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Fix server actions in standalone mode with cacheComponents#91711

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Mar 20, 2026
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Fix server actions in standalone mode with cacheComponents#91711
unstubbable merged 1 commit intocanaryfrom
hl/fix-server-actions-in-standalone-mode

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The staticPathKey condition added in #91231 inadvertently applies to server action requests on dynamic SSG routes when cacheComponents is enabled.

Server action fetch requests from the client do not send the RSC header (rsc: 1). They only send Accept: text/x-component and the Next-Action header. This means isRSCRequest and isDynamicRSCRequest are both false for action requests. The new staticPathKey condition (isSSG && pageIsDynamic && prerenderInfo?.fallbackRouteParams) evaluates to true for dynamic PPR routes, setting staticPathKey even though ssgCacheKey is null for actions.

With staticPathKey set, the request enters the fallback rendering block, which serves the cached fallback HTML shell with the action result appended to it, instead of responding with just the RSC action result.

The fix excludes server action requests from the staticPathKey computation by adding !isPossibleServerAction to the condition, restoring the pre-#91231 behavior where staticPathKey was always null for server actions in production.

fixes #91662
closes #91677
closes #91669

The `staticPathKey` condition added in #91231 inadvertently applies to
server action requests on dynamic SSG routes when `cacheComponents` is
enabled.

Server action fetch requests from the client do not send the `RSC`
header (`rsc: 1`). They only send `Accept: text/x-component` and the
`Next-Action` header. This means `isRSCRequest` and
`isDynamicRSCRequest` are both `false` for action requests. The new
`staticPathKey` condition (`isSSG && pageIsDynamic &&
prerenderInfo?.fallbackRouteParams`) evaluates to `true` for dynamic PPR
routes, setting `staticPathKey` even though `ssgCacheKey` is `null` for
actions.

With `staticPathKey` set, the request enters the fallback rendering
block, which serves the cached fallback HTML shell with the action
result appended to it, instead of responding with just the RSC action
result.

The fix excludes server action requests from the `staticPathKey`
computation by adding `!isPossibleServerAction` to the condition,
restoring the pre-#91231 behavior where `staticPathKey` was always
`null` for server actions in production.

fixes #91662
closes #91677
closes #91669
@unstubbable unstubbable force-pushed the hl/fix-server-actions-in-standalone-mode branch from 2dd7712 to 62c15cb Compare March 20, 2026 12:18
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Tests Passed

@unstubbable unstubbable marked this pull request as ready for review March 20, 2026 12:59
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Stats from current PR

✅ No significant changes detected

📊 All Metrics
📖 Metrics Glossary

Dev Server Metrics:

  • Listen = TCP port starts accepting connections
  • First Request = HTTP server returns successful response
  • Cold = Fresh build (no cache)
  • Warm = With cached build artifacts

Build Metrics:

  • Fresh = Clean build (no .next directory)
  • Cached = With existing .next directory

Change Thresholds:

  • Time: Changes < 50ms AND < 10%, OR < 2% are insignificant
  • Size: Changes < 1KB AND < 1% are insignificant
  • All other changes are flagged to catch regressions

⚡ Dev Server

Metric Canary PR Change Trend
Cold (Listen) 963ms 909ms ▂▁▁▁▁
Cold (Ready in log) 947ms 917ms ▂▁▁▁▁
Cold (First Request) 1.537s 1.576s ▃▁▁▃▄
Warm (Listen) 914ms 964ms ▂▁▁▁▁
Warm (Ready in log) 891ms 949ms ▂▁▁▁▁
Warm (First Request) 687ms 698ms ▃▁▁▁▁
📦 Dev Server (Webpack) (Legacy)

📦 Dev Server (Webpack)

Metric Canary PR Change Trend
Cold (Listen) 458ms 458ms ▁█▅▁▁
Cold (Ready in log) 461ms 461ms ▁█▅▁▁
Cold (First Request) 2.063s 2.062s ▂█▆▁▂
Warm (Listen) 507ms 507ms ▁█▅▁▁
Warm (Ready in log) 462ms 462ms ▁█▆▁▁
Warm (First Request) 2.062s 2.065s ▁█▆▁▁

⚡ Production Builds

Metric Canary PR Change Trend
Fresh Build 6.435s 6.399s ▃▁▂▂▁
Cached Build 6.390s 6.368s ▃▁▂▂▁
📦 Production Builds (Webpack) (Legacy)

📦 Production Builds (Webpack)

Metric Canary PR Change Trend
Fresh Build 15.217s 15.214s ▁█▆▁▁
Cached Build 15.412s 15.349s ▁█▆▁▁
node_modules Size 484 MB 484 MB ▁▁▁▁▁
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@unstubbable unstubbable requested a review from ztanner March 20, 2026 13:21
@unstubbable unstubbable merged commit 8cbc037 into canary Mar 20, 2026
280 of 287 checks passed
@unstubbable unstubbable deleted the hl/fix-server-actions-in-standalone-mode branch March 20, 2026 13:38
ijjk pushed a commit that referenced this pull request Mar 20, 2026
The `staticPathKey` condition added in #91231 inadvertently applies to
server action requests on dynamic SSG routes when `cacheComponents` is
enabled.

Server action fetch requests from the client do not send the `RSC`
header (`rsc: 1`). They only send `Accept: text/x-component` and the
`Next-Action` header. This means `isRSCRequest` and
`isDynamicRSCRequest` are both `false` for action requests. The new
`staticPathKey` condition (`isSSG && pageIsDynamic &&
prerenderInfo?.fallbackRouteParams`) evaluates to `true` for dynamic PPR
routes, setting `staticPathKey` even though `ssgCacheKey` is `null` for
actions.

With `staticPathKey` set, the request enters the fallback rendering
block, which serves the cached fallback HTML shell with the action
result appended to it, instead of responding with just the RSC action
result.

The fix excludes server action requests from the `staticPathKey`
computation by adding `!isPossibleServerAction` to the condition,
restoring the pre-#91231 behavior where `staticPathKey` was always
`null` for server actions in production.

fixes #91662
closes #91677
closes #91669
@cashpilotthrive-hue
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Server Action POST returns text/html PPR shell instead of RSC payload after upgrading to 16.2.0

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