[BUG] Sonnet 4.6 agent misspells .claude as .claire in file path, creating stray directory

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

A Sonnet 4.6 subagent running in an isolated worktree (via isolation: worktree) misspelled .claude as .claire when constructing a file path for a Write tool call. This created a stray .claire/ directory tree in the main repository root.

The agent was writing files to .claude/worktrees/agent-XXXX/src/api/ — a series of batch writes in the same model response. The first Write used the correct path, but the second drifted from .claude to .claire:

Correct (first write in the batch):

.claude/worktrees/agent-XXXX/src/api/comments.ts ✅

Incorrect (second write, same model response):

.claire/worktrees/agent-XXXX/src/api/notifications.ts ❌

The model self-corrected on the next turn:

{
  "type": "text",
  "text": "I wrote notifications.ts to the wrong path (`.claire` instead of `.claude`). Let me fix that and also write the service files."
}

It then re-wrote the file to the correct .claude/worktrees/... path, but never cleaned up the .claire/ directory it accidentally created.

Relevant log excerpts

The incorrect Write tool call (abbreviated):

{
  "role": "assistant",
  "content": [{
    "type": "tool_use",
    "id": "toolu_013Kdaf3VaBMUmkzTxyayaPU",
    "name": "Write",
    "input": {
      "file_path": "/path/to/repo/.claire/worktrees/agent-XXXX/src/api/notifications.ts",
      "content": "..."
    }
  }]
}

The tool result confirming the stray file was created:

{
  "type": "tool_result",
  "content": "File created successfully at: /path/to/repo/.claire/worktrees/agent-XXXX/src/api/notifications.ts"
}

The model's self-correction on the next turn:

{
  "role": "assistant",
  "content": [
    {
      "type": "text",
      "text": "I wrote notifications.ts to the wrong path (`.claire` instead of `.claude`). Let me fix that and also write the service files."
    },
    {
      "type": "tool_use",
      "name": "Write",
      "input": {
        "file_path": "/path/to/repo/.claude/worktrees/agent-XXXX/src/api/notifications.ts",
        "content": "..."
      }
    }
  ]
}

Impact

• A .claire/worktrees/agent-XXXX/src/api/ directory tree was created in the main repo root (outside the worktree)
• The stray directory was never cleaned up despite the model self-correcting
• The guard-files.sh PreToolUse hook only checks for sensitive files — it doesn't validate that the path is within the worktree boundary, so the write was not blocked

Related issues

This is the same class of bug as:

• #10580 — Sonnet misspells /home/tbekolay as /home/tbekolag
• #25402 — Opus misspells rcorre as rconte
• #17893 — Username jdpruett corrupted to jdprueet

The difference here is that the misspelling hit a directory name (.claude → .claire) rather than a username, and because the Write tool creates intermediate directories, it silently produced a stray directory tree instead of failing with a "not found" error.

What Should Happen?

1. The model should not misspell well-known path components like .claude
2. When running in a worktree, writes outside the worktree root could be blocked or warned about at the tool level (not just via user hooks)
3. When the model self-corrects a wrong-path write, it should clean up the stray file/directory

Steps to Reproduce

Not reliably reproducible — this is a stochastic model generation error. It occurred during a batch of Write tool calls in a single model response where the agent was constructing long absolute paths from memory.

Claude Model

Sonnet 4.6 (claude-sonnet-4-6)

Claude Code Version

2.1.70

Platform

macOS (Darwin 25.3.0)