feat(glowm): add interactive pager

[denolfe]

Overview

Adds a less-style interactive pager to glowm for viewing long markdown documents. The pager activates automatically when content exceeds terminal height, with --no-pager flag to disable.

Key Changes

• Interactive pager with less-compatible keybindings

  • Scroll: j/k, arrows, space/b, d/u, g/G
  • Search: / forward, ? backward with match highlighting
  • Header navigation: n/N to jump between headers
  • Mouse scroll support via SGR protocol
  • Info display with =

• Line wrapping that preserves ANSI escape codes

  • Splits content into Line objects for viewport display
  • Handles image placeholders and header markers

• Image handling in pager mode

  • Shows framed box with alt text instead of rendering images
  • Prevents layout issues from variable image heights

• Terminal resize handling

  • Re-wraps content for new width
  • Preserves relative scroll position and search state

Design Decisions

The pager uses a state machine with PagerState holding lines, scroll position, terminal dimensions, and search state. Rendering writes directly to stdout with ANSI clear/cursor sequences rather than using a canvas abstraction.

Images display as styled placeholder boxes in pager mode because terminal image rendering (Kitty protocol or ANSI blocks) doesn't integrate well with viewport scrolling. The non-pager mode still renders actual images.

Header navigation detects headers via a HEADING_MARKER character injected during markdown rendering, stripped before final output.

Overall Flow

sequenceDiagram
    participant User
    participant CLI
    participant Pager
    participant Render

    User->>CLI: glowm file.md
    CLI->>CLI: Render markdown
    CLI->>CLI: Check content height vs terminal
    alt Content fits
        CLI->>User: Output directly
    else Content exceeds terminal
        CLI->>Pager: runPager(content, images)
        Pager->>Render: Initial render
        loop Input handling
            User->>Pager: Keypress/scroll
            Pager->>Pager: Update state
            Pager->>Render: Re-render viewport
        end
        User->>Pager: q
        Pager->>CLI: Cleanup and exit
    end

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