fix : server actions POST to return RSC payload#91669
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nehaaprasad wants to merge 2 commits intovercel:canaryfrom
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fix : server actions POST to return RSC payload#91669nehaaprasad wants to merge 2 commits intovercel:canaryfrom
nehaaprasad wants to merge 2 commits intovercel:canaryfrom
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| // return the generated payload. Server Action POSTs expect RSC payload | ||
| // but do not send the RSC header, so we treat them as RSC requests here. | ||
| if ((isRSCRequest || isPossibleServerAction) && !isDraftMode) { |
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The condition (isRSCRequest || isPossibleServerAction) && !isDraftMode incorrectly routes HTML responses from MPA server actions and false-positive form POSTs into the RSC serving path, causing either 404 responses (with cacheComponents) or InvariantError throws.
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I tested this with my example project for this error #91662 and I indeed now get a 404 Error for a valid server action
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Thanks for confirming @lucasra1 — that matches the analysis. The root cause is that isPossibleServerAction is a broad heuristic (true for any multipart/form-data or application/x-www-form-urlencoded POST), so it matches MPA form submissions and non-action POSTs that produce HTML responses. When those HTML responses enter the RSC branch, they fail the content type check and 404.
The suggested fix above guards the isPossibleServerAction path with an additional check that the response actually contains RSC content (rscData is defined or html.contentType is the RSC content type), so only fetch-based server actions that genuinely produce RSC payloads take this path.
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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
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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
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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
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Fixes : #91662