[BUG] Bash permission walker: "Unhandled node type" forces prompts on pipes/semicolons nested inside $(...) command substitution

### Preflight Checklist

- [x] I have searched [existing issues](https://github.com/anthropics/claude-code/issues?q=is%3Aissue%20state%3Aopen%20label%3Abug) and this hasn't been reported yet
- [x] This is a single bug report (please file separate reports for different bugs)
- [x] I am using the latest version of Claude Code

### What's Wrong?

The Bash permission walker's tree-sitter AST dispatcher fails to handle control-operator nodes (`;` / "list", `|` / "pipeline") when they occur
nested inside a `$(...)` command substitution, even though the same operators are handled fine at the top level of a command. This forces an
unnecessary manual approval prompt on a command whose every component is individually allow-listed — and in the semicolon case, leaks the walker's
internal fallback error string ("Unhandled node type: ;") directly into the permission prompt shown to the user.

This looks like a third variant of the same underlying gap already reported in #55170 (parenthesized subshell form `(cmd1; cmd2)`) and #47752 /
#56019 (heredoc+pipe combinations) — all three were closed as not_planned/duplicate by the stale-issue bot without an actual fix. Filing this to
document the `$(...)` substitution case specifically and flag that the underlying architectural issue is still open.

### What Should Happen?

When every individual command inside a `$(...)` command substitution is already allow-listed (e.g. `cat`, `wc`, `echo`), a compound form of those
commands joined by `;` or `|` inside the substitution should be auto-approved the same way it already is at the top level of a command — with no
prompt, and no raw internal error text ever shown to the user.

### Error Messages/Logs

```shell
Unhandled node type: ;
```

### Steps to Reproduce

With `cat`, `wc`, `echo`, `pwd` all individually allow-listed / auto-allowed (all are on the built-in read-only allowlist):

1. Run: echo "x: $(pwd)"
→ Clean, no prompt. Single simple command inside $(...).

2. Run: echo "x: $(cat file.txt 2>/dev/null)"
→ Clean, no prompt. Single command + redirect inside $(...).

3. Run: echo "x: $(cat file.txt | wc -l)"
→ PROMPTS. Pipe nested inside $(...).

4. Run: echo "x: $(echo a; echo b)"
→ PROMPTS, and shows the literal internal error "Unhandled node type: ;" as the reason for the prompt.

Every inner command (cat, wc, echo) is independently auto-allowed. Top-level use of `;` and `|` outside any substitution is also handled correctly
and does not prompt. The failure is specific to a control-operator node appearing inside a $(...) subtree.

Suggested fix: either (1) extend the AST walker to recurse into $(...) (and backtick) command-substitution bodies the same way it already handles
top-level list/pipeline nodes, or (2) as a stopgap, catch the "unhandled node type" fallback case and present a generic "this command needs
approval" prompt instead of leaking the raw internal error string.

Related issues (same underlying gap, different syntactic forms, all closed by stale-bot without a maintainer fix):
- #55170 — (cmd1; cmd2) subshell form → Unhandled node type: ; (closed, not_planned)
- #47752 / #56019 — heredoc+pipe combinations → Unhandled node type: pipeline (closed, duplicate)
- #47701 / #47706 — redirects → Unhandled node type: file_redirect (closed)
- #46868 — feature request: auto-allow compound commands when every component is individually allowed (closed)

### Claude Model

Sonnet (default)

### Is this a regression?

I don't know

### Last Working Version

_No response_

### Claude Code Version

2.1.126

### Platform

Anthropic API

### Operating System

Ubuntu/Debian Linux

### Terminal/Shell

WSL (Windows Subsystem for Linux)

### Additional Information

_No response_

Start by locating the Bash permission walker's tree-sitter AST dispatcher and reproduce the listed pipe and semicolon commands inside $(...). Trace how top-level list and pipeline nodes are handled versus command-substitution bodies. Done means allow-listed inner commands no longer prompt, and no raw "Unhandled node type" text appears in the prompt.

Written by the indexing model from the issue text.