fix(tui): forward OSC 8 hyperlinks under tmux when the client supports them

detectCapabilities previously disabled hyperlinks under tmux unconditionally. tmux re-emits OSC 8 to the outer terminal only when the attached client advertises the 'hyperlinks' feature in client_termfeatures, and strips them otherwise.

Probe the running server with 'tmux display-message -p #{client_termfeatures}' and enable hyperlinks only when the feature is listed. The probe fails closed: any error (no tmux/server, timeout, old tmux) yields false. images stays null; only the hyperlink decision changed. The probe is injected into detectCapabilities so it stays testable without spawning a process.

packages/tui/src/terminal-image.ts

@@ -1,3 +1,5 @@
+import { execSync } from "node:child_process";
+
 export type ImageProtocol = "kitty" | "iterm2" | null;
 
 export interface TerminalCapabilities {
@@ -39,19 +41,42 @@ export function setCellDimensions(dims: CellDimensions): void {
 	cellDimensions = dims;
 }
 
-export function detectCapabilities(): TerminalCapabilities {
+/**
+ * Checks whether the attached tmux client forwards OSC 8 hyperlinks to the
+ * outer terminal. tmux only re-emits them when its `client_termfeatures` lists
+ * `hyperlinks`, and strips them otherwise. On any error fallbacks `false`.
+ */
+function probeTmuxHyperlinks(): boolean {
+	try {
+		const termfeatures = execSync("tmux display-message -p '#{client_termfeatures}'", {
+			encoding: "utf8",
+			timeout: 250,
+			stdio: ["ignore", "pipe", "ignore"],
+		});
+		return termfeatures
+			.split(",")
+			.map((feature) => feature.trim())
+			.includes("hyperlinks");
+	} catch {
+		return false;
+	}
+}
+
+export function detectCapabilities(tmuxForwardsHyperlink: () => boolean = probeTmuxHyperlinks): TerminalCapabilities {
 	const termProgram = process.env.TERM_PROGRAM?.toLowerCase() || "";
 	const terminalEmulator = process.env.TERMINAL_EMULATOR?.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
-	// when the outer terminal would otherwise support OSC 8. Image protocols are
-	// also unreliable under tmux/screen, so leave `images: null` for safety.
-	const inTmuxOrScreen = !!process.env.TMUX || term.startsWith("tmux") || term.startsWith("screen");
-	if (inTmuxOrScreen) {
+	// Emit OSC 8 hyperlinks only when tmux confirms it forwards.
+	// Image protocols are unreliable under tmux, so leave `images: null`.
+	if (process.env.TMUX || term.startsWith("tmux")) {
+		return { images: null, trueColor: hasTrueColorHint, hyperlinks: tmuxForwardsHyperlink() };
+	}
+
+	// screen does not forward OSC 8 hyperlinks, so keep them off there.
+	if (term.startsWith("screen")) {
 		return { images: null, trueColor: hasTrueColorHint, hyperlinks: false };
 	}
 

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

@@ -207,19 +207,30 @@ describe("detectCapabilities", () => {
 		});
 	});
 
-	it("forces hyperlinks: false under tmux even if outer terminal supports OSC 8", () => {
+	it("enables hyperlinks under tmux when the client forwards them", () => {
 		withEnv({ TMUX: "/tmp/tmux-1000/default,1234,0", TERM_PROGRAM: "ghostty" }, () => {
-			const caps = detectCapabilities();
+			const caps = detectCapabilities(() => true);
+			assert.strictEqual(caps.hyperlinks, true);
+			assert.strictEqual(caps.images, null);
+		});
+	});
+
+	it("disables hyperlinks under tmux when the client does not forward them", () => {
+		withEnv({ TMUX: "/tmp/tmux-1000/default,1234,0", TERM_PROGRAM: "ghostty" }, () => {
+			const caps = detectCapabilities(() => false);
 			assert.strictEqual(caps.hyperlinks, false);
 			assert.strictEqual(caps.images, null);
 		});
 	});
 
-	it("forces hyperlinks: false when TERM starts with 'tmux'", () => {
+	it("checks tmux capability when TERM starts with 'tmux'", () => {
 		withEnv({ TERM: "tmux-256color", TERM_PROGRAM: "iterm.app" }, () => {
-			const caps = detectCapabilities();
-			assert.strictEqual(caps.hyperlinks, false);
+			const caps = detectCapabilities(() => true);
+			assert.strictEqual(caps.hyperlinks, true);
 			assert.strictEqual(caps.images, null);
+
+			const caps2 = detectCapabilities(() => false);
+			assert.strictEqual(caps2.hyperlinks, false);
 		});
 	});
 
@@ -294,7 +305,7 @@ describe("detectCapabilities", () => {
 
 	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();
+			const caps = detectCapabilities(() => false);
 			assert.strictEqual(caps.trueColor, false);
 			assert.strictEqual(caps.hyperlinks, false);
 			assert.strictEqual(caps.images, null);
@@ -303,7 +314,7 @@ describe("detectCapabilities", () => {
 
 	it("trusts explicit truecolor hints through tmux", () => {
 		withEnv({ COLORTERM: "truecolor", TMUX: "/tmp/tmux-1000/default,1234,0", TERM: "tmux-256color" }, () => {
-			const caps = detectCapabilities();
+			const caps = detectCapabilities(() => false);
 			assert.strictEqual(caps.trueColor, true);
 			assert.strictEqual(caps.hyperlinks, false);
 			assert.strictEqual(caps.images, null);