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App Router: A <Link> Clicked While Its Prefetch Is In Flight Commits With No <Title> (And Can Commit An Empty Segment) — Pending Segment-Cache Entry Is Handed To React As A Plain Promise

When a navigation clicks a Link during an in-flight prefetch, a pending segment-cache entry is passed to React as a plain promise. In partial or rejected prefetches the promise resolves to null, causing React to commit an empty segment and drop the document title.

highConfidence 90%Next.js Affected V16.2.11 Affected V16.3.5 Affected Vcanary

Origin Analysis

In createCacheNodeForSegment, EntryStatus.Pending entries are handled by storing waitForSegmentCacheEntry(...).then(...) promises directly as prefetchRsc and head. React's InnerLayoutRouter only unwraps DeferredRsc values, not plain promises. The pending entry is partial (isPartial: false) so the head is assigned from the promise; when it resolves to null, the title is wiped and the segment can commit empty.

1. Load /deal and wait for viewport prefetches to start.\n2. Click 'Open trip' (<Link href="/deal/trip">).\n3. Immediately click the 'Guests' tab (<Link href="/deal/trip/guests">) while the prefetches are still pending and the first navigation has not committed.\n4. Observe that /deal/trip/guests renders but document.title becomes empty and does not recover; in some cases the URL commits with an empty content slot.

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

Treating pending entries as a miss may trigger an extra server round-trip for the same prefetch, reducing prefetch effectiveness under high latency. Under rapid repeated navigation, duplicate requests could occur if the router does not deduplicate by URL. Rollback: revert the two null assignments and the partial flags to restore promise-based pending handling. Test across Next.js 16.2.x, 16.3.x, and canary with PPR both off and on; also add a Playwright test for the click-during-prefetch race.