fix(route): --last-model learns Fable 5.1, and the set stays closed

Fable 5.1 shipped 2026-09-01. The closed set at route.sh:212 refused it,
so a session that actually ran it could not record what it ran: the
record was either omitted or LIED, and a lied record reads back months
later as a measurement rather than as the gap it is.

TDD, test first. The exact failure the new check produced before the fix:

  route: --last-model: 'Fable 5.1' is not a row-table model (Sonnet 5|Opus 5|Fable 5)

Two boundary decisions, both taken here and both written into the code:

(a) "Fable 5" is KEPT alongside the point release. The reason is not
    backward compatibility with existing route-last lines - measured
    across the machine, exactly 1 of 45 carries it. It is that route.sh's
    OWN row table spells rows 5-6 "Fable 5/high" and "Fable 5/xhigh", so
    dropping the value would make the script refuse to record a name its
    own spec writes.

(b) The set is WIDENED, never replaced by form validation. A pattern like
    "<family> <digits>[.<digits>]" would still catch a misspelled family
    and a drifted case, and would stop catching a version that does not
    exist: "Fable 5.2" and "Opus 7" would both pass and read back as
    evidence that a model ran when it never shipped. This field is
    telemetry read as evidence, so a silently-accepted lie is worse than
    a loud refusal. The cost is real and was paid before the choice was
    made, so the die message now names the repair instead of leaving the
    caller to approximate to a value already in the list.

Both edit sites, never one: the usage block (route.sh:116) and the case
itself. Fixing the case alone is the two-copies-of-one-policy defect this
repo names repeatedly.

Selftest, 69 -> 73 checks:
  - Fable 5.1 is accepted                                   (was RED)
  - route-last carries "Fable 5.1" verbatim into the line    (was RED)
  - Fable 5.2 / Fable 6 / Fable 5.10 are still REFUSED - the
    check that makes "we did not switch to form validation"
    machine-verified rather than prose                       (control)
  - board parses back a hand-written Fable 5.1 next-cost     (control)

MEASURED GAP, stated rather than closed: "Fable 5.1/xhigh" is 15
characters and overflows board.sh's %-14s KOST column, shifting the rest
of that row one column right. Parsing is unaffected. Widening the column
is a board.sh rendering change nobody ordered in this session, so it is
reported rather than fixed - which is also why the value is deliberately
absent from the widest-value loop in selftest section 6.

Not touched: the row table (still six rows, route.sh still emits only
1-4), and the note that a Fable session runs without an advisor because
the CLI does not enforce it.

Order: 20260901T185028Z-3612729538-from-.claude

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

scripts/route-selftest.sh

@@ -169,6 +169,16 @@ done
 # rather than produced by "$R".
 rt_case "rt-5" "Fable 5/high"
 rt_case "rt-6" "Fable 5/xhigh"
+# A hand-written Fable 5.1 board line. next-cost extraction is free text, so
+# board.sh parses the point release back unchanged - pinned here so a later
+# narrowing of that extraction fails in this suite rather than in the
+# operator's eye. MEASURED GAP, stated rather than closed: at 15 characters it
+# overflows the %-14s KOST column and shifts the rest of that row one column
+# right. That is a board.sh rendering change nobody ordered in this session, so
+# it is reported to .claude, not fixed here - which is also why "Fable
+# 5.1/xhigh" is deliberately absent from the widest-value loop below. Adding it
+# there would go red, and the red would be the unfixed gap, not a broken test.
+rt_case "rt-51" "Fable 5.1/xhigh"
 
 OUT="$(CLAUDE_COORD_DIR="$MBOX" "$BOARD" --roots "$ROOT" 2>/dev/null)"
 for want in "Sonnet 5/high" "Sonnet 5/xhigh" "Opus 5/high" "Opus 5/xhigh" \
@@ -176,6 +186,8 @@ for want in "Sonnet 5/high" "Sonnet 5/xhigh" "Opus 5/high" "Opus 5/xhigh" \
   printf '%s' "$OUT" | grep -q "$want" || { rt_bad=$((rt_bad+1)); echo "    board lost: [$want]"; }
 done
 [ "$rt_bad" -eq 0 ]; check "round trip: board.sh parses back all 6 emitted values" $?
+printf '%s' "$OUT" | grep -q 'Fable 5\.1/xhigh'
+check "board parses back a hand-written Fable 5.1 next-cost" $?
 
 # board.sh renders KOST with %-14s; a longer value shoves the whole row right
 # even though it parsed fine. Measure the widest string the table can emit -
@@ -272,6 +284,43 @@ check "no route-last line when the record is omitted" "$rc"
      --last-completed yes --last-corrections 0 >/dev/null 2>&1
 [ $? -eq 0 ]; check "--last-model/-effort accept every legal value" $?
 
+# Fable 5.1 shipped 2026-09-01 and the closed set refused it, so a session that
+# actually ran it could not record what it ran: the record was either omitted
+# or LIED, and a lied record reads back months later as a measurement. The set
+# is WIDENED, never replaced by form validation - the check below is what makes
+# that choice machine-verified instead of prose. "Fable 5" stays legal for a
+# reason stronger than the one STATE.md on this machine that still carries it:
+# route.sh's OWN row table spells rows 5-6 "Fable 5/high" and "Fable 5/xhigh",
+# so dropping it would make the script refuse to record a value its own spec
+# names. The check above this one is what goes red if anyone drops it.
+"$R" --path known --verification strong --reversibility cheap --scope local \
+     --rationale x --last-model "Fable 5.1" --last-effort xhigh \
+     --last-completed yes --last-corrections 0 >/dev/null 2>&1
+[ $? -eq 0 ]; check "--last-model accepts the Fable 5.1 point release" $?
+
+# The set is still CLOSED after being widened, and this is the whole cost of
+# NOT switching to form validation. A pattern like "<family> <digits>[.<digits>]"
+# would accept every line below, and would stop catching a version that does
+# not exist - which reads back later as evidence that a model ran when it never
+# shipped. That is the positive-looking null this repo refuses everywhere else.
+fable_bad=0
+for bad in "Fable 5.2" "Fable 6" "Fable 5.10"; do
+  "$R" --path known --verification strong --reversibility cheap --scope local \
+       --rationale x --last-model "$bad" --last-effort xhigh \
+       --last-completed yes --last-corrections 0 >/dev/null 2>&1
+  [ $? -eq 2 ] || { fable_bad=$((fable_bad+1)); echo "    accepted a model that does not exist: [$bad]"; }
+done
+[ "$fable_bad" -eq 0 ]; check "the model set stays CLOSED after Fable 5.1 (no form validation)" $?
+
+# Accepting the value is not the same as RECORDING it. The record is what the
+# next session reads back, so the emitted line must carry the point release
+# verbatim rather than collapsing it to the family name.
+LAST51="$("$R" --path known --verification strong --reversibility cheap --scope local \
+          --rationale x --last-model "Fable 5.1" --last-effort xhigh \
+          --last-completed yes --last-corrections 0 2>/dev/null | sed -n 's/^route-last=//p')"
+printf '%s' "$LAST51" | grep -q '^<!-- route-last: model=Fable 5.1; effort=xhigh; completed=yes; corrections=0 -->$'
+check "route-last carries Fable 5.1 verbatim into the emitted line" $?
+
 # The record is telemetry and must NOT silently change what the calculator
 # outputs - a "completed=no" record describes what happened, and covers
 # context exhaustion, an operator interrupt and a block on another repo just

scripts/route.sh

@@ -113,7 +113,7 @@
 #   route.sh --path <v> --verification <v> --reversibility <v> --scope <v>
 #            --rationale <text>
 #
-#   route.sh ... --last-model <Sonnet 5|Opus 5|Fable 5>
+#   route.sh ... --last-model <Sonnet 5|Opus 5|Fable 5|Fable 5.1>
 #                --last-effort <low|medium|high|xhigh|max>
 #                --last-completed <yes|no> --last-corrections <n>
 #
@@ -208,9 +208,31 @@ if [ "$L_SET" -eq 1 ]; then
   # this record back as evidence months from now, so a drifted spelling
   # ("opus 5" for "Opus 5") rebuilds the reader-versus-writer drift this whole
   # script exists to remove, one field over.
+  # THE SET IS CLOSED, AND STAYS CLOSED - decided 2026-09-01 when Fable 5.1
+  # shipped and was refused here. Both boundary questions were live:
+  #
+  # (a) "Fable 5" is KEPT alongside the point release. The reason is not
+  #     backward compatibility with the one STATE.md on this machine that still
+  #     carries it (measured: 1 of 45 route-last lines) - it is that the row
+  #     table above spells rows 5-6 "Fable 5/high" and "Fable 5/xhigh".
+  #     Dropping the value would make this script refuse to record a name its
+  #     own spec writes.
+  #
+  # (b) The set was WIDENED rather than replaced by form validation. A pattern
+  #     like "<family> <digits>[.<digits>]" would still catch a misspelled
+  #     family and a drifted case, and would stop catching A VERSION THAT DOES
+  #     NOT EXIST: "Fable 5.2" and "Opus 7" would both pass and read back
+  #     months later as evidence that a model ran when it never shipped. This
+  #     field is telemetry read as evidence, so a silently-accepted lie is
+  #     worse than a loud refusal.
+  #
+  # The cost of that choice is real and was paid before it was made: a session
+  # that genuinely ran Fable 5.1 could not record it, so its record was omitted
+  # or lied. The list must therefore be extended the day a model ships, and the
+  # die message says so rather than leaving the caller to guess.
   case "$L_MODEL" in
-    "Sonnet 5"|"Opus 5"|"Fable 5") ;;
+    "Sonnet 5"|"Opus 5"|"Fable 5"|"Fable 5.1") ;;
-    *) die "--last-model: '$L_MODEL' is not a row-table model (Sonnet 5|Opus 5|Fable 5)" ;;
+    *) die "--last-model: '$L_MODEL' is not a row-table model (Sonnet 5|Opus 5|Fable 5|Fable 5.1) - a newly shipped model must be added to this list in route.sh, never approximated to a name that is already in it" ;;
   esac
   case "$L_EFFORT" in
     low|medium|high|xhigh|max) ;;