channels: complete carousel header review fixes

Fall back to the ucid-based channel URL when a legacy auto-generated header omits urlCanonical, and cover it with a focused regression spec.

Remove the unrelated selected-tab guard and its spec so this change remains scoped to auto-generated channel headers.

spec/invidious/channels/about_spec.cr

@@ -200,6 +200,27 @@ Spectator.describe "extract_auto_generated_channel_header" do
     expect(header[:tags]).to eq(["Gaming"])
   end
 
+  it "falls back to the channel URL when the canonical URL is missing" do
+    initdata = JSON.parse(<<-JSON).as_h
+      {
+        "header": {
+          "interactiveTabbedHeaderRenderer": {
+            "title": {"simpleText": "Legacy gaming"}
+          }
+        },
+        "microformat": {
+          "microformatDataRenderer": {
+            "familySafe": true
+          }
+        }
+      }
+      JSON
+
+    header = extract_auto_generated_channel_header(initdata, "UCMissingCanonical")
+
+    expect(header[:author_url]).to eq("https://www.youtube.com/channel/UCMissingCanonical")
+  end
+
   it "keeps an explicit familySafe: false" do
     initdata = JSON.parse(<<-JSON).as_h
       {

spec/invidious/yt_backend/extractors_spec.cr

@@ -1,22 +0,0 @@
-require "../../parsers_helper"
-
-Spectator.describe "YouTubeTabs" do
-  it "treats a selected tab without content as empty" do
-    initdata = JSON.parse(<<-JSON).as_h
-      {
-        "contents": {
-          "twoColumnBrowseResultsRenderer": {
-            "tabs": [
-              {"tabRenderer": {"selected": true}}
-            ]
-          }
-        }
-      }
-      JSON
-
-    items, continuation = extract_items(initdata)
-
-    expect(items).to be_empty
-    expect(continuation).to be_nil
-  end
-end

src/invidious/channels/about.cr

@@ -42,7 +42,8 @@ def extract_auto_generated_channel_header(initdata : Hash(String, JSON::Any), uc
 
   if header = initdata.dig?("header", "interactiveTabbedHeaderRenderer")
     author = header.dig("title", "simpleText").as_s
-    author_url = initdata.dig("microformat", "microformatDataRenderer", "urlCanonical").as_s
+    author_url = initdata.dig?("microformat", "microformatDataRenderer", "urlCanonical").try &.as_s?
+    author_url ||= "https://www.youtube.com/channel/#{ucid}"
     author_thumbnail = header.dig?("boxArt", "thumbnails", 0, "url").try &.as_s || ""
 
     banner = header.dig?("banner", "thumbnails").try &.[-1]?.try &.["url"].as_s?

src/invidious/yt_backend/extractors.cr

@@ -964,8 +964,7 @@ private module Extractors
 
     private def self.extract(target)
       raw_items = [] of JSON::Any
-      content = extract_selected_tab(target["tabs"])["content"]?
-      return raw_items if content.nil?
+      content = extract_selected_tab(target["tabs"])["content"]
 
       if section_list_contents = content.dig?("sectionListRenderer", "contents")
         raw_items = unpack_section_list(section_list_contents)