…rch#25071)

* tui: make URLs clickable + hover-highlight in any terminal

Problem
-------
URLs printed by `hermes --tui` were not clickable in basic macOS Terminal.app.
Cmd+click did nothing, the cursor didn't change shape — like nothing was
detected — even though arrow buttons and other Box onClick handlers worked
fine.

Root cause
----------
Two layers of dead plumbing:

1. `<Link>` only emitted the underlying `<ink-link>` (which carries the
   hyperlink metadata into the screen buffer) when `supportsHyperlinks()`
   said yes. On Apple_Terminal that's false, so the per-cell hyperlink
   field stayed empty, so `Ink.getHyperlinkAt()` had nothing to return on
   click. The visible underline was just decorative.

2. `Ink.openHyperlink()` calls `this.onHyperlinkClick?.(url)`, but
   `onHyperlinkClick` was never assigned anywhere in the codebase. The
   click pipeline (`App.tsx → onOpenHyperlink → Ink.openHyperlink`) ran
   but bailed silently on the optional chain.

Bonus discovery: even when wired up, there was no hover affordance —
terminal apps can't change the system mouse cursor, so users had no
visual signal that a cell was clickable. Arrow buttons in the chrome
worked because they had explicit `<Box onClick>` styling; inline link
URLs didn't.

Fix
---
- `Link.tsx`: always emit `<ink-link>` regardless of terminal capability.
  The renderer's `wrapWithOsc8Link` already gates the actual OSC 8 escape
  on `supportsHyperlinks()` further down — so terminals that don't
  understand OSC 8 still don't see the escape, but the screen-buffer
  metadata (which the click dispatcher reads) is now populated everywhere.

- `ink.tsx + root.ts`: add `onHyperlinkClick?: (url: string) => void` to
  `Options` / `RenderOptions`, wire it to the existing `Ink.onHyperlinkClick`
  field in the constructor.

- `src/lib/openExternalUrl.ts`: small platform-aware opener using
  `child_process.spawn` with arg-array (no shell) — http(s) only, rejects
  `file:`, `javascript:`, `data:`, etc., so a hostile model can't trigger
  arbitrary local handlers via `<Link url="file:///...">`. Detached + stdio
  ignore so closing the TUI doesn't kill the browser and Chrome stderr
  doesn't leak into the alt screen.

- `entry.tsx`: pass `onHyperlinkClick: openExternalUrl` to `ink.render`.

- `hyperlinkHover.ts` + Ink hover wiring: track the URL under the pointer
  in `Ink.hoveredHyperlink`, update it from `dispatchHover`, and inverse-
  highlight every cell of the matching link in the render-pass overlay
  (same pattern as `applySearchHighlight`). This is the cursor-hover
  affordance for clickable links — terminals don't expose cursor shape,
  so we light up the link itself.

- `types/hermes-ink.d.ts`: add `onHyperlinkClick` to the `RenderOptions`
  shim so consumers (`entry.tsx`) type-check against the new option.

Tests
-----
- `src/lib/openExternalUrl.test.ts` (15 cases): http(s) accepted; file/js/
  data/mailto/ftp/ssh rejected; macOS open(1), Windows cmd.exe start with
  empty title slot, Linux xdg-open dispatch; shell-metacharacter URLs
  pass through unmolested as a single argv element; synchronous spawn
  failure returns false.

Verified empirically in Apple Terminal 455.1 (macOS 15.7.3): clicking a
URL opens in default browser, hovering inverts the link cells, and
moving away clears the highlight. Full TUI suite: 713 passing, 0
type errors.

Reverts
-------
The earlier attempt that version-gated Apple_Terminal in
`supports-hyperlinks.ts` was based on a wrong assumption — Terminal.app
silently strips OSC 8 sequences but does not render them as clickable
hyperlinks. Reverted to the original allowlist.

* tui: address Copilot review — explorer.exe on win32 + comment fixes

- openExternalUrl: switch win32 from `cmd.exe /c start` to `explorer.exe`.
  cmd.exe's `start` builtin reparses the URL through cmd's tokenizer, so
  `&`, `|`, `^`, `<`, `>` either split the command or get reinterpreted —
  breaking both the protocol-allowlist safety story AND plain http(s) URLs
  with `&` in query strings. `explorer.exe <url>` invokes the registered
  protocol handler directly with no shell.

- openExternalUrl.test.ts: rename the win32 test to reflect the new
  contract and add two regression tests — one with `&|^<>` metachars,
  one with the common analytics-URL `&` query-param pattern — both pinned
  to single-argv-element delivery via explorer.exe.

- Link.tsx: fix misleading comment. OSC 8 escapes are emitted
  unconditionally by the renderer (`wrapWithOsc8Link` in
  render-node-to-output.ts, `oscLink` in log-update.ts). Non-supporting
  terminals silently strip the sequence, which is why hover/click
  affordance has to come from the in-process overlay rather than the
  terminal's own link rendering.

Verified: 715/715 tests pass, type-check + build clean.

* tui: address Copilot review #2 — async spawn errors + hover scope + docs

1. openExternalUrl: attach a no-op `'error'` listener on the spawned
   child BEFORE unref(). spawn() returns a ChildProcess synchronously
   even when the binary is missing (ENOENT on xdg-open / explorer.exe),
   unreachable, or otherwise unusable; the failure surfaces later as
   an 'error' event. An unhandled 'error' on an EventEmitter crashes
   Node, which would tear down the whole TUI. The listener is a
   deliberate no-op — we already returned `true` synchronously and the
   user just doesn't see the browser pop.

2. openExternalUrl.test.ts: add a regression test using a real
   EventEmitter to simulate the async-error path. Pins both the
   listener-attached contract and the "doesn't throw on emit" behavior.
   Was 17/17, now 18/18.

3. ink.tsx dispatchHover: bypass `getHyperlinkAt()` and read
   `cellAt(...).hyperlink` directly. `getHyperlinkAt` falls back to
   `findPlainTextUrlAt` for cells without an OSC 8 hyperlink, but the
   render-pass overlay (`applyHyperlinkHoverHighlight`) only matches on
   `cell.hyperlink === hoveredUrl` — so plain-text URLs would burn
   re-renders without ever producing the highlight. Hover is now a
   strictly 1:1 fit for what the overlay can paint. Plain-text URLs
   still get the click action via the existing dispatch path.

4. root.ts + ink.tsx doc comments: replace the misleading "typically
   `open` / `xdg-open` / `start` shell" wording with the actual safe
   recipe — argv-array spawn into `open` / `xdg-open` / `explorer.exe`,
   with an explicit warning that `cmd.exe /c start` reparses the URL
   through cmd's tokenizer and is unsafe + breaks `&`-query URLs.

Verified: 716/716 tests pass, type-check + build clean.

* tui: address Copilot review #3 — hover damage, alt-screen cleanup, opener allowlist

1. ink.tsx onRender: stop folding steady-state hover into hlActive.
   hlActive forces a full-screen damage diff so previous-frame inverted
   cells get re-emitted when the highlight set changes. The transition
   IS the trigger — enter / leave / change-to-other-link. While the
   pointer just sits on a link the painted cells don't change and the
   per-cell diff handles the no-op. Folding the steady state in would
   burn a full-screen diff on every frame. Added a
   lastRenderedHoveredHyperlink tracker and gate the hlActive bump on
   `hovered !== lastRendered`.

2. ink.tsx setAltScreenActive: clear hoveredHyperlink (and the tracker)
   when toggling alt-screen state. Hover dispatch is alt-screen-gated,
   so once we leave there's no path to clear it. Without this, remounting
   <AlternateScreen> would paint a phantom hover from the previous
   session until the next mouse-move arrived.

3. openExternalUrl.ts openCommand: allowlist linux + the BSD family for
   xdg-open and return null for everything else (aix, sunos, cygwin,
   haiku, etc.). Previously the default-fallback always returned
   xdg-open, which made the caller's `if (!command) return false` dead
   and yielded a misleading `true` on platforms that probably don't
   have xdg-open. New tests cover the null path AND the
   openExternalUrl-returns-false-without-spawning behavior.

Verified: 718/718 tests pass, type-check + build clean.

* tui: address Copilot review #4 — doc comment accuracy

1. openExternalUrl return-value doc: now lists all three false paths
   (URL rejected / no opener for platform / synchronous spawn throw)
   plus a note that async 'error' events still return true because the
   spawn was attempted.

2. ink.tsx onHyperlinkClick field doc: clarifies the callback receives
   either an OSC 8 hyperlink OR a plain-text URL detected by
   findPlainTextUrlAt — App.tsx routes both into the same callback.

3. hyperlinkHover applyHyperlinkHoverHighlight doc: drops the misleading
   'caller forces full-frame damage' promise. Caller decides; for hover
   the current caller only forces full damage on transitions.

No behavior change. 718/718 tests pass.

* tui: address Copilot review #5 — lint fixes

1. ink.tsx: reorder `./hyperlinkHover.js` import before `./screen.js` to
   satisfy perfectionist/sort-imports.

2. Link.tsx: drop unused `fallback` parameter destructuring + the
   trailing `void (null as ...)` dead-statement (would trip
   no-unused-expressions). Kept `fallback?: ReactNode` on the Props
   interface as a documented compat shim so existing call sites still
   compile, with a comment explaining why it's no longer wired up.

3. openExternalUrl.test.ts: replace `typeof import('node:child_process').spawn`
   inline annotations (forbidden by @typescript-eslint/consistent-type-imports)
   with a `SpawnLike` type alias backed by a real `import type { spawn as SpawnFn }`.

No behavior change. 718/718 tests pass, type-check clean, lint clean on
all modified files.