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GitHub Copilot cdcc9bfc23 Always download SVG screenshots

The dashboard now always downloads SVG on right-click even when
PNG thumbnails are enabled, while keeping SVG as the default mode
in the docs and tests.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

2026-02-18 15:56:41 +00:00

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Architecture

Overview

webterm is a Go HTTP/WebSocket server that hosts one or more terminal sessions and renders screenshot/telemetry surfaces for a dashboard UI.

Browser (terminal.js + ghostty-vt.wasm)
        │
        │ WS / HTTP / SSE
        ▼
webterm/server.go (LocalServer)
        │
        ├── session_manager.go      (route/app/session registry)
        ├── terminal_session.go     (PTY-backed local sessions)
        ├── docker_exec_session.go  (Docker exec-backed sessions)
        ├── docker_watcher.go       (container add/remove discovery)
        ├── docker_stats.go         (CPU sampling + sparkline data)
        ├── svg_exporter.go         (terminal snapshot -> SVG)
        └── png_exporter.go         (terminal snapshot -> PNG via coverage blending)

Packages

cmd/webterm: CLI entrypoint
webterm: server/runtime/domain logic
internal/terminalstate: Go terminal emulator wrapper (go-te) used for screenshots
webterm/coverage_table.go: coverage map for approximate PNG rendering

Runtime data flow

Browser connects to /ws/{route_key}.
SessionManager resolves or creates a session.
Session reads PTY output and updates:
- live WS stream (stdout)
- replay buffer (reconnect support)
- terminal-state tracker (go-te) for screenshots
Dashboard pulls /screenshot.svg (default) or /screenshot.png when WEBTERM_SCREENSHOT_MODE=png, and listens on /events for activity.

Static assets

Assets live in webterm/static:

js/terminal.ts source
js/terminal.js bundled client
js/ghostty-vt.wasm
monospace.css, icons, manifest.json

The server resolves static files from:

WEBTERM_STATIC_PATH (if set)
local repository-relative fallbacks rooted at webterm/static
embedded assets bundled into the Go binary

Docker integration

Compose mode loads services from a compose manifest and creates tiles for services carrying webterm-command.
Watch mode subscribes to Docker events and adds/removes tiles at runtime.
webterm-theme controls tile theme; default theme applies if unset. Available themes: tango, xterm, monokai, monokai-pro, ristretto, dark, light, dracula, catppuccin, nord, gruvbox, solarized, tokyo, miasma, github, gotham.

Reliability notes

WebSocket writes are serialized through a sender queue.
Session-manager maps are lock-protected and race-tested.
Replay buffers are bounded to avoid unbounded memory growth.

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