fix: keep the folders a half-typed path already names

The trailing-separator guard gave up on `f/demo/` entirely, which dropped the
whole trail to the kind chip and brought `f/demo` back on the first character of
the name. The levels the path does name come back now; only the leaf waits.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

frontend/src/lib/components/EditorHeader.svelte

@@ -156,6 +156,8 @@
 							onPick={handlePickerSelect}
 						/>
 					{/each}
+				{/if}
+				{#if segments?.leaf}
 					{@const leafKey = leafKeyFor(kind, segments.leaf.fullPath)}
 					{@const leafParent = segments.dirs[segments.dirs.length - 1]?.fullPath}
 					<ChevronRight size={10} class="shrink-0" />

frontend/src/lib/components/breadcrumbPath.test.ts

@@ -12,9 +12,16 @@ describe('splitItemPath', () => {
 		})
 	})
 
-	it('gives up on a path that names nothing yet, trailing separator included', () => {
-		// The editor binds the path live, so every keystroke reaches the breadcrumb.
+	it('gives up before there is a scope', () => {
 		expect(splitItemPath('f/demo')).toBeUndefined()
-		expect(splitItemPath('f/demo/')).toBeUndefined()
+	})
+
+	it('keeps the folders while the name is still being typed', () => {
+		// The editor binds the path live, so every keystroke reaches the breadcrumb: the trail must
+		// not drop out and come back on the first character of the name.
+		expect(splitItemPath('f/demo/')).toEqual({
+			dirs: [{ name: 'f/demo', fullPath: 'f/demo' }],
+			leaf: undefined
+		})
 	})
 })

frontend/src/lib/components/breadcrumbPath.ts

@@ -6,21 +6,25 @@ export type PathDir = { name: string; fullPath: string }
  * `u/<user>`), then each subfolder, then the item itself. Each level carries the cumulative path,
  * which is what the picker opens and highlights.
  *
- * Returns undefined for anything shorter than scope + name, such as a path still being typed.
+ * Returns undefined before there is even a scope. The leaf is undefined while the path names a
+ * folder but no item yet (`f/demo/`) — the levels it does name still come back.
  */
-export function splitItemPath(path: string): { dirs: PathDir[]; leaf: PathDir } | undefined {
+export function splitItemPath(
+	path: string
+): { dirs: PathDir[]; leaf: PathDir | undefined } | undefined {
 	const parts = path.split('/')
 	if (parts.length < 3) return undefined
 	const scope = parts.slice(0, 2).join('/')
 	const slug = parts.slice(2)
-	// `f/demo/` is three parts but names nothing yet, and a leaf with an empty name draws a blank
-	// segment. The editor's path is bound live, so the breadcrumb sees every keystroke.
-	if (slug[slug.length - 1] === '') return undefined
 	const dirs: PathDir[] = [{ name: scope, fullPath: scope }]
 	let acc = scope
 	for (let i = 0; i < slug.length - 1; i++) {
 		acc = `${acc}/${slug[i]}`
 		dirs.push({ name: slug[i], fullPath: acc })
 	}
-	return { dirs, leaf: { name: slug[slug.length - 1], fullPath: path } }
+	// A leaf with an empty name draws a blank segment. The editor binds the path live, so the
+	// breadcrumb sees every keystroke: the folders stay put while the name is being typed rather
+	// than the whole trail dropping out and coming back.
+	const name = slug[slug.length - 1]
+	return { dirs, leaf: name ? { name, fullPath: path } : undefined }
 }