Commit `Claude-Session:` attribution trailer ignores `attribution: {commit: ""}` setting

Summary

With commit attribution disabled via settings (attribution: { "commit": "", "pr": "" }), Claude Code still appends a Claude-Session: https://claude.ai/code/session_<id> trailer to git commit messages. The trailer is injected into the model's Bash tool description (a # Git section instructing the model to "End git commit messages with: Claude-Session: <url>"), and it does not honor the local attribution config.

The legacy Co-Authored-By / "Generated with Claude Code" footer is correctly suppressed by the setting — only this newer Claude-Session: header ignores it.

Environment

• Claude Code: 2.1.210
• OS: macOS 15.6.1 (24G90)

Steps to reproduce

1. In ~/.claude/settings.json, disable attribution:

``json
"attribution": { "commit": "", "pr": "" }
``

1. Have Claude Code (or a subagent) create a git commit.
2. Inspect the commit message.

Expected

With attribution.commit set to empty, no attribution trailer is added to commit messages (no Co-Authored-By, and no Claude-Session:).

Actual

The commit message ends with:

Claude-Session: https://claude.ai/code/session_<session-id>

and PR bodies get the same URL appended. Confirmed across both the main session and spawned subagents (each subagent's Bash tool carries the same directive).

Root cause (as far as I can tell)

No local settings layer enables attribution — all are empty/absent:

| Layer | attribution |
|---|---|
| ~/.claude/settings.json (user) | {"commit":"","pr":""} |
| project .claude/settings.json | absent |
| project .claude/settings.local.json | absent |
| ~/.claude.json | null |

However ~/.claude.json shows a cached server-side gate:

cachedStatsigGates.tengu_ant_attribution_header_new = true

This "new attribution header" feature appears to be what injects the Claude-Session: trailer into the Bash-tool git guidance, and it bypasses the user's attribution setting.

Impact

Users who deliberately disable commit attribution (clean history, org policy, contributing to upstream repos where Claude attribution is unwanted) get Claude attribution on commits anyway, and must strip it manually after every commit. The attribution setting reads as honored (no Co-Authored-By) but silently isn't for the new header.

Request

Have the tengu_ant_attribution_header_new attribution-header feature respect the local attribution: { "commit": "", "pr": "" } configuration (and/or provide a documented way to disable the Claude-Session: trailer).