fix(tui): consolidated TUI fixes for overflow, positioning, and panic prevention

[echobt]

Summary

This PR consolidates 7 individual TUI fixes into a single, cohesive change:

Included PRs:

• fix(tui): prevent usize to u16 overflow in interactive renderer #38: Prevent usize to u16 overflow in interactive renderer
• fix(tui): prevent usize to u16 overflow in card count displays #42: Prevent usize to u16 overflow in card count displays
• fix(tui): fix cursor positioning and underflow in selection list #58: Fix cursor positioning and underflow in selection list
• fix(tui): fix mention popup positioning and Unicode width calculation #59: Fix mention popup positioning and Unicode width calculation
• fix(tui): improve autocomplete popup positioning and width calculation #60: Improve autocomplete popup positioning and width calculation
• fix(tui): prevent underflow in dropdown navigation and scroll calculations #64: Prevent underflow in dropdown navigation and scroll calculations
• fix(tui): prevent panic in HelpBrowserState when sections empty #66: Prevent panic in HelpBrowserState when sections empty

Changes:

• Added saturating casts for u16 conversions to prevent overflow
• Fixed cursor positioning calculations in selection lists
• Added bounds checking for empty sections in help browser
• Improved Unicode width handling for popup positioning

Files Modified:

• src/cortex-tui-components/src/dropdown.rs
• src/cortex-tui-components/src/scroll.rs
• src/cortex-tui-components/src/selection_list.rs
• src/cortex-tui/src/cards/commands.rs
• src/cortex-tui/src/cards/models.rs
• src/cortex-tui/src/cards/sessions.rs
• src/cortex-tui/src/interactive/renderer.rs
• src/cortex-tui/src/widgets/autocomplete.rs
• src/cortex-tui/src/widgets/help_browser/render.rs
• src/cortex-tui/src/widgets/help_browser/state.rs
• src/cortex-tui/src/widgets/help_browser/tests.rs
• src/cortex-tui/src/widgets/mention_popup.rs
• src/cortex-tui/src/widgets/scrollable_dropdown.rs

Closes #38, #42, #58, #59, #60, #64, #66

[greptile-apps]

Greptile Overview

Greptile Summary

This PR consolidates 7 individual TUI fixes addressing overflow, underflow, and panic issues across dropdown, scroll, and popup components.

Key Changes:

• Overflow Prevention: Replaced direct usize as u16 casts with u16::try_from().unwrap_or(u16::MAX) in card height calculations and interactive renderer to handle cases where item counts exceed 65,535
• Underflow Prevention: Added comprehensive max_visible == 0 guards and double saturating_sub patterns (e.g., max_visible.saturating_sub(1)) throughout scroll offset calculations to prevent integer underflow
• Panic Prevention: Changed HelpBrowserState::current_section() to return Option<&HelpSection> with empty sections guard, preventing index-out-of-bounds panics
• Unicode Width Handling: Replaced .len() with .chars().count() in mention popup and cursor positioning for accurate multi-byte character support
• Popup Positioning: Improved autocomplete and mention popup positioning with fits_above checks to prevent rendering off-screen

All changes use defensive programming patterns (saturating arithmetic, bounds checking, early returns) consistently applied across 13 files. Test coverage includes the new empty sections case.

Confidence Score: 5/5

• Safe to merge - defensive fixes prevent crashes without changing functional behavior
• All changes are defensive safety improvements using well-established Rust patterns (saturating arithmetic, Option types, bounds checking). Each fix targets a specific panic/overflow scenario with appropriate tests. No logic changes to core functionality.
• No files require special attention

Important Files Changed

Filename	Overview
src/cortex-tui-components/src/scroll.rs	Added zero visible items guard and double saturating_sub to prevent underflow in scroll calculations
src/cortex-tui-components/src/selection_list.rs	Fixed cursor positioning with character count and saturating arithmetic for disabled reason alignment
src/cortex-tui/src/widgets/autocomplete.rs	Changed width calculation to use visible items instead of all items, and improved popup positioning fallback logic
src/cortex-tui/src/widgets/help_browser/state.rs	Changed current_section() return type to Option<&HelpSection> with empty sections guard
src/cortex-tui/src/widgets/scrollable_dropdown.rs	Added comprehensive zero max_visible guards and bounds checking with double saturating_sub throughout

Sequence Diagram

sequenceDiagram
    participant User
    participant TUI as TUI Component
    participant State as Component State
    participant Render as Render Logic
    
    User->>TUI: Navigate/Scroll Action
    TUI->>State: Update selection/scroll
    
    alt Empty or Zero Visible Items
        State->>State: Check max_visible == 0 || items.is_empty()
        State-->>TUI: Return early (prevent underflow)
    else Normal Case
        State->>State: Calculate new position
        State->>State: Use saturating_sub(max_visible.saturating_sub(1))
        State-->>TUI: Safe position value
    end
    
    TUI->>Render: Calculate dimensions
    
    alt Large Item Count
        Render->>Render: u16::try_from(count).unwrap_or(u16::MAX)
        Render->>Render: saturating_add for height components
        Render-->>TUI: Clamped u16 dimensions
    else Unicode/Wide Characters
        Render->>Render: Use chars().count() for width
        Render-->>TUI: Accurate Unicode-aware dimensions
    end
    
    alt Popup Positioning
        Render->>Render: Check if area.y >= height
        alt Fits Above
            Render->>Render: Position above input
        else No Room Above
            Render->>Render: Position below input
        end
    end
    
    TUI->>User: Display UI (no panic/overflow)

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[greptile-apps]

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[echobt]

Closing this PR to consolidate into a single mega-PR combining all bug fixes. The changes will be included in a new consolidated PR.