host: the tab bridge ships from waybetter-host; create-waybetter uses it

tab-bridge.js (moved from wayBetter for X) is served by bridge::SOURCE,
or by bridge::script(BridgeOptions) with shortcut and link-drag
forwarding switched off for a shell that does not handle them (a
forwarded shortcut is taken from the page). Tests: one options line,
only tab_report/tab_shortcut/tab_link_drag, every forwarded shortcut is
one tabs::valid_shortcut accepts. Generated apps now inject
bridge::script(BridgeOptions::REPORT_ONLY) instead of writing their own
duplicated src-tauri/runtime/tab-bridge.js.

crates/waybetter-host/src/bridge.rs

@@ -0,0 +1,67 @@
+//! The tab bridge: the script every tab webview gets as a main-frame initialization script
+//! ([`script`]). It reports the tab's own URL, title, favicon and focus to the shell (`tab_report`)
+//! and, when the app enables them, forwards browser shortcuts pressed in the page (`tab_shortcut`,
+//! [`crate::tabs::valid_shortcut`]) and link drags (`tab_link_drag`, [`crate::tabs::link_drag`]).
+//! The app's `tab-chrome` capability grants exactly the commands it calls, about the tab itself.
+
+/// The bridge source (`tab-bridge.js` next to this crate's `Cargo.toml`), all features on.
+pub const SOURCE: &str = include_str!("../tab-bridge.js");
+const DEFAULT_OPTIONS: &str = "const options = { shortcuts: true, linkDrags: true };";
+
+/// What the bridge forwards besides the tab report. Turn a feature off when the app's shell does
+/// not handle it: a forwarded shortcut is taken from the page (`preventDefault`).
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct BridgeOptions {
+    /// Browser shortcuts (new/close/reopen tab, reload, back/forward, split, palette, deck keys).
+    pub shortcuts: bool,
+    /// Link drags out of (or into) the page, for the shell's split/tab drop zones.
+    pub link_drags: bool,
+}
+
+impl BridgeOptions {
+    pub const ALL: Self = Self { shortcuts: true, link_drags: true };
+    /// Only `tab_report` (URL, title, favicon, focus).
+    pub const REPORT_ONLY: Self = Self { shortcuts: false, link_drags: false };
+}
+
+/// The bridge script with `options`.
+pub fn script(options: BridgeOptions) -> String {
+    let set = format!("const options = {{ shortcuts: {}, linkDrags: {} }};", options.shortcuts, options.link_drags);
+    SOURCE.replacen(DEFAULT_OPTIONS, &set, 1)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn options_are_set_in_the_one_options_line() {
+        assert_eq!(SOURCE.matches(DEFAULT_OPTIONS).count(), 1);
+        assert_eq!(script(BridgeOptions::ALL), SOURCE);
+        let report = script(BridgeOptions::REPORT_ONLY);
+        assert!(report.contains("const options = { shortcuts: false, linkDrags: false };"));
+        assert!(!report.contains(DEFAULT_OPTIONS));
+        assert!(report.contains("if (options.shortcuts) addEventListener('keydown'"));
+        assert!(report.contains("if (options.linkDrags) {"));
+    }
+
+    #[test]
+    fn bridge_calls_only_the_tab_chrome_commands() {
+        let mut commands: Vec<&str> = SOURCE.match_indices("invoke('").map(|(at, _)| SOURCE[at + 8..].split('\'').next().unwrap()).collect();
+        commands.sort();
+        commands.dedup();
+        assert_eq!(commands, ["tab_link_drag", "tab_report", "tab_shortcut"]);
+        assert!(SOURCE.contains("if (window.top !== window || window.__wbTabBridge) return;"), "top frame only, once");
+    }
+
+    #[test]
+    fn forwarded_shortcuts_are_ones_the_host_accepts() {
+        for name in ["deck-toggle", "deck-compose", "column-page-prev", "column-page-next", "column-prev", "column-next", "reopen-tab", "new-tab",
+            "open-panel", "close-tab", "focus-address", "command-palette", "prev-tab", "next-tab", "hard-reload", "reload", "split-down",
+            "split-right", "back", "forward"] {
+            assert!(SOURCE.contains(&format!("'{name}'")), "{name} is not in the bridge");
+            assert!(crate::tabs::valid_shortcut(name), "{name} would be refused");
+        }
+        assert!(crate::tabs::valid_shortcut("column-3"));
+    }
+}