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james-elicx merged 2 commits into from
May 16, 2026
+489 −6
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feat(cache): classify private and dynamic render downgrades #1247

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b54090e
feat(cache): classify private and dynamic render downgrades
NathanDrake2406 May 16, 2026
3e358d3
chore(cache): rename public cache candidate flag
NathanDrake2406 May 16, 2026
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337 changes: 331 additions & 6 deletions packages/vinext/src/server/cache-proof.ts
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Original file line number Diff line number Diff line change
@@ -1,8 +1,8 @@
import type { AppRouteSemanticIds } from "../routing/app-route-graph.js";
import { fnv1a64 } from "../utils/hash.js";

export const CACHE_PROOF_MODEL_SCHEMA_VERSION = 0;
export type CacheProofModelSchemaVersion = 0;
export const CACHE_PROOF_MODEL_SCHEMA_VERSION = 1;
export type CacheProofModelSchemaVersion = 1;
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@james-elicx james-elicx May 16, 2026

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couldnt this type's value be inferred from the constant?


export type CacheProofRejectionCode =
| "CP_MODEL_DISABLED"
Expand All @@ -17,7 +17,8 @@ export type CacheProofRejectionCode =
| "CP_ROUTE_VARIANT_CEILING_EXCEEDED"
| "CP_UNSAFE_PUBLIC_DIMENSION"
| "CP_BOUNDARY_OUTCOME_MISMATCH"
| "CP_BOUNDARY_OUTCOME_UNKNOWN";
| "CP_BOUNDARY_OUTCOME_UNKNOWN"
| "CP_PRIVATE_DYNAMIC_DOWNGRADE";

export type CacheProofTraceFieldValue = string | number | boolean | null | readonly string[];

Expand Down Expand Up @@ -208,11 +209,93 @@ export type RenderRequestApiObservation = Readonly<{
status: RenderRequestApiStatus;
}>;

export type CacheProofDowngradeTarget =
| "freshRender"
| "private"
| "privateUncacheable"
| "public"
| "publicVariant";
Comment on lines +212 to +217
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@james-elicx james-elicx May 16, 2026

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this type could just be a union of the all the target values in the below type


export type CacheProofDowngradeReason =
| Readonly<{
code: "CP_DOWNGRADE_CACHEABILITY_PRIVATE";
target: "private";
}>
| Readonly<{
code: "CP_DOWNGRADE_CACHEABILITY_UNCACHEABLE";
target: "privateUncacheable";
}>
| Readonly<{
code: "CP_DOWNGRADE_CACHEABILITY_UNKNOWN";
target: "freshRender";
}>
| Readonly<{
code: "CP_DOWNGRADE_DYNAMIC_FETCH";
dynamicFetchCount: number;
target: "freshRender";
}>
| Readonly<{
code: "CP_DOWNGRADE_DYNAMIC_REQUEST_API";
requestApi: "connection";
target: "freshRender";
}>
| Readonly<{
code: "CP_DOWNGRADE_DRAFT_MODE";
requestApi: "draftMode";
target: "privateUncacheable";
}>
| Readonly<{
code: "CP_DOWNGRADE_INCOMPLETE_OBSERVATION";
completeness: Exclude<RenderObservationCompleteness, "complete">;
target: "freshRender";
}>
| Readonly<{
code: "CP_DOWNGRADE_PRIVATE_DIMENSION";
inputClass: "auth" | "draft" | "private" | "session";
source: "auth" | "cookie" | "draft-mode" | "header" | "session";
target: "private" | "privateUncacheable";
}>
| Readonly<{
code: "CP_DOWNGRADE_PRIVATE_REQUEST_API";
requestApi: "cookies" | "headers";
target: "private";
}>
| Readonly<{
code: "CP_DOWNGRADE_PUBLIC_REQUEST_API";
requestApi: "params" | "searchParams";
target: "publicVariant";
}>
| Readonly<{
code: "CP_DOWNGRADE_UNKNOWN_REQUEST_API";
requestApi: RenderRequestApiKind;
target: "freshRender";
}>;

export type CacheProofDowngradeClassification = Readonly<{
fallback: CacheProofBreakerFallback | null;
isPublicCacheCandidate: boolean;
reasons: readonly CacheProofDowngradeReason[];
target: CacheProofDowngradeTarget;
}>;

export type ClassifyRenderObservationDowngradeInput = Readonly<{
cacheability: RenderCacheability;
completeness: RenderObservationCompleteness;
dynamicFetches: readonly string[];
requestApis: readonly RenderRequestApiObservation[];
}>;

export type ClassifyCacheVariantDimensionDowngradeInput = Pick<
CacheVariantDimensionInput,
"source"
>;

export type RenderObservation = Readonly<{
boundaryOutcome: BoundaryOutcome;
cacheTags: readonly string[];
cacheability: RenderCacheability;
completeness: RenderObservationCompleteness;
downgrade: CacheProofDowngradeClassification;
dynamicFetches: readonly string[];
output: CacheProofOutputScope;
pathTags: readonly string[];
Expand Down Expand Up @@ -592,7 +675,7 @@ export function buildCacheVariant(input: BuildCacheVariantInput): BuildCacheVari
kind: "variant",
variant: {
schemaVersion: CACHE_PROOF_MODEL_SCHEMA_VERSION,
cacheKey: `cp0:${fnv1a64(encoded)}`,
cacheKey: `cp${CACHE_PROOF_MODEL_SCHEMA_VERSION}:${fnv1a64(encoded)}`,
output: input.output,
dimensions,
encodedLength: encoded.length,
Expand Down Expand Up @@ -697,6 +780,239 @@ function normalizeRequestApiObservations(
.map(([kind, status]) => ({ kind, status }));
}

function cacheProofDowngradeTargetRank(target: CacheProofDowngradeTarget): number {
switch (target) {
case "public":
return 0;
case "publicVariant":
return 1;
case "private":
return 2;
case "privateUncacheable":
return 3;
case "freshRender":
return 4;
default:
return assertNever(target);
}
}

function maxCacheProofDowngradeTarget(
current: CacheProofDowngradeTarget,
candidate: CacheProofDowngradeTarget,
): CacheProofDowngradeTarget {
return cacheProofDowngradeTargetRank(candidate) > cacheProofDowngradeTargetRank(current)
? candidate
: current;
}

function createDowngradeFallback(
target: CacheProofDowngradeTarget,
reasons: readonly CacheProofDowngradeReason[],
): CacheProofBreakerFallback | null {
switch (target) {
case "public":
case "publicVariant":
case "private":
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@ask-bonk ask-bonk Bot May 16, 2026

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Design note: private target returns null fallback (no breaker), which means a render that only observes cookies/headers won't produce a CacheProofBreakerFallback. This is correct for the current model — private is still cacheable in a per-user cache, so no breaker is needed. Just calling it out since the jump from private → null to privateUncacheable → breaker is the critical semantic boundary and it's easy to miss in the fall-through.

return null;
case "privateUncacheable":
return buildBreakerFallback(
"CP_PRIVATE_DYNAMIC_DOWNGRADE",
{
reasonCodes: reasons.map((reason) => reason.code),
target,
},
"privateUncacheable",
);
case "freshRender":
return buildBreakerFallback("CP_PRIVATE_DYNAMIC_DOWNGRADE", {
reasonCodes: reasons.map((reason) => reason.code),
target,
});
default:
return assertNever(target);
}
}

function classifyObservedRequestApiDowngrade(
kind: RenderRequestApiKind,
): CacheProofDowngradeReason {
switch (kind) {
case "connection":
return {
code: "CP_DOWNGRADE_DYNAMIC_REQUEST_API",
requestApi: "connection",
target: "freshRender",
};
case "cookies":
return {
code: "CP_DOWNGRADE_PRIVATE_REQUEST_API",
requestApi: "cookies",
target: "private",
};
case "draftMode":
return {
code: "CP_DOWNGRADE_DRAFT_MODE",
requestApi: "draftMode",
target: "privateUncacheable",
};
case "headers":
return {
code: "CP_DOWNGRADE_PRIVATE_REQUEST_API",
requestApi: "headers",
target: "private",
};
case "params":
return {
code: "CP_DOWNGRADE_PUBLIC_REQUEST_API",
requestApi: "params",
target: "publicVariant",
};
case "searchParams":
return {
code: "CP_DOWNGRADE_PUBLIC_REQUEST_API",
requestApi: "searchParams",
target: "publicVariant",
};
default:
return assertNever(kind);
Comment on lines +877 to +878
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@james-elicx james-elicx May 16, 2026

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im a bit surprised we need these to be honest

}
}

export function classifyCacheVariantDimensionDowngrade(
input: ClassifyCacheVariantDimensionDowngradeInput,
): CacheProofDowngradeReason | null {
switch (input.source) {
case "auth":
return {
code: "CP_DOWNGRADE_PRIVATE_DIMENSION",
inputClass: "auth",
source: "auth",
target: "private",
};
case "cookie":
return {
code: "CP_DOWNGRADE_PRIVATE_DIMENSION",
inputClass: "private",
source: "cookie",
target: "private",
};
case "draft-mode":
return {
code: "CP_DOWNGRADE_PRIVATE_DIMENSION",
inputClass: "draft",
source: "draft-mode",
target: "privateUncacheable",
};
case "header":
return {
code: "CP_DOWNGRADE_PRIVATE_DIMENSION",
inputClass: "private",
source: "header",
target: "private",
};
case "session":
return {
code: "CP_DOWNGRADE_PRIVATE_DIMENSION",
inputClass: "session",
source: "session",
target: "private",
};
case "custom":
case "interception":
case "mounted-slots":
case "params":
case "route":
case "search":
return null;
default:
return assertNever(input.source);
}
}

export function classifyRenderObservationDowngrade(
input: ClassifyRenderObservationDowngradeInput,
): CacheProofDowngradeClassification {
const reasons: CacheProofDowngradeReason[] = [];
let target: CacheProofDowngradeTarget = "public";

switch (input.cacheability) {
case "public":
break;
case "private": {
const reason = {
code: "CP_DOWNGRADE_CACHEABILITY_PRIVATE",
target: "private",
} satisfies CacheProofDowngradeReason;
reasons.push(reason);
target = maxCacheProofDowngradeTarget(target, reason.target);
break;
}
case "uncacheable": {
const reason = {
code: "CP_DOWNGRADE_CACHEABILITY_UNCACHEABLE",
target: "privateUncacheable",
} satisfies CacheProofDowngradeReason;
reasons.push(reason);
target = maxCacheProofDowngradeTarget(target, reason.target);
break;
}
case "unknown": {
const reason = {
code: "CP_DOWNGRADE_CACHEABILITY_UNKNOWN",
target: "freshRender",
} satisfies CacheProofDowngradeReason;
reasons.push(reason);
target = maxCacheProofDowngradeTarget(target, reason.target);
break;
}
default:
assertNever(input.cacheability);
}

if (input.completeness !== "complete") {
const reason = {
code: "CP_DOWNGRADE_INCOMPLETE_OBSERVATION",
completeness: input.completeness,
target: "freshRender",
} satisfies CacheProofDowngradeReason;
reasons.push(reason);
target = maxCacheProofDowngradeTarget(target, reason.target);
}

if (input.dynamicFetches.length > 0) {
const reason = {
code: "CP_DOWNGRADE_DYNAMIC_FETCH",
dynamicFetchCount: input.dynamicFetches.length,
target: "freshRender",
} satisfies CacheProofDowngradeReason;
reasons.push(reason);
target = maxCacheProofDowngradeTarget(target, reason.target);
}

const requestApis = normalizeRequestApiObservations(input.requestApis);
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@ask-bonk ask-bonk Bot May 16, 2026

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Double normalization of requestApis.

buildRenderObservation (line 1030) normalizes input.requestApis via normalizeRequestApiObservations and then passes the already-normalized result into classifyRenderObservationDowngrade (line 1047). But classifyRenderObservationDowngrade calls normalizeRequestApiObservations again here on line 993.

This is harmless today — normalization is idempotent (dedup-by-max-rank, then sort) — and the test on cache-proof.test.ts:399 proves the round-trip produces identical results. But it's still redundant work on the hot path. More importantly, it means the public API contract of classifyRenderObservationDowngrade accepts denormalized input, which could surprise a future caller who expects pre-normalized data to pass through unchanged without the extra allocation.

Two options:

  1. Remove the normalizeRequestApiObservations call here and document that ClassifyRenderObservationDowngradeInput.requestApis must be pre-normalized.
  2. Keep it (defense in depth) and add a one-line comment explaining the idempotency expectation.

Either is fine. Not blocking.

for (const requestApi of requestApis) {
if (requestApi.status === "notObserved") continue;
const reason =
requestApi.status === "unknown"
? ({
code: "CP_DOWNGRADE_UNKNOWN_REQUEST_API",
requestApi: requestApi.kind,
target: "freshRender",
} satisfies CacheProofDowngradeReason)
: classifyObservedRequestApiDowngrade(requestApi.kind);
reasons.push(reason);
target = maxCacheProofDowngradeTarget(target, reason.target);
}

return {
target,
reasons,
fallback: createDowngradeFallback(target, reasons),
isPublicCacheCandidate: target === "public" || target === "publicVariant",
};
}

export function buildRenderRequestApiObservations(
input: BuildRenderRequestApiObservationsInput,
): RenderRequestApiObservation[] {
Expand All @@ -711,16 +1027,25 @@ export function buildRenderRequestApiObservations(
}

export function buildRenderObservation(input: BuildRenderObservationInput): RenderObservation {
const requestApis = normalizeRequestApiObservations(input.requestApis);
const dynamicFetches = sortedUniqueRedacted(input.dynamicFetches);

return {
schemaVersion: CACHE_PROOF_MODEL_SCHEMA_VERSION,
output: input.output,
completeness: input.completeness,
boundaryOutcome: input.boundaryOutcome,
requestApis: normalizeRequestApiObservations(input.requestApis),
dynamicFetches: sortedUniqueRedacted(input.dynamicFetches),
requestApis,
dynamicFetches,
cacheTags: sortedUnique(input.cacheTags),
pathTags: sortedUnique(input.pathTags),
cacheability: input.cacheability,
downgrade: classifyRenderObservationDowngrade({
cacheability: input.cacheability,
completeness: input.completeness,
dynamicFetches,
requestApis,
}),
};
}

Expand Down
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