AI & Agent Dev Bug Sandbox Back to Radar

Refresh Under Intercepted Modal Triggers MPA Fallback When Background Page Is Interceptable

When a modal is opened via interception over a page that is itself interceptable, performing a router.refresh() or revalidatePath causes the background route refresh request to incorrectly include the Next-Url header, leading to an intercepted response and an MPA fallback, resulting in a full page load and loss of client state.

highConfidence 95%Next.js Affected V16.3.5 Affected V16.3.8 Affected V16.4.0-Canary.59

Origin Analysis

The refresh logic for reused background routes sends the current Next-Url header (from the primary refresh request) instead of the Next-Url that was used when the route was originally fetched. For document-loaded pages (no interception), this should be omitted, but the code incorrectly includes it, causing the server to apply interception rewrites and return an intercepted tree, which mismatches the expected page tree and triggers a hard navigation.

1. Run the reproduction app. 2. Open /photo directly (document load). 3. Click 'Settings' nav link; the intercepted modal opens. 4. Click 'router.refresh()' or trigger a Server Action with revalidatePath. Observe that the page reloads as /settings (MPA fallback) instead of refreshing in place. Compare with /plain (non-interceptable) where refresh works as expected.

Fixing Code Block

0x7F 45 4C 46 02 01 01 000x90 12 AB 04 C1 7E 33 08
0xA4 1C 90 3E 77 0B D2 580x11 F6 6A 2C 80 19 DE 44
0x00 00 00 00 03 00 3E 000x01 00 B7 4D 55 90 0C 61
0x6C 69 62 63 2E 73 6F 2E0x36 00 8E 17 42 AA 05 F3
0xDE C0 DE 01 8B 45 FC 890xC7 5D 20 6F 91 03 E4 78
0x13 37 00 4F 9A 2D E1 700x08 B4 5C 22 71 D0 4A 16
0x48 8D 3D 22 01 00 00 E80x91 FF 0A 63 2E 57 B8 04
0x5A 91 C3 0E 44 70 1B 880x02 6F 39 C4 15 80 ED 27
0xFF 15 40 20 60 00 48 890xC3 90 7A 01 4C 28 B1 56
0x0F 1F 44 00 00 55 48 890xE5 C3 18 6D 92 0B 33 A7

Edge Case Audit

This hotfix may not cover all cases where the Next-Url should be different but not undefined (e.g., nested interceptions). It could also break scenarios where a background route was originally intercepted but is refreshed while a different URL is active. A more robust fix would track the Next-Url per route segment in the router state. Rollback: revert to the previous code; the bug will reappear but no new issues introduced. Test thoroughly with parallel routes and nested interceptions.