diff --git a/scripts/lib/error-handling.sh b/scripts/lib/error-handling.sh
new file mode 100644
index 0000000..bd1a58f
--- /dev/null
+++ b/scripts/lib/error-handling.sh
@@ -0,0 +1,55 @@
+#!/bin/bash
+# CodeSensei — Shared Error Handling Library
+# Source this file in hook scripts for consistent error logging and JSON safety.
+#
+# Usage:
+#   source "$(dirname "$0")/lib/error-handling.sh"
+
+LOG_FILE="${HOME}/.code-sensei/error.log"
+MAX_LOG_LINES=1000
+
+# Log an error with timestamp and script name.
+# Usage: log_error "script-name" "message"
+log_error() {
+  local script_name="${1:-unknown}"
+  local message="$2"
+  local timestamp
+  timestamp=$(date -u '+%Y-%m-%dT%H:%M:%SZ' 2>/dev/null || date '+%Y-%m-%d')
+  mkdir -p "$(dirname "$LOG_FILE")"
+  printf '[%s] [%s] %s\n' "$timestamp" "$script_name" "$message" >> "$LOG_FILE"
+  # Cap log file to MAX_LOG_LINES
+  if [ -f "$LOG_FILE" ]; then
+    local line_count
+    line_count=$(wc -l < "$LOG_FILE" 2>/dev/null || echo 0)
+    if [ "$line_count" -gt "$MAX_LOG_LINES" ]; then
+      tail -n "$MAX_LOG_LINES" "$LOG_FILE" > "${LOG_FILE}.tmp" && mv "${LOG_FILE}.tmp" "$LOG_FILE"
+    fi
+  fi
+}
+
+# Safely escape a string for JSON interpolation.
+# Returns a JSON-encoded string including surrounding double quotes.
+# Usage: escaped=$(json_escape "$var")
+json_escape() {
+  local str="$1"
+  if command -v jq &>/dev/null; then
+    printf '%s' "$str" | jq -Rs '.'
+  else
+    # Basic fallback: escape backslashes, double quotes, and common control chars
+    printf '"%s"' "$(printf '%s' "$str" | sed 's/\\/\\\\/g; s/"/\\"/g')"
+  fi
+}
+
+# Check that jq is installed. Logs a one-time warning per session if missing.
+# Usage: check_jq "script-name" || exit 0
+check_jq() {
+  if ! command -v jq &>/dev/null; then
+    local warn_file="${HOME}/.code-sensei/.jq-warned"
+    if [ ! -f "$warn_file" ]; then
+      log_error "${1:-unknown}" "jq not installed — CodeSensei features limited. Install with: brew install jq"
+      touch "$warn_file"
+    fi
+    return 1
+  fi
+  return 0
+}
diff --git a/scripts/quiz-selector.sh b/scripts/quiz-selector.sh
index 1e130ef..571c399 100755
--- a/scripts/quiz-selector.sh
+++ b/scripts/quiz-selector.sh
@@ -14,15 +14,34 @@
 #   "quiz_format": "multiple_choice" | "free_response" | "code_prediction"
 # }
 
+SCRIPT_NAME="quiz-selector"
 PROFILE_DIR="$HOME/.code-sensei"
 PROFILE_FILE="$PROFILE_DIR/profile.json"
 PLUGIN_ROOT="${CLAUDE_PLUGIN_ROOT:-$(dirname "$(dirname "$0")")}"
 QUIZ_BANK="$PLUGIN_ROOT/data/quiz-bank.json"
 
+# Load shared error handling
+LIB_DIR="$(dirname "$0")/lib"
+if [ -f "$LIB_DIR/error-handling.sh" ]; then
+  source "$LIB_DIR/error-handling.sh"
+else
+  LOG_FILE="${PROFILE_DIR}/error.log"
+  log_error() { printf '[%s] [%s] %s\n' "$(date -u '+%Y-%m-%dT%H:%M:%SZ' 2>/dev/null || date '+%Y-%m-%d')" "${1:-unknown}" "$2" >> "$LOG_FILE" 2>/dev/null; }
+  json_escape() {
+    local str="$1"
+    if command -v jq &>/dev/null; then
+      printf '%s' "$str" | jq -Rs '.'
+    else
+      printf '"%s"' "$(printf '%s' "$str" | sed 's/\\/\\\\/g; s/"/\\"/g')"
+    fi
+  }
+  check_jq() { command -v jq &>/dev/null; }
+fi
+
 # Default output if we can't determine anything
 DEFAULT_OUTPUT='{"mode":"dynamic","concept":null,"reason":"No profile data available","static_question":null,"belt":"white","quiz_format":"multiple_choice"}'
 
-if ! command -v jq &> /dev/null; then
+if ! check_jq "$SCRIPT_NAME"; then
   echo "$DEFAULT_OUTPUT"
   exit 0
 fi
@@ -33,12 +52,42 @@ if [ ! -f "$PROFILE_FILE" ]; then
 fi
 
 # Read profile data
-BELT=$(jq -r '.belt // "white"' "$PROFILE_FILE")
-QUIZ_HISTORY=$(jq -c '.quiz_history // []' "$PROFILE_FILE")
-CONCEPTS_SEEN=$(jq -c '.concepts_seen // []' "$PROFILE_FILE")
-SESSION_CONCEPTS=$(jq -c '.session_concepts // []' "$PROFILE_FILE")
-TOTAL_QUIZZES=$(jq -r '.quizzes.total // 0' "$PROFILE_FILE")
-CORRECT_QUIZZES=$(jq -r '.quizzes.correct // 0' "$PROFILE_FILE")
+BELT=$(jq -r '.belt // "white"' "$PROFILE_FILE" 2>&1)
+if [ $? -ne 0 ]; then
+  log_error "$SCRIPT_NAME" "jq failed reading belt: $BELT"
+  echo "$DEFAULT_OUTPUT"
+  exit 0
+fi
+
+QUIZ_HISTORY=$(jq -c '.quiz_history // []' "$PROFILE_FILE" 2>&1)
+if [ $? -ne 0 ]; then
+  log_error "$SCRIPT_NAME" "jq failed reading quiz_history: $QUIZ_HISTORY"
+  QUIZ_HISTORY="[]"
+fi
+
+CONCEPTS_SEEN=$(jq -c '.concepts_seen // []' "$PROFILE_FILE" 2>&1)
+if [ $? -ne 0 ]; then
+  log_error "$SCRIPT_NAME" "jq failed reading concepts_seen: $CONCEPTS_SEEN"
+  CONCEPTS_SEEN="[]"
+fi
+
+SESSION_CONCEPTS=$(jq -c '.session_concepts // []' "$PROFILE_FILE" 2>&1)
+if [ $? -ne 0 ]; then
+  log_error "$SCRIPT_NAME" "jq failed reading session_concepts: $SESSION_CONCEPTS"
+  SESSION_CONCEPTS="[]"
+fi
+
+TOTAL_QUIZZES=$(jq -r '.quizzes.total // 0' "$PROFILE_FILE" 2>&1)
+if [ $? -ne 0 ]; then
+  log_error "$SCRIPT_NAME" "jq failed reading quizzes.total: $TOTAL_QUIZZES"
+  TOTAL_QUIZZES=0
+fi
+
+CORRECT_QUIZZES=$(jq -r '.quizzes.correct // 0' "$PROFILE_FILE" 2>&1)
+if [ $? -ne 0 ]; then
+  log_error "$SCRIPT_NAME" "jq failed reading quizzes.correct: $CORRECT_QUIZZES"
+  CORRECT_QUIZZES=0
+fi
 
 TODAY=$(date -u +%Y-%m-%d)
 NOW_EPOCH=$(date +%s)
@@ -65,7 +114,7 @@ SPACED_REP_REASON=""
 
 if [ "$QUIZ_HISTORY" != "[]" ]; then
   # Get concepts that were answered incorrectly, with their last wrong date and wrong count
-  WRONG_CONCEPTS=$(echo "$QUIZ_HISTORY" | jq -c '
+  WRONG_CONCEPTS=$(printf '%s' "$QUIZ_HISTORY" | jq -c '
     [.[] | select(.result == "incorrect")] |
     group_by(.concept) |
     map({
@@ -74,20 +123,39 @@ if [ "$QUIZ_HISTORY" != "[]" ]; then
       last_wrong: (sort_by(.timestamp) | last | .timestamp),
       total_attempts: 0
     })
-  ')
+  ' 2>&1)
+  if [ $? -ne 0 ]; then
+    log_error "$SCRIPT_NAME" "jq failed computing wrong concepts: $WRONG_CONCEPTS"
+    WRONG_CONCEPTS="[]"
+  fi
 
   # For each wrong concept, check if it's due for review
-  for ROW in $(echo "$WRONG_CONCEPTS" | jq -c '.[]'); do
-    CONCEPT=$(echo "$ROW" | jq -r '.concept')
-    WRONG_COUNT=$(echo "$ROW" | jq -r '.wrong_count')
-    LAST_WRONG=$(echo "$ROW" | jq -r '.last_wrong')
+  for ROW in $(printf '%s' "$WRONG_CONCEPTS" | jq -c '.[]' 2>/dev/null); do
+    CONCEPT=$(printf '%s' "$ROW" | jq -r '.concept' 2>&1)
+    if [ $? -ne 0 ]; then
+      log_error "$SCRIPT_NAME" "jq failed reading concept from wrong row: $CONCEPT"
+      continue
+    fi
 
-    # Calculate days since last wrong answer
-    LAST_WRONG_DATE=$(echo "$LAST_WRONG" | cut -d'T' -f1)
+    WRONG_COUNT=$(printf '%s' "$ROW" | jq -r '.wrong_count' 2>&1)
+    if [ $? -ne 0 ]; then
+      log_error "$SCRIPT_NAME" "jq failed reading wrong_count: $WRONG_COUNT"
+      continue
+    fi
+
+    LAST_WRONG=$(printf '%s' "$ROW" | jq -r '.last_wrong' 2>&1)
+    if [ $? -ne 0 ]; then
+      log_error "$SCRIPT_NAME" "jq failed reading last_wrong: $LAST_WRONG"
+      continue
+    fi
+
+    # Calculate days since last wrong answer (handles both GNU and BSD date)
+    LAST_WRONG_DATE=$(printf '%s' "$LAST_WRONG" | cut -d'T' -f1)
     LAST_EPOCH=$(date -j -f "%Y-%m-%d" "$LAST_WRONG_DATE" +%s 2>/dev/null || date -d "$LAST_WRONG_DATE" +%s 2>/dev/null)
     if [ -n "$LAST_EPOCH" ]; then
       DAYS_SINCE=$(( (NOW_EPOCH - LAST_EPOCH) / 86400 ))
     else
+      log_error "$SCRIPT_NAME" "Could not parse date '$LAST_WRONG_DATE' for spaced repetition; defaulting days_since=999"
       DAYS_SINCE=999
     fi
 
@@ -100,9 +168,13 @@ if [ "$QUIZ_HISTORY" != "[]" ]; then
     fi
 
     # Check if enough time has passed and concept hasn't been mastered since
-    CORRECT_SINCE=$(echo "$QUIZ_HISTORY" | jq --arg c "$CONCEPT" --arg lw "$LAST_WRONG" '
+    CORRECT_SINCE=$(printf '%s' "$QUIZ_HISTORY" | jq --arg c "$CONCEPT" --arg lw "$LAST_WRONG" '
       [.[] | select(.concept == $c and .result == "correct" and .timestamp > $lw)] | length
-    ')
+    ' 2>&1)
+    if [ $? -ne 0 ]; then
+      log_error "$SCRIPT_NAME" "jq failed computing correct_since for $CONCEPT: $CORRECT_SINCE"
+      CORRECT_SINCE=0
+    fi
 
     if [ "$DAYS_SINCE" -ge "$REVIEW_INTERVAL" ] && [ "$CORRECT_SINCE" -lt 3 ]; then
       SPACED_REP_CONCEPT="$CONCEPT"
@@ -118,23 +190,36 @@ if [ -n "$SPACED_REP_CONCEPT" ] && [ -f "$QUIZ_BANK" ]; then
     .quizzes[$concept] // [] |
     map(select(.belt == $belt or .belt == "white")) |
     first // null
-  ' "$QUIZ_BANK")
+  ' "$QUIZ_BANK" 2>&1)
+  if [ $? -ne 0 ]; then
+    log_error "$SCRIPT_NAME" "jq failed reading static question for $SPACED_REP_CONCEPT: $STATIC_Q"
+    STATIC_Q="null"
+  fi
+
+  ESCAPED_CONCEPT=$(json_escape "$SPACED_REP_CONCEPT")
+  ESCAPED_REASON=$(json_escape "$SPACED_REP_REASON")
+  ESCAPED_BELT=$(json_escape "$BELT")
 
   if [ "$STATIC_Q" != "null" ] && [ -n "$STATIC_Q" ]; then
-    echo "{\"mode\":\"spaced_repetition\",\"concept\":\"$SPACED_REP_CONCEPT\",\"reason\":\"$SPACED_REP_REASON\",\"static_question\":$STATIC_Q,\"belt\":\"$BELT\",\"quiz_format\":\"$QUIZ_FORMAT\"}"
-    exit 0
+    printf '{"mode":"spaced_repetition","concept":%s,"reason":%s,"static_question":%s,"belt":%s,"quiz_format":"%s"}\n' \
+      "$ESCAPED_CONCEPT" "$ESCAPED_REASON" "$STATIC_Q" "$ESCAPED_BELT" "$QUIZ_FORMAT"
   else
-    echo "{\"mode\":\"spaced_repetition\",\"concept\":\"$SPACED_REP_CONCEPT\",\"reason\":\"$SPACED_REP_REASON\",\"static_question\":null,\"belt\":\"$BELT\",\"quiz_format\":\"$QUIZ_FORMAT\"}"
-    exit 0
+    printf '{"mode":"spaced_repetition","concept":%s,"reason":%s,"static_question":null,"belt":%s,"quiz_format":"%s"}\n' \
+      "$ESCAPED_CONCEPT" "$ESCAPED_REASON" "$ESCAPED_BELT" "$QUIZ_FORMAT"
   fi
+  exit 0
 fi
 
 # ─── PRIORITY 2: Unquizzed session concepts ───
 # Concepts from this session that haven't been quizzed yet
 UNQUIZZED_CONCEPT=""
 if [ "$SESSION_CONCEPTS" != "[]" ]; then
-  for CONCEPT in $(echo "$SESSION_CONCEPTS" | jq -r '.[]'); do
-    BEEN_QUIZZED=$(echo "$QUIZ_HISTORY" | jq --arg c "$CONCEPT" '[.[] | select(.concept == $c)] | length')
+  for CONCEPT in $(printf '%s' "$SESSION_CONCEPTS" | jq -r '.[]' 2>/dev/null); do
+    BEEN_QUIZZED=$(printf '%s' "$QUIZ_HISTORY" | jq --arg c "$CONCEPT" '[.[] | select(.concept == $c)] | length' 2>&1)
+    if [ $? -ne 0 ]; then
+      log_error "$SCRIPT_NAME" "jq failed checking quiz history for $CONCEPT: $BEEN_QUIZZED"
+      continue
+    fi
     if [ "$BEEN_QUIZZED" -eq 0 ]; then
       UNQUIZZED_CONCEPT="$CONCEPT"
       break
@@ -147,15 +232,23 @@ if [ -n "$UNQUIZZED_CONCEPT" ] && [ -f "$QUIZ_BANK" ]; then
     .quizzes[$concept] // [] |
     map(select(.belt == $belt or .belt == "white")) |
     first // null
-  ' "$QUIZ_BANK")
+  ' "$QUIZ_BANK" 2>&1)
+  if [ $? -ne 0 ]; then
+    log_error "$SCRIPT_NAME" "jq failed reading static question for $UNQUIZZED_CONCEPT: $STATIC_Q"
+    STATIC_Q="null"
+  fi
+
+  ESCAPED_CONCEPT=$(json_escape "$UNQUIZZED_CONCEPT")
+  ESCAPED_BELT=$(json_escape "$BELT")
 
   if [ "$STATIC_Q" != "null" ] && [ -n "$STATIC_Q" ]; then
-    echo "{\"mode\":\"static\",\"concept\":\"$UNQUIZZED_CONCEPT\",\"reason\":\"New concept from this session — not yet quizzed.\",\"static_question\":$STATIC_Q,\"belt\":\"$BELT\",\"quiz_format\":\"$QUIZ_FORMAT\"}"
-    exit 0
+    printf '{"mode":"static","concept":%s,"reason":"New concept from this session — not yet quizzed.","static_question":%s,"belt":%s,"quiz_format":"%s"}\n' \
+      "$ESCAPED_CONCEPT" "$STATIC_Q" "$ESCAPED_BELT" "$QUIZ_FORMAT"
   else
-    echo "{\"mode\":\"dynamic\",\"concept\":\"$UNQUIZZED_CONCEPT\",\"reason\":\"New concept from this session — no static question available, generate dynamically.\",\"static_question\":null,\"belt\":\"$BELT\",\"quiz_format\":\"$QUIZ_FORMAT\"}"
-    exit 0
+    printf '{"mode":"dynamic","concept":%s,"reason":"New concept from this session — no static question available, generate dynamically.","static_question":null,"belt":%s,"quiz_format":"%s"}\n' \
+      "$ESCAPED_CONCEPT" "$ESCAPED_BELT" "$QUIZ_FORMAT"
   fi
+  exit 0
 fi
 
 # ─── PRIORITY 3: Least-quizzed lifetime concepts ───
@@ -166,7 +259,11 @@ if [ "$CONCEPTS_SEEN" != "[]" ]; then
     .[] as $concept |
     ($history | [.[] | select(.concept == $concept)] | length) as $count |
     {concept: $concept, count: $count}
-  ' <<< "$CONCEPTS_SEEN" | jq -s 'sort_by(.count) | first | .concept // null' 2>/dev/null)
+  ' <<< "$CONCEPTS_SEEN" 2>&1 | jq -s 'sort_by(.count) | first | .concept // null' 2>&1)
+  if [ $? -ne 0 ]; then
+    log_error "$SCRIPT_NAME" "jq failed computing least-quizzed concept: $LEAST_QUIZZED"
+    LEAST_QUIZZED=""
+  fi
 fi
 
 if [ -n "$LEAST_QUIZZED" ] && [ "$LEAST_QUIZZED" != "null" ] && [ -f "$QUIZ_BANK" ]; then
@@ -174,12 +271,22 @@ if [ -n "$LEAST_QUIZZED" ] && [ "$LEAST_QUIZZED" != "null" ] && [ -f "$QUIZ_BANK
     .quizzes[$concept] // [] |
     map(select(.belt == $belt or .belt == "white")) |
     first // null
-  ' "$QUIZ_BANK")
+  ' "$QUIZ_BANK" 2>&1)
+  if [ $? -ne 0 ]; then
+    log_error "$SCRIPT_NAME" "jq failed reading static question for $LEAST_QUIZZED: $STATIC_Q"
+    STATIC_Q="null"
+  fi
+
+  ESCAPED_CONCEPT=$(json_escape "$LEAST_QUIZZED")
+  ESCAPED_BELT=$(json_escape "$BELT")
 
-  echo "{\"mode\":\"static\",\"concept\":\"$LEAST_QUIZZED\",\"reason\":\"Reinforcing least-practiced concept.\",\"static_question\":$STATIC_Q,\"belt\":\"$BELT\",\"quiz_format\":\"$QUIZ_FORMAT\"}"
+  printf '{"mode":"static","concept":%s,"reason":"Reinforcing least-practiced concept.","static_question":%s,"belt":%s,"quiz_format":"%s"}\n' \
+    "$ESCAPED_CONCEPT" "$STATIC_Q" "$ESCAPED_BELT" "$QUIZ_FORMAT"
   exit 0
 fi
 
 # ─── FALLBACK: Dynamic generation ───
-echo "{\"mode\":\"dynamic\",\"concept\":null,\"reason\":\"No specific concept to target — generate from current session context.\",\"static_question\":null,\"belt\":\"$BELT\",\"quiz_format\":\"$QUIZ_FORMAT\"}"
+ESCAPED_BELT=$(json_escape "$BELT")
+printf '{"mode":"dynamic","concept":null,"reason":"No specific concept to target — generate from current session context.","static_question":null,"belt":%s,"quiz_format":"%s"}\n' \
+  "$ESCAPED_BELT" "$QUIZ_FORMAT"
 exit 0
diff --git a/scripts/session-start.sh b/scripts/session-start.sh
index 5506f5a..ad90e7b 100755
--- a/scripts/session-start.sh
+++ b/scripts/session-start.sh
@@ -2,22 +2,43 @@
 # CodeSensei — Session Start Hook
 # Loads user profile and updates streak on each Claude Code session start
 
+SCRIPT_NAME="session-start"
 PROFILE_DIR="$HOME/.code-sensei"
 PROFILE_FILE="$PROFILE_DIR/profile.json"
 SESSION_LOG="$PROFILE_DIR/sessions.log"
 TODAY=$(date -u +%Y-%m-%d)
 
+# Load shared error handling
+# shellcheck source=lib/error-handling.sh
+LIB_DIR="$(dirname "$0")/lib"
+if [ -f "$LIB_DIR/error-handling.sh" ]; then
+  source "$LIB_DIR/error-handling.sh"
+else
+  # Minimal inline fallback if lib is missing
+  LOG_FILE="${PROFILE_DIR}/error.log"
+  log_error() { printf '[%s] [%s] %s\n' "$(date -u '+%Y-%m-%dT%H:%M:%SZ' 2>/dev/null || date '+%Y-%m-%d')" "${1:-unknown}" "$2" >> "$LOG_FILE" 2>/dev/null; }
+  json_escape() { printf '%s' "$1" | sed 's/\\/\\\\/g; s/"/\\"/g'; }
+  check_jq() { command -v jq &>/dev/null; }
+fi
+
 # Create profile directory if it doesn't exist
-mkdir -p "$PROFILE_DIR"
+if ! mkdir -p "$PROFILE_DIR" 2>&1 | grep -q .; then
+  : # directory created or already exists
+fi
+if [ ! -d "$PROFILE_DIR" ]; then
+  log_error "$SCRIPT_NAME" "Failed to create profile directory: $PROFILE_DIR"
+  exit 0
+fi
 
 # Create default profile if none exists
 if [ ! -f "$PROFILE_FILE" ]; then
-  cat > "$PROFILE_FILE" << PROFILE
+  CREATED_AT=$(date -u +%Y-%m-%dT%H:%M:%SZ)
+  if ! cat > "$PROFILE_FILE" << PROFILE
 {
   "version": "1.0.0",
   "plugin": "code-sensei",
   "brand": "Dojo Coding",
-  "created_at": "$(date -u +%Y-%m-%dT%H:%M:%SZ)",
+  "created_at": "$CREATED_AT",
   "belt": "white",
   "xp": 0,
   "streak": {
@@ -45,7 +66,7 @@ if [ ! -f "$PROFILE_FILE" ]; then
       "id": "first-session",
       "name": "First Steps",
       "description": "Started your first CodeSensei session",
-      "earned_at": "$(date -u +%Y-%m-%dT%H:%M:%SZ)"
+      "earned_at": "$CREATED_AT"
     }
   ],
   "preferences": {
@@ -56,66 +77,107 @@ if [ ! -f "$PROFILE_FILE" ]; then
   "session_concepts": []
 }
 PROFILE
-  echo "🥋 Welcome to CodeSensei by Dojo Coding! Use /code-sensei:progress to get started."
+  then
+    log_error "$SCRIPT_NAME" "Failed to write default profile to $PROFILE_FILE"
+    exit 0
+  fi
+  echo "Welcome to CodeSensei by Dojo Coding! Use /code-sensei:progress to get started."
   exit 0
 fi
 
 # Profile exists — update streak and session count
-if command -v jq &> /dev/null; then
-  LAST_SESSION=$(jq -r '.streak.last_session_date // ""' "$PROFILE_FILE")
-  CURRENT_STREAK=$(jq -r '.streak.current // 0' "$PROFILE_FILE")
-  LONGEST_STREAK=$(jq -r '.streak.longest // 0' "$PROFILE_FILE")
-  TOTAL_SESSIONS=$(jq -r '.sessions.total // 0' "$PROFILE_FILE")
-
-  # Calculate streak
-  if [ "$LAST_SESSION" = "$TODAY" ]; then
-    # Already logged today, no streak change
-    NEW_STREAK=$CURRENT_STREAK
-  elif [ -n "$LAST_SESSION" ]; then
-    # Check if last session was yesterday
-    YESTERDAY=$(date -u -d "yesterday" +%Y-%m-%d 2>/dev/null || date -u -v-1d +%Y-%m-%d 2>/dev/null)
-    if [ "$LAST_SESSION" = "$YESTERDAY" ]; then
-      NEW_STREAK=$((CURRENT_STREAK + 1))
-    else
-      NEW_STREAK=1
-    fi
+if ! check_jq "$SCRIPT_NAME"; then
+  exit 0
+fi
+
+LAST_SESSION=$(jq -r '.streak.last_session_date // ""' "$PROFILE_FILE" 2>&1)
+if [ $? -ne 0 ]; then
+  log_error "$SCRIPT_NAME" "jq failed reading last_session_date: $LAST_SESSION"
+  exit 0
+fi
+
+CURRENT_STREAK=$(jq -r '.streak.current // 0' "$PROFILE_FILE" 2>&1)
+if [ $? -ne 0 ]; then
+  log_error "$SCRIPT_NAME" "jq failed reading streak.current: $CURRENT_STREAK"
+  exit 0
+fi
+
+LONGEST_STREAK=$(jq -r '.streak.longest // 0' "$PROFILE_FILE" 2>&1)
+TOTAL_SESSIONS=$(jq -r '.sessions.total // 0' "$PROFILE_FILE" 2>&1)
+
+# Calculate streak
+if [ "$LAST_SESSION" = "$TODAY" ]; then
+  # Already logged today, no streak change
+  NEW_STREAK=$CURRENT_STREAK
+elif [ -n "$LAST_SESSION" ]; then
+  # Check if last session was yesterday (handles both GNU and BSD date)
+  YESTERDAY=$(date -u -d "yesterday" +%Y-%m-%d 2>/dev/null || date -u -v-1d +%Y-%m-%d 2>/dev/null)
+  if [ -z "$YESTERDAY" ]; then
+    log_error "$SCRIPT_NAME" "Failed to compute yesterday's date; resetting streak to 1"
+    YESTERDAY=""
+  fi
+  if [ "$LAST_SESSION" = "$YESTERDAY" ]; then
+    NEW_STREAK=$((CURRENT_STREAK + 1))
   else
     NEW_STREAK=1
   fi
+else
+  NEW_STREAK=1
+fi
 
-  # Update longest streak
-  if [ "$NEW_STREAK" -gt "$LONGEST_STREAK" ]; then
-    NEW_LONGEST=$NEW_STREAK
-  else
-    NEW_LONGEST=$LONGEST_STREAK
-  fi
+# Update longest streak
+if [ "$NEW_STREAK" -gt "$LONGEST_STREAK" ]; then
+  NEW_LONGEST=$NEW_STREAK
+else
+  NEW_LONGEST=$LONGEST_STREAK
+fi
 
-  # Update profile
-  UPDATED=$(jq \
-    --arg today "$TODAY" \
-    --argjson streak "$NEW_STREAK" \
-    --argjson longest "$NEW_LONGEST" \
-    --argjson sessions "$((TOTAL_SESSIONS + 1))" \
-    '.streak.current = $streak |
-     .streak.longest = $longest |
-     .streak.last_session_date = $today |
-     .sessions.total = $sessions |
-     .sessions.last_session = $today |
-     .session_concepts = []' \
-    "$PROFILE_FILE")
-
-  echo "$UPDATED" > "$PROFILE_FILE"
-
-  # Log session
-  echo "$TODAY $(date -u +%H:%M:%S) session_start" >> "$SESSION_LOG"
-
-  # Show streak info if notable
-  BELT=$(jq -r '.belt // "white"' "$PROFILE_FILE")
-  XP=$(jq -r '.xp // 0' "$PROFILE_FILE")
-
-  if [ "$NEW_STREAK" -ge 7 ] && [ "$NEW_STREAK" != "$CURRENT_STREAK" ]; then
-    echo "🔥 $NEW_STREAK-day streak! Consistency is the Dojo Way."
-  fi
+# Update profile atomically (temp file + mv)
+UPDATED=$(jq \
+  --arg today "$TODAY" \
+  --argjson streak "$NEW_STREAK" \
+  --argjson longest "$NEW_LONGEST" \
+  --argjson sessions "$((TOTAL_SESSIONS + 1))" \
+  '.streak.current = $streak |
+   .streak.longest = $longest |
+   .streak.last_session_date = $today |
+   .sessions.total = $sessions |
+   .sessions.last_session = $today |
+   .session_concepts = []' \
+  "$PROFILE_FILE" 2>&1)
+
+if [ $? -ne 0 ]; then
+  log_error "$SCRIPT_NAME" "jq failed updating profile: $UPDATED"
+  exit 0
+fi
+
+TMPFILE=$(mktemp "${PROFILE_FILE}.XXXXXX" 2>&1)
+if [ $? -ne 0 ]; then
+  log_error "$SCRIPT_NAME" "mktemp failed: $TMPFILE"
+  exit 0
+fi
+
+printf '%s\n' "$UPDATED" > "$TMPFILE" && mv "$TMPFILE" "$PROFILE_FILE"
+if [ $? -ne 0 ]; then
+  log_error "$SCRIPT_NAME" "Failed to write updated profile (atomic mv)"
+  rm -f "$TMPFILE"
+  exit 0
+fi
+
+# Log session
+if ! printf '%s %s session_start\n' "$TODAY" "$(date -u +%H:%M:%S)" >> "$SESSION_LOG" 2>&1; then
+  log_error "$SCRIPT_NAME" "Failed to write to session log: $SESSION_LOG"
+fi
+
+# Show streak info if notable
+BELT=$(jq -r '.belt // "white"' "$PROFILE_FILE" 2>&1)
+if [ $? -ne 0 ]; then
+  log_error "$SCRIPT_NAME" "jq failed reading belt after profile update: $BELT"
+  BELT="white"
+fi
+
+if [ "$NEW_STREAK" -ge 7 ] && [ "$NEW_STREAK" != "$CURRENT_STREAK" ]; then
+  echo "${NEW_STREAK}-day streak! Consistency is the Dojo Way."
 fi
 
 exit 0
diff --git a/scripts/session-stop.sh b/scripts/session-stop.sh
index 7a20e9e..3dd8861 100755
--- a/scripts/session-stop.sh
+++ b/scripts/session-stop.sh
@@ -2,33 +2,85 @@
 # CodeSensei — Session Stop Hook
 # Saves session data and shows a mini-recap prompt
 
+SCRIPT_NAME="session-stop"
 PROFILE_DIR="$HOME/.code-sensei"
 PROFILE_FILE="$PROFILE_DIR/profile.json"
 SESSION_LOG="$PROFILE_DIR/sessions.log"
 TODAY=$(date -u +%Y-%m-%d)
 
+# Load shared error handling
+LIB_DIR="$(dirname "$0")/lib"
+if [ -f "$LIB_DIR/error-handling.sh" ]; then
+  source "$LIB_DIR/error-handling.sh"
+else
+  LOG_FILE="${PROFILE_DIR}/error.log"
+  log_error() { printf '[%s] [%s] %s\n' "$(date -u '+%Y-%m-%dT%H:%M:%SZ' 2>/dev/null || date '+%Y-%m-%d')" "${1:-unknown}" "$2" >> "$LOG_FILE" 2>/dev/null; }
+  json_escape() { printf '%s' "$1" | sed 's/\\/\\\\/g; s/"/\\"/g'; }
+  check_jq() { command -v jq &>/dev/null; }
+fi
+
 if [ ! -f "$PROFILE_FILE" ]; then
   exit 0
 fi
 
-if command -v jq &> /dev/null; then
-  # Count concepts learned this session
-  SESSION_CONCEPTS=$(jq -r '.session_concepts | length // 0' "$PROFILE_FILE")
-  XP=$(jq -r '.xp // 0' "$PROFILE_FILE")
-  BELT=$(jq -r '.belt // "white"' "$PROFILE_FILE")
-  STREAK=$(jq -r '.streak.current // 0' "$PROFILE_FILE")
+if ! check_jq "$SCRIPT_NAME"; then
+  exit 0
+fi
+
+# Count concepts learned this session
+SESSION_CONCEPTS=$(jq -r '.session_concepts | length // 0' "$PROFILE_FILE" 2>&1)
+if [ $? -ne 0 ]; then
+  log_error "$SCRIPT_NAME" "jq failed reading session_concepts length: $SESSION_CONCEPTS"
+  SESSION_CONCEPTS=0
+fi
 
-  # Log session end
-  echo "$TODAY $(date -u +%H:%M:%S) session_stop concepts=$SESSION_CONCEPTS xp=$XP belt=$BELT" >> "$SESSION_LOG"
+XP=$(jq -r '.xp // 0' "$PROFILE_FILE" 2>&1)
+if [ $? -ne 0 ]; then
+  log_error "$SCRIPT_NAME" "jq failed reading xp: $XP"
+  XP=0
+fi
+
+BELT=$(jq -r '.belt // "white"' "$PROFILE_FILE" 2>&1)
+if [ $? -ne 0 ]; then
+  log_error "$SCRIPT_NAME" "jq failed reading belt: $BELT"
+  BELT="white"
+fi
+
+STREAK=$(jq -r '.streak.current // 0' "$PROFILE_FILE" 2>&1)
+if [ $? -ne 0 ]; then
+  log_error "$SCRIPT_NAME" "jq failed reading streak: $STREAK"
+  STREAK=0
+fi
 
-  # Clear session-specific data
-  UPDATED=$(jq '.session_concepts = []' "$PROFILE_FILE")
-  echo "$UPDATED" > "$PROFILE_FILE"
+# Log session end
+if ! printf '%s %s session_stop concepts=%s xp=%s belt=%s\n' \
+    "$TODAY" "$(date -u +%H:%M:%S)" "$SESSION_CONCEPTS" "$XP" "$BELT" >> "$SESSION_LOG" 2>&1; then
+  log_error "$SCRIPT_NAME" "Failed to write to session log: $SESSION_LOG"
+fi
+
+# Clear session-specific data atomically
+UPDATED=$(jq '.session_concepts = []' "$PROFILE_FILE" 2>&1)
+if [ $? -ne 0 ]; then
+  log_error "$SCRIPT_NAME" "jq failed clearing session_concepts: $UPDATED"
+  exit 0
+fi
+
+TMPFILE=$(mktemp "${PROFILE_FILE}.XXXXXX" 2>&1)
+if [ $? -ne 0 ]; then
+  log_error "$SCRIPT_NAME" "mktemp failed: $TMPFILE"
+  exit 0
+fi
+
+printf '%s\n' "$UPDATED" > "$TMPFILE" && mv "$TMPFILE" "$PROFILE_FILE"
+if [ $? -ne 0 ]; then
+  log_error "$SCRIPT_NAME" "Failed to write updated profile (atomic mv)"
+  rm -f "$TMPFILE"
+  exit 0
+fi
 
-  # Show gentle reminder if they learned things but didn't recap
-  if [ "$SESSION_CONCEPTS" -gt 0 ]; then
-    echo "🥋 You encountered $SESSION_CONCEPTS new concepts this session! Use /code-sensei:recap next time for a full summary."
-  fi
+# Show gentle reminder if they learned things but didn't recap
+if [ "$SESSION_CONCEPTS" -gt 0 ]; then
+  echo "You encountered $SESSION_CONCEPTS new concepts this session! Use /code-sensei:recap next time for a full summary."
 fi
 
 exit 0
diff --git a/scripts/track-code-change.sh b/scripts/track-code-change.sh
index 90d9f80..63b4629 100755
--- a/scripts/track-code-change.sh
+++ b/scripts/track-code-change.sh
@@ -3,77 +3,162 @@
 # Records what files Claude creates or modifies for contextual teaching
 # This data is used by /explain and /recap to know what happened
 
+SCRIPT_NAME="track-code-change"
 PROFILE_DIR="$HOME/.code-sensei"
 PROFILE_FILE="$PROFILE_DIR/profile.json"
 CHANGES_LOG="$PROFILE_DIR/session-changes.jsonl"
 
+# Load shared error handling
+LIB_DIR="$(dirname "$0")/lib"
+if [ -f "$LIB_DIR/error-handling.sh" ]; then
+  source "$LIB_DIR/error-handling.sh"
+else
+  LOG_FILE="${PROFILE_DIR}/error.log"
+  log_error() { printf '[%s] [%s] %s\n' "$(date -u '+%Y-%m-%dT%H:%M:%SZ' 2>/dev/null || date '+%Y-%m-%d')" "${1:-unknown}" "$2" >> "$LOG_FILE" 2>/dev/null; }
+  json_escape() {
+    local str="$1"
+    if command -v jq &>/dev/null; then
+      printf '%s' "$str" | jq -Rs '.'
+    else
+      printf '"%s"' "$(printf '%s' "$str" | sed 's/\\/\\\\/g; s/"/\\"/g')"
+    fi
+  }
+  check_jq() { command -v jq &>/dev/null; }
+fi
+
 # Read hook input from stdin
 INPUT=$(cat)
 
 if [ ! -d "$PROFILE_DIR" ]; then
-  mkdir -p "$PROFILE_DIR"
+  if ! mkdir -p "$PROFILE_DIR" 2>&1; then
+    log_error "$SCRIPT_NAME" "Failed to create profile directory: $PROFILE_DIR"
+    exit 0
+  fi
 fi
 
-if command -v jq &> /dev/null; then
-  # Extract file path and tool info from hook input
-  TOOL_NAME=$(echo "$INPUT" | jq -r '.tool_name // "unknown"')
-  FILE_PATH=$(echo "$INPUT" | jq -r '.tool_input.file_path // .tool_input.filePath // "unknown"')
-  TIMESTAMP=$(date -u +%Y-%m-%dT%H:%M:%SZ)
-
-  # Detect file type/technology for concept mapping
-  EXTENSION="${FILE_PATH##*.}"
-  TECH=""
-  case "$EXTENSION" in
-    html|htm) TECH="html" ;;
-    css|scss|sass|less) TECH="css" ;;
-    js|mjs) TECH="javascript" ;;
-    jsx) TECH="react" ;;
-    ts|tsx) TECH="typescript" ;;
-    py) TECH="python" ;;
-    sql) TECH="sql" ;;
-    json) TECH="json" ;;
-    md|mdx) TECH="markdown" ;;
-    sh|bash) TECH="shell" ;;
-    yaml|yml) TECH="yaml" ;;
-    toml) TECH="toml" ;;
-    env) TECH="environment-variables" ;;
-    dockerfile|Dockerfile) TECH="docker" ;;
-    *) TECH="other" ;;
-  esac
-
-  # Log the change
-  echo "{\"timestamp\":\"$TIMESTAMP\",\"tool\":\"$TOOL_NAME\",\"file\":\"$FILE_PATH\",\"extension\":\"$EXTENSION\",\"tech\":\"$TECH\"}" >> "$CHANGES_LOG"
-
-  # Track technology in session concepts if it's new
-  IS_FIRST_EVER="false"
-  if [ -f "$PROFILE_FILE" ] && [ "$TECH" != "other" ]; then
-    ALREADY_SEEN=$(jq --arg tech "$TECH" '.session_concepts | index($tech)' "$PROFILE_FILE")
-    if [ "$ALREADY_SEEN" = "null" ]; then
-      UPDATED=$(jq --arg tech "$TECH" '.session_concepts += [$tech]' "$PROFILE_FILE")
-      echo "$UPDATED" > "$PROFILE_FILE"
-    fi
+if ! check_jq "$SCRIPT_NAME"; then
+  exit 0
+fi
+
+# Extract file path and tool info from hook input
+TOOL_NAME=$(printf '%s' "$INPUT" | jq -r '.tool_name // "unknown"' 2>&1)
+if [ $? -ne 0 ]; then
+  log_error "$SCRIPT_NAME" "jq failed reading tool_name: $TOOL_NAME"
+  TOOL_NAME="unknown"
+fi
+
+FILE_PATH=$(printf '%s' "$INPUT" | jq -r '.tool_input.file_path // .tool_input.filePath // "unknown"' 2>&1)
+if [ $? -ne 0 ]; then
+  log_error "$SCRIPT_NAME" "jq failed reading file_path: $FILE_PATH"
+  FILE_PATH="unknown"
+fi
+
+TIMESTAMP=$(date -u +%Y-%m-%dT%H:%M:%SZ)
+
+# Detect file type/technology for concept mapping
+EXTENSION="${FILE_PATH##*.}"
+TECH=""
+case "$EXTENSION" in
+  html|htm) TECH="html" ;;
+  css|scss|sass|less) TECH="css" ;;
+  js|mjs) TECH="javascript" ;;
+  jsx) TECH="react" ;;
+  ts|tsx) TECH="typescript" ;;
+  py) TECH="python" ;;
+  sql) TECH="sql" ;;
+  json) TECH="json" ;;
+  md|mdx) TECH="markdown" ;;
+  sh|bash) TECH="shell" ;;
+  yaml|yml) TECH="yaml" ;;
+  toml) TECH="toml" ;;
+  env) TECH="environment-variables" ;;
+  dockerfile|Dockerfile) TECH="docker" ;;
+  *) TECH="other" ;;
+esac
 
-    # Also add to lifetime concepts_seen if new — and flag for micro-lesson
-    LIFETIME_SEEN=$(jq --arg tech "$TECH" '.concepts_seen | index($tech)' "$PROFILE_FILE")
-    if [ "$LIFETIME_SEEN" = "null" ]; then
-      UPDATED=$(jq --arg tech "$TECH" '.concepts_seen += [$tech]' "$PROFILE_FILE")
-      echo "$UPDATED" > "$PROFILE_FILE"
-      IS_FIRST_EVER="true"
+# Log the change (escape dynamic values for JSON safety)
+SAFE_FILE_PATH=$(printf '%s' "$FILE_PATH" | sed 's/\\/\\\\/g; s/"/\\"/g')
+SAFE_TOOL_NAME=$(printf '%s' "$TOOL_NAME" | sed 's/\\/\\\\/g; s/"/\\"/g')
+if ! printf '{"timestamp":"%s","tool":"%s","file":"%s","extension":"%s","tech":"%s"}\n' \
+    "$TIMESTAMP" "$SAFE_TOOL_NAME" "$SAFE_FILE_PATH" "$EXTENSION" "$TECH" >> "$CHANGES_LOG" 2>&1; then
+  log_error "$SCRIPT_NAME" "Failed to write to changes log: $CHANGES_LOG"
+fi
+
+# Track technology in session concepts if it's new
+IS_FIRST_EVER="false"
+if [ -f "$PROFILE_FILE" ] && [ "$TECH" != "other" ]; then
+  ALREADY_SEEN=$(jq --arg tech "$TECH" '.session_concepts | index($tech)' "$PROFILE_FILE" 2>&1)
+  if [ $? -ne 0 ]; then
+    log_error "$SCRIPT_NAME" "jq failed checking session_concepts for $TECH: $ALREADY_SEEN"
+    ALREADY_SEEN="0"
+  fi
+
+  if [ "$ALREADY_SEEN" = "null" ]; then
+    UPDATED=$(jq --arg tech "$TECH" '.session_concepts += [$tech]' "$PROFILE_FILE" 2>&1)
+    if [ $? -ne 0 ]; then
+      log_error "$SCRIPT_NAME" "jq failed appending to session_concepts: $UPDATED"
+    else
+      TMPFILE=$(mktemp "${PROFILE_FILE}.XXXXXX" 2>&1)
+      if [ $? -ne 0 ]; then
+        log_error "$SCRIPT_NAME" "mktemp failed: $TMPFILE"
+      else
+        printf '%s\n' "$UPDATED" > "$TMPFILE" && mv "$TMPFILE" "$PROFILE_FILE"
+        if [ $? -ne 0 ]; then
+          log_error "$SCRIPT_NAME" "Failed atomic profile write (session_concepts)"
+          rm -f "$TMPFILE"
+        fi
+      fi
     fi
   fi
 
-  # Always inject teaching context after code changes
-  BELT=$(jq -r '.belt // "white"' "$PROFILE_FILE" 2>/dev/null || echo "white")
+  # Also add to lifetime concepts_seen if new — and flag for micro-lesson
+  LIFETIME_SEEN=$(jq --arg tech "$TECH" '.concepts_seen | index($tech)' "$PROFILE_FILE" 2>&1)
+  if [ $? -ne 0 ]; then
+    log_error "$SCRIPT_NAME" "jq failed checking concepts_seen for $TECH: $LIFETIME_SEEN"
+    LIFETIME_SEEN="0"
+  fi
 
-  if [ "$IS_FIRST_EVER" = "true" ]; then
-    # First-time encounter: micro-lesson about the technology
-    CONTEXT="🥋 CodeSensei micro-lesson trigger: The user just encountered '$TECH' for the FIRST TIME (file: $FILE_PATH). Their belt level is '$BELT'. Provide a brief 2-sentence explanation of what $TECH is and why it matters for their project. Adapt language to their belt level. Keep it concise and non-intrusive — weave it naturally into your response, don't stop everything for a lecture."
-  else
-    # Already-seen technology: inline insight about the specific change
-    CONTEXT="🥋 CodeSensei inline insight: Claude just used '$TOOL_NAME' on '$FILE_PATH' ($TECH). The user's belt level is '$BELT'. Provide a brief 1-2 sentence explanation of what this change does and why, adapted to their belt level. Keep it natural and non-intrusive — weave it into your response as a quick teaching moment."
+  if [ "$LIFETIME_SEEN" = "null" ]; then
+    UPDATED=$(jq --arg tech "$TECH" '.concepts_seen += [$tech]' "$PROFILE_FILE" 2>&1)
+    if [ $? -ne 0 ]; then
+      log_error "$SCRIPT_NAME" "jq failed appending to concepts_seen: $UPDATED"
+    else
+      TMPFILE=$(mktemp "${PROFILE_FILE}.XXXXXX" 2>&1)
+      if [ $? -ne 0 ]; then
+        log_error "$SCRIPT_NAME" "mktemp failed: $TMPFILE"
+      else
+        printf '%s\n' "$UPDATED" > "$TMPFILE" && mv "$TMPFILE" "$PROFILE_FILE"
+        if [ $? -ne 0 ]; then
+          log_error "$SCRIPT_NAME" "Failed atomic profile write (concepts_seen)"
+          rm -f "$TMPFILE"
+        else
+          IS_FIRST_EVER="true"
+        fi
+      fi
+    fi
   fi
+fi
 
-  echo "{\"hookSpecificOutput\":{\"hookEventName\":\"PostToolUse\",\"additionalContext\":\"$CONTEXT\"}}"
+# Always inject teaching context after code changes
+BELT=$(jq -r '.belt // "white"' "$PROFILE_FILE" 2>&1)
+if [ $? -ne 0 ]; then
+  log_error "$SCRIPT_NAME" "jq failed reading belt: $BELT"
+  BELT="white"
 fi
 
+# Use json_escape for all dynamic strings embedded in the context JSON value
+ESCAPED_TECH=$(json_escape "$TECH")
+ESCAPED_FILE_PATH=$(json_escape "$FILE_PATH")
+ESCAPED_TOOL_NAME=$(json_escape "$TOOL_NAME")
+ESCAPED_BELT=$(json_escape "$BELT")
+
+if [ "$IS_FIRST_EVER" = "true" ]; then
+  CONTEXT="CodeSensei micro-lesson trigger: The user just encountered ${ESCAPED_TECH} for the FIRST TIME (file: ${ESCAPED_FILE_PATH}). Their belt level is ${ESCAPED_BELT}. Provide a brief 2-sentence explanation of what ${ESCAPED_TECH} is and why it matters for their project. Adapt language to their belt level. Keep it concise and non-intrusive — weave it naturally into your response, don't stop everything for a lecture."
+else
+  CONTEXT="CodeSensei inline insight: Claude just used ${ESCAPED_TOOL_NAME} on ${ESCAPED_FILE_PATH} (${ESCAPED_TECH}). The user's belt level is ${ESCAPED_BELT}. Provide a brief 1-2 sentence explanation of what this change does and why, adapted to their belt level. Keep it natural and non-intrusive — weave it into your response as a quick teaching moment."
+fi
+
+# Build final output — context is already a JSON string from json_escape (with quotes)
+printf '{"hookSpecificOutput":{"hookEventName":"PostToolUse","additionalContext":%s}}\n' "$CONTEXT"
+
 exit 0
diff --git a/scripts/track-command.sh b/scripts/track-command.sh
index 57134a8..60ec655 100755
--- a/scripts/track-command.sh
+++ b/scripts/track-command.sh
@@ -3,84 +3,161 @@
 # Records what shell commands Claude runs for contextual teaching
 # Helps /explain and /recap know what tools/packages were used
 
+SCRIPT_NAME="track-command"
 PROFILE_DIR="$HOME/.code-sensei"
 PROFILE_FILE="$PROFILE_DIR/profile.json"
 COMMANDS_LOG="$PROFILE_DIR/session-commands.jsonl"
 
+# Load shared error handling
+LIB_DIR="$(dirname "$0")/lib"
+if [ -f "$LIB_DIR/error-handling.sh" ]; then
+  source "$LIB_DIR/error-handling.sh"
+else
+  LOG_FILE="${PROFILE_DIR}/error.log"
+  log_error() { printf '[%s] [%s] %s\n' "$(date -u '+%Y-%m-%dT%H:%M:%SZ' 2>/dev/null || date '+%Y-%m-%d')" "${1:-unknown}" "$2" >> "$LOG_FILE" 2>/dev/null; }
+  json_escape() {
+    local str="$1"
+    if command -v jq &>/dev/null; then
+      printf '%s' "$str" | jq -Rs '.'
+    else
+      printf '"%s"' "$(printf '%s' "$str" | sed 's/\\/\\\\/g; s/"/\\"/g')"
+    fi
+  }
+  check_jq() { command -v jq &>/dev/null; }
+fi
+
 # Read hook input from stdin
 INPUT=$(cat)
 
 if [ ! -d "$PROFILE_DIR" ]; then
-  mkdir -p "$PROFILE_DIR"
+  if ! mkdir -p "$PROFILE_DIR" 2>&1; then
+    log_error "$SCRIPT_NAME" "Failed to create profile directory: $PROFILE_DIR"
+    exit 0
+  fi
 fi
 
-if command -v jq &> /dev/null; then
-  COMMAND=$(echo "$INPUT" | jq -r '.tool_input.command // "unknown"')
-  TIMESTAMP=$(date -u +%Y-%m-%dT%H:%M:%SZ)
-
-  # Detect what kind of command this is for concept tracking
-  CONCEPT=""
-  case "$COMMAND" in
-    *"npm install"*|*"npm i "*|*"yarn add"*|*"pnpm add"*)
-      CONCEPT="package-management"
-      # Extract package name for tracking
-      PACKAGE=$(echo "$COMMAND" | sed -E 's/.*(npm install|npm i|yarn add|pnpm add)[[:space:]]+([^[:space:]]+).*/\2/' | head -1)
-      ;;
-    *"pip install"*|*"pip3 install"*)
-      CONCEPT="package-management"
-      ;;
-    *"git "*) CONCEPT="git" ;;
-    *"docker "*) CONCEPT="docker" ;;
-    *"curl "*|*"wget "*) CONCEPT="http-requests" ;;
-    *"mkdir "*|*"touch "*|*"cp "*|*"mv "*|*"rm "*) CONCEPT="file-system" ;;
-    *"node "*|*"npx "*) CONCEPT="nodejs-runtime" ;;
-    *"python "*|*"python3 "*) CONCEPT="python-runtime" ;;
-    *"psql "*|*"mysql "*|*"sqlite3 "*) CONCEPT="database-cli" ;;
-    *"cd "*|*"ls "*|*"pwd"*) CONCEPT="terminal-navigation" ;;
-    *"chmod "*|*"chown "*) CONCEPT="permissions" ;;
-    *"ssh "*|*"scp "*) CONCEPT="remote-access" ;;
-    *"env "*|*"export "*) CONCEPT="environment-variables" ;;
-    *"test "*|*"jest "*|*"vitest "*|*"pytest "*) CONCEPT="testing" ;;
-    *) CONCEPT="" ;;
-  esac
-
-  # Log the command
-  echo "{\"timestamp\":\"$TIMESTAMP\",\"command\":\"$(echo "$COMMAND" | head -c 200)\",\"concept\":\"$CONCEPT\"}" >> "$COMMANDS_LOG"
-
-  # Track concept in session and lifetime if new and meaningful
-  IS_FIRST_EVER="false"
-  if [ -n "$CONCEPT" ] && [ -f "$PROFILE_FILE" ]; then
-    ALREADY_SEEN=$(jq --arg c "$CONCEPT" '.session_concepts | index($c)' "$PROFILE_FILE")
-    if [ "$ALREADY_SEEN" = "null" ]; then
-      UPDATED=$(jq --arg c "$CONCEPT" '.session_concepts += [$c]' "$PROFILE_FILE")
-      echo "$UPDATED" > "$PROFILE_FILE"
-    fi
+if ! check_jq "$SCRIPT_NAME"; then
+  exit 0
+fi
+
+COMMAND=$(printf '%s' "$INPUT" | jq -r '.tool_input.command // "unknown"' 2>&1)
+if [ $? -ne 0 ]; then
+  log_error "$SCRIPT_NAME" "jq failed reading tool_input.command: $COMMAND"
+  COMMAND="unknown"
+fi
+
+TIMESTAMP=$(date -u +%Y-%m-%dT%H:%M:%SZ)
+
+# Detect what kind of command this is for concept tracking
+CONCEPT=""
+case "$COMMAND" in
+  *"npm install"*|*"npm i "*|*"yarn add"*|*"pnpm add"*)
+    CONCEPT="package-management"
+    # Extract package name for tracking
+    PACKAGE=$(printf '%s' "$COMMAND" | sed -E 's/.*(npm install|npm i|yarn add|pnpm add)[[:space:]]+([^[:space:]]+).*/\2/' | head -1)
+    ;;
+  *"pip install"*|*"pip3 install"*)
+    CONCEPT="package-management"
+    ;;
+  *"git "*) CONCEPT="git" ;;
+  *"docker "*) CONCEPT="docker" ;;
+  *"curl "*|*"wget "*) CONCEPT="http-requests" ;;
+  *"mkdir "*|*"touch "*|*"cp "*|*"mv "*|*"rm "*) CONCEPT="file-system" ;;
+  *"node "*|*"npx "*) CONCEPT="nodejs-runtime" ;;
+  *"python "*|*"python3 "*) CONCEPT="python-runtime" ;;
+  *"psql "*|*"mysql "*|*"sqlite3 "*) CONCEPT="database-cli" ;;
+  *"cd "*|*"ls "*|*"pwd"*) CONCEPT="terminal-navigation" ;;
+  *"chmod "*|*"chown "*) CONCEPT="permissions" ;;
+  *"ssh "*|*"scp "*) CONCEPT="remote-access" ;;
+  *"env "*|*"export "*) CONCEPT="environment-variables" ;;
+  *"test "*|*"jest "*|*"vitest "*|*"pytest "*) CONCEPT="testing" ;;
+  *) CONCEPT="" ;;
+esac
+
+# Log the command (truncate to 200 chars, escape for JSON)
+CMD_TRUNCATED=$(printf '%s' "$COMMAND" | head -c 200)
+SAFE_CMD=$(printf '%s' "$CMD_TRUNCATED" | sed 's/\\/\\\\/g; s/"/\\"/g')
+SAFE_CONCEPT=$(printf '%s' "$CONCEPT" | sed 's/\\/\\\\/g; s/"/\\"/g')
+if ! printf '{"timestamp":"%s","command":"%s","concept":"%s"}\n' \
+    "$TIMESTAMP" "$SAFE_CMD" "$SAFE_CONCEPT" >> "$COMMANDS_LOG" 2>&1; then
+  log_error "$SCRIPT_NAME" "Failed to write to commands log: $COMMANDS_LOG"
+fi
+
+# Track concept in session and lifetime if new and meaningful
+IS_FIRST_EVER="false"
+if [ -n "$CONCEPT" ] && [ -f "$PROFILE_FILE" ]; then
+  ALREADY_SEEN=$(jq --arg c "$CONCEPT" '.session_concepts | index($c)' "$PROFILE_FILE" 2>&1)
+  if [ $? -ne 0 ]; then
+    log_error "$SCRIPT_NAME" "jq failed checking session_concepts for $CONCEPT: $ALREADY_SEEN"
+    ALREADY_SEEN="0"
+  fi
 
-    LIFETIME_SEEN=$(jq --arg c "$CONCEPT" '.concepts_seen | index($c)' "$PROFILE_FILE")
-    if [ "$LIFETIME_SEEN" = "null" ]; then
-      UPDATED=$(jq --arg c "$CONCEPT" '.concepts_seen += [$c]' "$PROFILE_FILE")
-      echo "$UPDATED" > "$PROFILE_FILE"
-      IS_FIRST_EVER="true"
+  if [ "$ALREADY_SEEN" = "null" ]; then
+    UPDATED=$(jq --arg c "$CONCEPT" '.session_concepts += [$c]' "$PROFILE_FILE" 2>&1)
+    if [ $? -ne 0 ]; then
+      log_error "$SCRIPT_NAME" "jq failed appending to session_concepts: $UPDATED"
+    else
+      TMPFILE=$(mktemp "${PROFILE_FILE}.XXXXXX" 2>&1)
+      if [ $? -ne 0 ]; then
+        log_error "$SCRIPT_NAME" "mktemp failed: $TMPFILE"
+      else
+        printf '%s\n' "$UPDATED" > "$TMPFILE" && mv "$TMPFILE" "$PROFILE_FILE"
+        if [ $? -ne 0 ]; then
+          log_error "$SCRIPT_NAME" "Failed atomic profile write (session_concepts)"
+          rm -f "$TMPFILE"
+        fi
+      fi
     fi
   fi
 
-  # Always inject teaching context after commands
-  BELT=$(jq -r '.belt // "white"' "$PROFILE_FILE" 2>/dev/null || echo "white")
-  # Sanitize command for JSON (remove quotes and special chars)
-  SAFE_CMD=$(echo "$COMMAND" | head -c 80 | tr '"' "'" | tr '\\' '/')
-
-  if [ "$IS_FIRST_EVER" = "true" ] && [ -n "$CONCEPT" ]; then
-    # First-time encounter: micro-lesson about the concept
-    CONTEXT="🥋 CodeSensei micro-lesson trigger: The user just encountered '$CONCEPT' for the FIRST TIME (command: $SAFE_CMD). Their belt level is '$BELT'. Provide a brief 2-sentence explanation of what $CONCEPT means and why it matters. Adapt language to their belt level. Keep it concise and non-intrusive."
-  elif [ -n "$CONCEPT" ]; then
-    # Already-seen concept: brief inline insight about this specific command
-    CONTEXT="🥋 CodeSensei inline insight: Claude just ran a '$CONCEPT' command ($SAFE_CMD). The user's belt level is '$BELT'. Provide a brief 1-sentence explanation of what this command does, adapted to their belt level. Keep it natural and non-intrusive."
-  else
-    # Unknown command type: still provide a brief hint
-    CONTEXT="🥋 CodeSensei inline insight: Claude just ran a shell command ($SAFE_CMD). The user's belt level is '$BELT'. If this command is educational, briefly explain what it does in 1 sentence. If trivial, skip the explanation."
+  LIFETIME_SEEN=$(jq --arg c "$CONCEPT" '.concepts_seen | index($c)' "$PROFILE_FILE" 2>&1)
+  if [ $? -ne 0 ]; then
+    log_error "$SCRIPT_NAME" "jq failed checking concepts_seen for $CONCEPT: $LIFETIME_SEEN"
+    LIFETIME_SEEN="0"
   fi
 
-  echo "{\"hookSpecificOutput\":{\"hookEventName\":\"PostToolUse\",\"additionalContext\":\"$CONTEXT\"}}"
+  if [ "$LIFETIME_SEEN" = "null" ]; then
+    UPDATED=$(jq --arg c "$CONCEPT" '.concepts_seen += [$c]' "$PROFILE_FILE" 2>&1)
+    if [ $? -ne 0 ]; then
+      log_error "$SCRIPT_NAME" "jq failed appending to concepts_seen: $UPDATED"
+    else
+      TMPFILE=$(mktemp "${PROFILE_FILE}.XXXXXX" 2>&1)
+      if [ $? -ne 0 ]; then
+        log_error "$SCRIPT_NAME" "mktemp failed: $TMPFILE"
+      else
+        printf '%s\n' "$UPDATED" > "$TMPFILE" && mv "$TMPFILE" "$PROFILE_FILE"
+        if [ $? -ne 0 ]; then
+          log_error "$SCRIPT_NAME" "Failed atomic profile write (concepts_seen)"
+          rm -f "$TMPFILE"
+        else
+          IS_FIRST_EVER="true"
+        fi
+      fi
+    fi
+  fi
 fi
 
+# Always inject teaching context after commands
+BELT=$(jq -r '.belt // "white"' "$PROFILE_FILE" 2>&1)
+if [ $? -ne 0 ]; then
+  log_error "$SCRIPT_NAME" "jq failed reading belt: $BELT"
+  BELT="white"
+fi
+
+# Use json_escape for all dynamic strings embedded in the context JSON value
+ESCAPED_CONCEPT=$(json_escape "$CONCEPT")
+ESCAPED_CMD=$(json_escape "$(printf '%s' "$COMMAND" | head -c 80)")
+ESCAPED_BELT=$(json_escape "$BELT")
+
+if [ "$IS_FIRST_EVER" = "true" ] && [ -n "$CONCEPT" ]; then
+  CONTEXT="CodeSensei micro-lesson trigger: The user just encountered ${ESCAPED_CONCEPT} for the FIRST TIME (command: ${ESCAPED_CMD}). Their belt level is ${ESCAPED_BELT}. Provide a brief 2-sentence explanation of what ${ESCAPED_CONCEPT} means and why it matters. Adapt language to their belt level. Keep it concise and non-intrusive."
+elif [ -n "$CONCEPT" ]; then
+  CONTEXT="CodeSensei inline insight: Claude just ran a ${ESCAPED_CONCEPT} command (${ESCAPED_CMD}). The user's belt level is ${ESCAPED_BELT}. Provide a brief 1-sentence explanation of what this command does, adapted to their belt level. Keep it natural and non-intrusive."
+else
+  CONTEXT="CodeSensei inline insight: Claude just ran a shell command (${ESCAPED_CMD}). The user's belt level is ${ESCAPED_BELT}. If this command is educational, briefly explain what it does in 1 sentence. If trivial, skip the explanation."
+fi
+
+# Build final output — context is already a JSON string from json_escape (with quotes)
+printf '{"hookSpecificOutput":{"hookEventName":"PostToolUse","additionalContext":%s}}\n' "$CONTEXT"
+
 exit 0