Close the class: a caller can no longer forget where the article lives

The fix before this made site-relative images zoomable by resolving them
against the article's own address. It left the parameter optional, which leaves
the bug one forgetful call site away from coming back -- and coming back
silently, as every image on a site-relative feed quietly refusing to zoom,
which is exactly how it went unnoticed on Ftrain in the first place.

It has no default now. Null is still a legitimate answer, because an article
with no address genuinely cannot resolve anything, but it has to be given on
purpose. A future reader surface that omits it fails to compile rather than
shipping the old behaviour.

Nothing about what the app does changed: the same 157 tests pass, and the six
test call sites that relied on the default now say baseUrl = null, which is
what they always meant.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018AwnALZL6bD4VBtATDVv3B

2 files changed, 14 insertions, 8 deletions

diff --git a/app/src/main/java/org/terst/feedreader/ui/ImageZoomLinks.kt b/app/src/main/java/org/terst/feedreader/ui/ImageZoomLinks.kt
index d924c02..179955e 100644
--- a/app/src/main/java/org/terst/feedreader/ui/ImageZoomLinks.kt
+++ b/app/src/main/java/org/terst/feedreader/ui/ImageZoomLinks.kt
@@ -36,8 +36,14 @@ private val imageFileExtensions = listOf(".jpg", ".jpeg", ".png", ".gif", ".webp
  * something already (ReaderExtractor's synthesized YouTube thumbnail is precisely this shape,
  * and wrapping it would swallow the tap that plays the video). Those are still zoomable when
  * the link points at an image file, which [zoomableImageTarget] handles on the other side.
+ *
+ * [baseUrl] is where the article itself lives, used to resolve an image address the feed wrote
+ * in shorthand. It has no default, deliberately: a caller that omits it does not silently get
+ * the behaviour that caused this bug -- every image on a site-relative feed like Ftrain's
+ * un-zoomable -- it fails to compile. Null is still a legitimate answer when there genuinely is
+ * no article address, but it has to be given on purpose rather than by forgetting.
  */
-fun linkifyImagesForZoom(html: String, baseUrl: String? = null): String = buildString {
+fun linkifyImagesForZoom(html: String, baseUrl: String?): String = buildString {
     var copiedUpTo = 0
     var anchorDepth = 0
     for (tag in anchorOrImageTagRegex.findAll(html)) {
diff --git a/app/src/test/java/org/terst/feedreader/ui/ImageZoomTest.kt b/app/src/test/java/org/terst/feedreader/ui/ImageZoomTest.kt
index aead885..5939bf8 100644
--- a/app/src/test/java/org/terst/feedreader/ui/ImageZoomTest.kt
+++ b/app/src/test/java/org/terst/feedreader/ui/ImageZoomTest.kt
@@ -9,7 +9,7 @@ class ImageZoomTest {
 
     @Test
     fun `a bare image is wrapped in a zoom link pointing at its own source`() {
-        val html = linkifyImagesForZoom("""<p>hi</p><img src="https://ex.com/a.jpg" alt="x">""")
+        val html = linkifyImagesForZoom("""<p>hi</p><img src="https://ex.com/a.jpg" alt="x">""", baseUrl = null)
         assertEquals(
             """<p>hi</p><a href="feedreader-image:https://ex.com/a.jpg"><img src="https://ex.com/a.jpg" alt="x"></a>""",
             html
@@ -22,18 +22,18 @@ class ImageZoomTest {
         // again would swallow the tap that's supposed to play the video.
         val original =
             """<a href="https://www.youtube.com/watch?v=abcdefghijk"><img src="https://i.ytimg.com/vi/x/hq720.jpg"></a>"""
-        assertEquals(original, linkifyImagesForZoom(original))
+        assertEquals(original, linkifyImagesForZoom(original, baseUrl = null))
     }
 
     @Test
     fun `an image after a closed link is still wrapped`() {
-        val html = linkifyImagesForZoom("""<a href="https://ex.com/">t</a><img src="https://ex.com/a.png">""")
+        val html = linkifyImagesForZoom("""<a href="https://ex.com/">t</a><img src="https://ex.com/a.png">""", baseUrl = null)
         assertTrue(html.endsWith("""<a href="feedreader-image:https://ex.com/a.png"><img src="https://ex.com/a.png"></a>"""))
     }
 
     @Test
     fun `a protocol-relative image source becomes an https zoom target`() {
-        val html = linkifyImagesForZoom("""<img src="//ex.com/a.jpg">""")
+        val html = linkifyImagesForZoom("""<img src="//ex.com/a.jpg">""", baseUrl = null)
         assertEquals("""<a href="feedreader-image:https://ex.com/a.jpg"><img src="//ex.com/a.jpg"></a>""", html)
     }
 
@@ -42,7 +42,7 @@ class ImageZoomTest {
         // Relative srcs resolve against the WebView's base URL -- with no base URL to resolve
         // against, better to leave the image un-zoomable than to build a dead link.
         val original = """<img src="/local/a.jpg">"""
-        assertEquals(original, linkifyImagesForZoom(original))
+        assertEquals(original, linkifyImagesForZoom(original, baseUrl = null))
     }
 
     @Test
@@ -80,12 +80,12 @@ class ImageZoomTest {
     @Test
     fun `a data uri image is left alone`() {
         val original = """<img src="data:image/png;base64,AAAA">"""
-        assertEquals(original, linkifyImagesForZoom(original))
+        assertEquals(original, linkifyImagesForZoom(original, baseUrl = null))
     }
 
     @Test
     fun `wrapping is not confused by tags that merely start with the letter a`() {
-        val html = linkifyImagesForZoom("""<abbr title="x">y</abbr><img src="https://ex.com/a.jpg">""")
+        val html = linkifyImagesForZoom("""<abbr title="x">y</abbr><img src="https://ex.com/a.jpg">""", baseUrl = null)
         assertTrue(html.contains("""<a href="feedreader-image:https://ex.com/a.jpg">"""))
     }