feat(android): blockquote fill via LineBackgroundSpan and container span flags

- Add SPAN_FLAGS_CONTAINER_BACKGROUND (max priority) so blockquote draws
  before lower-priority LineBackgroundSpans on the same line.
- Implement LineBackgroundSpan on BlockquoteSpan and move fill from
  drawLeadingMargin to drawBackground; keep accent bars in drawLeadingMargin.
- Unblocks inline chip/pill backgrounds rendering above blockquote fill.

Made-with: Cursor

Author: xindixu

android/src/main/java/com/swmansion/enriched/markdown/renderer/BlockquoteRenderer.kt

@@ -3,6 +3,7 @@ package com.swmansion.enriched.markdown.renderer
 import android.text.SpannableStringBuilder
 import com.swmansion.enriched.markdown.parser.MarkdownASTNode
 import com.swmansion.enriched.markdown.spans.BlockquoteSpan
+import com.swmansion.enriched.markdown.utils.text.span.SPAN_FLAGS_CONTAINER_BACKGROUND
 import com.swmansion.enriched.markdown.utils.text.span.SPAN_FLAGS_EXCLUSIVE_EXCLUSIVE
 import com.swmansion.enriched.markdown.utils.text.span.applyMarginBottom
 import com.swmansion.enriched.markdown.utils.text.span.applyMarginTop
@@ -45,12 +46,16 @@ class BlockquoteRenderer(
         .map { builder.getSpanStart(it) to builder.getSpanEnd(it) }
         .sortedBy { it.first }
 
-    // The Accent Bar Span covers the full range for visual continuity
+    // The Accent Bar Span covers the full range for visual continuity.
+    // Use high-priority flags so BlockquoteSpan's LineBackgroundSpan pass
+    // runs FIRST on each line — the blockquote fill is painted first, then
+    // inline chip/pill backgrounds (mention pills etc.) draw on top of it
+    // instead of being covered by it.
     builder.setSpan(
       BlockquoteSpan(style, depth, factory.context, factory.styleCache),
       start,
       end,
-      SPAN_FLAGS_EXCLUSIVE_EXCLUSIVE,
+      SPAN_FLAGS_CONTAINER_BACKGROUND,
     )
 
     // Apply styling only to segments that are NOT nested quotes

android/src/main/java/com/swmansion/enriched/markdown/spans/BlockquoteSpan.kt

@@ -10,6 +10,7 @@ import android.text.Layout
 import android.text.Spanned
 import android.text.TextPaint
 import android.text.style.LeadingMarginSpan
+import android.text.style.LineBackgroundSpan
 import android.text.style.MetricAffectingSpan
 import com.swmansion.enriched.markdown.renderer.BlockStyle
 import com.swmansion.enriched.markdown.renderer.SpanStyleCache
@@ -23,7 +24,8 @@ class BlockquoteSpan(
   private val context: Context,
   private val styleCache: SpanStyleCache,
 ) : MetricAffectingSpan(),
-  LeadingMarginSpan {
+  LeadingMarginSpan,
+  LineBackgroundSpan {
   private val levelSpacing: Float = blockquoteStyle.borderWidth + blockquoteStyle.gapWidth
   private val blockStyle =
     BlockStyle(
@@ -60,8 +62,6 @@ class BlockquoteSpan(
     // Essential check from original: only the deepest span draws to prevent over-rendering background
     if (shouldSkipDrawing(text, start)) return
 
-    drawBackground(c, top, bottom, layout)
-
     val borderPaint = configureBorderPaint()
     val borderTop = top.toFloat()
     val borderBottom = bottom.toFloat()
@@ -73,6 +73,31 @@ class BlockquoteSpan(
     }
   }
 
+  /**
+   * Drawn BEFORE glyphs and before other [LineBackgroundSpan]s attached to the
+   * same line, so inline backgrounds painted by mention / code spans render on
+   * top of the blockquote fill instead of being covered by it (the previous
+   * implementation painted the blockquote fill from [drawLeadingMargin], which
+   * runs AFTER [LineBackgroundSpan.drawBackground] and erased the mention
+   * pill).
+   */
+  override fun drawBackground(
+    canvas: Canvas,
+    paint: Paint,
+    left: Int,
+    right: Int,
+    top: Int,
+    baseline: Int,
+    bottom: Int,
+    text: CharSequence,
+    start: Int,
+    end: Int,
+    lineNum: Int,
+  ) {
+    if (shouldSkipDrawing(text, start)) return
+    drawBackground(canvas, top, bottom, right)
+  }
+
   @SuppressLint("WrongConstant") // Result of mask is always valid: 0, 1, 2, or 3
   private fun applyTextStyle(tp: TextPaint) {
     tp.textSize = blockStyle.fontSize
@@ -125,10 +150,10 @@ class BlockquoteSpan(
     c: Canvas,
     top: Int,
     bottom: Int,
-    layout: Layout?,
+    right: Int,
   ) {
     val bgColor = blockquoteStyle.backgroundColor?.takeIf { it != Color.TRANSPARENT } ?: return
     val backgroundPaint = configureBackgroundPaint(bgColor)
-    c.drawRect(0f, top.toFloat(), layout?.width?.toFloat() ?: 0f, bottom.toFloat(), backgroundPaint)
+    c.drawRect(0f, top.toFloat(), right.toFloat(), bottom.toFloat(), backgroundPaint)
   }
 }

android/src/main/java/com/swmansion/enriched/markdown/utils/text/span/SpanFlags.kt

@@ -1,5 +1,17 @@
 package com.swmansion.enriched.markdown.utils.text.span
 
 import android.text.SpannableString
+import android.text.Spanned
 
 const val SPAN_FLAGS_EXCLUSIVE_EXCLUSIVE = SpannableString.SPAN_EXCLUSIVE_EXCLUSIVE
+
+/**
+ * EXCLUSIVE_EXCLUSIVE flags with the maximum span priority bit set. Higher
+ * priority means the span is iterated FIRST during the text view's draw
+ * passes (e.g. `Layout.drawBackground`), which means it's painted FIRST — so
+ * lower-priority spans drawn afterwards end up on top visually. Use this for
+ * full-width container backgrounds (like blockquote) that must sit UNDER any
+ * inline chip / pill backgrounds on the same line.
+ */
+const val SPAN_FLAGS_CONTAINER_BACKGROUND =
+  SpannableString.SPAN_EXCLUSIVE_EXCLUSIVE or ((0xFF) shl Spanned.SPAN_PRIORITY_SHIFT)