fix(host): review round 16 — UNC/forward-slash home forms; root-crumb separator; scrollbar symmetry; test dedup

packages/host/directory-picker-browse/src/client/DirectoryBrowser.module.css

@@ -62,6 +62,12 @@
   scrollbar-width: none;
 }
 
+/* Pseudo-element-path engines (see .millerRow's twin rule): the 20px crumb
+ * bar has no room for a bar at all. */
+.crumbTrail::-webkit-scrollbar {
+  display: none;
+}
+
 .crumbSeat {
   display: inline-flex;
   align-items: center;
@@ -299,9 +305,8 @@
   color: var(--dsw-alias-label-primary);
 }
 
-/* Trailing pressed check (Menu's .check parallel): flex-none so wrap or
- * narrow-viewport clamp pressure never squashes the glyph — the nowrap
- * label refuses to shrink, leaving the icon as the only compressible item. */
+/* Flex-none: the nowrap label refuses to shrink, which would leave the
+ * glyph as the only compressible item under wrap or narrow-viewport clamp. */
 .toggleCheck {
   flex: none;
 }

packages/host/directory-picker-browse/src/client/DirectoryBrowser.tsx

@@ -73,30 +73,37 @@ function foldPathFor(sep: '\\' | '/'): (value: string) => string {
 }
 
 /**
- * Lexically normalizes an absolute host path for comparisons: collapses
- * repeated and trailing separators, drops `.` segments, and applies `..` —
- * mirroring the backend's resolve() for the shapes an environment-supplied
- * HOME legally carries verbatim (`/home/u/`, `/home//u`, `/home/u/.`)
- * while the backend's paths arrive already resolved. A lexical mirror
- * only: symlinks are the backend's business, and the input always
- * contains the separator (it is an absolute path).
+ * Lexically normalizes an absolute host path for comparisons: folds
+ * forward slashes on Windows (win32 accepts either), collapses repeated
+ * and trailing separators, drops `.` segments, and applies `..` without
+ * ever crossing the root — POSIX's `/`, a drive's `C:`, or UNC's
+ * `\\server\share` pair — mirroring the backend's resolve() for the
+ * shapes an environment-supplied HOME legally carries verbatim while the
+ * backend's own paths arrive already resolved. A lexical mirror only:
+ * symlinks are the backend's business.
  */
 function normalizePathFor(sep: '\\' | '/'): (value: string) => string {
-  return (value) => {
-    const segments = value.split(sep)
-    const head = segments.shift()
-    /* v8 ignore next -- narrowing guard: split always yields at least one segment. */
-    if (head === undefined) return value
-    const out: string[] = []
-    for (const segment of segments) {
+  return (raw) => {
+    // win32 treats a forward slash as a separator too (resolve() folds
+    // them); POSIX must not — a backslash there is a name character.
+    const value = sep === '\\' ? raw.replaceAll('/', sep) : raw
+    const unc = sep === '\\' && value.startsWith(`${sep}${sep}`)
+    const segments = (unc ? value.slice(2) : value).split(sep)
+    // The unpoppable root: POSIX's leading empty segment / the drive
+    // segment, or UNC's server + share pair.
+    const rootLength = unc ? 2 : 1
+    const out = segments.slice(0, rootLength)
+    for (const segment of segments.slice(rootLength)) {
       if (segment === '' || segment === '.') continue
       if (segment === '..') {
-        out.pop()
+        if (out.length > rootLength) out.pop()
         continue
       }
       out.push(segment)
     }
-    return `${head}${sep}${out.join(sep)}`
+    // A bare root keeps (or regains) the trailing separator resolve()
+    // emits for `/`, `C:\`, and `\\server\share\`.
+    return `${unc ? sep + sep : ''}${out.join(sep)}${out.length === rootLength ? sep : ''}`
   }
 }
 
@@ -119,16 +126,20 @@ function displayCrumbs(listing: DirectoryListing, homeLabel: string): DirectoryE
 }
 
 /**
- * The listing's platform separator, inferred from the home path the host
- * stamped — never from typed text or entry paths, where a backslash is a
- * legal POSIX name character. Still a heuristic at the last step: a POSIX
- * home directory whose own name contains a backslash would misread.
+ * The listing's platform separator, read from the host-resolved root crumb
+ * (`/`, `C:\`, `\\server\share\`) — exact for every root form the backend
+ * emits, immune both to a home delivered in the other slash flavor
+ * (`USERPROFILE=C:/Users/Alice`) and to backslashes inside POSIX names.
  * TODO: replace with a host-stamped `separator` field on the wire
  * DirectoryListing so the platform fact travels verbatim (the trade-off is
  * recorded in the directory-picker capability seam Agent Note).
  */
 function separatorOf(listing: DirectoryListing): '\\' | '/' {
-  return listing.home.includes('\\') ? '\\' : '/'
+  const rootCrumb = listing.crumbs.at(0)
+  // Home is the honest fallback for an impossible empty chain.
+  /* v8 ignore next -- narrowing guard: the wire chain is root-to-target inclusive. */
+  if (rootCrumb === undefined) return listing.home.includes('\\') ? '\\' : '/'
+  return rootCrumb.path.includes('\\') ? '\\' : '/'
 }
 
 /**

packages/host/directory-picker-browse/tests/directory-browser.spec.tsx

@@ -240,20 +240,12 @@ describe('DirectoryBrowser', () => {
     expect(within(columns()[1]!).getByText('harness')).toBeTruthy()
   })
 
-  it('a trailing-separator home is still the display root (single pane on open)', async () => {
-    const listDirectory = vi.fn(async (path?: string) => ({ ...listingFor(path), home: `${HOME}/` }))
-    mount({ listDirectory })
-    await waitFor(() => { expect(screen.getByRole('listitem')).toBeTruthy() })
-    // `HOME=/home/u/` ships verbatim while the listing path resolves without
-    // the trailing separator; the normalized comparison still collapses to
-    // the Home crumb and no parent leg launches.
-    expect(columns()).toHaveLength(1)
-    expect(screen.getByRole('button', { name: 'browser.home' })).toBeTruthy()
-    expect(listDirectory).toHaveBeenCalledTimes(1)
-  })
-
-  it('a home with several trailing separators is still the display root', async () => {
-    const listDirectory = vi.fn(async (path?: string) => ({ ...listingFor(path), home: `${HOME}//` }))
+  // HOME ships verbatim from the environment while listing paths arrive
+  // resolved; each decoration (trailing, repeated, dot, dot-dot segments)
+  // must still normalize to the display root — single pane, Home crumb,
+  // and no parent leg launched.
+  it.each(['/', '//', '/foo/../.'])('a home decorated with "%s" is still the display root', async (decoration) => {
+    const listDirectory = vi.fn(async (path?: string) => ({ ...listingFor(path), home: `${HOME}${decoration}` }))
     mount({ listDirectory })
     await waitFor(() => { expect(screen.getByRole('listitem')).toBeTruthy() })
     expect(columns()).toHaveLength(1)
@@ -349,16 +341,6 @@ describe('DirectoryBrowser', () => {
     expect(document.activeElement).toBe(screen.getByRole('button', { name: 'browser.editPath' }))
   })
 
-  it('a home carrying dot segments is still the display root', async () => {
-    // os.homedir() ships HOME verbatim; the backend resolves listing paths.
-    const listDirectory = vi.fn(async (path?: string) => ({ ...listingFor(path), home: `${HOME}/foo/../.` }))
-    mount({ listDirectory })
-    await waitFor(() => { expect(screen.getByRole('listitem')).toBeTruthy() })
-    expect(columns()).toHaveLength(1)
-    expect(screen.getByRole('button', { name: 'browser.home' })).toBeTruthy()
-    expect(listDirectory).toHaveBeenCalledTimes(1)
-  })
-
   it('a navigation to the filesystem root keeps the single wide level', async () => {
     mount()
     await waitFor(() => { expect(screen.getByRole('listitem')).toBeTruthy() })
@@ -425,6 +407,51 @@ describe('DirectoryBrowser', () => {
     expect(document.activeElement?.getAttribute('aria-current')).toBe('true')
   })
 
+  it('a UNC home with dot-dot never pops the share root and still collapses to Home', async () => {
+    const SHARE = '\\\\server\\share'
+    const listing: DirectoryListing = {
+      path: `${SHARE}\\x`,
+      // USERPROFILE ships verbatim; win32.resolve keeps \\server\share as
+      // the unpoppable root, so this normalizes to \\server\share\x.
+      home: `${SHARE}\\..\\x`,
+      crumbs: [
+        { name: `${SHARE}\\`, path: `${SHARE}\\`, hidden: false },
+        { name: 'x', path: `${SHARE}\\x`, hidden: false },
+      ],
+      entries: [],
+      truncated: false,
+    }
+    const listDirectory = vi.fn(async () => listing)
+    mount({ listDirectory })
+    await waitFor(() => { expect(listDirectory).toHaveBeenCalled() })
+    await waitFor(() => { expect(screen.getByRole('button', { name: 'browser.home' })).toBeTruthy() })
+    expect(columns()).toHaveLength(1)
+    expect(listDirectory).toHaveBeenCalledTimes(1)
+  })
+
+  it('a forward-slash Windows home still reads as the display root', async () => {
+    const listing: DirectoryListing = {
+      path: 'C:\\Users\\Alice',
+      // USERPROFILE may legally use forward slashes; the root crumb (not
+      // the home text) carries the platform, and normalization folds the
+      // slashes before comparing.
+      home: 'C:/Users/Alice',
+      crumbs: [
+        { name: 'C:\\', path: 'C:\\', hidden: false },
+        { name: 'Users', path: 'C:\\Users', hidden: false },
+        { name: 'Alice', path: 'C:\\Users\\Alice', hidden: false },
+      ],
+      entries: [{ name: 'Desktop', path: 'C:\\Users\\Alice\\Desktop', hidden: false }],
+      truncated: false,
+    }
+    const listDirectory = vi.fn(async () => listing)
+    mount({ listDirectory })
+    await waitFor(() => { expect(screen.getByRole('listitem')).toBeTruthy() })
+    expect(columns()).toHaveLength(1)
+    expect(screen.getByRole('button', { name: 'browser.home' })).toBeTruthy()
+    expect(listDirectory).toHaveBeenCalledTimes(1)
+  })
+
   it('collapses a typed-case Windows home to the display root (single pane, Home crumb)', async () => {
     const CANON = 'C:\\Users\\Alice'
     const TYPED = 'c:\\users\\alice'