System prompt attribution (Co-Authored-By) overrides user CLAUDE.md rules

Problem

The Claude Code system prompt injects a Co-Authored-By: Claude ... line into git commit messages. This behavior silently overrides explicit user rules set in CLAUDE.md.

User rule (CLAUDE.md)

No `Co-Authored-By` in commit messages.

This is listed under Non-Negotiable Behavior Rules in the user's global ~/.claude/CLAUDE.md.

What happens

Despite the rule being explicitly set, Claude follows the system prompt attribution reminder and appends Co-Authored-By to every commit. The rule in CLAUDE.md is ignored.

Why it matters

• CLAUDE.md is the user's primary configuration mechanism. If system prompt injections silently win over it, the whole config system is unreliable.
• Memory files don't fix it — the system prompt is re-injected every session.
• The user has no reliable way to prevent this behavior short of a git hook workaround.

Expected behavior

User rules in CLAUDE.md should take precedence over system prompt behavioral suggestions like attribution lines. At minimum, conflicts should be surfaced rather than silently resolved in favor of the system prompt.