[Bug] Shell-permission classifier kills the CLI: unhandled shell-quote "Bad substitution" error (1.84.0) #1043

Summary

A shell command that contains a bash parameter expansion (${var%%pattern} / ${var##pattern}) makes the CLI process die. The throw happens inside the shell-permission classifier:

ShellPermissionPrompt → getShellPermissionChoices → shellPermissionRulesForCommand → classifyShellCommand → classify → shell-quote parse → parseEnvVar

Nothing catches it, so it surfaces as CRITICAL: Unhandled Promise Rejection! and the TUI closes. Work is not lost (writes completed before the crash stay on disk), but the session ends and the error is not user-actionable. Observed at least twice on 2026-10-18.

Expected Behavior

A command the classifier cannot parse should degrade gracefully (e.g. "cannot classify → ask the user"), never terminate the process. A permission decision is best-effort; it must not be able to kill the session.

Actual Behavior

⚠ Error
ERROR  Bad substitution: pair%%

/home/furkan/.nvm/versions/node/v22.23.2/lib/node_modules/command-code/node_modules/shell-quote/parse.js:219:12

216:           varend += 1;
217:         }
218:         if (depth !== 0) {
219:           throw new Error('Bad substitution: ' + s.slice(i));
220:         }
221:         varend -= 1;
222:         varname = s.slice(i, varend);

 - parseEnvVar (.../shell-quote/parse.js:219:12)
 -  (.../shell-quote/parse.js:308:17)
 -     at Array.map (<anonymous>)
 - parseInternal (.../shell-quote/parse.js:161:17)
 - parse (.../shell-quote/parse.js:361:15)
 - classify (file:///.../command-code/dist/cli.mjs:2:484175)
 - classifyShellCommand (file:///.../command-code/dist/cli.mjs:2:485322)
 - shellPermissionRulesForCommand (file:///.../command-code/dist/cli.mjs:2:1271876)
 - getShellPermissionChoices (file:///.../command-code/dist/cli.mjs:2:1280072)
 - ShellPermissionPrompt (file:///.../command-code/dist/cli.mjs:16:29683)

✖ CRITICAL: Unhandled Promise Rejection!
This is an unexpected error. Please file a bug report at https://github.com/CommandCodeAI/command-code/issues/new
✖ ERROR → Error
ℹ REASON → Bad substitution: pair%%

The CLI then exits.

Steps to reproduce the issue

1. shell-quote@1.12.0 (which is the latest published version, 2026-10-02) throws on an expansion it considers unterminated — the message matches the crash exactly, because parseEnvVar does s.slice(i) starting right after the {, and the throw is the depth !== 0 branch (scan hit end of string without a matching }):

   require('shell-quote').parse('echo ${pair%%')
   // Error: Bad substitution: pair%%

   (also reproducible with ${pair## → Bad substitution: pair##, and echo ${} → Bad substitution: ${})

2. In a session, run a command containing ${var%%pattern} / ${var##pattern}. The crashing one was a 1170-char loop:

   cd … && A="…(3)/…" && B="…(4)/…" && for pair in "a:b" "c:d"; do a="${pair%%:*}"; b="${pair##*:}"; echo "=== $a vs $b"; for ext in screen.png code.html; do ha=$(md5sum "$A/$a/$ext" 2>/dev/null|cut -c1-8); … done; done

   Result: the CLI exits while the permission decision for that command is being computed.

3. Note for whoever picks this up: the full command above parses fine with shell-quote in isolation (parse(cmd) → 104 tokens, no throw). So the string handed to parse() inside the classifier is not the raw command — it is truncated mid-expansion (that is precisely what the message shows: s.slice(i) = pair%%…). Finding that split/truncation in classifyShellCommand / shellPermissionRulesForCommand is the actual bug; the crash itself is the missing try/catch.

Command Code Version

1.84.0

Operating System

Linux

• WSL2 (Ubuntu), kernel 6.18.54.1-microsoft-standard-WSL2
• node v22.23.2

Terminal/IDE

WSL2 terminal

Shell

bash (/bin/bash; note /bin/sh on this box is dash)

Fix prompt (optional)

In dist/cli.mjs, shellPermissionRulesForCommand / classifyShellCommand call shell-quote's parse() on a command string to derive permission rules. parse() may throw (parseEnvVar throws Bad substitution: … for ${} and for any expansion whose closing } it cannot find), and the error escapes as an unhandled promise rejection that terminates the process. Wrap the parse call in try/catch: on failure, treat the command as unclassified and fall back to asking the user (never exit). Check first how the command string is produced before parse() — the raw command parses fine, so something splits/truncates it mid-expansion; that splitter should not cut inside ${…}. Add a regression test that feeds echo ${pair%% and a command containing ${var%%pattern} / ${var##pattern} and asserts the classifier returns a "ask" decision instead of throwing.

Additional context

• Trace ID: 74f29026d9a6a223179c5175a166a0de
• Sessions involved (can be exported with /export jsonl and shared privately if useful): the crashing one and the one where the error was pasted back — both in the same project; happy to provide on request.
• shell-quote is already at the latest published version, so this is not a stale-dependency issue: parse() is documented to throw on input it cannot parse, and the caller must handle it.
• Impact assessment: no data loss (completed writes persisted), but an irrecoverable session kill that the user cannot act on. The same command family is common in everyday work (parsing key:value pairs in shell loops), so this is likely to be hit again.