGS` is provably a subset of what `focus_slugs()` finds
+  by scanning the same `$RECORDS`, and `focus_declares()` re-checks the
+  identical regex against the identical `$RECORDS`, so `fp_names` cannot be
+  empty while the filter is applied 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 the fix, which this
+  repo's own CLAUDE.md already names as the "unmeasured assumption wearing a
+  passing test" defect class. The fix is applied anyway, but for a different
+  reason: it is a live counter-example to a rule the file states about
+  itself, and a trap for the next session that greps `NR==FNR` expecting
+  every hit to be a bug and finds one that quietly works. Selftest section 21
+  pins it structurally - `board.sh` has no `NR==FNR` outside a comment line,
+  with a known-positive control proving the comment-stripping grep can still
+  find a live one when planted - never behaviourally, because there is no
+  behaviour to pin.**
+
 - **Route (`scripts/route.sh`):** pure calculator for the next session's model
   and effort. Takes four scored traits of the next task plus a required
   rationale, and prints one block of `key=value` lines: the rubric row, the rule
@@ -686,7 +715,7 @@ obligations in another repo.
   builtins only in hook and tests.
 - TDD: no behavior change without a failing selftest check first.
   `bash scripts/coord-selftest.sh` must exit 0 (220/220),
-  `bash scripts/board-selftest.sh` must exit 0 (237/237),
+  `bash scripts/board-selftest.sh` must exit 0 (239/239),
   `bash scripts/route-selftest.sh` must exit 0 (69/69),
   `bash scripts/orders-selftest.sh` must exit 0 (99/99) and
   `bash scripts/state-line-guard-selftest.sh` must exit 0 (40/40).

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