From 7208ffc10f0f52f95f63b7f57e5c9d745530bd68 Mon Sep 17 00:00:00 2001
From: Guilhem Lemouel <guilhemlemouel@gmail.com>
Date: Wed, 30 Sep 2026 10:27:33 -0700
Subject: [PATCH] fix: a path that names nothing yet has no breadcrumb leaf
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`splitItemPath` documents that it gives up on a path still being typed, but
`f/demo/` is three parts and returned a leaf with an empty name — a blank
segment in the trail. The editor binds the path live, so the breadcrumb sees
every keystroke.

Tested here rather than `navPageFor`'s sort: no two `NAV_PAGES` paths nest, so
the longest-prefix case that test claimed to pin has only one candidate. Renamed
it to what it actually checks.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
---
 .../src/lib/components/breadcrumbPath.test.ts | 20 +++++++++++++++++++
 frontend/src/lib/components/breadcrumbPath.ts |  3 +++
 .../lib/components/sidebar/navPages.test.ts   |  2 +-
 3 files changed, 24 insertions(+), 1 deletion(-)
 create mode 100644 frontend/src/lib/components/breadcrumbPath.test.ts

diff --git a/frontend/src/lib/components/breadcrumbPath.test.ts b/frontend/src/lib/components/breadcrumbPath.test.ts
new file mode 100644
index 0000000000..987403e2e2
--- /dev/null
+++ b/frontend/src/lib/components/breadcrumbPath.test.ts
@@ -0,0 +1,20 @@
+import { describe, it, expect } from 'vitest'
+import { splitItemPath } from './breadcrumbPath'
+
+describe('splitItemPath', () => {
+	it('walks the scope, each subfolder, then the item, each with its cumulative path', () => {
+		expect(splitItemPath('f/demo/sub/weather_report')).toEqual({
+			dirs: [
+				{ name: 'f/demo', fullPath: 'f/demo' },
+				{ name: 'sub', fullPath: 'f/demo/sub' }
+			],
+			leaf: { name: 'weather_report', fullPath: 'f/demo/sub/weather_report' }
+		})
+	})
+
+	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.
+		expect(splitItemPath('f/demo')).toBeUndefined()
+		expect(splitItemPath('f/demo/')).toBeUndefined()
+	})
+})
diff --git a/frontend/src/lib/components/breadcrumbPath.ts b/frontend/src/lib/components/breadcrumbPath.ts
index 8c041518f5..25834181ad 100644
--- a/frontend/src/lib/components/breadcrumbPath.ts
+++ b/frontend/src/lib/components/breadcrumbPath.ts
@@ -13,6 +13,9 @@ export function splitItemPath(path: string): { dirs: PathDir[]; leaf: PathDir }
 	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++) {
diff --git a/frontend/src/lib/components/sidebar/navPages.test.ts b/frontend/src/lib/components/sidebar/navPages.test.ts
index 73f5ea456e..6e68912a15 100644
--- a/frontend/src/lib/components/sidebar/navPages.test.ts
+++ b/frontend/src/lib/components/sidebar/navPages.test.ts
@@ -6,7 +6,7 @@ describe('navPageFor', () => {
 		expect(navPageFor('/base/runs', '/base')?.label).toBe('Runs')
 	})
 
-	it('keeps an item route on its page (longest prefix wins)', () => {
+	it('keeps an item route on its page', () => {
 		expect(navPageFor('/runs/f/demo/x', '')?.label).toBe('Runs')
 	})