diff --git a/packages/dashboard/app/components/ListView.css b/packages/dashboard/app/components/ListView.css
index 327375c272..da1a8c1840 100644
--- a/packages/dashboard/app/components/ListView.css
+++ b/packages/dashboard/app/components/ListView.css
@@ -439,21 +439,25 @@ Widen the split resize column so the task-list sidebar is easy to grab and drag
   overflow: auto;
 }
 
+/*
+FNXC:SidebarDivider 2026-06-23-01:45:
+The List split divider must read identically to the Chat sidebar divider: a single 1px var(--border) line, with the wider var(--space-sm) handle track acting only as an invisible drag hit-area that tints on hover/focus. Previously the handle painted a persistent color-mix band across its full var(--space-sm) width plus a 2px ::after grip, so the List divider looked noticeably thicker than Chat's clean 1px line. Keep the drag hit-area width (var(--space-sm) grid track) for usability; only the visible line thickness/color changes — handle background is transparent and the centered ::after line is 1px var(--border).
+*/
 .list-split-resize-handle {
   position: relative;
   cursor: col-resize;
-  background: color-mix(in srgb, var(--border) 70%, transparent);
+  background: transparent;
   transition: background var(--transition-fast);
   touch-action: none;
 }
 
-/* Centered grip line so the drag affordance is visible. */
+/* Centered 1px grip line — the static visible divider, matching Chat's 1px sidebar border. */
 .list-split-resize-handle::after {
   content: "";
   position: absolute;
   inset-block: 0;
   inset-inline-start: 50%;
-  width: 2px;
+  width: 1px;
   transform: translateX(-50%);
   background: var(--border);
   transition: background var(--transition-fast);
diff --git a/packages/dashboard/app/components/MailboxModal.css b/packages/dashboard/app/components/MailboxModal.css
index 1ae0cadc1e..cefec5320f 100644
--- a/packages/dashboard/app/components/MailboxModal.css
+++ b/packages/dashboard/app/components/MailboxModal.css
@@ -681,6 +681,9 @@ FN-6912 requires the full-page Messages divider to read thinner between the mess
 /*
 FNXC:Mailbox 2026-06-22-18:20:
 The mailbox resize divider mirrors the Chat sidebar divider exactly — handle hit area var(--space-sm), centered visible line var(--space-xs), transparent until hover — so the two views' dividers read identically (the widths were previously swapped + the mailbox handle had an always-on background).
+
+FNXC:SidebarDivider 2026-06-23-01:45:
+Tighten the mailbox divider's static visible line to a single 1px var(--border) line so it matches Chat/List exactly (previously the centered ::before was var(--space-xs)=4px wide and had no static color, reading inconsistently next to the panes' own borders). The handle hit-area stays var(--space-sm) (invisible drag target); only the visible centered line changes — 1px var(--border) by default, tinting to var(--todo) on hover/active. Focus ring preserved.
 */
 .mailbox-view .mailbox-split-resize-handle {
   position: relative;
@@ -699,8 +702,10 @@ The mailbox resize divider mirrors the Chat sidebar divider exactly — handle h
   top: 0;
   bottom: 0;
   left: 50%;
-  width: var(--space-xs);
+  width: var(--btn-border-width);
   transform: translateX(-50%);
+  background: var(--border);
+  transition: background var(--transition-fast);
 }
 
 .mailbox-view .mailbox-split-resize-handle:hover::before,
diff --git a/packages/dashboard/app/components/__tests__/MailboxView.test.tsx b/packages/dashboard/app/components/__tests__/MailboxView.test.tsx
index 43be43816b..f2fb613c9d 100644
--- a/packages/dashboard/app/components/__tests__/MailboxView.test.tsx
+++ b/packages/dashboard/app/components/__tests__/MailboxView.test.tsx
@@ -1884,14 +1884,16 @@ describe("MailboxView", () => {
       const resizeHandleBlockMatch = css.match(/\.mailbox-view\s+\.mailbox-split-resize-handle\s*\{([^}]*)\}/);
       expect(resizeHandleBlockMatch).toBeTruthy();
       const resizeHandleBlock = resizeHandleBlockMatch![1];
-      // FNXC:Mailbox 2026-06-22-18:20: handle mirrors the Chat sidebar divider — hit area var(--space-sm), transparent until hover, centered var(--space-xs) line.
+      // FNXC:SidebarDivider 2026-06-23-01:45: handle mirrors the Chat sidebar divider — hit area var(--space-sm), transparent handle background, centered static 1px var(--border) line (tightened from var(--space-xs)) so List/Chat/Mailbox dividers read identically.
       expect(resizeHandleBlock).toContain("width: var(--space-sm);");
       expect(resizeHandleBlock).toContain("cursor: col-resize;");
       expect(resizeHandleBlock).toContain("background: transparent;");
 
       const resizeHandleTargetBlockMatch = css.match(/\.mailbox-view\s+\.mailbox-split-resize-handle::before\s*\{([^}]*)\}/);
       expect(resizeHandleTargetBlockMatch).toBeTruthy();
-      expect(resizeHandleTargetBlockMatch![1]).toContain("width: var(--space-xs);");
+      // Static visible divider is a single 1px var(--border) line, matching Chat's sidebar border.
+      expect(resizeHandleTargetBlockMatch![1]).toContain("width: var(--btn-border-width);");
+      expect(resizeHandleTargetBlockMatch![1]).toContain("background: var(--border);");
       expect(css).toMatch(/\.mailbox-view\s+\.mailbox-split-resize-handle:hover::before,\s*\n\.mailbox-view\s+\.mailbox-split-resize-handle:active::before\s*\{[^}]*background:\s*color-mix\(in srgb,\s*var\(--todo\)\s*35%,\s*transparent\);[^}]*\}/);
 
       const splitEmptyBlockMatch = css.match(/\.mailbox-view\s+\.mailbox-split-empty\s*\{([^}]*)\}/);