fix(ui): Custom commands file path autocompletion

[dracic]

TLDR

Enables file path autocompletion for custom commands by implementing dual-mode completion that allows @ file suggestions to work with /custom-command @path/to/file syntax. Also fixes post-rebase 35% width constraint issue affecting file path suggestion display.

Key Changes:

• Dual-mode completion: Custom commands (.toml files) now support both slash command completion and @ file path completion
• Width constraint fix: File path completions use full width instead of being constrained to 35% like slash commands
• Performance optimizations: O(1) command lookups with memoized Map, regex-based parsing
• Comprehensive testing: 23 tests including edge cases

Dive Deeper

This PR addresses a fundamental UX limitation where custom commands couldn't use file path autocompletion. The implementation introduces a dual-mode completion strategy:

Architecture Overview

1. Command Detection: Uses CommandKind.FILE enum to differentiate custom commands from built-in commands
2. Mode Selection Logic:
   • Built-in commands: Early return with SLASH mode (preserves existing behavior)
   • Custom commands: Allow fall-through to @ detection for file path completion
3. UI Improvement: Replaces brittle string parsing with explicit CompletionMode propagation

Technical Implementation

• File: useCommandCompletion.tsx - Core dual-mode logic using isCustomCommand helper
• File: SuggestionsDisplay.tsx - Width constraint fix using explicit completion mode
• File: InputPrompt.tsx - Pass completion mode to UI components

Performance Enhancements

• O(1) Lookups: Memoized Map<string, SlashCommand> replaces O(n) array searches
• Robust Parsing: Regex-based command extraction handles edge cases gracefully
• Logic Optimization: Single command type determination eliminates redundant calls
• UI Polish: Ellipsis truncation prevents long file path overflow

Reviewer Test Plan

Manual Testing Scenarios

1. Basic Dual-Mode Functionality

# Custom command file path completion (NEW)
/my-custom @src/  # Should show file suggestions with full width

# Built-in command behavior (PRESERVED) 
/memory @src/     # Should NOT show file suggestions

# Custom command name completion (PRESERVED)
/my-cus           # Should show command name suggestions and adjust to longest command

2. Edge Cases

# Extra whitespace
/my-custom   @some/path   # Should work correctly

# Empty @ query  
/my-custom @              # Should trigger file completion

# Command substring conflicts
/log vs /logs             # Should differentiate correctly

# No-op command
/                         # Should show slash completion

3. Visual Validation

• File path suggestions should use full width (not 35% constraint)
• Slash command suggestions should use minimum 15 chars, maximum 35% of terminal width, but adapts to fit the longest visible command
• Long file paths should truncate with ellipsis (no overflow)

Automated Testing

cd packages/cli
npm run typecheck  # Type safety
npm run lint       # Code standards
npm test -- useCommandCompletion  # 23 tests including edge cases
npm test -- SuggestionsDisplay InputPrompt  # UI component tests

Testing Matrix

	🍏	🪟	🐧
npm run	✅	✅	❓
npx	❓	❓	❓
Docker	❓	❓	❓
Podman	❓	-	-
Seatbelt	❓	-	-

Test Results:

• ✅ 112/112 completion-related tests PASSED
• ✅ TypeScript compilation clean
• ✅ ESLint passes
• ✅ Zero regressions in existing functionality

Linked issues / bugs

Resolves #6685

Additional Context:

[gemini-code-assist]

Summary of Changes

Hello @dracic, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the user interface by introducing dual-mode autocompletion for custom commands, allowing them to support both command name suggestions and file path suggestions. It also addresses a critical UI display bug that previously limited file path suggestion width. The changes include performance optimizations for command lookups and robust parsing, all backed by extensive new test cases to ensure stability and prevent regressions.

Highlights

• Dual-Mode Autocompletion for Custom Commands: Custom commands now support both traditional slash command completion and new @ file path completion, allowing users to easily select files within custom command contexts.
• Improved UI Display for File Paths: Resolved a UI issue where file path suggestions were constrained to 35% width, ensuring they now utilize the full available width for better readability.
• Performance Optimizations: Implemented a memoized Map for O(1) command lookups and utilized regex-based parsing for command extraction, significantly enhancing performance and responsiveness.
• Comprehensive Test Coverage: Added 23 new tests, including a focus on paranoid edge cases, to ensure the stability and correctness of the new dual-mode completion system.

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[gemini-code-assist]

Code Review

This is an excellent pull request that thoughtfully implements file path autocompletion for custom commands. The introduction of a dual-mode completion system is a clever solution. I'm particularly impressed by the performance optimizations, such as the memoized map for O(1) command lookups, and the addition of a comprehensive suite of tests covering many edge cases. The code is clean, the logic is sound, and the UI improvements for handling long file paths are a great touch. Overall, this is a high-quality contribution that significantly improves the user experience.

[dracic]

Rebased, now includes changes from #6957

[dracic]

@abhipatel12 this is also custom commands related. When you have some time, review it, and then tell me what you think.

[dracic]

Rebased. now includes changes from #7797 and #7847

[abhipatel12]

Hey thanks for making this change and sorry for the delayed review. Left a few comments, let me know what you think.

[abhipatel12]

Is there a case where we want this for MCP prompts as commands? Or are they being excluded on purpose?

[dracic]

I did it on purpose because of discussion on #6685:

This is intentional. Commands do not necessarily take file path inputs and it would be misleading to imply that they do. Commands that do take file path inputs can support autocomplete if they want to, tho.

So i focused only on custom commands

[dracic]

What do you suggest?

[abhipatel12]

What happens to the autocomplete for the command if the cursor is moved back? For example:

/foo-command<CURSOR> @some/file?

Do you still get suggestions for the command?

[dracic]

You're right. I have a bug in line 132 where the backwards search for '@' symbol starts at cursorCol - 1 instead of cursorCol. When the cursor is positioned right before the '@' symbol, the loop misses it entirely.

[dracic]

      // Start from cursorCol, but if it's a space, also check cursorCol - 1
      const startSearch =
        cursorCol < codePoints.length && codePoints[cursorCol] === ' '
          ? cursorCol - 1
          : cursorCol;

[dracic]

Given the multiple changes, it no longer makes sense to correct this. It is better to do everything from scratch.