EnterWorktree corrupts git index with marketplace repo entries (GIT_INDEX_FILE leak)

Description

Team session worktrees created via EnterWorktree have their git index overwritten with entries from the claude-plugins-official marketplace repo (~/.claude/plugins/marketplaces/claude-plugins-official/). The worktree index references blobs that don't exist in the project's object store, making git commit, git diff, and pre-commit hooks fail with fatal: unable to read <sha>.

This is the same root cause as #38181 (GIT_INDEX_FILE leaking into marketplace git operations), but triggered by team session worktree creation rather than git hooks.

Reproduction

1. Start a claude-team session that creates worktrees via EnterWorktree
2. Two worktrees are created in .worktrees/ (e.g., picard-XXXX, q-XXXX)
3. Attempt git commit or git status in either worktree

Expected: Normal git operations against the project's files.
Actual: Index contains marketplace plugin files. Pre-commit hooks fail with:

error: invalid object 100644 01c5c1ce... for '.claude-plugin/marketplace.json'
fatal: unable to read d9c5ddb...

Evidence

The corrupted worktree index contains marketplace files instead of project files:

$ GIT_DIR=.../.git/worktrees/q-73c12fc5-autouse-and-ci git ls-files | head -5
.claude-plugin/marketplace.json
.github/scripts/check-marketplace-sorted.ts
.github/scripts/validate-frontmatter.ts
.github/scripts/validate-marketplace.ts
.github/workflows/close-external-prs.yml

The marketplace repo's own .git/index is missing — its content was moved into the worktree indexes:

$ ls ~/.claude/plugins/marketplaces/claude-plugins-official/.git/index
ls: cannot access '.../.git/index': No such file or directory

$ git -C ~/.claude/plugins/marketplaces/claude-plugins-official status
Changes to be committed:
    deleted:    .claude-plugin/marketplace.json
    deleted:    .github/scripts/check-marketplace-sorted.ts
    [... all files shown as staged for deletion ...]

Key observations:

• Both team session worktrees (.worktrees/picard-*, .worktrees/q-*) are affected identically — created at the same second
• Agent worktrees (.claude/worktrees/agent-*) created via a different code path are not affected
• git fsck shows missing blobs (marketplace blob SHAs) and invalid cache-tree pointers in both corrupted worktree indexes
• Deleting the worktree index and running git reset HEAD recovers the worktree

Root cause

Same as #38181: GIT_INDEX_FILE (or equivalent git environment state) leaks from the worktree creation context into a subprocess that runs git commands against the marketplace directory. The marketplace git operations write their file entries into the project worktree's index instead of their own.

Workaround

Delete the corrupted index and rebuild:

rm -f .git/worktrees/<name>/index
git reset HEAD

Related issues

• #38181 — Same root cause, triggered by git hooks instead of EnterWorktree
• #32793 — Marketplace git ops corrupt project git remote URL (same isolation failure)
• #33045 — isolation: "worktree" has no effect for team agents

Environment

• Claude Code CLI (team session mode)
• Linux (Ubuntu 24.04)
• Git 2.43.0