fix: backport tf_working_days to Python + crossval (audit R9 LOW)

JS computed tf_working_days (TF in working days on the activity's own
calendar, signed for negative-float). Python emitted only tf (calendar
days). An expert quoting JS's tf=13 against a MonFri-cal activity
would be impeached when P6 / Python showed 10.

Backported:
  python_reference/cpm.py: new _count_work_days_between() helper
    mirroring JS cpm-engine.js:814. Reuses the v2.9.27 holiday-Set
    cache for performance.
  python_reference/cpm.py: per-node tf_working_days populated in the
    post-pass loop (lines 1326-1335), mirroring JS:2270.

Crossval harness extended:
  - PY_HARNESS extractor now emits node.tf_working_days
  - JS extractor now emits node.tf_working_days
  - compareFixture compares the two bit-identically when both sides
    emit the field

Crossval went from 444 → 545 checks (+101 tf_working_days
comparisons across all 43 fixtures); all bit-identical.

Tests: 1064/0 unit, 43/43 crossval (545/545 checks).

Author: danafitkowski

cpm-engine.crossval.js

@@ -128,6 +128,8 @@ result_json = {
             'tf': n['tf'],
             'es_date': n['es_date'], 'ef_date': n['ef_date'],
             'ls_date': n['ls_date'], 'lf_date': n['lf_date'],
+            # v2.9.27 — audit R9 LOW PAIRED FIX. Backported field.
+            'tf_working_days': n.get('tf_working_days'),
         }
         for c, n in result['nodes'].items()
     }
@@ -173,6 +175,8 @@ function runJS(payload) {
             tf: n.tf,
             es_date: n.es_date, ef_date: n.ef_date,
             ls_date: n.ls_date, lf_date: n.lf_date,
+            // v2.9.27 — audit R9 LOW PAIRED FIX. Backported field.
+            tf_working_days: n.tf_working_days,
         };
     }
     // Severity-level alert breakdown for crossval parity (Round 6).
@@ -285,6 +289,12 @@ function compareFixture(name, payload, opts) {
         eq('node ' + code + '.dates',
             { es_date: a.es_date, ef_date: a.ef_date, ls_date: a.ls_date, lf_date: a.lf_date },
             { es_date: b.es_date, ef_date: b.ef_date, ls_date: b.ls_date, lf_date: b.lf_date });
+        // v2.9.27 — audit R9 LOW. tf_working_days now backported to Python;
+        // compare bit-identically. Only compare if BOTH sides emit the field.
+        if (a.tf_working_days !== undefined && b.tf_working_days !== undefined) {
+            eq('node ' + code + '.tf_working_days',
+                a.tf_working_days, b.tf_working_days);
+        }
     }
     if (fails === 0) fixturesPassed += 1; else fixturesFailed += 1;
 }

python_reference/cpm.py

@@ -361,6 +361,56 @@ def _is_clean_monfri(work_days, holidays):
     return m == 62  # 0b00111110 = Mon..Fri bits set
 
 
+def _count_work_days_between(from_num, to_num, calendar_info=None):
+    """Count working days between two date-offsets on the given calendar.
+
+    v2.9.27 — audit R9 LOW PAIRED FIX. Mirrors JS _countWorkDaysBetween
+    at cpm-engine.js:814. Returns a signed integer count so callers
+    (tf_working_days, ff_working_days) can preserve negative-float
+    forensic signal on over-constrained networks.
+
+    from_num / to_num are integer day-offsets from the engine epoch
+    (2020-01-01). Without a calendar, returns the calendar-day count
+    (signed). With a calendar, walks day-by-day counting only working
+    days on that calendar.
+    """
+    if not isinstance(from_num, int) and not isinstance(from_num, float):
+        return 0
+    if not isinstance(to_num, int) and not isinstance(to_num, float):
+        return 0
+    from math import isfinite
+    if not isfinite(from_num) or not isfinite(to_num):
+        return 0
+    if to_num == from_num:
+        return 0
+    if to_num < from_num:
+        return -_count_work_days_between(to_num, from_num, calendar_info)
+    if calendar_info is None:
+        return _round_half_up(to_num - from_num)
+    work_days = calendar_info.get('work_days') or [1, 2, 3, 4, 5]
+    # Reuse the cached holiday Set added in v2.9.27.
+    _hs = calendar_info.get('_holidays_set_cache')
+    if _hs is None:
+        _hs = set(calendar_info.get('holidays') or [])
+        try:
+            calendar_info['_holidays_set_cache'] = _hs
+        except TypeError:
+            pass
+    holidays = _hs
+    if not work_days:
+        return 0
+    # Walk day-by-day from from_num+1 to to_num inclusive.
+    n = 0
+    cur = _round_half_up(from_num)
+    end = _round_half_up(to_num)
+    while cur < end:
+        cur += 1
+        dt = date.fromordinal(cur + _epoch_ordinal())
+        if _is_work_day(dt, work_days, holidays):
+            n += 1
+    return n
+
+
 def add_work_days(start_date, n_workdays, calendar_info=None):
     """Advance start_date by n_workdays working days on the given calendar."""
     if n_workdays is None:
@@ -1269,6 +1319,16 @@ def _cal_for(node):
         n['ef_date'] = num_to_date(n['ef'])
         n['ls_date'] = num_to_date(n['ls'])
         n['lf_date'] = num_to_date(n['lf'])
+        # v2.9.27 — audit R9 LOW PAIRED FIX. tf_working_days companion to
+        # tf (calendar days). P6 reports float in working days on the
+        # activity's own calendar; an expert quoting tf=13 against a
+        # MonFri-cal activity will be impeached if P6 shows 10. Mirrors
+        # JS cpm-engine.js:2270.
+        if n['is_complete']:
+            n['tf_working_days'] = 0
+        else:
+            n_cal = cal_map.get(n.get('clndr_id', '')) if n.get('clndr_id') else None
+            n['tf_working_days'] = _count_work_days_between(n['ef'], n['lf'], n_cal)
 
     critical = {c for c, n in nodes.items() if n['tf'] <= 0.0 and not n['is_complete']}