Fix reflect skill: remove $() substitution that fails permission checks

The !`command` blocks in SKILL.md go through Claude Code's Bash permission
checker, which rejects $() command substitution. Simplified the git log
command, replaced dynamic verify script path with a Read tool instruction,
and narrowed allowed-tools to specific command patterns. Also documented
the constraints in CLAUDE.md for future skill development.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -32,3 +32,13 @@ custom-claude-skills/
 - **Restrict tools** with `allowed-tools` to the minimum needed — this reduces permission prompts
 - **Use $ARGUMENTS** for user input, `$0`, `$1` etc. for positional args
 - Dynamic commands in `!`command`` run at skill load time, not during Claude's execution
+
+## `!`command`` Gotchas
+
+The `!`command`` syntax in SKILL.md runs shell commands at skill load time to pre-gather context. These commands go through Claude Code's Bash permission checker against the `allowed-tools` patterns. Key constraints:
+
+- **No `$()` command substitution** — the permission checker rejects commands containing `$()` even if the outer command matches an allowed pattern. This means you cannot nest subshells (e.g., `git log --since="$(git log ...)"` will fail).
+- **No complex shell pipelines relying on subshells** — keep `!`command`` commands simple and self-contained. If you need complex logic, have the skill instructions tell Claude to run it via tool calls instead.
+- **`allowed-tools` patterns must match the command binary** — `Bash(git *)` allows any `git` subcommand, but `Bash(cat *)`, `Bash(sed *)`, `Bash(ls *)` must be listed separately if those commands appear in `!`command`` blocks.
+- **Prefer specific tool patterns over broad ones** — `Bash(git log *)`, `Bash(git diff *)` is safer than `Bash(git *)` to avoid accidentally allowing destructive git commands (e.g., `git reset`, `git push --force`).
+- **Fallback to tool instructions for dynamic paths** — if a command needs `$ARGUMENTS` to compute a file path (e.g., `cat scripts/verify-m${N}.sh`), replace the `!`command`` with a plain-text instruction telling Claude to use the Read tool. This avoids `$()` substitution and is more reliable.