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diff --git a/data/backup/knowledge_detailed_description_2025-04-21T00-33-06-807Z.db b/data/backup/knowledge_detailed_description_2025-04-21T00-33-06-807Z.db
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diff --git a/docs/security/GIT_HISTORY_CLEANUP.md b/docs/security/GIT_HISTORY_CLEANUP.md
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+# Security: Git History Cleanup Guide
+
+## Problem
+
+Several files containing sensitive data were committed to the repository before `.gitignore` rules were added:
+
+| File | Issue | Status |
+|------|-------|--------|
+| `.env` | Contains `JWT_SECRET`, `SESSION_SECRET`, admin credentials, OAuth secrets | Removed from tracking, **still in git history** |
+| `knowledge.db` | SQLite database at repo root | Removed from tracking in this PR |
+| `data/backup/knowledge_backup.db` | 7.2 MB database backup | Removed from tracking in this PR |
+| `data/backup/knowledge_detailed_description_*.db` | 14 MB database backup | Removed from tracking in this PR |
+
+Even though these files are now in `.gitignore` and untracked, **anyone with repo access can still retrieve the secrets from git history** using commands like:
+
+```bash
+git log --all --oneline -- .env
+git show <commit-hash>:.env
+```
+
+## Solution
+
+### Step 1: Clean Git History (repo owner action required)
+
+Git history rewriting can only be done by the repo owner. We've provided an automated script:
+
+```bash
+# 1. Make a FRESH clone (required by git-filter-repo)
+git clone https://github.com/iamtouchskyer/math-project-server.git math-project-server-clean
+cd math-project-server-clean
+
+# 2. Install git-filter-repo
+pip install git-filter-repo
+
+# 3. Run the cleanup script
+bash scripts/clean-git-history.sh
+
+# 4. Force-push
+git push origin --force --all
+git push origin --force --tags
+```
+
+### Step 2: Rotate All Exposed Credentials
+
+**This is critical** — even after cleaning git history, the secrets may have been cached by GitHub, cloned by others, or indexed by bots. Rotate everything:
+
+- [ ] `JWT_SECRET` — Generate a new random 256-bit key
+- [ ] `SESSION_SECRET` — Generate a new random 256-bit key
+- [ ] `ADMIN_USERNAME` / `ADMIN_PASSWORD` — Change admin credentials
+- [ ] `GOOGLE_CLIENT_ID` / `GOOGLE_CLIENT_SECRET` — Rotate in Google Cloud Console
+- [ ] `STRIPE_SECRET_KEY` / `STRIPE_PUBLISHABLE_KEY` — Roll keys in Stripe Dashboard
+- [ ] `APPLE_CLIENT_ID` / `APPLE_TEAM_ID` / `APPLE_KEY_ID` — Update in Apple Developer
+- [ ] `WECHAT_APP_ID` / `WECHAT_APP_SECRET` — Rotate in WeChat Developer Platform
+
+### Step 3: Notify Collaborators
+
+After force-pushing, all existing clones will be out of sync. Collaborators need to:
+
+```bash
+# Option A: Re-clone (recommended)
+rm -rf math-project-server
+git clone https://github.com/iamtouchskyer/math-project-server.git
+
+# Option B: Reset existing clone
+cd math-project-server
+git fetch origin
+git reset --hard origin/main
+```
+
+### Step 4: Verify
+
+```bash
+# These should all return no results:
+git log --all --full-history -- .env
+git log --all --full-history -- .env.development
+git log --all --full-history -- knowledge.db
+git log --all --full-history -- data/backup/knowledge_backup.db
+```
+
+## Prevention
+
+The following safeguards are now in place:
+
+1. **`.gitignore`** — Blocks `.env*`, `*.db`, `*.sqlite`, `*.sqlite3` files
+2. **`.env.example`** — Provides a template with placeholder values
+3. **This guide** — Documents the cleanup process
+
+### Recommended: Add a Pre-commit Hook
+
+Add this to `.git/hooks/pre-commit` to prevent accidental commits of sensitive files:
+
+```bash
+#!/bin/bash
+# Prevent committing sensitive files
+SENSITIVE_PATTERNS=("\.env$" "\.env\." "\.db$" "\.sqlite" "secret" "password")
+STAGED_FILES=$(git diff --cached --name-only)
+
+for file in $STAGED_FILES; do
+    for pattern in "${SENSITIVE_PATTERNS[@]}"; do
+        if echo "$file" | grep -qiE "$pattern"; then
+            echo "❌ Blocked: '$file' matches sensitive pattern '$pattern'"
+            echo "   If intentional, use: git commit --no-verify"
+            exit 1
+        fi
+    done
+done
+```
+
+## References
+
+- [git-filter-repo documentation](https://github.com/newren/git-filter-repo)
+- [GitHub: Removing sensitive data](https://docs.github.com/en/authentication/keeping-your-account-and-data-secure/removing-sensitive-data-from-a-repository)
+- [BFG Repo-Cleaner](https://rtyley.github.io/bfg-repo-cleaner/) (alternative tool)
diff --git a/knowledge.db b/knowledge.db
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diff --git a/scripts/clean-git-history.sh b/scripts/clean-git-history.sh
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+++ b/scripts/clean-git-history.sh
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+#!/usr/bin/env bash
+# =============================================================================
+# clean-git-history.sh — Remove sensitive files from git history
+# =============================================================================
+#
+# This script uses git-filter-repo to permanently remove files that were
+# accidentally committed to git history, including:
+#   - .env files (containing secrets like JWT_SECRET, SESSION_SECRET, etc.)
+#   - .db files (SQLite database backups)
+#
+# ⚠️  IMPORTANT: This rewrites git history. All collaborators must re-clone
+#     the repository after this is run.
+#
+# Prerequisites:
+#   pip install git-filter-repo
+#
+# Usage:
+#   1. Make a FRESH clone of the repo (required by git-filter-repo)
+#      git clone https://github.com/iamtouchskyer/math-project-server.git math-project-server-clean
+#      cd math-project-server-clean
+#
+#   2. Run this script:
+#      bash scripts/clean-git-history.sh
+#
+#   3. Verify the cleanup worked:
+#      git log --all --full-history -- .env          # should return nothing
+#      git log --all --full-history -- knowledge.db   # should return nothing
+#
+#   4. Force-push to GitHub:
+#      git push origin --force --all
+#      git push origin --force --tags
+#
+#   5. ROTATE ALL CREDENTIALS that were exposed:
+#      - JWT_SECRET
+#      - SESSION_SECRET
+#      - Google OAuth credentials
+#      - Stripe API keys
+#      - Apple Sign-In configuration
+#      - WeChat OAuth secrets
+#      - Admin credentials
+#
+# =============================================================================
+
+set -euo pipefail
+
+# Colors for output
+RED='\033[0;31m'
+GREEN='\033[0;32m'
+YELLOW='\033[1;33m'
+NC='\033[0m' # No Color
+
+echo -e "${YELLOW}╔══════════════════════════════════════════════════════╗${NC}"
+echo -e "${YELLOW}║  Git History Cleanup — Removing Sensitive Files     ║${NC}"
+echo -e "${YELLOW}╚══════════════════════════════════════════════════════╝${NC}"
+echo ""
+
+# Check prerequisites
+if ! command -v git-filter-repo &> /dev/null; then
+    echo -e "${RED}Error: git-filter-repo is not installed.${NC}"
+    echo "Install it with: pip install git-filter-repo"
+    exit 1
+fi
+
+# Verify we're in a git repo
+if ! git rev-parse --is-inside-work-tree &> /dev/null; then
+    echo -e "${RED}Error: Not in a git repository.${NC}"
+    exit 1
+fi
+
+# Show what will be removed
+echo -e "${YELLOW}Files to remove from history:${NC}"
+echo ""
+
+FILES_TO_REMOVE=(
+    ".env"
+    ".env.development"
+    ".env.local"
+    "knowledge.db"
+    "data/backup/knowledge_backup.db"
+    "data/backup/knowledge_detailed_description_2025-04-21T00-33-06-807Z.db"
+)
+
+for file in "${FILES_TO_REMOVE[@]}"; do
+    COMMITS=$(git log --all --oneline -- "$file" 2>/dev/null | wc -l)
+    if [ "$COMMITS" -gt 0 ]; then
+        echo -e "  ${RED}✗${NC} $file (found in $COMMITS commits)"
+    else
+        echo -e "  ${GREEN}✓${NC} $file (not found — already clean)"
+    fi
+done
+
+echo ""
+echo -e "${YELLOW}⚠️  This will PERMANENTLY rewrite git history.${NC}"
+echo -e "${YELLOW}   All collaborators must re-clone after this.${NC}"
+echo ""
+read -p "Continue? (yes/no): " CONFIRM
+
+if [ "$CONFIRM" != "yes" ]; then
+    echo "Aborted."
+    exit 0
+fi
+
+echo ""
+echo -e "${GREEN}Running git-filter-repo...${NC}"
+
+# Build the filter-repo arguments
+ARGS=""
+for file in "${FILES_TO_REMOVE[@]}"; do
+    ARGS="$ARGS --path $file"
+done
+
+# Run git-filter-repo to remove the files
+git filter-repo --invert-paths $ARGS --force
+
+echo ""
+echo -e "${GREEN}╔══════════════════════════════════════════════════════╗${NC}"
+echo -e "${GREEN}║  ✅ Cleanup complete!                               ║${NC}"
+echo -e "${GREEN}╚══════════════════════════════════════════════════════╝${NC}"
+echo ""
+echo -e "Next steps:"
+echo -e "  1. Verify: ${YELLOW}git log --all --full-history -- .env${NC}"
+echo -e "  2. Re-add remote: ${YELLOW}git remote add origin https://github.com/iamtouchskyer/math-project-server.git${NC}"
+echo -e "  3. Force-push: ${YELLOW}git push origin --force --all && git push origin --force --tags${NC}"
+echo -e "  4. ${RED}ROTATE ALL EXPOSED CREDENTIALS${NC}"
+echo -e "  5. Tell collaborators to re-clone"
+echo ""