[BUG] Worktree isolation spams duplicate custom-title entries, causing title 'sticking' across sessions

Summary

When using isolation: "worktree" with the Agent tool, Claude Code writes duplicate custom-title entries to the session JSONL file on every action. This causes:

1. Session file bloat (100+ duplicate entries)
2. Title "sticking" — the same title appears for multiple unrelated sessions in /resume picker

Environment

• Claude Code version: 2.1.143
• OS: Windows 10 Pro
• Shell: Git Bash

Steps to Reproduce

1. Start a new session
2. Use Agent tool with isolation: "worktree"
3. Let the agent perform multiple actions
4. Check the session JSONL file for custom-title entries

Expected Behavior

• custom-title should be written once (or deduplicated)
• Each session should have its own unique title based on content

Actual Behavior

• custom-title with (Branch) suffix is written on every action (up to 117 times in one session)
• The title "sticks" and appears for multiple different sessions in /resume picker
• New sessions inherit the previous worktree session's title

Evidence

# Count duplicate custom-title entries per session
for f in ~/.claude/projects/PROJECT/*.jsonl; do
  count=$(grep -c '"custom-title"' "$f" 2>/dev/null)
  if [ "$count" -gt 5 ]; then
    echo "$count duplicates in $(basename $f)"
  fi
done

# Output:
# 117 duplicates in 09b4aeea-....jsonl
# 44 duplicates in c53abaa8-....jsonl
# 42 duplicates in 77e2bf9f-....jsonl
# ... (10+ files affected)

Screenshot

Multiple sessions showing the same title in /resume picker:

> попробуй найди агентом репозиторий... (Branch)
  10 minutes ago · master · 1.2MB

  попробуй найди агентом репозиторий... (Branch)
  55 minutes ago · master · 261.2KB

  попробуй найди агентом репозиторий... (Branch)  
  3 hours ago · master · 1.4MB

Workaround

Manually clean duplicate custom-title entries:

# Keep only last custom-title entry in each file
for f in ~/.claude/projects/PROJECT/*.jsonl; do
  last=$(grep '"custom-title"' "$f" | tail -1)
  grep -v '"custom-title"' "$f" > "$f.tmp"
  [ -n "$last" ] && echo "$last" >> "$f.tmp"
  mv "$f.tmp" "$f"
done

Related Issues

• #32150 - Session titles revert to last-prompt text
• #53338 - Session auto-titler reverts manual rename
• #36379 - AI-generated titles override custom-title entries

Suggested Fix

1. Deduplicate custom-title writes — check if title already exists before writing
2. Don't propagate worktree session title to parent/sibling sessions
3. Clear title cache when starting a new session