Tab completion for slash command arguments (file paths)

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

When typing slash command arguments like /swagger-doc src/controllers/..., pressing Tab does not trigger file path completion. Shell-level tab
completion would be helpful here with zero token cost impact.

Proposed Solution

Integrate file path tab completion into the Claude Code CLI input handler for slash command arguments. When a user types a slash command followed by a
partial file path and presses Tab, the CLI should enumerate matching files/directories (similar to standard shell completion) and suggest completions
inline — without sending anything to the model, keeping token usage unaffected.

Example:
/swagger-doc src/co<TAB> → shows src/controllers/
/swagger-doc src/controllers/api<TAB> → shows src/controllers/apikey/apikey.controller.ts

Alternative Solutions

_No response_

Priority

High - Significant impact on productivity

Feature Category

CLI commands and flags

Use Case Example

▎ /swagger-doc src/co<TAB>
▎ → src/controllers/
▎
▎ /swagger-doc src/controllers/api<TAB>
▎ → src/controllers/apikey/
▎
▎ /swagger-doc src/controllers/apikey/api<TAB>
▎ → src/controllers/apikey/apikey.controller.ts
▎
▎ /swagger-doc src/controllers/apikey/apikey.controller.ts GET /api<TAB>
▎ → /apikey
▎ → /apikey/{id}
▎
▎ /review src/services/or<TAB>
▎ → src/services/org-utility.service.ts

Additional Context

_No response_