cv0: open YouTube links in an alternative browser

The 'o' open key now routes youtube.com/youtu.be video links to an
optional alternative browser (e.g. chromium) via the new
--youtube-browser-cmd flag, while every other URL keeps using
--browser-cmd. When the flag is unset, YouTube links fall back to the
default browser as before.

- add youtubeBrowserCmd field and SetYouTubeBrowserCmd setter
- add youtubeHostRegex plus isYouTubeURL and browserForURL helpers
- wire --youtube-browser-cmd flag in main.go
- unit-test URL detection and browser selection
- document the flag in README

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

1 files changed, 23 insertions, 5 deletions

diff --git a/internal/ui/table.go b/internal/ui/table.go
index e168ba7..5efb41e 100644
--- a/internal/ui/table.go
+++ b/internal/ui/table.go
@@ -35,7 +35,12 @@ var (
 	// fileRefRegex matches an @-prefixed file reference such as
 	// "@path/to/file.txt". The leading (^|\s) anchor keeps it from matching
 	// the "@host" part of an email address; capture group 2 is the path.
-	fileRefRegex     = regexp.MustCompile(`(^|\s)@(\S+)`)
+	fileRefRegex = regexp.MustCompile(`(^|\s)@(\S+)`)
+	// youtubeHostRegex matches the host of a YouTube video link so the "o"
+	// key can route it to an alternative browser. It covers youtube.com (with
+	// optional www./m. subdomains) and the youtu.be short-link domain. Case is
+	// ignored because hostnames are case-insensitive.
+	youtubeHostRegex = regexp.MustCompile(`(?i)^(www\.|m\.)?(youtube\.com|youtu\.be)$`)
 	searchRegexCache = make(map[string]*regexp.Regexp, 16)
 	searchRegexMu    sync.RWMutex
 )
@@ -221,10 +226,15 @@ type Model struct {
 	inProgress int
 	due        int
 
-	filters           []string
-	tasks             []task.Task
-	undoStack         []undoAction
-	browserCmd        string
+	filters    []string
+	tasks      []task.Task
+	undoStack  []undoAction
+	browserCmd string
+	// youtubeBrowserCmd, when non-empty, overrides browserCmd for YouTube
+	// links opened with the "o" key. This lets the user route videos to a
+	// browser better suited for them (e.g. chromium) while keeping the
+	// default browser (e.g. firefox) for everything else.
+	youtubeBrowserCmd string
 	agentFilterHotkey string
 	taskwarrior       task.Taskwarrior
 
@@ -1436,6 +1446,14 @@ func (m *Model) SetAgentFilterHotkey(key string) error {
 	return nil
 }
 
+// SetYouTubeBrowserCmd configures the browser command used specifically for
+// YouTube links opened with the "o" key. An empty value (the default) means
+// YouTube links are opened with the regular browser command like any other
+// URL. Surrounding whitespace is trimmed so a blank flag value counts as unset.
+func (m *Model) SetYouTubeBrowserCmd(cmd string) {
+	m.youtubeBrowserCmd = strings.TrimSpace(cmd)
+}
+
 func (m *Model) agentFilterHotkeyLabel() string {
 	if strings.TrimSpace(m.agentFilterHotkey) == "" {
 		return "3"