Advanced Patterns & Edge Cases

Advanced Git Worktree Patterns & Edge Cases

Architectural Deep Dive: Worktree State Management

Understanding Git’s worktree implementation at a fundamental level enables developers to leverage advanced patterns that transcend basic parallel development workflows. This section examines the internal mechanics that govern worktree behavior and explores sophisticated use cases that emerge from this architectural foundation.

Git’s Worktree Storage Architecture

Git maintains worktree metadata through a hierarchical reference system within the primary repository’s .git directory:

project/.git/
├── worktrees/
│   ├── feature-authentication/
│   │   ├── HEAD                    # Current branch/commit reference
│   │   ├── ORIG_HEAD              # Previous HEAD (for undo operations)
│   │   ├── index                  # Staging area state
│   │   ├── gitdir                 # Path to worktree directory
│   │   ├── commondir              # Points to shared .git directory
│   │   └── locked                 # Lock file (if worktree is locked)
│   └── hotfix-critical/
│       ├── HEAD
│       ├── index
│       └── gitdir
├── objects/                        # Shared object database
├── refs/
│   ├── heads/                     # Branch references (shared)
│   └── worktree/                  # Worktree-specific refs
│       ├── feature-authentication/
│       └── hotfix-critical/
└── config                         # Global repository configuration

Key Architectural Insights:

  • Shared Object Storage: All worktrees reference the same .git/objects database. A commit created in any worktree becomes immediately visible in all others through shared references.
  • Isolated Index: Each worktree maintains an independent staging area (.git/worktrees/<name>/index), enabling concurrent staging operations without interference.
  • Reference Namespacing: Worktree-specific references live under .git/refs/worktree/<name>/, allowing per-worktree HEAD manipulation without affecting other instances.

Technical Implication: Atomic Multi-Worktree Operations

This architecture enables sophisticated patterns unavailable in traditional multi-clone workflows:

# Scenario: Implement feature across multiple codebases with atomic commit visibility

# In worktree 1: Commit backend implementation
cd ~/project-backend
git commit -m "feat: Add user authentication endpoint"
# Commit SHA: abc123def

# In worktree 2: Backend commit immediately visible for integration
cd ~/project-frontend
git log --all | grep "user authentication"  # Shows abc123def instantly

# Reference the backend commit in frontend implementation
git commit -m "feat: Integrate authentication (refs: abc123def)"

Why This Matters: In multi-clone workflows, developers must explicitly git fetch to synchronize commit visibility. Worktrees eliminate this synchronization overhead through shared object storage.


Pattern 1: Nested Worktree Hierarchies (Advanced Organization)

For large-scale projects with multiple development streams, flat worktree organization becomes cognitively overwhelming. Nested hierarchies provide logical grouping:

# Create organizational structure
project/                              # Primary worktree
├── feature-work/                     # Feature development namespace
│   ├── auth-implementation/         # Worktree: authentication feature
│   ├── payment-integration/         # Worktree: payment system
│   └── notification-service/        # Worktree: notifications
├── maintenance/                      # Maintenance namespace
│   ├── security-patches/            # Worktree: security updates
│   └── dependency-upgrades/         # Worktree: dependency management
└── release-preparation/              # Release namespace
    ├── v2.0.0-candidate/            # Worktree: release candidate testing
    └── v2.0.0-documentation/        # Worktree: release documentation

Implementation Strategy:

# Create nested worktree organization
cd ~/projects/application

# Feature development namespace
mkdir -p ../application-worktrees/feature-work
git worktree add -b auth-v2 ../application-worktrees/feature-work/auth-implementation
git worktree add -b payment-stripe ../application-worktrees/feature-work/payment-integration

# Maintenance namespace
mkdir -p ../application-worktrees/maintenance
git worktree add -b security-nov-2024 ../application-worktrees/maintenance/security-patches

# Release namespace
mkdir -p ../application-worktrees/release-preparation
git worktree add --detach ../application-worktrees/release-preparation/v2.0.0-candidate v2.0.0-rc1

Maintenance Operations:

# List all worktrees with hierarchical structure
git worktree list | sort

# Bulk operations on namespace
cd ~/projects
for worktree in application-worktrees/feature-work/*; do
    echo "Testing: $worktree"
    (cd "$worktree" && npm test)
done

# Namespace-specific cleanup
rm -rf application-worktrees/maintenance/security-patches
git worktree prune

Organizational Benefits:

  • Cognitive Clarity: Related worktrees grouped logically reduce mental overhead
  • Bulk Operations: Scripting across worktree subsets becomes straightforward
  • Lifecycle Management: Different namespaces have different retention policies (features: merge then delete, maintenance: ongoing, releases: archive)

Pattern 2: Temporary Worktrees for Forensic Analysis

When investigating complex bugs or performing regression analysis, temporary worktrees provide isolated environments for historical code execution without disrupting active development:

# Scenario: Investigate when a bug was introduced

# Create temporary forensic worktree
git worktree add --detach /tmp/forensic-analysis v1.5.0

# Execute historical code
cd /tmp/forensic-analysis
npm install
npm test  # Verify bug doesn't exist in v1.5.0

# Binary search through history (manual bisect alternative)
cd ~/projects/application
git worktree add --detach /tmp/forensic-v1.6.0 v1.6.0
cd /tmp/forensic-v1.6.0
npm install && npm test  # Bug introduced between v1.5.0 and v1.6.0

# Cleanup after investigation
cd ~/projects/application
git worktree remove /tmp/forensic-analysis
git worktree remove /tmp/forensic-v1.6.0

Advanced Forensic Pattern: Concurrent Historical Analysis

# Investigate multiple historical states simultaneously
for version in v1.4.0 v1.5.0 v1.6.0 v1.7.0; do
    git worktree add --detach "/tmp/forensic-$version" "$version"
    (cd "/tmp/forensic-$version" && npm install > /dev/null 2>&1 &)
done

# Wait for all installations
wait

# Run tests across all versions concurrently
for version in v1.4.0 v1.5.0 v1.6.0 v1.7.0; do
    echo "Testing $version:"
    (cd "/tmp/forensic-$version" && npm test 2>&1 | grep -E "(PASS|FAIL)")
done

# Cleanup
for version in v1.4.0 v1.5.0 v1.6.0 v1.7.0; do
    git worktree remove "/tmp/forensic-$version"
done

Why Temporary Worktrees Excel Here:

  • No History Pollution: No need to checkout historical commits in main worktree, leaving HEAD undisturbed
  • Parallel Execution: Multiple historical states can be analyzed concurrently
  • Ephemeral by Design: /tmp location ensures automatic cleanup on reboot if manual cleanup forgotten

Pattern 3: Worktree-Specific Hook Isolation

Git hooks traditionally apply globally across all worktrees. Advanced workflows require worktree-specific hook behavior:

Problem Statement: You need different pre-commit validation rules for:

  • Production hotfixes (strict linting, full test suite)
  • Feature development (relaxed linting, unit tests only)
  • Experimental branches (no validation)

Solution Architecture: Worktree-specific hook directories with conditional execution

# Setup: Configure worktree-specific hooks directory
cd ~/projects/application-hotfix
mkdir -p .worktree-hooks

# Create worktree-specific pre-commit hook
cat > .worktree-hooks/pre-commit << 'EOF'
#!/bin/bash
# Strict validation for hotfix worktree

set -e

echo "🔒 Hotfix Pre-Commit Validation (Strict Mode)"

# Full test suite (no skipping)
npm run test:all

# Strict linting (fail on warnings)
npm run lint -- --max-warnings=0

# Security audit
npm audit --audit-level=moderate

# Ensure no console.log statements
if git diff --cached | grep -E "console\.(log|debug|info)"; then
    echo "❌ ERROR: Console statements detected in hotfix"
    exit 1
fi

echo "✅ Hotfix validation passed"
EOF

chmod +x .worktree-hooks/pre-commit

# Configure Git to use worktree-specific hooks
git config core.hooksPath .worktree-hooks

Feature Development Worktree (relaxed validation):

cd ~/projects/application-feature
mkdir -p .worktree-hooks

cat > .worktree-hooks/pre-commit << 'EOF'
#!/bin/bash
# Relaxed validation for feature development

echo "🚀 Feature Pre-Commit Validation (Relaxed Mode)"

# Unit tests only (skip integration/e2e)
npm run test:unit

# Linting (warnings allowed)
npm run lint || echo "⚠️  Linting warnings present (non-blocking)"

echo "✅ Feature validation complete"
EOF

chmod +x .worktree-hooks/pre-commit
git config core.hooksPath .worktree-hooks

Experimental Worktree (no validation):

cd ~/projects/application-experimental

# Explicitly disable hooks for maximum development velocity
git config core.hooksPath /dev/null

Centralized Hook Management (maintaining DRY principles):

# Create shared hook library in main repository
mkdir -p ~/projects/application/.git-hooks-library

# Shared validation functions
cat > ~/projects/application/.git-hooks-library/validation-functions.sh << 'EOF'
#!/bin/bash

run_unit_tests() {
    npm run test:unit
}

run_full_tests() {
    npm run test:all
}

strict_linting() {
    npm run lint -- --max-warnings=0
}

relaxed_linting() {
    npm run lint || true
}

check_console_statements() {
    if git diff --cached | grep -E "console\.(log|debug)"; then
        return 1
    fi
    return 0
}
EOF

# In each worktree, source shared library
cat > ~/projects/application-hotfix/.worktree-hooks/pre-commit << 'EOF'
#!/bin/bash
source "$(git rev-parse --show-toplevel)/.git-hooks-library/validation-functions.sh"

echo "🔒 Hotfix Validation"
run_full_tests
strict_linting
check_console_statements || { echo "❌ Console statements found"; exit 1; }
EOF

Benefits:

  • Context-Appropriate Validation: Different quality gates for different development contexts
  • Developer Velocity: Experimental work not slowed by validation overhead
  • Shared Logic: Hook functions maintained centrally, referenced by worktree-specific hooks

Pattern 4: Worktree-Based Continuous Integration Staging

For teams without dedicated CI infrastructure, worktrees can serve as local CI environments:

Architecture: Long-lived CI worktrees that mirror production CI behavior

# Create dedicated CI worktree (never used for development)
git worktree add -b ci-staging ~/projects/application-ci
cd ~/projects/application-ci

# Configure as clean environment
rm -rf node_modules
npm ci  # Clean install (respect package-lock.json)

# Configure environment variables matching CI
cat > .env.ci << 'EOF'
NODE_ENV=test
CI=true
DISABLE_ESLINT_PLUGIN=false
EOF

Pre-Push Validation Workflow:

#!/bin/bash
# Script: validate-before-push.sh
# Purpose: Run CI validation locally before pushing

set -e

CURRENT_BRANCH=$(git branch --show-current)
CI_WORKTREE="$HOME/projects/application-ci"

echo "🔍 Running CI validation for: $CURRENT_BRANCH"

# Sync CI worktree with current branch
cd "$CI_WORKTREE"
git fetch origin
git switch "$CURRENT_BRANCH"

# Clean state (like CI does)
rm -rf node_modules dist
npm ci

# Run CI pipeline steps
echo "📦 Installing dependencies..."
npm ci

echo "🔨 Building..."
npm run build

echo "🧪 Testing..."
npm run test:ci

echo "📊 Coverage check..."
npm run test:coverage -- --coverageThreshold='{"global":{"branches":80,"functions":80,"lines":80}}'

echo "✅ CI validation passed. Safe to push."

Integration with Git Workflow:

# Install as pre-push hook
cd ~/projects/application
cat > .git/hooks/pre-push << 'EOF'
#!/bin/bash
# Optional: Prompt user before running full CI validation
read -p "Run full CI validation before push? (y/n) " -n 1 -r
echo
if [[ $REPLY =~ ^[Yy]$ ]]; then
    ~/projects/application/scripts/validate-before-push.sh
fi
EOF

chmod +x .git/hooks/pre-push

Benefits:

  • Early Failure Detection: Catch CI failures locally before pushing
  • Consistent Environment: CI worktree mirrors production CI exactly
  • No Network Dependency: Validation runs locally without CI queue delays

Pattern 5: Worktree-Based A/B Performance Testing

When evaluating performance implications of implementation changes, worktrees enable rigorous comparative analysis:

Scenario: Evaluating two different database query optimization strategies

# Baseline: Current implementation
cd ~/projects/application
git worktree add -b perf-baseline-$(date +%Y%m%d) ../app-perf-baseline

# Strategy A: Query result caching
git worktree add -b perf-cache-strategy ../app-perf-cache
cd ../app-perf-cache
# Implement caching strategy

# Strategy B: Database index optimization
git worktree add -b perf-index-strategy ../app-perf-index
cd ../app-perf-index
# Implement index optimization

Benchmark Harness (runs identically across all implementations):

#!/bin/bash
# benchmark-performance.sh

WORKTREE_PATH="$1"
RESULTS_FILE="perf-results-$(basename $WORKTREE_PATH).json"

cd "$WORKTREE_PATH"

# Ensure clean state
npm ci > /dev/null 2>&1

# Start application in background
npm start &
APP_PID=$!

# Wait for application readiness
sleep 10

# Run benchmark suite (using Apache Bench)
ab -n 10000 -c 100 -g "$RESULTS_FILE" http://localhost:3000/api/users/search?q=test

# Capture memory usage
ps -o rss= -p "$APP_PID" > "memory-${RESULTS_FILE}"

# Shutdown application
kill "$APP_PID"

# Parse results
echo "Results for $(basename $WORKTREE_PATH):"
jq '.mean_response_time, .requests_per_second' "$RESULTS_FILE"

Automated Comparative Analysis:

# Run benchmarks across all strategies
for worktree in app-perf-baseline app-perf-cache app-perf-index; do
    ./benchmark-performance.sh "../$worktree"
done

# Generate comparison report
python3 << 'EOF'
import json
import glob

results = {}
for file in glob.glob("perf-results-*.json"):
    with open(file) as f:
        data = json.load(f)
        strategy = file.replace("perf-results-app-perf-", "").replace(".json", "")
        results[strategy] = {
            "mean_response_ms": data["mean_response_time"],
            "req_per_sec": data["requests_per_second"]
        }

# Identify winner
winner = max(results.items(), key=lambda x: x[1]["req_per_sec"])
print(f"\n🏆 Winner: {winner[0]}")
print(f"   Response Time: {winner[1]['mean_response_ms']}ms")
print(f"   Throughput: {winner[1]['req_per_sec']} req/s")

# Print comparison table
print("\nComparative Results:")
for strategy, metrics in sorted(results.items(), key=lambda x: x[1]["req_per_sec"], reverse=True):
    print(f"  {strategy:20s} | {metrics['mean_response_ms']:6.2f}ms | {metrics['req_per_sec']:8.1f} req/s")
EOF

Expected Output:

🏆 Winner: cache-strategy
   Response Time: 45.23ms
   Throughput: 2234.5 req/s

Comparative Results:
  cache-strategy       |  45.23ms |   2234.5 req/s
  index-strategy       |  78.45ms |   1274.2 req/s
  baseline             | 123.67ms |    808.9 req/s

Post-Analysis: Merge winning strategy, discard alternatives

cd ~/projects/application
git merge --no-ff perf-cache-strategy
git worktree remove ../app-perf-baseline
git worktree remove ../app-perf-cache
git worktree remove ../app-perf-index

Edge Case 1: Handling Submodule State Across Worktrees

Technical Challenge: Git submodules complicate worktree workflows because submodule state is tracked in the working tree, not in Git’s object database.

Problem Manifestation:

# Main worktree: Update submodule
cd ~/projects/application
git submodule update --remote vendor/external-lib
git commit -am "chore: Update external-lib to v2.0"

# Feature worktree: Submodule still at old version
cd ~/projects/application-feature
ls -la vendor/external-lib  # Still contains v1.5 files
git submodule status  # Shows v1.5 commit

Root Cause: Each worktree maintains independent submodule checkouts. Submodule references in .gitmodules are shared, but checked-out content is per-worktree.

Solution Strategy 1: Automatic Submodule Synchronization

# Configure post-checkout hook in each worktree
cat > .git/hooks/post-checkout << 'EOF'
#!/bin/bash
# Automatically sync submodules after checkout

echo "Syncing submodules after checkout..."
git submodule update --init --recursive
EOF

chmod +x .git/hooks/post-checkout

Solution Strategy 2: Shared Submodule Worktrees

# Advanced: Use worktrees for submodules too
cd ~/projects/application/vendor/external-lib

# Convert submodule to use worktrees
git worktree add ../../../application-feature/vendor/external-lib

# Now submodule state is independent per worktree
# Each can checkout different submodule versions

Solution Strategy 3: Avoid Submodules (Recommended)

# Modern alternative: Use package manager instead
# Replace Git submodule with npm/yarn dependency

# In package.json:
{
  "dependencies": {
    "external-lib": "github:vendor/external-lib#v2.0.0"
  }
}

# Remove submodule
git submodule deinit vendor/external-lib
git rm vendor/external-lib
rm -rf .git/modules/vendor/external-lib

Edge Case 2: Worktree Locks and Recovery

Scenario: A worktree directory is accidentally deleted without using git worktree remove:

# Accidental deletion
cd ~/projects
rm -rf application-feature  # ❌ WRONG WAY

# Git still tracks the worktree
cd application
git worktree list
# Output still shows application-feature

Problem: Git’s worktree metadata is now stale, preventing reuse of the branch:

git switch feature-branch
# ERROR: fatal: 'feature-branch' is already checked out at '/path/to/application-feature'

Recovery Procedure:

# Step 1: Prune stale worktree references
git worktree prune -v
# Output: Removing worktrees/application-feature: gitdir file points to non-existent location

# Step 2: Verify branch is now available
git switch feature-branch  # ✅ Works now

# Step 3: If prune fails (rare), force unlock
git worktree list --porcelain | grep "locked"
# If locked, manually unlock:
rm .git/worktrees/application-feature/locked

# Step 4: Manual cleanup if automatic prune fails
rm -rf .git/worktrees/application-feature

Prevention: Automated Cleanup Script

#!/bin/bash
# cleanup-worktrees.sh
# Run weekly to detect and clean stale worktrees

cd "$(git rev-parse --show-toplevel)"

echo "Auditing worktrees..."
git worktree list --porcelain | awk '
  /^worktree / { path = $2 }
  /^HEAD / {
    if (system("[ -d " path " ]") != 0) {
      print "Stale worktree detected: " path
      stale[path] = 1
    }
  }
  END {
    if (length(stale) > 0) {
      print "\nPruning stale references..."
      system("git worktree prune -v")
    } else {
      print "No stale worktrees found."
    }
  }
'

Add to cron for automatic maintenance:

# Run every Sunday at 2 AM
0 2 * * 0 cd ~/projects/application && ./cleanup-worktrees.sh >> /var/log/git-worktree-cleanup.log 2>&1

Edge Case 3: Case-Sensitive Filesystem Issues

Problem: macOS (APFS) and Windows (NTFS) use case-insensitive filesystems by default, creating subtle bugs with worktree branch names:

# Create worktree on macOS
git worktree add -b feature-Authentication ../app-auth

# Later, another developer tries:
git worktree add -b feature-authentication ../app-auth-2
# ERROR: Branch feature-authentication already exists (but shows feature-Authentication)

Root Cause: Git stores branch names case-sensitively in .git/refs/heads/, but macOS/Windows filesystems treat feature-authentication and feature-Authentication as identical.

Solution 1: Enforce Lowercase Branch Naming

# Pre-commit hook enforcing lowercase branches
cat > .git/hooks/pre-commit << 'EOF'
#!/bin/bash

BRANCH=$(git branch --show-current)

if [[ "$BRANCH" =~ [A-Z] ]]; then
    echo "❌ ERROR: Branch name contains uppercase letters: $BRANCH"
    echo "   Branch names must be lowercase (e.g., ${BRANCH,,})"
    exit 1
fi
EOF

chmod +x .git/hooks/pre-commit

Solution 2: Use Branch Naming Prefixes

# Structure enforces uniqueness through prefixes
git worktree add -b user/alice/authentication ../auth-alice
git worktree add -b user/bob/authentication ../auth-bob
# No collision: Different prefixes create unique names

Edge Case 4: Worktree Branch Mutual Exclusion Bypass

Advanced Technique: Detached HEAD states allow “checking out” the same commit in multiple worktrees:

# Normal behavior: Branch mutual exclusion
cd ~/projects/application
git switch main

cd ~/projects/application-hotfix
git switch main  # ❌ ERROR: main already checked out

# Bypass using detached HEAD
cd ~/projects/application-hotfix
git switch --detach main  # ✅ Works: Both worktrees at main tip, neither "owns" the branch

Use Case: Read-only inspection of the same commit in multiple worktrees:

# Code review: Multiple reviewers inspect same commit simultaneously
git worktree add --detach ~/reviews/pr-123-alice v2.5.0
git worktree add --detach ~/reviews/pr-123-bob v2.5.0
# Both worktrees at v2.5.0, neither owns a branch

Warning: Commits made in detached HEAD state require manual branch creation:

cd ~/reviews/pr-123-alice
# Make changes, commit
git commit -am "Review comment implementation"

# Commit is orphaned (not on any branch)
git log --oneline -1
# abc123 (HEAD) Review comment implementation

# Create branch to save work
git switch -c review-comments-alice
# Now commit is on a named branch and won't be garbage collected

Edge Case 5: Sparse Checkout with Worktrees

Scenario: Large monorepos where full checkouts in every worktree consume excessive disk space.

Solution: Combine worktrees with sparse-checkout for selective file population:

# Setup sparse-checkout in a worktree
git worktree add -b docs-only ../app-docs
cd ../app-docs

# Initialize sparse-checkout
git sparse-checkout init --cone

# Only checkout documentation directories
git sparse-checkout set docs/ README.md CONTRIBUTING.md

# Verify: Only specified paths exist
ls -la  # Shows only docs/, README.md, CONTRIBUTING.md

Use Case: Specialized Worktrees

# Documentation worktree (docs only)
git worktree add -b docs-worktree ../app-docs
cd ../app-docs
git sparse-checkout set docs/

# Frontend worktree (frontend code only)
git worktree add -b frontend-worktree ../app-frontend
cd ../app-frontend
git sparse-checkout set frontend/ package.json

# Backend worktree (backend code only)
git worktree add -b backend-worktree ../app-backend
cd ../app-backend
git sparse-checkout set backend/ package.json

Benefits:

  • Reduced Disk Usage: Each worktree contains only relevant files
  • Faster Checkouts: Fewer files to process during branch switches
  • Cognitive Focus: Developers only see relevant code

Disk Usage Comparison:

# Without sparse-checkout
du -sh */
# 2.3G    app-docs
# 2.3G    app-frontend
# 2.3G    app-backend
# Total: 6.9G

# With sparse-checkout
du -sh */
# 45M     app-docs
# 680M    app-frontend
# 890M    app-backend
# Total: 1.6G (77% savings)

Advanced Troubleshooting: Corrupted Worktree Recovery

Scenario: Worktree enters corrupted state after system crash or improper termination.

Symptoms:

cd ~/projects/application-feature
git status
# fatal: unable to read tree <sha>
# fatal: index file corrupt

Recovery Procedure:

# Step 1: Backup current state (if possible)
cd ~/projects/application-feature
cp -r . ../application-feature-backup

# Step 2: Remove corrupted index
rm .git/index

# Step 3: Restore index from HEAD
git reset

# Step 4: Verify recovery
git status  # Should show untracked/modified files, but no errors

# Step 5: If step 2-3 fail, nuclear option: recreate worktree
cd ~/projects/application
BRANCH=$(cd ../application-feature && git branch --show-current)
git worktree remove --force ../application-feature
git worktree add -b "$BRANCH" ../application-feature

# Step 6: Restore uncommitted work from backup
cp -r ../application-feature-backup/* ../application-feature/
cd ../application-feature
git status  # Review and commit changes

Summary: Mastering Advanced Worktree Patterns

These advanced patterns demonstrate Git worktrees’ versatility beyond simple parallel development:

Key Takeaways:

  1. Nested Hierarchies: Organize worktrees logically for large-scale projects
  2. Forensic Analysis: Use temporary worktrees for historical code investigation
  3. Hook Isolation: Implement context-specific validation rules per worktree
  4. Local CI: Worktrees can serve as pre-push validation environments
  5. A/B Testing: Rigorous comparative performance analysis across implementations
  6. Edge Cases: Understanding submodule state, locks, filesystem quirks, and corruption recovery prevents production disruptions

When to Apply Advanced Patterns:

  • ✅ Large teams with complex branching strategies
  • ✅ Monorepos requiring selective file access
  • ✅ Performance-critical applications needing empirical optimization validation
  • ✅ Projects with sophisticated CI/CD requirements

When to Avoid:

  • ❌ Small projects where complexity exceeds benefit
  • ❌ Teams unfamiliar with fundamental Git concepts
  • ❌ Scenarios where Docker/VMs provide better isolation

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