macos: prevent stale search selection crash (#13645)

Fixes #13266

Keep search text and its selection range synchronized as a single state
transition.

Deleting or replacing a search term could leave a String.Index range
from the old value attached to the text field. Applying that range could
crash the app.

Clear selection before publishing new text.

macos/Sources/Ghostty/Ghostty.App.swift

@@ -2164,7 +2164,7 @@ extension Ghostty {
                 DispatchQueue.main.async {
                     if let searchState = surfaceView.searchState {
                         if let needle = startSearch.needle, !needle.isEmpty {
-                            searchState.needle = needle
+                            searchState.setNeedle(needle)
                         }
                     } else {
                         surfaceView.searchState = Ghostty.SurfaceView.SearchState(from: startSearch)

macos/Sources/Ghostty/Surface View/OSSurfaceView.swift

@@ -122,12 +122,12 @@ extension Ghostty.OSSurfaceView {
         /// The `.find` pasteboard lets us sync our needle across the system and other find bars.
         private let pasteboard: OSPasteboard
 
-        @Published var needle: String = ""
+        @Published private(set) var needle: String = ""
         @Published var selected: UInt?
         @Published var total: UInt?
 
         /// The range of the needle's text selection in the find bar.
-        @Published var needleSelection: Range<String.Index>?
+        @Published private(set) var needleSelection: Range<String.Index>?
 
         init(
             from startSearch: Ghostty.Action.StartSearch,
@@ -135,18 +135,49 @@ extension Ghostty.OSSurfaceView {
         ) {
             self.pasteboard = pasteboard
             if let needle = startSearch.needle, !needle.isEmpty {
-                self.needle = needle
+                setNeedle(needle)
                 writePasteboardNeedle()
             } else {
                 readPasteboardNeedle()
             }
         }
 
+        /// Replaces the search needle while keeping its selection valid.
+        func setNeedle(_ needle: String, selectAll: Bool = false) {
+            if needle != self.needle {
+                // String.Index values are only valid for the string that created
+                // them, so publish a nil selection before changing the string.
+                needleSelection = nil
+                self.needle = needle
+            }
+
+            if selectAll {
+                needleSelection = self.needle.startIndex..<self.needle.endIndex
+            }
+        }
+
+        /// Updates the selection only when both indices are valid for the needle.
+        func setNeedleSelection(_ selection: Range<String.Index>?) {
+            guard let selection else {
+                needleSelection = nil
+                return
+            }
+
+            guard
+                let lowerBound = String.Index(selection.lowerBound, within: needle),
+                let upperBound = String.Index(selection.upperBound, within: needle)
+            else {
+                needleSelection = nil
+                return
+            }
+
+            needleSelection = lowerBound..<upperBound
+        }
+
         func readPasteboardNeedle() {
             let pasteboardNeedle = pasteboard.string
             if let pasteboardNeedle, pasteboardNeedle != needle {
-                needle = pasteboardNeedle
-                needleSelection = needle.startIndex..<needle.endIndex
+                setNeedle(pasteboardNeedle, selectAll: true)
             }
         }
 

macos/Sources/Ghostty/Surface View/SurfaceView.swift

@@ -379,8 +379,14 @@ extension Ghostty {
                 HStack(spacing: 4) {
                     BackportSelectionTextField(
                         "Search",
-                        text: $searchState.needle,
-                        selection: $searchState.needleSelection
+                        text: Binding(
+                            get: { searchState.needle },
+                            set: { searchState.setNeedle($0) }
+                        ),
+                        selection: Binding(
+                            get: { searchState.needleSelection },
+                            set: { searchState.setNeedleSelection($0) }
+                        )
                     )
                     .textFieldStyle(.plain)
                     .frame(width: 180)

macos/Tests/Ghostty/Surface View/SurfaceView+SearchStateTests.swift

@@ -57,18 +57,44 @@ import Testing
             from: StartSearch(c: .init(needle: nil)),
             pasteboard: pasteboard
         )
-        sut.needle = "sut"
+        sut.setNeedle("sut")
         sut.writePasteboardNeedle()
         #expect(pasteboard.string(forType: .string) == "sut")
     }
 
+    @Test func setNeedle_clearsNeedleSelection() {
+        let sut = SearchState(
+            from: StartSearch(c: .init(needle: nil)),
+            pasteboard: pasteboard
+        )
+        sut.setNeedleSelection(sut.needle.startIndex..<sut.needle.endIndex)
+
+        sut.setNeedle("x")
+
+        #expect(sut.needle == "x")
+        #expect(sut.needleSelection == nil)
+    }
+
+    @Test func setNeedleSelection_ignoresRangeFromLongerNeedle() {
+        let sut = SearchState(
+            from: StartSearch(c: .init(needle: nil)),
+            pasteboard: pasteboard
+        )
+        let oldNeedle = "abcdefghijklmnopqrstuvwxyz"
+
+        sut.setNeedle("x")
+        sut.setNeedleSelection(oldNeedle.startIndex..<oldNeedle.endIndex)
+
+        #expect(sut.needleSelection == nil)
+    }
+
     @Test func readPasteboardNeedle_whenPasteboardNeedleIsNil() {
         let sut = SearchState(
             from: StartSearch(c: .init(needle: nil)),
             pasteboard: pasteboard
         )
         pasteboard.clearContents()
-        sut.needle = "sut"
+        sut.setNeedle("sut")
         sut.readPasteboardNeedle()
         #expect(sut.needle == "sut")
     }
@@ -78,7 +104,7 @@ import Testing
             from: StartSearch(c: .init(needle: nil)),
             pasteboard: pasteboard
         )
-        sut.needle = "sut"
+        sut.setNeedle("sut")
         sut.readPasteboardNeedle()
         #expect(sut.needle == "pb")
     }
@@ -88,7 +114,7 @@ import Testing
             from: StartSearch(c: .init(needle: nil)),
             pasteboard: pasteboard
         )
-        sut.needle = "sut"
+        sut.setNeedle("sut")
         sut.readPasteboardNeedle()
 
         let expected = "pb".startIndex..<"pb".endIndex