[BUG] Write/Edit tools silently accept relative paths despite spec requiring absolute — confused Claude can trample files

Bug description

The Write and Edit tool descriptions state file_path must be absolute:

The file_path parameter must be an absolute path, not a relative path

However, both tools silently accept and resolve relative paths. This is a safety issue, not just a UX bug:

1. If Claude passes a relative path, it is not following the tool spec, which usually means Claude is confused about which file it is targeting
2. Silently resolving the path masks the confusion — Claude thinks it succeeded at writing what it intended
3. A confused Claude writing to an unexpected resolved path can trample files

Steps to reproduce

1. Have Claude use Write with file_path="scratch/test.txt" (relative)
2. File is created successfully — no error, no warning
3. Claude does not realize it violated the tool spec

Expected behavior

The tool should reject relative paths with a clear error: "file_path must be absolute (got relative path: scratch/test.txt)". This forces Claude to clarify which file it actually means, catching confusion early.

Security impact

Relative path acceptance means Claude can write files based on whatever cwd happens to be, which varies by context (worktrees, subagents, plan-mode transitions). An absolute path requirement ensures Claude is explicit about where it is writing, making writes auditable and predictable.

Related

• #29841 — Write tool shows error but still writes with relative paths (same root cause, different symptom)

Environment

• Claude Code v2.1.x on Linux (WSL2)
• Discovered via PreToolUse hook that inspects file_path for permission decisions