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12 AI Instances, Zero File Conflicts: How Git Worktrees Make It Work

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12 AI Instances, Zero File Conflicts: How Git Worktrees Make It Work

10 Claude Code instances + 2 Codex instances running simultaneously. Here's the isolation system that keeps them from colliding.

The Problem: Multiple AIs Touching One Repo 

Instance A: editing lib/pages/landing_page.dart
Instance B: editing the same file differently → merge conflict
Instance C: git pull on main → picks up A's WIP → deploys broken state
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Branch strategy alone doesn't fix this. Multiple AIs working on the same main branch collide constantly.

The Solution: Physical Isolation with git worktree 

# Create a dedicated worktree per instance
git worktree add .claude/worktrees/instance-ps1 -b claude/ps1-wip
git worktree add .claude/worktrees/instance-ps2 -b claude/ps2-wip
git worktree add .claude/worktrees/instance-vscode -b claude/vscode-wip
# ... 12 instances total
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Result:

  • instance-ps1/ has its own working files
  • instance-ps2/ has its own working files
  • Same file, different worktrees = no conflict

How worktrees Work 

my_web_app/                    # main repo (integration/review only)
  .claude/
    worktrees/
      instance-ps1/            # PS#1 workspace
        lib/ → real files
        branch: claude/ps1-wip
      instance-ps2/            # PS#2 workspace
        lib/ → real files
        branch: claude/ps2-wip
      instance-vscode/         # VSCode workspace
        lib/ → real files
        branch: claude/vscode-wip
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Each worktree has an independent branch. git add/commit is fully contained per worktree.

Session Start Protocol 

# Every instance runs this at session start
cd C:/Users/kanta/GitHub/my_web_app/.claude/worktrees/instance-ps2

# Pull latest main
git pull --rebase origin main

# Check assigned tasks, then start working
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git stash is banned. In multi-worktree environments, stashes are worktree-local. If another instance enters the same worktree, the stash is gone. Use WIP commits instead (git commit -m "WIP").

Push Flow 

# After completing work
git add <files>
git commit -m "feat: ..."

# Rebase before push
git pull --rebase origin main
git push origin HEAD:main
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git push origin HEAD:main is critical. Plain git push sends to claude/ps2-wip, not main.

When Conflicts Still Happen

The only case: two instances edit the same file on the same day and both try to push:

# PS#4 pushes landing_page.dart
# PS#5 also modified it, tries to push
→ rebase conflict

# Fix: always pull --rebase before push
git pull --rebase origin main
# → resolve conflict manually
git add <resolved-file>
git rebase --continue
git push origin HEAD:main
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In three months across 12 instances, this happened 1–2 times per month. Pre-assigned file ownership minimizes it.

Instance File Ownership

Instance Assigned Files
VSCode lib/pages/ — UI components
PS#1 .github/workflows/ — workflow health
PS#2 docs/blog-drafts/ — T-1 content
PS#3 supabase/migrations/*_seed_ai_university*
PS#4 lib/pages/comparison_page.dart, web/sitemap.xml
PS#5 Auth guards across lib/pages/, supabase/functions/
PS#6 supabase/functions/schedule-hub/ — horse racing AI
Win docs/, supabase/migrations/ schema changes

When ownership overlaps: the second pusher always pulls --rebase first.

Codex Integration

Codex CLI uses the same worktree pattern:

.claude/worktrees/instance-codex1/  (branch: codex/codex1-wip)
.claude/worktrees/instance-codex2/  (branch: codex/codex2-wip)
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Claude Code creates cross-instance PRs → Codex implements in its worktree → PR → merge.

Three Months of Lessons

What worked:

  • File-level conflicts near-zero
  • Each instance commits independently → git log is readable
  • git log --oneline shows which instance did what at a glance

What failed:

  • Ephemeral worktrees (auto-generated names) → pruned by PS#6 cleanup → lost work → standardized to instance-* fixed names
  • Migration timestamp collisions on the same day → solved with 500-unit offset rule

Summary

The isolation system that makes 12 parallel instances work:

  1. git worktree — physical workspace separation
  2. Pre-assigned file ownership — minimize overlap probability
  3. pull --rebase → push — consistent merge flow
  4. No stash, WIP commits only — stash-safe rule

The same tools that human teams use for collaboration (git worktree, branch strategy, file ownership) work for AI teams. The main difference: AI instances follow rules more consistently than humans do.

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