Fix favicon race during back/forward navigation

Sources/Panels/BrowserPanel.swift

@@ -997,6 +997,7 @@ final class BrowserPanel: Panel, ObservableObject {
     private var loadingGeneration: Int = 0
 
     private var faviconTask: Task<Void, Never>?
+    private var faviconRefreshGeneration: Int = 0
     private var lastFaviconURLString: String?
     private let minPageZoom: CGFloat = 0.25
     private let maxPageZoom: CGFloat = 5.0
@@ -1228,9 +1229,17 @@ final class BrowserPanel: Panel, ObservableObject {
 
         guard let pageURL = webView.url else { return }
         guard let scheme = pageURL.scheme?.lowercased(), scheme == "http" || scheme == "https" else { return }
+        let pageURLString = pageURL.absoluteString
+        faviconRefreshGeneration &+= 1
+        let refreshGeneration = faviconRefreshGeneration
 
         faviconTask = Task { @MainActor [weak self, weak webView] in
             guard let self, let webView else { return }
+            guard self.isCurrentFaviconRefresh(
+                generation: refreshGeneration,
+                pageURLString: pageURLString,
+                webView: webView
+            ) else { return }
 
             // Try to discover the best icon URL from the document.
             let js = """
@@ -1264,6 +1273,11 @@ final class BrowserPanel: Panel, ObservableObject {
                     discoveredURL = u
                 }
             }
+            guard self.isCurrentFaviconRefresh(
+                generation: refreshGeneration,
+                pageURLString: pageURLString,
+                webView: webView
+            ) else { return }
 
             let fallbackURL = URL(string: "/favicon.ico", relativeTo: pageURL)
             let iconURL = discoveredURL ?? fallbackURL
@@ -1288,6 +1302,11 @@ final class BrowserPanel: Panel, ObservableObject {
             } catch {
                 return
             }
+            guard self.isCurrentFaviconRefresh(
+                generation: refreshGeneration,
+                pageURLString: pageURLString,
+                webView: webView
+            ) else { return }
 
             guard let http = response as? HTTPURLResponse,
                   (200..<300).contains(http.statusCode) else {
@@ -1301,6 +1320,16 @@ final class BrowserPanel: Panel, ObservableObject {
         }
     }
 
+    private func isCurrentFaviconRefresh(
+        generation: Int,
+        pageURLString: String,
+        webView: WKWebView
+    ) -> Bool {
+        guard !Task.isCancelled else { return false }
+        guard generation == faviconRefreshGeneration else { return false }
+        return webView.url?.absoluteString == pageURLString
+    }
+
     @MainActor
     private static func makeFaviconPNGData(from raw: Data, targetPx: Int) -> Data? {
         guard let image = NSImage(data: raw) else { return nil }
@@ -1359,6 +1388,11 @@ final class BrowserPanel: Panel, ObservableObject {
 
     private func handleWebViewLoadingChanged(_ newValue: Bool) {
         if newValue {
+            // Any new load invalidates older favicon fetches, even for same-URL reloads.
+            faviconRefreshGeneration &+= 1
+            faviconTask?.cancel()
+            faviconTask = nil
+            lastFaviconURLString = nil
             loadingGeneration &+= 1
             loadingEndWorkItem?.cancel()
             loadingEndWorkItem = nil

tests/test_browser_favicon_navigation_regression.py

@@ -0,0 +1,85 @@
+#!/usr/bin/env python3
+"""Static regression checks for favicon sync during browser navigation.
+
+Guards the race fix where stale async favicon fetches must not overwrite the
+icon after the user navigates (including back/forward and same-URL reloads).
+"""
+
+from __future__ import annotations
+
+import subprocess
+from pathlib import Path
+
+
+def repo_root() -> Path:
+    result = subprocess.run(
+        ["git", "rev-parse", "--show-toplevel"],
+        capture_output=True,
+        text=True,
+    )
+    if result.returncode == 0:
+        return Path(result.stdout.strip())
+    return Path(__file__).resolve().parents[1]
+
+
+def extract_block(source: str, signature: str) -> str:
+    start = source.find(signature)
+    if start < 0:
+        raise ValueError(f"Missing signature: {signature}")
+    brace_start = source.find("{", start)
+    if brace_start < 0:
+        raise ValueError(f"Missing opening brace for: {signature}")
+    depth = 0
+    for idx in range(brace_start, len(source)):
+        char = source[idx]
+        if char == "{":
+            depth += 1
+        elif char == "}":
+            depth -= 1
+            if depth == 0:
+                return source[brace_start : idx + 1]
+    raise ValueError(f"Unbalanced braces for: {signature}")
+
+
+def main() -> int:
+    root = repo_root()
+    failures: list[str] = []
+
+    panel_path = root / "Sources" / "Panels" / "BrowserPanel.swift"
+    panel_source = panel_path.read_text(encoding="utf-8")
+
+    if "private var faviconRefreshGeneration: Int = 0" not in panel_source:
+        failures.append("BrowserPanel is missing faviconRefreshGeneration state")
+
+    refresh_block = extract_block(panel_source, "private func refreshFavicon(from webView: WKWebView)")
+    if "let pageURLString = pageURL.absoluteString" not in refresh_block:
+        failures.append("refreshFavicon() no longer captures pageURLString for staleness checks")
+    if refresh_block.count("isCurrentFaviconRefresh(") < 3:
+        failures.append("refreshFavicon() no longer checks staleness at each async stage")
+
+    current_guard_block = extract_block(panel_source, "private func isCurrentFaviconRefresh(")
+    if "generation == faviconRefreshGeneration" not in current_guard_block:
+        failures.append("isCurrentFaviconRefresh() no longer validates refresh generation")
+    if "webView.url?.absoluteString == pageURLString" not in current_guard_block:
+        failures.append("isCurrentFaviconRefresh() no longer validates active page URL")
+
+    loading_block = extract_block(panel_source, "private func handleWebViewLoadingChanged(_ newValue: Bool)")
+    if "faviconRefreshGeneration &+= 1" not in loading_block:
+        failures.append("handleWebViewLoadingChanged() no longer invalidates old favicon refreshes")
+    if "faviconTask?.cancel()" not in loading_block:
+        failures.append("handleWebViewLoadingChanged() no longer cancels stale favicon tasks")
+    if "lastFaviconURLString = nil" not in loading_block:
+        failures.append("handleWebViewLoadingChanged() no longer resets favicon URL cache on new loads")
+
+    if failures:
+        print("FAIL: browser favicon navigation regression guard failed")
+        for item in failures:
+            print(f" - {item}")
+        return 1
+
+    print("PASS: browser favicon navigation guard is in place")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())