Answer prose round 1: 0 🔴, 2 🟡 (0 misread); say what insideRun's callers rely on, delete sharedRuns's comment, clear the termination comment

src/markdown/mark-spellings.ts

@@ -44,7 +44,7 @@ export function isEmphasis(mark: AdfMark): boolean {
   return markSpelling(mark.type)?.kind === 'emphasis'
 }
 
-// spec/flavour.md, Marks. The writers and the portable reducer group runs alike only while both ask this.
+// spec/flavour.md, Marks. The portable reducer must ask this too, or it trims edge whitespace by runs the writers do not spell.
 export function insideRun({ node, outer }: RunNode, mark: AdfMark): RunNode | undefined {
   const held = nodeMarks(node)[outer]
   return held !== undefined && identicalMark(held, mark) ? { node, outer: outer + 1 } : undefined

src/markdown/portable/inline-reduction.ts

@@ -162,7 +162,7 @@ function withMarks(leaf: AdfNode, marks: readonly AdfMark[]): AdfNode {
 }
 
 export function trimmedEdges(leaves: readonly AdfNode[]): AdfNode[] {
-  // Terminates: a pass that changes a leaf drops its edge whitespace or takes a mark off that whitespace, and merging adds neither.
+  // Terminates: a pass that changes a leaf drops whitespace from the leaf's edge or takes a mark off that whitespace, and merging adds no whitespace or mark.
   for (let current = leaves; ; ) {
     const merged = withoutEdgeBreaks(mergeAdjacentText(current, joinsWhenEditorNormal))
     let changed = false
@@ -218,7 +218,6 @@ function edgeDepth(marks: readonly AdfMark[], neighbour: AdfNode | undefined, wh
   return kept === 0 && lineEdge ? undefined : kept
 }
 
-// How many of the runs around a leaf holding `marks`, outermost first, hold `neighbour` too.
 function sharedRuns(marks: readonly AdfMark[], neighbour: AdfNode): number {
   let inside: RunNode | undefined = { node: neighbour, outer: 0 }
   for (const [depth, mark] of marks.entries()) {