fix: improve light terminal detection and text contrast

- Add COLORFGBG env var fallback when OSC 11 detection times out
- Use dark foreground (#1a1a1a) instead of palette[7] (#c0c0c0) for light mode system theme
- Use backgroundElement for inline code blocks to ensure contrast on transparent backgrounds

Closes #704

Author: saravmajestic

packages/opencode/src/cli/cmd/tui/app.tsx

@@ -165,7 +165,20 @@ async function getTerminalBackgroundColor(): Promise<"dark" | "light"> {
 
     timeout = setTimeout(() => {
       cleanup()
+      // altimate_change start — fix: use COLORFGBG env var as fallback before defaulting to dark
+      // Many terminals (iTerm2, xterm, etc.) set COLORFGBG=<fg>;<bg> to indicate color scheme.
+      // When bg component >= 8, the terminal likely has a light background.
+      const colorfgbg = process.env.COLORFGBG
+      if (colorfgbg) {
+        const parts = colorfgbg.split(";")
+        const bg = parseInt(parts[parts.length - 1])
+        if (!isNaN(bg) && bg >= 8) {
+          resolve("light")
+          return
+        }
+      }
       resolve("dark")
+      // altimate_change end
     }, 1000)
   })
 }

packages/opencode/src/cli/cmd/tui/context/theme.tsx

@@ -430,10 +430,15 @@ export function tint(base: RGBA, overlay: RGBA, alpha: number): RGBA {
 
 function generateSystem(colors: TerminalColors, mode: "dark" | "light"): ThemeJson {
   const bg = RGBA.fromHex(colors.defaultBackground ?? colors.palette[0]!)
-  const fg = RGBA.fromHex(colors.defaultForeground ?? colors.palette[7]!)
   const transparent = RGBA.fromInts(0, 0, 0, 0)
   const isDark = mode == "dark"
 
+  // altimate_change start — fix: use contrast-appropriate fallback for light terminals
+  // palette[7] is #c0c0c0 (light gray) which is invisible on white backgrounds
+  const fgFallback = isDark ? colors.palette[7]! : "#1a1a1a"
+  const fg = RGBA.fromHex(colors.defaultForeground ?? fgFallback)
+  // altimate_change end
+
   const col = (i: number) => {
     const value = colors.palette[i]
     if (value) return RGBA.fromHex(value)
@@ -948,7 +953,10 @@ function getSyntaxRules(theme: Theme) {
       scope: ["markup.raw.inline"],
       style: {
         foreground: theme.markdownCode,
-        background: theme.background, // inline code blends with page background
+        // altimate_change start — fix: use backgroundElement for inline code contrast on light themes
+        // theme.background can be transparent, leaving inline code with no contrast protection
+        background: theme.backgroundElement,
+        // altimate_change end
       },
     },
     {