$0 / $ARGUMENTS template variables not substituted in skills with context: fork

Version

Claude Code 2.1.110, macOS

Description

When a skill uses context: fork (with or without an agent field), the template variables $0, $ARGUMENTS, etc. are substituted with empty strings instead of the actual arguments passed by the user. The same $0 syntax works correctly in skills using disable-model-invocation: true.

Reproduction

1. Create a skill with the following SKILL.md:

---
name: test-fork-args
description: "Test argument passing in forked context"
argument-hint: <subcommand>
context: fork
---

# Test

Received subcommand: `$0`
All arguments: `$ARGUMENTS`

1. Invoke: /test-fork-args hello

1. The forked agent receives:

Received subcommand: ``
All arguments: ``

Expected

$0 = hello, $ARGUMENTS = hello

Actual

Both $0 and $ARGUMENTS are empty strings. The forked agent has no access to the user's arguments.

Workaround

Skills using disable-model-invocation: true (inline mode) substitute $0 correctly. Removing context: fork resolves the issue but loses the isolated subagent behavior.

Notes

• Tested with both agent: general-purpose and agent: helper — same result.
• The argument-hint frontmatter field is present and correctly defined.
• Multiple skills in the same project using disable-model-invocation: true with $0 work as expected, confirming the syntax is correct.