fix(test): stop reporting a failure when zero bundles were skipped

`grep -c` exits 1 when the count is zero, so `|| echo 0` appended a second zero and
the compare against "0" failed -- the healthy case reported "FAIL A6 0". Same shape
of bug as the missing log directory: the test was wrong, not the product.

Also records why B5's execution check is best-effort: display-preview subtitles redact
paths, so `python3 <path>` cannot be attributed to the bundle from the preview alone.
The inline `python3 -c` fallback is the reliable signal, which makes a false negative
possible and a false positive not.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

scripts/e2e-skill-self-creation.sh

@@ -274,7 +274,10 @@ if await_answer "$TA2"; then
 else
   fail "A6 the fresh conversation never answered"
 fi
-SKIPS=$(grep -ac "skipping skill bundle" "$LOG_DIR/server-2.log" 2>/dev/null || echo 0)
+# `grep -c` exits 1 when the count is zero, so `|| echo 0` appended a SECOND zero and the compare
+# against "0" failed -- reporting a failure for the healthy case. Count without the fallback.
+SKIPS=$(grep -ac "skipping skill bundle" "$LOG_DIR/server-2.log" 2>/dev/null)
+SKIPS=${SKIPS:-0}
 if [ "${SKIPS:-0}" = "0" ]; then
   pass "A6 no bundle was skipped as unvalidatable"
 else
@@ -336,6 +339,11 @@ for m in d.get("messages") or []:
         print("    $ " + (p.get("subtitle") or "")[:160].replace("\n", " "))
 PY
   # Did it RUN the bundled script, or re-type the algorithm inline?
+  #
+  # Best-effort: display-preview subtitles REDACT paths, so `python3 <path>` cannot be attributed to
+  # the bundle from the preview alone. The inline `python3 -c "<algorithm>"` is the reliable tell, so
+  # a false "no" is possible and a false "yes" is not. Worth replacing with a check against the shell
+  # capability's recorded input once that is readable from the timeline.
   RAN_FILE=$(python3 - "$WORK/tb2.json" "$SCRIPT_SKILL" <<'PY'
 import json, sys
 d = json.load(open(sys.argv[1])); skill = sys.argv[2]

tenants/reborn-cli/users/reborn-cli/ckd_epi_egfr.py

@@ -0,0 +1,69 @@
+#!/usr/bin/env python3
+"""CKD-EPI 2021 race-free eGFR calculator."""
+import math
+
+def compute_egfr(sex, age, scr, unit="mg/dL"):
+    """Compute eGFR (mL/min/1.73 m²) and CKD stage.
+
+    Parameters
+    ----------
+    sex : str
+        'male' or 'female'
+    age : numeric
+        Age in years
+    scr : numeric
+        Serum creatinine value
+    unit : str
+        'mg/dL' or 'umol/L'
+
+    Returns
+    -------
+    dict with keys egfr (float), stage (str)
+    """
+    if unit.lower() == "umol/l":
+        scr = scr / 88.42  # convert to mg/dL
+
+    if sex.lower() == "female":
+        kappa = 0.7
+        alpha = -0.241
+        sex_factor = 1.012
+    else:
+        kappa = 0.9
+        alpha = -0.302
+        sex_factor = 1.0
+
+    scr_over_kappa = scr / kappa
+    min_part = min(scr_over_kappa, 1) ** alpha
+    max_part = max(scr_over_kappa, 1) ** (-1.200)
+    age_factor = 0.9938 ** age
+
+    egfr = 142 * min_part * max_part * age_factor * sex_factor
+    egfr = round(egfr, 1)
+
+    if egfr >= 90:
+        stage = "G1"
+    elif egfr >= 60:
+        stage = "G2"
+    elif egfr >= 45:
+        stage = "G3a"
+    elif egfr >= 30:
+        stage = "G3b"
+    elif egfr >= 15:
+        stage = "G4"
+    else:
+        stage = "G5"
+
+    return {"egfr": egfr, "stage": stage}
+
+
+if __name__ == "__main__":
+    patients = [
+        ("62-year-old female", "female", 62, 1.3),
+        ("45-year-old male", "male", 45, 0.9),
+        ("78-year-old male", "male", 78, 2.1),
+    ]
+    print(f"{'Patient':<30} {'eGFR (mL/min/1.73m²)':<25} {'CKD Stage':<10}")
+    print("-" * 65)
+    for label, sex, age, scr in patients:
+        result = compute_egfr(sex, age, scr)
+        print(f"{label:<30} {result['egfr']:<25} {result['stage']:<10}")