fix(tui): detect Herdr as supporting OSC 8 hyperlinks

TERM_PROGRAM=herdr enables hyperlinks with image protocols off. Herdr is
checked before outer-terminal detection so leaked variables such as
KITTY_WINDOW_ID do not enable images inside Herdr panes.

closes #10573

packages/tui/CHANGELOG.md

@@ -6,6 +6,10 @@
 
 - Added `Box.setPaddingX(...)` and `Text.setPaddingX(...)` ([#10557](https://github.com/earendil-works/pi/pull/10557) by [@rwachtler](https://github.com/rwachtler))
 
+### Fixed
+
+- Fixed Markdown links not being clickable in Herdr: `TERM_PROGRAM=herdr` is now detected as supporting OSC 8 hyperlinks ([#10573](https://github.com/earendil-works/pi/issues/10573))
+
 ## [1.0.4] - 2026-10-05
 
 ## [1.0.3] - 2026-10-05

packages/tui/src/terminal-image.ts

@@ -86,6 +86,12 @@ function detectCapabilitiesFromEnvironment(tmuxForwardsHyperlink: () => boolean)
 		return { images: null, trueColor: hasTrueColorHint, hyperlinks: false };
 	}
 
+	// Herdr forwards OSC 8 hyperlinks. It runs inside another terminal whose variables, such as
+	// KITTY_WINDOW_ID, may leak into its panes, so check it first and leave image protocols off.
+	if (termProgram === "herdr") {
+		return { images: null, trueColor: hasTrueColorHint, hyperlinks: true };
+	}
+
 	if (process.env.KITTY_WINDOW_ID || termProgram === "kitty") {
 		return { images: "kitty", trueColor: true, hyperlinks: true };
 	}

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

@@ -317,6 +317,19 @@ describe("detectCapabilities", () => {
 		});
 	});
 
+	// #10573
+	it("enables hyperlinks without images for Herdr", () => {
+		withEnv({ TERM_PROGRAM: "herdr", TERM: "xterm-256color", COLORTERM: "truecolor", KITTY_WINDOW_ID: "1" }, () => {
+			const caps = detectCapabilities();
+			assert.strictEqual(caps.hyperlinks, true);
+			assert.strictEqual(caps.images, null);
+			assert.strictEqual(caps.trueColor, true);
+		});
+		withEnv({ TERM_PROGRAM: "herdr", PI_HYPERLINKS: "0" }, () => {
+			assert.strictEqual(detectCapabilities().hyperlinks, false);
+		});
+	});
+
 	it("enables hyperlinks for Ghostty", () => {
 		withEnv({ TERM_PROGRAM: "ghostty" }, () => {
 			const caps = detectCapabilities();