[Bug]: $ARGUMENTS placeholder not substituted in Kiro CLI — file-based prompts don't support arguments #1926

Summary

$ARGUMENTS is never substituted when SpecKit prompts are invoked via the Kiro CLI (kiro-cli chat). The literal string $ARGUMENTS is passed to the AI model, causing the agent to either error out or prompt the user to re-enter their input.

Environment

• AI Tool: Kiro CLI (kiro-cli chat)
• SpecKit version: latest (github/spec-kit)
• OS: macOS

Steps to Reproduce

1. Install SpecKit into a project (.specify/ directory present)
2. Open kiro-cli chat in the project root
3. Invoke /speckit.specify Add employee onboarding flow
4. Observe the prompt fires but $ARGUMENTS is passed literally to the model

Expected Behaviour

The text typed after /speckit.specify (i.e. Add employee onboarding flow) should be substituted for $ARGUMENTS in the prompt body before the model receives it.

Actual Behaviour

The model receives the literal string $ARGUMENTS and responds:

The $ARGUMENTS placeholder wasn't replaced — no feature description was provided.

Root Cause

Kiro CLI's file-based prompt system does not support argument substitution. Per the official Kiro documentation:

"File-based prompts (local and global) do not support arguments."

Arguments are only supported for MCP server prompts (@server-name/prompt-name <arg>). Local prompts stored in .kiro/prompts/ (or .specify/ via symlink/copy) receive no argument injection mechanism.

Impact

All SpecKit commands that rely on $ARGUMENTS substitution are broken on Kiro CLI:

• /speckit.specify
• Any other command that uses $ARGUMENTS in its prompt body

Suggested Fix

One or more of the following:

1. Document the limitation — add a note to the SpecKit README / agent compatibility matrix that Kiro CLI does not support $ARGUMENTS in file-based prompts.
2. Workaround guidance — instruct Kiro users to type their feature description as a follow-up message immediately after invoking the prompt (the prompt instructions already hint at this: "Assume you always have it available in this conversation even if $ARGUMENTS appears literally"), but this is not obvious to users.
3. MCP server prompt — expose SpecKit commands as MCP prompts, which Kiro does support with arguments (@speckit/specify "Add employee onboarding").
4. Prompt self-detection — add a preamble to affected prompts that detects the literal $ARGUMENTS string and instructs the model to ask the user for input gracefully rather than erroring.

References

• Kiro CLI — Manage Prompts