Add URL scheme actions: play, queue, download, bookmark, subscribe, player controls

yattee://play|play-next|queue|download|bookmark|subscribe|unsubscribe?url={link}
and yattee://player/play|pause|toggle|next|previous|close|seek|rate run through
one LinkActionPerformer that reports a LinkActionResult, ready for
x-callback-url. An unencoded url= keeps its own query; only the action's own
parameters end it.

Actions that change saved state ask first through a confirmation sheet
presented by the top-most sheet host, unless the new 'Run Link Actions
Without Asking' setting is on. Download skips the question when the quality
picker will show anyway. Player commands leave sheets and the player alone.

YatteeTests/NavigationTests.swift

@@ -881,3 +881,95 @@ struct ConnectivityMonitorTests {
         #expect(monitor.isOnline == true)
     }
 }
+
+// MARK: - LinkActionParser Tests
+
+@Suite("LinkActionParser Tests")
+struct LinkActionParserTests {
+    let parser = LinkActionParser()
+
+    private func parse(_ string: String) -> LinkAction? {
+        parser.parse(URL(string: string)!)
+    }
+
+    @Test("Encoded and raw url= give the same inner link with its own query")
+    func encodedAndRawTargets() {
+        let inner = URL(string: "https://www.youtube.com/watch?v=dQw4w9WgXcQ&list=PL123")!
+        #expect(parse("yattee://queue?url=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DdQw4w9WgXcQ%26list%3DPL123") == .addToQueue(inner))
+        #expect(parse("yattee://queue?url=https://www.youtube.com/watch?v=dQw4w9WgXcQ&list=PL123") == .addToQueue(inner))
+    }
+
+    @Test("Play takes the action's t, falling back to the link's own")
+    func playStartTime() {
+        #expect(parse("yattee://play?url=https://youtu.be/dQw4w9WgXcQ&t=1m30s")
+            == .play(URL(string: "https://youtu.be/dQw4w9WgXcQ")!, startTime: 90))
+        #expect(parse("yattee://play?url=https%3A%2F%2Fyoutu.be%2FdQw4w9WgXcQ%3Ft%3D42")
+            == .play(URL(string: "https://youtu.be/dQw4w9WgXcQ?t=42")!, startTime: 42))
+        #expect(parse("yattee://play?url=https://youtu.be/dQw4w9WgXcQ")
+            == .play(URL(string: "https://youtu.be/dQw4w9WgXcQ")!, startTime: nil))
+    }
+
+    @Test("x-callback parameters end the raw url")
+    func callbackParametersEndURL() {
+        let action = parse("yattee://bookmark?url=https://www.youtube.com/watch?v=dQw4w9WgXcQ&x-success=shortcuts://done")
+        #expect(action == .bookmark(URL(string: "https://www.youtube.com/watch?v=dQw4w9WgXcQ")!))
+    }
+
+    @Test("Every target verb parses", arguments: [
+        ("play-next", LinkAction.playNext(URL(string: "https://youtu.be/abc")!)),
+        ("download", .download(URL(string: "https://youtu.be/abc")!)),
+        ("subscribe", .subscribe(URL(string: "https://youtu.be/abc")!)),
+        ("unsubscribe", .unsubscribe(URL(string: "https://youtu.be/abc")!)),
+    ])
+    func targetVerbs(_ verb: String, _ expected: LinkAction) {
+        #expect(parse("yattee://\(verb)?url=https://youtu.be/abc") == expected)
+    }
+
+    @Test("Missing, local or non-web targets are rejected")
+    func badTargets() {
+        #expect(parse("yattee://play") == nil)
+        #expect(parse("yattee://play?url=") == nil)
+        #expect(parse("yattee://play?url=file:///etc/hosts") == nil)
+        #expect(parse("yattee://queue?url=javascript:alert(1)") == nil)
+    }
+
+    @Test("Player commands")
+    func playerCommands() {
+        #expect(parse("yattee://player/pause") == .player(.pause))
+        #expect(parse("yattee://player/play") == .player(.play))
+        #expect(parse("yattee://player/toggle") == .player(.toggle))
+        #expect(parse("yattee://player/next") == .player(.next))
+        #expect(parse("yattee://player/previous") == .player(.previous))
+        #expect(parse("yattee://player/close") == .player(.close))
+        #expect(parse("yattee://player/seek?t=90") == .player(.seek(to: 90)))
+        #expect(parse("yattee://player/seek?t=1m") == .player(.seek(to: 60)))
+        #expect(parse("yattee://player/seek?by=-10") == .player(.seekBy(-10)))
+        #expect(parse("yattee://player/rate?value=1.5") == .player(.rate(1.5)))
+    }
+
+    @Test("Invalid player commands are rejected")
+    func badPlayerCommands() {
+        #expect(parse("yattee://player") == nil)
+        #expect(parse("yattee://player/explode") == nil)
+        #expect(parse("yattee://player/seek") == nil)
+        #expect(parse("yattee://player/seek?by=nan") == nil)
+        #expect(parse("yattee://player/rate?value=0") == nil)
+        #expect(parse("yattee://player/rate?value=inf") == nil)
+    }
+
+    @Test("Screen links are not actions, and the router leaves action hosts alone")
+    func separationFromRouter() {
+        #expect(parse("yattee://playlist/PL123") == nil)
+        #expect(parse("yattee://video/abc") == nil)
+        #expect(URLRouter().route(URL(string: "yattee://play?url=https://youtu.be/abc")!) == nil)
+        #expect(URLRouter().route(URL(string: "yattee://player/pause")!) == nil)
+    }
+
+    @Test("Only play dismisses sheets")
+    func actionTraits() {
+        let url = URL(string: "https://youtu.be/abc")!
+        #expect(LinkAction.play(url, startTime: nil).dismissesPresentations)
+        #expect(!LinkAction.player(.pause).dismissesPresentations)
+        #expect(!LinkAction.bookmark(url).dismissesPresentations)
+    }
+}