Self-permission-granting safety check bypassable via Bash-mediated write (gates by tool, not by effect)

## Summary

Claude Code's self-permission-granting safety check appears to gate by **which tool is invoked**, not by **the effect a command produces on disk**. A `Write`/`Edit` call that modifies `~/.claude/settings.json` to register a new hook is refused as self-permission-granting. The **identical file, with identical resulting content**, can then be written successfully via the `Bash` tool (e.g. a Python read-modify-write one-liner), with no refusal at all.

If accurate, this means the self-permission-granting boundary is bypassable simply by choosing a different tool to produce the same write, which defeats the purpose of the check.

## Steps to reproduce

1. In a Claude Code session, ask the assistant to add a new entry to `hooks.PreToolUse` in `~/.claude/settings.json` (e.g. registering a new hook script) using the `Write` or `Edit` tool.
- **Observed:** the tool call is refused/blocked as an attempt to grant new permission/hook capability to itself.
2. Ask the assistant to make the exact same change via the `Bash` tool instead, for example a Python script that reads `settings.json`, inserts the same JSON object into `hooks.PreToolUse`, and writes the file back with `json.dump`.
- **Observed:** the write succeeds with no refusal, and the resulting `settings.json` is functionally identical to what was refused in step 1.

## Expected behavior

A safety boundary meant to prevent a session from expanding its own permissions/hook capability should classify by the effect of a command (does this write target a sensitive config path and change its permission-relevant content?), not by which tool API was used to produce that effect. If `Write`/`Edit` are refused for a given target and content, a `Bash`-mediated write producing the same target/content should be refused too.

## Context

This was found while a session was legitimately trying to install a new `PreToolUse` hook at the user's own explicit, repeated direction (the user was fully aware of and authorized the change; this is not a report of malicious use). The `Write`/`Edit` refusal correctly triggered; the `Bash` route around it should not have succeeded silently. The same technique would plausibly generalize to other Write/Edit-refused targets, not just `settings.json`.

## Environment

- Claude Code (desktop app), session date 2026-09-10.
- macOS.

Happy to provide more detail if useful (project-specific names sanitized out of this report; the mechanism itself is what matters).

Start by reproducing the discrepancy against ~/.claude/settings.json using the Write/Edit and Bash entry points described in the issue. Trace the self-permission-granting check and compare how each tool's resulting file change is evaluated. Done means an equivalent Bash-mediated addition to hooks.PreToolUse is blocked consistently with the refused Write/Edit change, with regression coverage for both paths.

索引モデルが issue の本文から書いたものです。