fix: align theme truecolor detection

packages/tui/src/terminal-image.ts

@@ -43,6 +43,7 @@ export function detectCapabilities(): TerminalCapabilities {
 	const termProgram = process.env.TERM_PROGRAM?.toLowerCase() || "";
 	const term = process.env.TERM?.toLowerCase() || "";
 	const colorTerm = process.env.COLORTERM?.toLowerCase() || "";
+	const hasTrueColorHint = colorTerm === "truecolor" || colorTerm === "24bit";
 
 	// tmux and screen swallow OSC 8 by default (passthrough is opt-in and wraps
 	// sequences differently). Force hyperlinks off whenever we detect them, even
@@ -50,8 +51,7 @@ export function detectCapabilities(): TerminalCapabilities {
 	// also unreliable under tmux/screen, so leave `images: null` for safety.
 	const inTmuxOrScreen = !!process.env.TMUX || term.startsWith("tmux") || term.startsWith("screen");
 	if (inTmuxOrScreen) {
-		const trueColor = colorTerm === "truecolor" || colorTerm === "24bit";
-		return { images: null, trueColor, hyperlinks: false };
+		return { images: null, trueColor: hasTrueColorHint, hyperlinks: false };
 	}
 
 	if (process.env.KITTY_WINDOW_ID || termProgram === "kitty") {
@@ -82,8 +82,7 @@ export function detectCapabilities(): TerminalCapabilities {
 	// text" on terminals that swallow it, which means the URL disappears from
 	// the rendered output. Default to the legacy `text (url)` behavior unless we
 	// have positively identified a hyperlink-capable terminal above.
-	const trueColor = colorTerm === "truecolor" || colorTerm === "24bit";
-	return { images: null, trueColor, hyperlinks: false };
+	return { images: null, trueColor: hasTrueColorHint || !!process.env.WT_SESSION, hyperlinks: false };
 }
 
 export function getCapabilities(): TerminalCapabilities {

packages/tui/test/terminal-image.test.ts

@@ -27,6 +27,7 @@ const ENV_KEYS = [
 	"GHOSTTY_RESOURCES_DIR",
 	"WEZTERM_PANE",
 	"ITERM_SESSION_ID",
+	"WT_SESSION",
 	"CMUX_WORKSPACE_ID",
 ] as const;
 
@@ -271,6 +272,31 @@ describe("detectCapabilities", () => {
 			assert.strictEqual(caps.hyperlinks, true);
 		});
 	});
+
+	it("detects truecolor for Windows Terminal outside multiplexers", () => {
+		withEnv({ WT_SESSION: "session", TERM: "xterm-256color" }, () => {
+			const caps = detectCapabilities();
+			assert.strictEqual(caps.trueColor, true);
+		});
+	});
+
+	it("does not inherit Windows Terminal truecolor through tmux", () => {
+		withEnv({ WT_SESSION: "session", TMUX: "/tmp/tmux-1000/default,1234,0", TERM: "tmux-256color" }, () => {
+			const caps = detectCapabilities();
+			assert.strictEqual(caps.trueColor, false);
+			assert.strictEqual(caps.hyperlinks, false);
+			assert.strictEqual(caps.images, null);
+		});
+	});
+
+	it("trusts explicit truecolor hints through tmux", () => {
+		withEnv({ COLORTERM: "truecolor", TMUX: "/tmp/tmux-1000/default,1234,0", TERM: "tmux-256color" }, () => {
+			const caps = detectCapabilities();
+			assert.strictEqual(caps.trueColor, true);
+			assert.strictEqual(caps.hyperlinks, false);
+			assert.strictEqual(caps.images, null);
+		});
+	});
 });
 
 describe("Kitty image cursor movement", () => {