feat(data-platform): add schema diff detection hook (#228)

Implements PostToolUse hook to warn about potentially breaking schema changes:
- DROP COLUMN/TABLE/INDEX detection
- Column type changes (ALTER TYPE, MODIFY COLUMN)
- NOT NULL constraint additions
- RENAME operations
- ORM model field removals

Non-blocking - outputs warnings only.
Configurable via DATA_PLATFORM_SCHEMA_WARN env var.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

plugins/data-platform/hooks/hooks.json

@@ -5,6 +5,17 @@
         "type": "command",
         "command": "${CLAUDE_PLUGIN_ROOT}/hooks/startup-check.sh"
       }
+    ],
+    "PostToolUse": [
+      {
+        "matcher": "Edit|Write",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "${CLAUDE_PLUGIN_ROOT}/hooks/schema-diff-check.sh"
+          }
+        ]
+      }
     ]
   }
 }

plugins/data-platform/hooks/schema-diff-check.sh

@@ -0,0 +1,138 @@
+#!/bin/bash
+# data-platform schema diff detection hook
+# Warns about potentially breaking schema changes
+# This is a command hook - non-blocking, warnings only
+
+PREFIX="[data-platform]"
+
+# Check if warnings are enabled (default: true)
+if [[ "${DATA_PLATFORM_SCHEMA_WARN:-true}" != "true" ]]; then
+    exit 0
+fi
+
+# Read tool input from stdin (JSON with file_path)
+INPUT=$(cat)
+
+# Extract file_path from JSON input
+FILE_PATH=$(echo "$INPUT" | grep -o '"file_path"[[:space:]]*:[[:space:]]*"[^"]*"' | head -1 | sed 's/.*"file_path"[[:space:]]*:[[:space:]]*"\([^"]*\)".*/\1/')
+
+# If no file_path found, exit silently
+if [ -z "$FILE_PATH" ]; then
+    exit 0
+fi
+
+# Check if file is a schema-related file
+is_schema_file() {
+    local file="$1"
+
+    # Check file extension
+    case "$file" in
+        *.sql) return 0 ;;
+        */migrations/*.py) return 0 ;;
+        */migrations/*.sql) return 0 ;;
+        */models/*.py) return 0 ;;
+        */models/*.sql) return 0 ;;
+        *schema.prisma) return 0 ;;
+        *schema.graphql) return 0 ;;
+        */dbt/models/*.sql) return 0 ;;
+        */dbt/models/*.yml) return 0 ;;
+        */alembic/versions/*.py) return 0 ;;
+    esac
+
+    # Check directory patterns
+    if echo "$file" | grep -qE "(migrations?|schemas?|models)/"; then
+        return 0
+    fi
+
+    return 1
+}
+
+# Exit if not a schema file
+if ! is_schema_file "$FILE_PATH"; then
+    exit 0
+fi
+
+# Read the file content (if it exists and is readable)
+if [[ ! -f "$FILE_PATH" ]]; then
+    exit 0
+fi
+
+FILE_CONTENT=$(cat "$FILE_PATH" 2>/dev/null || echo "")
+
+if [[ -z "$FILE_CONTENT" ]]; then
+    exit 0
+fi
+
+# Detect breaking changes
+BREAKING_CHANGES=()
+
+# Check for DROP COLUMN
+if echo "$FILE_CONTENT" | grep -qiE "DROP[[:space:]]+COLUMN"; then
+    BREAKING_CHANGES+=("DROP COLUMN detected - may break existing queries")
+fi
+
+# Check for DROP TABLE
+if echo "$FILE_CONTENT" | grep -qiE "DROP[[:space:]]+TABLE"; then
+    BREAKING_CHANGES+=("DROP TABLE detected - data loss risk")
+fi
+
+# Check for DROP INDEX
+if echo "$FILE_CONTENT" | grep -qiE "DROP[[:space:]]+INDEX"; then
+    BREAKING_CHANGES+=("DROP INDEX detected - may impact query performance")
+fi
+
+# Check for ALTER TYPE / MODIFY COLUMN type changes
+if echo "$FILE_CONTENT" | grep -qiE "ALTER[[:space:]]+.*(TYPE|COLUMN.*TYPE)"; then
+    BREAKING_CHANGES+=("Column type change detected - may cause data truncation")
+fi
+
+if echo "$FILE_CONTENT" | grep -qiE "MODIFY[[:space:]]+COLUMN"; then
+    BREAKING_CHANGES+=("MODIFY COLUMN detected - verify data compatibility")
+fi
+
+# Check for adding NOT NULL to existing column
+if echo "$FILE_CONTENT" | grep -qiE "ALTER[[:space:]]+.*SET[[:space:]]+NOT[[:space:]]+NULL"; then
+    BREAKING_CHANGES+=("Adding NOT NULL constraint - existing NULL values will fail")
+fi
+
+if echo "$FILE_CONTENT" | grep -qiE "ADD[[:space:]]+.*NOT[[:space:]]+NULL[^[:space:]]*[[:space:]]+DEFAULT"; then
+    # Adding NOT NULL with DEFAULT is usually safe - don't warn
+    :
+elif echo "$FILE_CONTENT" | grep -qiE "ADD[[:space:]]+.*NOT[[:space:]]+NULL"; then
+    BREAKING_CHANGES+=("Adding NOT NULL column without DEFAULT - INSERT may fail")
+fi
+
+# Check for RENAME TABLE/COLUMN
+if echo "$FILE_CONTENT" | grep -qiE "RENAME[[:space:]]+(TABLE|COLUMN|TO)"; then
+    BREAKING_CHANGES+=("RENAME detected - update all references")
+fi
+
+# Check for removing from Django/SQLAlchemy models (Python files)
+if [[ "$FILE_PATH" == *.py ]]; then
+    if echo "$FILE_CONTENT" | grep -qE "^-[[:space:]]*[a-z_]+[[:space:]]*=.*Field\("; then
+        BREAKING_CHANGES+=("Model field removal detected in Python ORM")
+    fi
+fi
+
+# Check for Prisma schema changes
+if [[ "$FILE_PATH" == *schema.prisma ]]; then
+    if echo "$FILE_CONTENT" | grep -qE "@relation.*onDelete.*Cascade"; then
+        BREAKING_CHANGES+=("Cascade delete detected - verify data safety")
+    fi
+fi
+
+# Output warnings if any breaking changes detected
+if [[ ${#BREAKING_CHANGES[@]} -gt 0 ]]; then
+    echo ""
+    echo "$PREFIX WARNING: Potential breaking schema changes in $(basename "$FILE_PATH")"
+    echo "$PREFIX ============================================"
+    for change in "${BREAKING_CHANGES[@]}"; do
+        echo "$PREFIX   - $change"
+    done
+    echo "$PREFIX ============================================"
+    echo "$PREFIX Review before deploying to production"
+    echo ""
+fi
+
+# Always exit 0 - non-blocking
+exit 0