fix(runtime): kitty key-release delivers input like Ink, not '' (parity) (#91)

useInput had an undocumented guard that blanked `input` to '' on any kitty key-RELEASE
event, so a printable release (and a ctrl+letter release) delivered nothing. Ink has no
release special-case -- it classifies a kitty event purely by isPrintable/ctrl+letter, so
a printable release delivers `text ?? name` and a ctrl+letter release delivers the letter
name (use-input.ts:204-217). Removes the guard to match.

The kept "Ctrl+C exits under kitty" divergence is unaffected: the exit check in emitInput
is already scoped to `eventType !== "release"`, so a Ctrl+C release flows through as
input='c' without spuriously exiting (press still exits).

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/runtime-tests/integration/composables/use-input.test.tsx

@@ -378,3 +378,67 @@ test("exitOnCtrlC intercepts \\x03 in raw mode", async () => {
   expect(handler).not.toHaveBeenCalled();
   await expect(waitUntilExit()).resolves.toBeUndefined();
 });
+
+// --- Kitty release events deliver the key, matching Ink (no release special-case) ---
+// Ink (use-input.ts:204-217) classifies a kitty event purely by isPrintable /
+// ctrl+letter, regardless of press/repeat/release. A printable release ('a' up,
+// CSI 97;1:3 u) therefore delivers input "a", not "". vue-tui previously had an
+// undocumented `eventType === "release"` guard that blanked input to ""; these
+// tests lock the Ink-matching behavior.
+
+test("useInput - kitty printable RELEASE delivers the key (input='a'), not ''", async () => {
+  const calls: Array<{ input: string; key: Key }> = [];
+  const App = defineComponent(() => {
+    useInput((input, key) => calls.push({ input, key }));
+    return () => <Text>listening</Text>;
+  });
+
+  const { stdin } = await render(App);
+  // 'a' release event (codepoint 97, modifier 1, eventType 3 = release)
+  await stdin.write("\x1b[97;1:3u");
+  expect(calls[0]?.input).toBe("a");
+  expect(calls[0]?.key.eventType).toBe("release");
+});
+
+test("useInput - kitty ctrl+letter RELEASE delivers the letter name (input='a'), not ''", async () => {
+  const calls: Array<{ input: string; key: Key }> = [];
+  const App = defineComponent(() => {
+    useInput((input, key) => calls.push({ input, key }));
+    return () => <Text>listening</Text>;
+  });
+
+  const { stdin } = await render(App);
+  // Ctrl+A via codepoint 1-26 form (codepoint 1), modifier 5 (ctrl),
+  // eventType 3 (release). Not printable, but the ctrl+letter branch must still
+  // flow the name "a" through on release — same as Ink.
+  await stdin.write("\x1b[1;5:3u");
+  expect(calls[0]?.input).toBe("a");
+  expect(calls[0]?.key.ctrl).toBe(true);
+  expect(calls[0]?.key.eventType).toBe("release");
+});
+
+// VERIFY no spurious exit from a Ctrl+C RELEASE under exitOnCtrlC. The kitty
+// exit guard lives in emitInput (render.ts) and is scoped to `eventType !==
+// "release"`, so removing the useInput release guard must NOT make a release
+// exit. A Ctrl+C release should instead be delivered to the handler (input "c").
+test("useInput - kitty Ctrl+C RELEASE does not exit (delivered to handler); press still exits", async () => {
+  const calls: Array<{ input: string; key: Key }> = [];
+  const App = defineComponent(() => {
+    useInput((input, key) => calls.push({ input, key }));
+    return () => <Text>running</Text>;
+  });
+  const { stdin, waitUntilExit } = await render(App, { exitOnCtrlC: true });
+
+  // Ctrl+C RELEASE (codepoint 99 'c', modifier 5 = ctrl, eventType 3 = release):
+  // must NOT exit; flows to the handler with input "c".
+  await stdin.write("\x1b[99;5:3u");
+  expect(calls[0]?.input).toBe("c");
+  expect(calls[0]?.key.ctrl).toBe(true);
+  expect(calls[0]?.key.eventType).toBe("release");
+
+  // Ctrl+C PRESS still exits (unchanged divergence behavior).
+  await stdin.write("\x1b[99;5:1u");
+  await expect(waitUntilExit()).resolves.toBeUndefined();
+  // Press was intercepted in emitInput and never reached the handler.
+  expect(calls.length).toBe(1);
+});

packages/runtime-tests/integration/pty/fixtures/use-input-kitty.tsx

@@ -58,7 +58,11 @@ const KittyInput = defineComponent({
         return;
       }
 
-      if (props.test === "release" && key.eventType === "release") {
+      // Ink (use-input.ts:204-217) has no release special-case: a printable
+      // 'a' release ('a' up, CSI 97;1:3 u) delivers input "a", not "".
+      // Asserting input === "a" here (not just eventType) is what guards against
+      // the old undocumented divergence that blanked input on release.
+      if (props.test === "release" && input === "a" && key.eventType === "release") {
         exit();
         return;
       }
@@ -108,11 +112,6 @@ const KittyInput = defineComponent({
         return;
       }
 
-      if (props.test === "releaseEmpty" && input === "" && key.eventType === "release") {
-        exit();
-        return;
-      }
-
       if (props.test === "queryResponse") {
         throw new Error("Query response should not reach handler");
       }

packages/runtime-tests/integration/pty/input-kitty.test.ts

@@ -66,8 +66,12 @@ it("useInput - handle kitty protocol repeat event", async () => {
   expect(ps.output).toContain("exited");
 });
 
-it("useInput - release event produces empty input", async () => {
+// Ink (use-input.ts:204-217) has no release special-case: a printable 'a'
-  const ps = term("use-input-kitty", ["releaseEmpty"]);
+// release delivers input "a" (the text), not "". The fixture exits only if
+// input === "a", so a regression to the old release->"" behavior would hang
+// (and fail). See .agents/docs/ink-divergences.md.
+it("useInput - release event delivers the key (input='a'), matching Ink", async () => {
+  const ps = term("use-input-kitty", ["release"]);
   ps.write(kittyKey(97, 1, 3));
   await ps.waitForExit();
   expect(ps.output).toContain("exited");

packages/runtime/src/composables/useInput.ts

@@ -70,9 +70,14 @@ export function useInput(
 
     let input: string;
     if (keypress.isKittyProtocol) {
-      if (keypress.eventType === "release") {
+      // No release special-case: Ink (use-input.ts:204-217) classifies a kitty
-        input = "";
+      // event purely by isPrintable / ctrl+letter, regardless of
-      } else if (keypress.isPrintable) {
+      // press/repeat/release. A printable release delivers `text ?? name` (e.g.
+      // 'a'); a ctrl+letter release delivers the letter name. Suppressing input
+      // on release here was an undocumented divergence — removed for byte-parity
+      // with Ink. (Ctrl+C exit is scoped to non-release in emitInput, so a
+      // Ctrl+C release flowing through here does not trigger a spurious exit.)
+      if (keypress.isPrintable) {
         input = keypress.text ?? keypress.name;
       } else if (keypress.ctrl && keypress.name.length === 1) {
         input = keypress.name;