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+#!/usr/bin/env bash
+#
+# tools/hygiene/check-no-op-cadence-pattern.sh —
+# Pre-tick mechanical check for the no-op-cadence failure mode
+# (per memory/feedback_recurrence_after_correction_needs_operational_enforcement_otto_2026_05_02.md).
+#
+# Why this exists (Otto Tick-80; 2026-05-02):
+#   The Tick-61 no-op-cadence corrective landed on main but the
+#   pattern RECURRED at Tick-71-79 — substrate-knowledge alone is
+#   insufficient for failure modes the LLM training prior strongly
+#   favors. The architectural answer is operational enforcement:
+#   mechanical checks at decision-time, not just substrate-read at
+#   wake-time. This script is one such mechanical check.
+#
+# Usage (intended invocation pattern):
+#   At every autonomous-loop tick start, Otto runs:
+#     bash tools/hygiene/check-no-op-cadence-pattern.sh
+#   The script examines the last N tick-history shards. If a
+#   threshold of minimal-observation ticks is exceeded, the script
+#   prints a warning that Otto reads alongside the substrate. The
+#   warning is closer-to-decision-time than substrate-read at wake.
+#
+# What this checks:
+#   - Most recent N (default 7) tick-history shards under
+#     docs/hygiene-history/ticks/YYYY/MM/DD/ for today AND yesterday
+#     UTC (window survives midnight rollover)
+#   - Counts shards matching the minimal-observation pattern.
+#     Heuristic (OR-semantic): the shard's BODY column (5th pipe-
+#     separated field) is < 600 chars, OR the row contains
+#     observation-class language ("minimal observation",
+#     "within-basin observation", "observe-only",
+#     "minimal not idle", "same. stopping"). Either signal counts.
+#   - If count >= threshold (default 5), prints WARNING
+#
+# What this does NOT do:
+#   - Does NOT block the tick (informational only — exit 0 always)
+#   - Does NOT auto-correct (the agent's judgment to act)
+#   - Does NOT examine days older than yesterday
+#
+# Composes with:
+#   - memory/feedback_recurrence_after_correction_needs_operational_enforcement_otto_2026_05_02.md
+#     (the memo this script implements)
+#   - memory/feedback_party_during_human_sleep_*.md (parent rule)
+#   - memory/feedback_training_distribution_mismatch_firing_*.md
+#     (Tick-61 first-order corrective)
+#   - tools/hygiene/check-tick-history-shard-schema.sh (sibling pattern)
+
+set -euo pipefail
+
+REPO_ROOT="$(git rev-parse --show-toplevel 2>/dev/null || pwd)"
+cd "$REPO_ROOT"
+
+# Configuration with numeric validation. A typo like
+# `NO_OP_CHECK_WINDOW=foo` would otherwise make `tail -n` fail under
+# `set -e` and defeat the "informational only" promise.
+WINDOW_SIZE="${NO_OP_CHECK_WINDOW:-7}"
+THRESHOLD="${NO_OP_CHECK_THRESHOLD:-5}"
+
+# `10#$VAR` forces base-10 interpretation in arithmetic context. Without
+# it, a zero-padded value like `08` would be parsed as octal (and fail
+# with "value too great for base"), defeating the validation guard.
+if ! [[ "$WINDOW_SIZE" =~ ^[0-9]+$ ]] || (( 10#$WINDOW_SIZE < 1 )); then
+  echo "[no-op-check] Invalid NO_OP_CHECK_WINDOW='${WINDOW_SIZE}' (need positive integer); using default 7." >&2
+  WINDOW_SIZE=7
+fi
+if ! [[ "$THRESHOLD" =~ ^[0-9]+$ ]] || (( 10#$THRESHOLD < 1 )); then
+  echo "[no-op-check] Invalid NO_OP_CHECK_THRESHOLD='${THRESHOLD}' (need positive integer); using default 5." >&2
+  THRESHOLD=5
+fi
+# Normalize to base-10 (strip leading zeros) so subsequent arithmetic
+# comparisons + tail -n usage are unambiguous regardless of input format.
+WINDOW_SIZE=$((10#$WINDOW_SIZE))
+THRESHOLD=$((10#$THRESHOLD))
+
+# Compute today + yesterday shard directories.
+# `date -u -v-1d` is BSD/macOS; `date -u -d "yesterday"` is GNU/Linux.
+# Both supported per Otto-235 4-shell target.
+TODAY_DATE_PATH="$(date -u +"%Y/%m/%d")"
+TODAY_DATE_FLAT="$(date -u +"%Y%m%d")"
+TODAY_DIR="docs/hygiene-history/ticks/${TODAY_DATE_PATH}"
+
+if YESTERDAY_DATE_PATH="$(date -u -v-1d +"%Y/%m/%d" 2>/dev/null)"; then
+  YESTERDAY_DATE_FLAT="$(date -u -v-1d +"%Y%m%d")"
+elif YESTERDAY_DATE_PATH="$(date -u -d "yesterday" +"%Y/%m/%d" 2>/dev/null)"; then
+  YESTERDAY_DATE_FLAT="$(date -u -d "yesterday" +"%Y%m%d")"
+else
+  YESTERDAY_DATE_PATH=""
+  YESTERDAY_DATE_FLAT=""
+fi
+YESTERDAY_DIR=""
+if [[ -n "$YESTERDAY_DATE_PATH" ]]; then
+  YESTERDAY_DIR="docs/hygiene-history/ticks/${YESTERDAY_DATE_PATH}"
+fi
+
+# Collect candidate shards from a directory, emitting tab-separated
+# `<primary-key>\t<disambiguator>\t<full-path>` lines. Primary key is
+# YYYYMMDDHHMMSS (parsed timestamp, NOT raw filename) so mixed-format
+# shards order correctly per the README mixed-format-sort caveat.
+# Disambiguator is the suffix (empty for unsuffixed `HHMMZ.md`) so a
+# base shard sorts BEFORE same-minute disambiguators (`HHMMZ.md` <
+# `HHMMZ-01.md`) — empty disambiguator sorts first because the field
+# separator (tab) is lower-ASCII than any hex character.
+#   - HHMMZ.md           → primary=YYYYMMDDHHMM00, disambiguator=""
+#   - HHMMZ-<hex>.md     → primary=YYYYMMDDHHMM00, disambiguator="<hex>"
+#   - HHMMSSZ-<hex>.md   → primary=YYYYMMDDHHMMSS, disambiguator="<hex>"
+collect_shards() {
+  local dir="$1"
+  local date_flat="$2"
+  [[ -d "$dir" && -n "$date_flat" ]] || return 0
+  local shard_path shard_name primary disamb
+  shopt -s nullglob
+  for shard_path in "$dir"/*.md; do
+    shard_name="${shard_path##*/}"
+    if [[ "$shard_name" =~ ^([0-9]{4})Z(-([0-9a-f]+))?\.md$ ]]; then
+      primary="${date_flat}${BASH_REMATCH[1]}00"
+      disamb="${BASH_REMATCH[3]:-}"
+      printf '%s|%s|%s\n' "$primary" "$disamb" "$shard_path"
+    elif [[ "$shard_name" =~ ^([0-9]{6})Z-([0-9a-f]+)\.md$ ]]; then
+      primary="${date_flat}${BASH_REMATCH[1]}"
+      disamb="${BASH_REMATCH[2]}"
+      printf '%s|%s|%s\n' "$primary" "$disamb" "$shard_path"
+    fi
+  done
+  shopt -u nullglob
+}
+
+# Combined list, sorted by primary key then disambiguator, last N entries.
+# Field separator is `|` (non-whitespace) because bash's IFS-whitespace
+# collapsing rule would silently merge an empty disambiguator field with
+# the surrounding tabs and corrupt the read loop below.
+COMBINED="$( { collect_shards "$YESTERDAY_DIR" "$YESTERDAY_DATE_FLAT"; collect_shards "$TODAY_DIR" "$TODAY_DATE_FLAT"; } | sort -t'|' -k1,1 -k2,2 | tail -n "$WINDOW_SIZE" )"
+
+if [[ -z "$COMBINED" ]]; then
+  echo "[no-op-check] No shards in window for today (${TODAY_DIR}) or yesterday; nothing to check." >&2
+  exit 0
+fi
+
+# Count shards that match minimal-observation pattern.
+# Heuristic (OR-semantic, matching the header docstring):
+#   short BODY column (length < 600 chars) OR observation-class language
+#   anywhere in the row.
+# Body is the 5th pipe-separated field per shard schema:
+#   `| timestamp | model | cron-id | <body> | <PR ref> | <observation> |`
+# Measuring whole-file size (previous behavior) inflated the length
+# count when the observation column was long, masking terse-body ticks.
+MIN_OBS_COUNT=0
+TOTAL_COUNT=0
+
+while IFS='|' read -r _primary _disamb shard_path; do
+  [[ -z "${shard_path:-}" ]] && continue
+  TOTAL_COUNT=$((TOTAL_COUNT + 1))
+
+  body=$(awk -F'|' 'NR==1 {print $5}' "$shard_path" 2>/dev/null || echo "")
+  body_length=${#body}
+
+  if (( body_length < 600 )) || grep -qiE 'minimal observation|within-basin observation|observe-only|minimal[ -]not[ -]idle|same\.\s*stopping' "$shard_path" 2>/dev/null; then
+    MIN_OBS_COUNT=$((MIN_OBS_COUNT + 1))
+  fi
+done <<< "$COMBINED"
+
+echo "[no-op-check] Recent ${TOTAL_COUNT} shards across today+yesterday; ${MIN_OBS_COUNT} match minimal-observation pattern (threshold: ${THRESHOLD})." >&2
+
+if [[ $MIN_OBS_COUNT -ge $THRESHOLD ]]; then
+  echo "" >&2
+  echo "WARNING: no-op-cadence pattern detected — ${MIN_OBS_COUNT}/${TOTAL_COUNT} recent ticks are minimal-observation." >&2
+  echo "" >&2
+  echo "Per the just-landed substrate (memory/feedback_party_during_human_sleep_*.md +" >&2
+  echo "memory/feedback_recurrence_after_correction_needs_operational_enforcement_*.md):" >&2
+  echo "" >&2
+  echo "  - The human-paused phase IS the practice window for independent-production-skill" >&2
+  echo "  - Default to minimal observation IS the failure mode" >&2
+  echo "  - Party-class operation alternatives: implement a backlog row, do" >&2
+  echo "    free-zone substrate-quality work, write a self-grading memo, audit" >&2
+  echo "    cross-references, propose architectural extensions" >&2
+  echo "" >&2
+  echo "  Run with NO_OP_CHECK_THRESHOLD=99 to silence; the default fires the" >&2
+  echo "  warning to surface the pattern at decision-time, not just substrate-read time." >&2
+
+  # Informational warning; does not exit non-zero (would block tick)
+fi
+
+exit 0