diff --git a/open-sse/services/autoCombo/engine.ts b/open-sse/services/autoCombo/engine.ts
index 6d238fc98f..9e91552f36 100644
--- a/open-sse/services/autoCombo/engine.ts
+++ b/open-sse/services/autoCombo/engine.ts
@@ -11,8 +11,8 @@
 
 import {
   scorePool,
-  validateWeights,
   DEFAULT_WEIGHTS,
+  normalizeScoringWeights,
   type ScoringWeights,
   type ProviderCandidate,
   type ScoredProvider,
@@ -110,12 +110,15 @@ class ScoreTierRotator {
     const tiers = groupIntoTiers(candidates);
     const best = candidates[0].score;
     const worst = candidates[candidates.length - 1].score;
-    if (tiers.top.length > 0 && (best - worst) >= CLEAR_WINNER_THRESHOLD) {
+    if (tiers.top.length > 0 && best - worst >= CLEAR_WINNER_THRESHOLD) {
       return this.pickFromPool(tiers.top);
     }
     const prefs = tierPreferencesForName(this.comboName);
-    const chosen = chooseTierWeighted(tiers, prefs, (pool) => this.pickFromPool(pool), () =>
-      this.advance(tiers, prefs, candidates)
+    const chosen = chooseTierWeighted(
+      tiers,
+      prefs,
+      (pool) => this.pickFromPool(pool),
+      () => this.advance(tiers, prefs, candidates)
     );
     return chosen;
   }
@@ -248,7 +251,7 @@ export function selectProvider(
     const pack = getModePack(config.modePack);
     if (pack) weights = pack;
   }
-  if (!validateWeights(weights)) weights = DEFAULT_WEIGHTS;
+  weights = normalizeScoringWeights(weights);
 
   // Filter out excluded providers
   const excluded: string[] = [];
@@ -322,7 +325,10 @@ export function selectProvider(
           (a, b) => estimatedCostFor(a) - estimatedCostFor(b)
         )[0];
         if (config.budgetFallback === "strict") {
-          throw new BudgetExceededError(config.budgetCap, cheapest ? estimatedCostFor(cheapest) : 0);
+          throw new BudgetExceededError(
+            config.budgetCap,
+            cheapest ? estimatedCostFor(cheapest) : 0
+          );
         }
         if (cheapest) selected = cheapest;
       }
diff --git a/open-sse/services/autoCombo/routerStrategy.ts b/open-sse/services/autoCombo/routerStrategy.ts
index b9923fe470..9bf207a28a 100644
--- a/open-sse/services/autoCombo/routerStrategy.ts
+++ b/open-sse/services/autoCombo/routerStrategy.ts
@@ -41,6 +41,7 @@ export interface RoutingDecision {
   reason: string;
   candidatesConsidered: number;
   finalScore: number;
+  connectionId?: string;
 }
 
 export interface RouterStrategy {
@@ -103,6 +104,7 @@ class RulesStrategyImpl implements RouterStrategy {
       reason: `RulesStrategy: score=${best.score.toFixed(3)} (quota=${best.factors.quota.toFixed(2)}, health=${best.factors.health.toFixed(2)}, cost=${best.factors.costInv.toFixed(2)}, taskFit=${best.factors.taskFit.toFixed(2)})`,
       candidatesConsidered: ranked.length,
       finalScore: best.score,
+      connectionId: best.connectionId,
     };
   }
 }
diff --git a/open-sse/services/autoCombo/scoring.ts b/open-sse/services/autoCombo/scoring.ts
index fccffa0191..ed410c36be 100644
--- a/open-sse/services/autoCombo/scoring.ts
+++ b/open-sse/services/autoCombo/scoring.ts
@@ -19,6 +19,7 @@ export interface ScoringFactors {
   tierAffinity: number;
   specificityMatch: number;
   contextAffinity: number;
+  cacheAffinity?: number;
   resetWindowAffinity: number;
   connectionDensity: number;
 }
@@ -34,6 +35,7 @@ export interface ScoringWeights {
   tierAffinity: number;
   specificityMatch: number;
   contextAffinity: number;
+  cacheAffinity?: number;
   resetWindowAffinity: number;
   connectionDensity: number;
 }
@@ -49,10 +51,30 @@ export const DEFAULT_WEIGHTS: ScoringWeights = {
   tierAffinity: 0.05,
   specificityMatch: 0.05,
   contextAffinity: 0.05,
+  cacheAffinity: 0,
   resetWindowAffinity: 0,
   connectionDensity: 0.05,
 };
 
+/** Normalize independently configured UI weights into a scoring distribution. */
+export function normalizeScoringWeights(
+  weights: Partial<ScoringWeights> | null | undefined
+): ScoringWeights {
+  if (!weights) return { ...DEFAULT_WEIGHTS };
+  const entries = Object.keys(DEFAULT_WEIGHTS) as Array<keyof ScoringWeights>;
+  const sanitized = Object.fromEntries(
+    entries.map((key) => {
+      const value = Number(weights?.[key]);
+      return [key, Number.isFinite(value) && value >= 0 ? value : 0];
+    })
+  ) as unknown as ScoringWeights;
+  const total = entries.reduce((sum, key) => sum + Number(sanitized[key] ?? 0), 0);
+  if (total <= 0) return { ...DEFAULT_WEIGHTS };
+  return Object.fromEntries(
+    entries.map((key) => [key, Number(sanitized[key] ?? 0) / total])
+  ) as unknown as ScoringWeights;
+}
+
 export interface ProviderCandidate {
   provider: string;
   model: string;
@@ -77,6 +99,8 @@ export interface ProviderCandidate {
   quotaResetIntervalSecs?: number;
   /** Score [0..1] for staying on the current session's provider/account/model path. */
   contextAffinity?: number;
+  /** Score [0..1] for the account selected by the stable prompt-cache key. */
+  cacheAffinity?: number;
   /** Score [0..1] for quota reset-window preference; sooner selected reset windows score higher. */
   resetWindowAffinity?: number;
   connectionPoolSize?: number;
@@ -110,6 +134,7 @@ export function calculateScore(factors: ScoringFactors, weights: ScoringWeights)
       (weights.tierAffinity ?? 0) * factors.tierAffinity +
       (weights.specificityMatch ?? 0) * factors.specificityMatch +
       (weights.contextAffinity ?? 0) * factors.contextAffinity +
+      (weights.cacheAffinity ?? 0) * (factors.cacheAffinity ?? 0) +
       (weights.resetWindowAffinity ?? 0) * factors.resetWindowAffinity +
       (weights.connectionDensity ?? 0) * factors.connectionDensity
   );
@@ -207,6 +232,7 @@ export function calculateFactors(
     tierAffinity: calculateTierAffinity(candidate, manifestHint),
     specificityMatch: calculateSpecificityMatch(candidate, manifestHint),
     contextAffinity: clamp01(candidate.contextAffinity ?? 0.5),
+    cacheAffinity: clamp01(candidate.cacheAffinity ?? 0),
     resetWindowAffinity: clamp01(candidate.resetWindowAffinity ?? 0.5),
     connectionDensity: clamp01(((candidate.connectionPoolSize ?? 1) - 1) / 10),
   };
diff --git a/open-sse/services/combo.ts b/open-sse/services/combo.ts
index 6fd60b4cf6..1a4b88de30 100644
--- a/open-sse/services/combo.ts
+++ b/open-sse/services/combo.ts
@@ -83,6 +83,12 @@ import { selectQuotaShareTarget } from "./combo/quotaShareStrategy.ts";
 import { makeConnectionConcurrencyResolver, lookupPositiveCap } from "./combo/concurrencyCaps.ts";
 import { acquireQuotaShareConcurrencySlot } from "./combo/quotaShareConcurrency.ts";
 import { orderTargetsByEvalScores } from "./evalRouting.ts";
+import {
+  applyPromptCacheAffinity,
+  expandPromptCacheAffinityTargets,
+  expandPromptCacheAffinityTargetsFromConnections,
+  resolvePromptCacheAffinityKey,
+} from "./combo/promptCacheAffinity.ts";
 import type { CompressionMode } from "./compression/types.ts";
 import { getCachedProviderConnections } from "../../src/lib/db/readCache";
 import {
@@ -387,7 +393,10 @@ export async function buildAutoCandidates(
   await Promise.all(
     uniqueProviders.map(async (provider) => {
       try {
-        const connections = (await getCachedProviderConnections({ provider, isActive: true })) as Array<Record<string, unknown>>;
+        const connections = (await getCachedProviderConnections({
+          provider,
+          isActive: true,
+        })) as Array<Record<string, unknown>>;
         const active = Array.isArray(connections) ? connections : [];
         connectionPoolCounts.set(provider, active.length);
         connectionsByProvider.set(provider, active);
@@ -403,40 +412,10 @@ export async function buildAutoCandidates(
     })
   );
 
-  const expandedTargets: ResolvedComboTarget[] = [];
-  for (const target of targets) {
-    const provider = target.provider || parseModel(target.modelStr).provider || "unknown";
-    const providerConnections = connectionsByProvider.get(provider) || [];
-    if (target.connectionId) {
-      expandedTargets.push(target);
-      continue;
-    }
-    const connectionIds = providerConnections
-      .map((c) => (c && typeof c === "object" && typeof c.id === "string" ? c.id : null))
-      .filter((id): id is string => id !== null);
-    const allowedConnectionIds = Array.isArray(target.allowedConnectionIds)
-      ? new Set(
-          target.allowedConnectionIds.filter(
-            (connectionId): connectionId is string =>
-              typeof connectionId === "string" && connectionId.trim().length > 0
-          )
-        )
-      : null;
-    const scopedConnectionIds = allowedConnectionIds
-      ? connectionIds.filter((connectionId) => allowedConnectionIds.has(connectionId))
-      : connectionIds;
-    if (scopedConnectionIds.length === 0) {
-      expandedTargets.push(target);
-      continue;
-    }
-    for (const connectionId of scopedConnectionIds) {
-      expandedTargets.push({
-        ...target,
-        connectionId,
-        executionKey: `${target.executionKey}@${connectionId}`,
-      });
-    }
-  }
+  const expandedTargets = expandPromptCacheAffinityTargetsFromConnections(
+    targets,
+    connectionsByProvider
+  );
 
   // #5521: Expand fingerprint-based providers (mimocode, mcode, opencode) so each
   // fingerprint gets its own combo slot instead of being bundled into one connection.
@@ -1298,14 +1277,21 @@ export async function handleComboChat({
       apiKeyAllowedConnections,
     });
   }
+  // An explicit cache-optimized combo outranks the global cache-affinity default,
+  // but only protects its ordering when this request actually produced a reusable
+  // cache key. Cache misses retain the normal session/eval routing behavior.
+  const cacheStrategyAffinityApplied =
+    strategy === "cache-optimized" && applyPromptCacheAffinity(orderedTargets, body).applied;
   // #6168: session stickiness opt-out. Per-combo `config.disableSessionStickiness`
   // overrides the global `settings.disableSessionStickiness` fallback (default false,
   // preserving the #3825 prompt-cache/504 fix). When disabled, skip the reorder and
   // treat the result as a no-op so the recordStickyBinding write-back below is skipped.
-  const disableSessionStickiness = resolveDisableSessionStickiness(
-    config as Record<string, unknown> | null | undefined,
-    settings as Record<string, unknown> | null | undefined
-  );
+  const disableSessionStickiness =
+    cacheStrategyAffinityApplied ||
+    resolveDisableSessionStickiness(
+      config as Record<string, unknown> | null | undefined,
+      settings as Record<string, unknown> | null | undefined
+    );
   const _sticky = disableSessionStickiness
     ? ({ targets: orderedTargets, messageHash: null, stuck: false } as const)
     : await applySessionStickiness(
@@ -1315,7 +1301,9 @@ export async function handleComboChat({
         normalizeStickinessMessages(body as { messages?: unknown; input?: unknown })
       );
   orderedTargets = _sticky.targets;
-  orderedTargets = orderTargetsByEvalScores(orderedTargets, config.evalRouting, log);
+  if (!cacheStrategyAffinityApplied) {
+    orderedTargets = orderTargetsByEvalScores(orderedTargets, config.evalRouting, log);
+  }
   orderedTargets = filterTargetsByRequestCompatibility(orderedTargets, body, log);
   orderedTargets = applyContextRequirements(orderedTargets, config.contextRequirements, log);
 
@@ -1347,6 +1335,62 @@ export async function handleComboChat({
     orderedTargets = nextOrder;
   }
 
+  // Prompt-cache locality is applied after request eligibility and task routing.
+  // Session stickiness and explicit auto-router pins remain stronger continuity
+  // decisions; quota, health, and circuit-breaker gates still run per attempt.
+  const autoConfigForCacheWeight =
+    strategy === "auto"
+      ? ((combo.autoConfig ||
+          ((config as Record<string, unknown>).auto &&
+          typeof (config as Record<string, unknown>).auto === "object"
+            ? (config as Record<string, unknown>).auto
+            : null) ||
+          config) as Record<string, unknown>)
+      : null;
+  const autoWeightsForCache =
+    autoConfigForCacheWeight?.weights && typeof autoConfigForCacheWeight.weights === "object"
+      ? (autoConfigForCacheWeight.weights as Record<string, unknown>)
+      : null;
+  const autoUsesCacheScore = Number(autoWeightsForCache?.cacheAffinity) > 0;
+  const promptCacheAffinityEnabled =
+    settings?.promptCacheAffinityEnabled !== false && !autoUsesCacheScore;
+  const promptCacheAffinityTargets =
+    promptCacheAffinityEnabled && resolvePromptCacheAffinityKey(body)
+      ? await expandPromptCacheAffinityTargets(orderedTargets)
+      : orderedTargets;
+  const promptCacheAffinity = applyPromptCacheAffinity(
+    promptCacheAffinityTargets,
+    body,
+    promptCacheAffinityEnabled
+  );
+  if (promptCacheAffinity.applied) {
+    const protectedOriginal =
+      (_sticky.stuck ||
+        autoUsedExplicitRouter ||
+        strategy === "quota-share" ||
+        strategy === "weighted") &&
+      orderedTargets[0];
+    const protectedFirst = protectedOriginal
+      ? (promptCacheAffinity.targets.find(
+          (target) =>
+            target === protectedOriginal ||
+            target.executionKey === protectedOriginal.executionKey ||
+            target.executionKey.startsWith(`${protectedOriginal.executionKey}@`)
+        ) ?? protectedOriginal)
+      : null;
+    orderedTargets = protectedFirst
+      ? [
+          protectedFirst,
+          ...promptCacheAffinity.targets.filter((target) => target !== protectedFirst),
+        ]
+      : promptCacheAffinity.targets;
+    log.debug?.("COMBO", "Prompt-cache affinity applied", {
+      source: promptCacheAffinity.source,
+      fingerprint: promptCacheAffinity.fingerprint,
+      targetCount: orderedTargets.length,
+    });
+  }
+
   // Parallel pre-screen: check provider profiles and model availability for all targets
   // Only runs for priority strategy where sequential checking causes latency
   const preScreenMap =
@@ -2251,7 +2295,11 @@ export async function handleComboChat({
             });
             recordedAttempts++;
             lastError = errorText || String(result.status);
-            comboErrors.push({ model: modelStr, status: result.status, error: errorText || String(result.status) });
+            comboErrors.push({
+              model: modelStr,
+              status: result.status,
+              error: errorText || String(result.status),
+            });
             if (!lastStatus) lastStatus = result.status;
             if (i > 0) fallbackCount++;
             log.warn("COMBO", `Model ${modelStr} failed with body-specific error, stopping combo`);
@@ -2345,7 +2393,11 @@ export async function handleComboChat({
           });
           recordedAttempts++;
           lastError = errorText || String(result.status);
-          comboErrors.push({ model: modelStr, status: result.status, error: errorText || String(result.status) });
+          comboErrors.push({
+            model: modelStr,
+            status: result.status,
+            error: errorText || String(result.status),
+          });
           if (!lastStatus) lastStatus = result.status;
           if (i > 0) fallbackCount++;
           // Wire combo failures into the resilience dashboard (model-level lockout)
@@ -2510,12 +2562,10 @@ export async function handleComboChat({
           latencyMs,
           fallbackCount,
         });
-        return errorResponseWithComboDiagnostics(
-          504,
-          msg,
-          buildComboDiag("combo_timeout"),
-          { code: "COMBO_TIMEOUT", type: "server_error" }
-        );
+        return errorResponseWithComboDiagnostics(504, msg, buildComboDiag("combo_timeout"), {
+          code: "COMBO_TIMEOUT",
+          type: "server_error",
+        });
       }
 
       // All models failed in this set try
@@ -2770,7 +2820,7 @@ async function handleRoundRobinCombo({
       { code: "context_length_exceeded", type: "invalid_request_error" }
     );
   }
-  const filteredTargets = filterTargetsByRequestCompatibility(
+  let filteredTargets = filterTargetsByRequestCompatibility(
     evalRankedTargets,
     body,
     log,
@@ -2783,7 +2833,7 @@ async function handleRoundRobinCombo({
   // permanently dropping a compat-rejected-but-healthy provider.
   const compatKeptSet = new Set(filteredTargets);
   const compatRejectedTargets = evalRankedTargets.filter((target) => !compatKeptSet.has(target));
-  const modelCount = filteredTargets.length;
+  let modelCount = filteredTargets.length;
   if (modelCount === 0) {
     return comboModelNotFoundResponse("Round-robin combo has no executable targets");
   }
@@ -2889,6 +2939,11 @@ async function handleRoundRobinCombo({
     config as Record<string, unknown> | null | undefined,
     settings as Record<string, unknown> | null | undefined
   );
+  const rrAffinityEnabled = settings?.promptCacheAffinityEnabled !== false;
+  if (rrAffinityEnabled && resolvePromptCacheAffinityKey(body)) {
+    filteredTargets = await expandPromptCacheAffinityTargets(filteredTargets);
+    modelCount = filteredTargets.length;
+  }
   const _rrSessionSticky = disableSessionStickiness
     ? ({ targets: filteredTargets, messageHash: null, stuck: false } as const)
     : await applySessionStickiness(
@@ -2897,7 +2952,22 @@ async function handleRoundRobinCombo({
         // stickiness engages on the /v1/responses surface, not just Chat Completions.
         normalizeStickinessMessages(body as { messages?: unknown; input?: unknown })
       );
+  const rrAffinity = applyPromptCacheAffinity(filteredTargets, body, rrAffinityEnabled);
+  if (rrAffinity.applied) {
+    const stickyFirst = _rrSessionSticky.stuck ? _rrSessionSticky.targets[0] : null;
+    filteredTargets = stickyFirst
+      ? [stickyFirst, ...rrAffinity.targets.filter((target) => target !== stickyFirst)]
+      : rrAffinity.targets;
+    log.debug?.("COMBO-RR", "Prompt-cache affinity applied", {
+      source: rrAffinity.source,
+      fingerprint: rrAffinity.fingerprint,
+      targetCount: filteredTargets.length,
+    });
+  }
   let rrStartIndex = startIndex;
+  if (rrAffinity.applied) {
+    rrStartIndex = 0;
+  }
   if (_rrSessionSticky.stuck) {
     const stickyIdx = filteredTargets.findIndex(
       (t) => t.connectionId === _rrSessionSticky.targets[0]?.connectionId
diff --git a/open-sse/services/combo/applyStrategyOrdering.ts b/open-sse/services/combo/applyStrategyOrdering.ts
index e8cb39ecf8..a2eba3a555 100644
--- a/open-sse/services/combo/applyStrategyOrdering.ts
+++ b/open-sse/services/combo/applyStrategyOrdering.ts
@@ -3,6 +3,11 @@ import { generateRoutingHints } from "../manifestAdapter";
 import { resolveMaxConcurrentByConnection } from "./concurrencyCaps.ts";
 import { sortTargetsByContextSize } from "./comboStructure.ts";
 import { selectQuotaShareTarget } from "./quotaShareStrategy.ts";
+import {
+  applyPromptCacheAffinity,
+  expandPromptCacheAffinityTargets,
+  resolvePromptCacheAffinityKey,
+} from "./promptCacheAffinity.ts";
 import {
   orderTargetsByHeadroom,
   orderTargetsByResetAwareQuota,
@@ -196,6 +201,16 @@ export async function applyStrategyOrdering(
   } else if (strategy === "context-optimized") {
     orderedTargets = sortTargetsByContextSize(orderedTargets);
     log.info("COMBO", `Context-optimized ordering: largest first (${orderedTargets[0]?.modelStr})`);
+  } else if (strategy === "cache-optimized") {
+    if (resolvePromptCacheAffinityKey(body)) {
+      orderedTargets = await expandPromptCacheAffinityTargets(orderedTargets);
+    }
+    const affinity = applyPromptCacheAffinity(orderedTargets, body);
+    orderedTargets = affinity.targets;
+    log.info(
+      "COMBO",
+      `Cache-optimized ordering: ${orderedTargets[0]?.modelStr}${orderedTargets[0]?.connectionId ? ` (${orderedTargets[0].connectionId})` : ""} first`
+    );
   } else if (strategy === "headroom") {
     orderedTargets = await orderTargetsByHeadroom(
       orderedTargets,
diff --git a/open-sse/services/combo/autoConfig.ts b/open-sse/services/combo/autoConfig.ts
index ed56f11989..3d5cf8ffda 100644
--- a/open-sse/services/combo/autoConfig.ts
+++ b/open-sse/services/combo/autoConfig.ts
@@ -1,4 +1,8 @@
-import { DEFAULT_WEIGHTS, type ScoringWeights } from "../autoCombo/scoring.ts";
+import {
+  DEFAULT_WEIGHTS,
+  normalizeScoringWeights,
+  type ScoringWeights,
+} from "../autoCombo/scoring.ts";
 import { getModePack } from "../autoCombo/modePacks.ts";
 import { isRecord } from "./comboData.ts";
 import { resolveResetWindowConfig, resolveSlaRoutingPolicy } from "./quotaScoring.ts";
@@ -53,7 +57,9 @@ export function parseAutoConfig(combo: ComboLike, eligibleTargets: ResolvedCombo
       : undefined;
   const modePack =
     typeof autoConfigSource.modePack === "string" ? autoConfigSource.modePack : undefined;
-  const weights = modePack ? getModePack(modePack) || configuredWeights : configuredWeights;
+  const weights = normalizeScoringWeights(
+    modePack ? getModePack(modePack) || configuredWeights : configuredWeights
+  );
   const resetWindowConfig = resolveResetWindowConfig(autoConfigSource);
   const slaPolicy = resolveSlaRoutingPolicy(autoConfigSource);
 
diff --git a/open-sse/services/combo/promptCacheAffinity.ts b/open-sse/services/combo/promptCacheAffinity.ts
new file mode 100644
index 0000000000..fdfe9e1352
--- /dev/null
+++ b/open-sse/services/combo/promptCacheAffinity.ts
@@ -0,0 +1,280 @@
+import { createHash } from "node:crypto";
+import {
+  analyzePrefix,
+  generatePromptCacheKey,
+} from "../../../src/lib/promptCache/prefixAnalyzer.ts";
+import { getCachedProviderConnections } from "../../../src/lib/db/readCache";
+import { parseModel } from "../model.ts";
+import type { ResolvedComboTarget } from "./types.ts";
+
+interface PromptCacheAffinityTarget {
+  executionKey: string;
+  connectionId?: string | null;
+}
+
+export type PromptCacheAffinitySource = "explicit" | "prefix";
+
+export interface PromptCacheAffinityResolution {
+  key: string;
+  source: PromptCacheAffinitySource;
+  fingerprint: string;
+}
+
+export interface PromptCacheAffinityResult {
+  targets: ResolvedComboTarget[];
+  applied: boolean;
+  source: PromptCacheAffinitySource | null;
+  fingerprint: string | null;
+}
+
+function asRecord(value: unknown): Record<string, unknown> | null {
+  return value && typeof value === "object" && !Array.isArray(value)
+    ? (value as Record<string, unknown>)
+    : null;
+}
+
+function normalizeMessageContent(value: unknown): string | unknown[] {
+  if (typeof value === "string" || Array.isArray(value)) return value;
+  try {
+    return JSON.stringify(value) || "";
+  } catch {
+    return "";
+  }
+}
+
+function normalizeResponsesInput(body: Record<string, unknown>): Array<{
+  role: string;
+  content: string | unknown[];
+}> | null {
+  if (Array.isArray(body.messages) && body.messages.length > 0) {
+    return body.messages
+      .map((item) => {
+        const record = asRecord(item);
+        return record && typeof record.role === "string"
+          ? { role: record.role, content: normalizeMessageContent(record.content) }
+          : null;
+      })
+      .filter((item): item is { role: string; content: string | unknown[] } => item !== null);
+  }
+
+  if (typeof body.input === "string" && body.input.length > 0) {
+    return [{ role: "user", content: body.input }];
+  }
+
+  if (Array.isArray(body.input) && body.input.length > 0) {
+    return body.input
+      .map((item) => {
+        if (typeof item === "string") return { role: "user", content: item };
+        const record = asRecord(item);
+        return record && typeof record.role === "string"
+          ? { role: record.role, content: normalizeMessageContent(record.content) }
+          : null;
+      })
+      .filter((item): item is { role: string; content: string | unknown[] } => item !== null);
+  }
+
+  return null;
+}
+
+function readExplicitPromptCacheKey(body: Record<string, unknown>): string | null {
+  const metadata = asRecord(body.metadata);
+  for (const value of [body.prompt_cache_key, metadata?.prompt_cache_key]) {
+    if (typeof value !== "string") continue;
+    const normalized = value.trim();
+    if (normalized.length > 0 && normalized.length <= 4096) return normalized;
+  }
+  return null;
+}
+
+/**
+ * Resolve a cache affinity key without exposing the key itself to callers that
+ * only need diagnostics. Explicit provider keys win; otherwise the existing
+ * prompt-prefix analyzer supplies a safe deterministic fallback.
+ */
+export function resolvePromptCacheAffinityKey(
+  body: Record<string, unknown> | null | undefined
+): PromptCacheAffinityResolution | null {
+  if (!body) return null;
+
+  const explicit = readExplicitPromptCacheKey(body);
+  const messages = normalizeResponsesInput(body);
+  const prefixAnalysis = messages ? analyzePrefix(messages) : null;
+  // The analyzer intentionally returns a legacy empty-content hash for callers
+  // that need that historical value. Affinity must not use it: a request with
+  // only a first user turn has no reusable prompt prefix and would collapse
+  // otherwise distinct conversations onto one account.
+  const prefixKey =
+    prefixAnalysis && prefixAnalysis.prefixEndIdx >= 0
+      ? generatePromptCacheKey(messages || [])
+      : "";
+  const key = explicit ?? prefixKey;
+  if (!key) return null;
+
+  const source: PromptCacheAffinitySource = explicit ? "explicit" : "prefix";
+  const fingerprint = createHash("sha256").update(key).digest("hex").slice(0, 12);
+  return { key, source, fingerprint };
+}
+
+export function promptCacheTargetIdentity(target: PromptCacheAffinityTarget): string {
+  const connectionId = typeof target.connectionId === "string" ? target.connectionId.trim() : "";
+  if (connectionId) return `connection:${connectionId}`;
+  return `execution:${target.executionKey}`;
+}
+
+function rendezvousScore(key: string, identity: string): bigint {
+  const digest = createHash("sha256").update(key).update("\0").update(identity).digest("hex");
+  return BigInt(`0x${digest.slice(0, 32)}`);
+}
+
+/**
+ * Return a normalized cache-locality score for auto-combo scoring. The target
+ * selected by rendezvous hashing receives 1; all other accounts receive 0.
+ * Reusing the same prompt key therefore keeps selecting the same account.
+ */
+export function calculatePromptCacheAffinityScores(
+  targets: PromptCacheAffinityTarget[],
+  body: Record<string, unknown> | null | undefined
+): Map<string, number> {
+  const resolution = resolvePromptCacheAffinityKey(body);
+  if (!resolution || targets.length === 0) return new Map();
+  let winnerIdentity = "";
+  let winnerScore = -1n;
+  for (const target of targets) {
+    const identity = promptCacheTargetIdentity(target);
+    const score = rendezvousScore(resolution.key, identity);
+    if (score > winnerScore || (score === winnerScore && identity < winnerIdentity)) {
+      winnerIdentity = identity;
+      winnerScore = score;
+    }
+  }
+  return new Map(
+    targets.map((target) => {
+      const identity = promptCacheTargetIdentity(target);
+      return [identity, identity === winnerIdentity ? 1 : 0];
+    })
+  );
+}
+
+/**
+ * Bind unscoped combo targets to concrete active provider accounts before
+ * rendezvous hashing. This keeps the selected cache identity identical to the
+ * account that credential resolution will execute, while preserving the
+ * original target as a fail-open fallback when no eligible account is known.
+ */
+export async function expandPromptCacheAffinityTargets(
+  targets: ResolvedComboTarget[]
+): Promise<ResolvedComboTarget[]> {
+  const providers = Array.from(
+    new Set(
+      targets
+        .filter((target) => !target.connectionId)
+        .map(
+          (target) =>
+            target.provider ||
+            parseModel(target.modelStr).provider ||
+            parseModel(target.modelStr).providerAlias ||
+            "unknown"
+        )
+    )
+  );
+  const connectionsByProvider = new Map<string, Array<Record<string, unknown>>>();
+  await Promise.all(
+    providers.map(async (provider) => {
+      try {
+        const connections = (await getCachedProviderConnections({
+          provider,
+          isActive: true,
+        })) as Array<Record<string, unknown>>;
+        connectionsByProvider.set(provider, Array.isArray(connections) ? connections : []);
+      } catch {
+        connectionsByProvider.set(provider, []);
+      }
+    })
+  );
+  return expandPromptCacheAffinityTargetsFromConnections(targets, connectionsByProvider);
+}
+
+export function expandPromptCacheAffinityTargetsFromConnections(
+  targets: ResolvedComboTarget[],
+  connectionsByProvider: Map<string, Array<Record<string, unknown>>>
+): ResolvedComboTarget[] {
+  const expandedTargets: ResolvedComboTarget[] = [];
+  for (const target of targets) {
+    if (target.connectionId) {
+      expandedTargets.push(target);
+      continue;
+    }
+    const parsed = parseModel(target.modelStr);
+    const provider = target.provider || parsed.provider || parsed.providerAlias || "unknown";
+    const connectionIds = (connectionsByProvider.get(provider) || [])
+      .map((connection) =>
+        connection && typeof connection.id === "string" ? connection.id.trim() : ""
+      )
+      .filter((connectionId) => connectionId.length > 0);
+    const allowedConnectionIds = Array.isArray(target.allowedConnectionIds)
+      ? new Set(
+          target.allowedConnectionIds.filter(
+            (connectionId): connectionId is string =>
+              typeof connectionId === "string" && connectionId.trim().length > 0
+          )
+        )
+      : null;
+    const scopedConnectionIds = allowedConnectionIds
+      ? connectionIds.filter((connectionId) => allowedConnectionIds.has(connectionId))
+      : connectionIds;
+    if (scopedConnectionIds.length === 0) {
+      expandedTargets.push(target);
+      continue;
+    }
+    for (const connectionId of scopedConnectionIds) {
+      expandedTargets.push({
+        ...target,
+        connectionId,
+        executionKey: `${target.executionKey}@${connectionId}`,
+      });
+    }
+  }
+  return expandedTargets;
+}
+
+/**
+ * Order eligible targets using rendezvous hashing. The original order is used
+ * as the final tie-breaker, so targets sharing one account identity remain
+ * stable without using modelStr as the affinity identity.
+ */
+export function applyPromptCacheAffinity(
+  targets: ResolvedComboTarget[],
+  body: Record<string, unknown> | null | undefined,
+  enabled: boolean = true
+): PromptCacheAffinityResult {
+  const resolution = enabled ? resolvePromptCacheAffinityKey(body) : null;
+  if (!resolution || targets.length <= 1) {
+    return {
+      targets,
+      applied: false,
+      source: resolution?.source ?? null,
+      fingerprint: resolution?.fingerprint ?? null,
+    };
+  }
+
+  const ranked = targets.map((target, index) => ({
+    target,
+    index,
+    identity: promptCacheTargetIdentity(target),
+    score: rendezvousScore(resolution.key, promptCacheTargetIdentity(target)),
+  }));
+
+  ranked.sort((a, b) => {
+    if (a.score > b.score) return -1;
+    if (a.score < b.score) return 1;
+    const identityOrder = a.identity.localeCompare(b.identity);
+    return identityOrder !== 0 ? identityOrder : a.index - b.index;
+  });
+
+  return {
+    targets: ranked.map((entry) => entry.target),
+    applied: true,
+    source: resolution.source,
+    fingerprint: resolution.fingerprint,
+  };
+}
diff --git a/open-sse/services/combo/resolveAutoStrategy.ts b/open-sse/services/combo/resolveAutoStrategy.ts
index 9d38801b35..c0d05cf650 100644
--- a/open-sse/services/combo/resolveAutoStrategy.ts
+++ b/open-sse/services/combo/resolveAutoStrategy.ts
@@ -1,8 +1,5 @@
 import { errorResponse, unavailableResponse } from "../../utils/error.ts";
-import {
-  BudgetExceededError,
-  selectProvider as selectAutoProvider,
-} from "../autoCombo/engine.ts";
+import { BudgetExceededError, selectProvider as selectAutoProvider } from "../autoCombo/engine.ts";
 import {
   resolveRequestModePack,
   parseRequestBudgetCap,
@@ -21,6 +18,10 @@ import type { ResilienceSettings } from "../../../src/lib/resilience/settings";
 import { parseAutoConfig } from "./autoConfig.ts";
 import { dedupeTargetsByExecutionKey } from "./comboData.ts";
 import { getModelContextLimitForModelString } from "./comboStructure.ts";
+import {
+  calculatePromptCacheAffinityScores,
+  promptCacheTargetIdentity,
+} from "./promptCacheAffinity.ts";
 import type { ResetWindowConfig } from "./quotaScoring.ts";
 import {
   _registerExecutionCandidates,
@@ -192,7 +193,11 @@ export async function resolveAutoStrategyOrder(
   // select-under-one-policy/rank-under-another bug this module's original fix
   // (parseAutoConfig honoring the combo's own stored modePack) set out to close.
   const weights = modePack ? getModePack(modePack) || configWeights : configWeights;
-  if (requestModePack.override || requestBudgetCap !== undefined || requestBudgetFallback !== undefined) {
+  if (
+    requestModePack.override ||
+    requestBudgetCap !== undefined ||
+    requestBudgetFallback !== undefined
+  ) {
     log.debug?.(
       "COMBO",
       `Auto strategy: per-request controls applied (mode=${
@@ -227,6 +232,10 @@ export async function resolveAutoStrategyOrder(
     resetWindowConfig,
     autoCandidateResilienceSettings
   );
+  const cacheAffinityScores = calculatePromptCacheAffinityScores(candidates, body);
+  for (const candidate of candidates) {
+    candidate.cacheAffinity = cacheAffinityScores.get(promptCacheTargetIdentity(candidate)) ?? 0;
+  }
   const routableCandidates = candidates.filter(
     (candidate) => candidate.quotaCutoffBlocked !== true
   );
@@ -250,6 +259,7 @@ export async function resolveAutoStrategyOrder(
   if (routableCandidates.length > 0) {
     let selectedProvider: string | null = null;
     let selectedModel: string | null = null;
+    let selectedConnectionId: string | null = null;
     let selectionReason = "";
 
     if (routingStrategy !== "rules") {
@@ -267,6 +277,7 @@ export async function resolveAutoStrategyOrder(
         );
         selectedProvider = decision.provider;
         selectedModel = decision.model;
+        selectedConnectionId = decision.connectionId ?? null;
         selectionReason = decision.reason;
         autoUsedExplicitRouter = true;
       } catch (err) {
@@ -306,6 +317,7 @@ export async function resolveAutoStrategyOrder(
       }
       selectedProvider = selection.provider;
       selectedModel = selection.model;
+      selectedConnectionId = selection.connectionId ?? null;
       selectionReason = `score=${selection.score.toFixed(3)}${selection.isExploration ? " (exploration)" : ""}`;
     }
 
@@ -333,7 +345,11 @@ export async function resolveAutoStrategyOrder(
       scoredTargets.find((entry) => {
         const parsed = parseModel(entry.target.modelStr);
         const modelId = parsed.model || entry.target.modelStr;
-        return entry.target.provider === selectedProvider && modelId === selectedModel;
+        return (
+          entry.target.provider === selectedProvider &&
+          modelId === selectedModel &&
+          (!selectedConnectionId || entry.target.connectionId === selectedConnectionId)
+        );
       })?.target ||
       rankedTargets[0] ||
       eligibleTargets[0];
diff --git a/src/app/(dashboard)/dashboard/settings/components/ComboDefaultsTab.tsx b/src/app/(dashboard)/dashboard/settings/components/ComboDefaultsTab.tsx
index 902a2fda31..dc79f5729e 100644
--- a/src/app/(dashboard)/dashboard/settings/components/ComboDefaultsTab.tsx
+++ b/src/app/(dashboard)/dashboard/settings/components/ComboDefaultsTab.tsx
@@ -104,6 +104,7 @@ export default function ComboDefaultsTab() {
     zeroLatencyOptimizationsEnabled: false,
   });
   const [sessionAffinityTtlMs, setSessionAffinityTtlMs] = useState(0);
+  const [promptCacheAffinityEnabled, setPromptCacheAffinityEnabled] = useState(true);
   const [providerOverrides, setProviderOverrides] = useState<any>({});
   const [availableProviders, setAvailableProviders] = useState<{ id: string; provider: string }[]>(
     []
@@ -183,6 +184,7 @@ export default function ComboDefaultsTab() {
             ? Number(settingsData.sessionAffinityTtlMs)
             : 0
         );
+        setPromptCacheAffinityEnabled(settingsData.promptCacheAffinityEnabled !== false);
       })
       .catch((err) => console.error("Failed to fetch combo defaults:", err));
   }, []);
@@ -228,6 +230,7 @@ export default function ComboDefaultsTab() {
         // #6168: global session-stickiness opt-out — persisted top-level on settings
         // (mirrors stickyRoundRobinLimit) so combo.ts resolution reads settings.disableSessionStickiness.
         disableSessionStickiness: disableSessionStickiness === true,
+        promptCacheAffinityEnabled,
       };
 
       const comboDefaultsRes = await fetch("/api/settings/combo-defaults", {
@@ -674,6 +677,24 @@ export default function ComboDefaultsTab() {
               }
             />
           </div>
+          <div className="flex items-center justify-between">
+            <div>
+              <p className="font-medium text-sm">
+                {translateOrFallback(t, "promptCacheAffinity", "Prompt-cache locality routing")}
+              </p>
+              <p className="text-xs text-text-muted">
+                {translateOrFallback(
+                  t,
+                  "promptCacheAffinityDesc",
+                  "Prefer the same provider account for matching prompt-cache keys while preserving health and quota failover."
+                )}
+              </p>
+            </div>
+            <Toggle
+              checked={promptCacheAffinityEnabled}
+              onChange={() => setPromptCacheAffinityEnabled((enabled) => !enabled)}
+            />
+          </div>
           <div className="flex items-center justify-between gap-4">
             <div>
               <p className="font-medium text-sm">
diff --git a/src/i18n/messages/de.json b/src/i18n/messages/de.json
index 60747b5af3..b03fd2d364 100644
--- a/src/i18n/messages/de.json
+++ b/src/i18n/messages/de.json
@@ -2294,6 +2294,7 @@
     "randomDesc": "Einheitliche Zufallsauswahl, dann Rückgriff auf verbleibende Modelle",
     "leastUsedDesc": "Wählt das Modell mit den wenigsten Anfragen aus und gleicht die Last über die Zeit aus",
     "costOptimizedDesc": "Leitet basierend auf dem Preis zuerst zum günstigsten Modell weiter",
+    "cacheOptimizedDesc": "Leitet jeden wiederverwendbaren Prompt-Präfix konsistent zum selben Provider-Konto",
     "resetAware": "Reset-Aware RR",
     "resetAwareDesc": "Gewichtet Restquote gegen 5h- und Wochen-Resets und rotiert ähnliche Scores per Round Robin",
     "strictRandom": "Strict Random",
@@ -2504,6 +2505,7 @@
     "weightTaskFit": "Task Fit",
     "weightStability": "Stability",
     "weightTierPriority": "Tier",
+    "weightCacheAffinity": "Cache-Treffer-Affinität",
     "reviewIntelligentTitle": "Intelligent Routing Config",
     "strategyRecommendations": {
       "priority": {
@@ -5112,6 +5114,8 @@
     "purgeLogsFailed": "Failed to purge logs",
     "contextOpt": "Context Optimized",
     "contextOptDesc": "Routes based on context window requirements and conversation length",
+    "cacheOpt": "Cache-optimiert",
+    "cacheOptDesc": "Hält denselben wiederverwendbaren Prompt-Präfix auf demselben Provider-Konto",
     "priorityDesc": "Sequential fallback - tries provider 1 first, then provider 2, and so on",
     "weightedDesc": "Distributes traffic by percentage weights across providers",
     "modelRoutingTitle": "Model Routing Rules",
diff --git a/src/i18n/messages/en.json b/src/i18n/messages/en.json
index 8e19bfd593..caca9da959 100644
--- a/src/i18n/messages/en.json
+++ b/src/i18n/messages/en.json
@@ -2998,6 +2998,7 @@
     "randomDesc": "Uniform random selection, then fallback to remaining models",
     "leastUsedDesc": "Picks the model with fewest requests, balancing load over time",
     "costOptimizedDesc": "Routes to the cheapest model first based on pricing",
+    "cacheOptimizedDesc": "Routes each reusable prompt prefix consistently to the same provider account",
     "resetAware": "Reset-Aware RR",
     "resetAwareDesc": "Balances remaining quota against 5h and weekly resets, then round-robins similar scores",
     "strictRandom": "Strict Random",
@@ -3261,6 +3262,7 @@
     "weightTaskFit": "Task Fit",
     "weightStability": "Stability",
     "weightTierPriority": "Tier",
+    "weightCacheAffinity": "Cache Hit Affinity",
     "reviewIntelligentTitle": "Intelligent Routing Config",
     "strategyRecommendations": {
       "priority": {
@@ -6763,6 +6765,8 @@
     "resetting": "Resetting...",
     "contextOpt": "Context Optimized",
     "contextOptDesc": "Routes based on context window requirements and conversation length",
+    "cacheOpt": "Cache Optimized",
+    "cacheOptDesc": "Keeps the same reusable prompt prefix on the same provider account",
     "priorityDesc": "Sequential fallback - tries provider 1 first, then provider 2, and so on",
     "weightedDesc": "Distributes traffic by percentage weights across providers",
     "modelRoutingTitle": "Model Routing Rules",
@@ -7505,6 +7509,8 @@
     "modelLockoutMaxBackoffStepsDescription": "Maximum number of backoff steps before the cooldown stops growing. The Max Cooldown cap is reached first in most configurations, making this a safety ceiling for when Max Cooldown is raised.",
     "disableSessionStickiness": "Disable session stickiness",
     "disableSessionStickinessDesc": "Round-robin and random combos rotate to a different connection on every request instead of pinning a whole conversation to one connection by the first-message hash. Leave off to preserve prompt-cache hits for multi-turn chats. Per-combo overrides take precedence.",
+    "promptCacheAffinity": "Prompt-cache locality routing",
+    "promptCacheAffinityDesc": "Prefer the same provider account for matching prompt-cache keys while preserving health and quota failover.",
     "credentialRedaction": "Credential Redaction",
     "credentialRedactionDesc": "Redact API keys, tokens, and secrets from context sent to providers and from responses.",
     "enableCredentialRedaction": "Enable credential redaction",
diff --git a/src/lib/combos/intelligentRouting.ts b/src/lib/combos/intelligentRouting.ts
index 628e1fe511..13cf531348 100644
--- a/src/lib/combos/intelligentRouting.ts
+++ b/src/lib/combos/intelligentRouting.ts
@@ -16,6 +16,7 @@ export type IntelligentRoutingWeights = {
   tierAffinity: number;
   specificityMatch: number;
   contextAffinity: number;
+  cacheAffinity: number;
   resetWindowAffinity: number;
 };
 
@@ -50,6 +51,7 @@ export const DEFAULT_INTELLIGENT_WEIGHTS: IntelligentRoutingWeights = {
   tierAffinity: 0.05,
   specificityMatch: 0.05,
   contextAffinity: 0.08,
+  cacheAffinity: 0,
   resetWindowAffinity: 0,
 };
 
@@ -79,6 +81,7 @@ export const FACTOR_LABELS: Record<keyof IntelligentRoutingWeights, string> = {
   tierAffinity: "Tier Affinity",
   specificityMatch: "Specificity",
   contextAffinity: "Context Affinity",
+  cacheAffinity: "Cache Hit Affinity",
   resetWindowAffinity: "Reset Window",
 };
 
@@ -153,6 +156,8 @@ export function normalizeIntelligentRoutingConfig(config: unknown): IntelligentR
         toFiniteNumber(rawWeights.specificityMatch) ?? DEFAULT_INTELLIGENT_WEIGHTS.specificityMatch,
       contextAffinity:
         toFiniteNumber(rawWeights.contextAffinity) ?? DEFAULT_INTELLIGENT_WEIGHTS.contextAffinity,
+      cacheAffinity:
+        toFiniteNumber(rawWeights.cacheAffinity) ?? DEFAULT_INTELLIGENT_WEIGHTS.cacheAffinity,
       resetWindowAffinity:
         toFiniteNumber(rawWeights.resetWindowAffinity) ??
         DEFAULT_INTELLIGENT_WEIGHTS.resetWindowAffinity,
diff --git a/src/lib/db/settings.ts b/src/lib/db/settings.ts
index 7cc6f499eb..5c997e4588 100644
--- a/src/lib/db/settings.ts
+++ b/src/lib/db/settings.ts
@@ -103,7 +103,9 @@ function withFamilyDefault(value: ProxyValue): ProxyValue {
 function applySessionAffinityLegacyFallback(settings: Record<string, unknown>): void {
   if (settings.sessionAffinityTtlMs === undefined) {
     settings.sessionAffinityTtlMs =
-      typeof settings.codexSessionAffinityTtlMs === "number" ? settings.codexSessionAffinityTtlMs : 0;
+      typeof settings.codexSessionAffinityTtlMs === "number"
+        ? settings.codexSessionAffinityTtlMs
+        : 0;
   }
 }
 
@@ -116,6 +118,7 @@ export async function getSettings() {
     tailscaleUrl: "",
     stickyRoundRobinLimit: 3,
     disableSessionStickiness: false,
+    promptCacheAffinityEnabled: true,
     comboStrategy: "fallback",
     comboStickyRoundRobinLimit: null, // null = inherit stickyRoundRobinLimit (a literal default here shadows the documented batched-rotation default of 3 — #6678 regression caught by the v3.8.47 release CI)
     providerStrategies: {},
diff --git a/src/shared/constants/routingStrategies.ts b/src/shared/constants/routingStrategies.ts
index a1287af553..b14b91d8fe 100644
--- a/src/shared/constants/routingStrategies.ts
+++ b/src/shared/constants/routingStrategies.ts
@@ -15,6 +15,7 @@ export const ROUTING_STRATEGY_VALUES = [
   "auto",
   "lkgp",
   "context-optimized",
+  "cache-optimized",
   "fusion",
   "pipeline",
 ] as const;
@@ -197,6 +198,13 @@ export const ROUTING_STRATEGIES: RoutingStrategyOption[] = [
     settingsDescKey: "contextOptDesc",
     icon: "text_snippet",
   },
+  {
+    value: "cache-optimized",
+    labelKey: "cacheOpt",
+    combosDescKey: "cacheOptimizedDesc",
+    settingsDescKey: "cacheOptDesc",
+    icon: "cached",
+  },
   {
     value: "fusion",
     labelKey: "fusion",
diff --git a/src/shared/validation/schemas/combo.ts b/src/shared/validation/schemas/combo.ts
index fbe95188cd..2d7b163be9 100644
--- a/src/shared/validation/schemas/combo.ts
+++ b/src/shared/validation/schemas/combo.ts
@@ -86,6 +86,7 @@ export const scoringWeightsSchema = z
     tierAffinity: z.number().min(0).max(1).optional().default(0.05),
     specificityMatch: z.number().min(0).max(1).optional().default(0.05),
     contextAffinity: z.number().min(0).max(1).optional().default(0.08),
+    cacheAffinity: z.number().min(0).max(1).optional().default(0),
     resetWindowAffinity: z.number().min(0).max(1).optional().default(0),
   })
   .optional();
diff --git a/src/shared/validation/settingsSchemas.ts b/src/shared/validation/settingsSchemas.ts
index 383e37075d..1ca0ff5f3f 100644
--- a/src/shared/validation/settingsSchemas.ts
+++ b/src/shared/validation/settingsSchemas.ts
@@ -218,12 +218,16 @@ export const updateSettingsSchema = z.object({
     .optional(),
   // #6168: global session-stickiness opt-out (per-combo config overrides this).
   disableSessionStickiness: z.boolean().optional(),
+  /** Keep eligible combo targets close to the provider-side prompt cache. */
+  promptCacheAffinityEnabled: z.boolean().optional(),
   /**
    * Per-operator quota row visibility on the usage dashboard, keyed by
    * provider id. Independent of the model catalog's isHidden/isDeleted flags.
    * Ported from upstream decolua/9router#2371.
    */
-  quotaVisibility: z.record(z.string().trim().min(1), z.object({ hidden: z.array(z.string()).max(500).optional() })).optional(),
+  quotaVisibility: z
+    .record(z.string().trim().min(1), z.object({ hidden: z.array(z.string()).max(500).optional() }))
+    .optional(),
   requestRetry: z.number().int().min(0).max(10).optional(),
   maxRetryIntervalSec: z.number().int().min(0).max(300).optional(),
   maxBodySizeMb: z
diff --git a/tests/unit/auto-combo-scoring-clamp.test.ts b/tests/unit/auto-combo-scoring-clamp.test.ts
index 025c9c1aef..1e00aca021 100644
--- a/tests/unit/auto-combo-scoring-clamp.test.ts
+++ b/tests/unit/auto-combo-scoring-clamp.test.ts
@@ -16,6 +16,7 @@ import {
   calculateScore,
   calculateFactors,
   DEFAULT_WEIGHTS,
+  normalizeScoringWeights,
 } from "../../open-sse/services/autoCombo/scoring.ts";
 import type {
   ScoringFactors,
@@ -92,15 +93,52 @@ test("calculateFactors — out-of-range contextAffinity is clamped", () => {
   );
 });
 
+test("calculateFactors — cache affinity is clamped and can be weighted", () => {
+  const factors = calculateFactors(candidate({ cacheAffinity: 4 }), [], "default", () => 0.5);
+  assert.equal(factors.cacheAffinity, 1);
+  const weights = Object.fromEntries(
+    Object.keys(DEFAULT_WEIGHTS).map((key) => [key, key === "cacheAffinity" ? 1 : 0])
+  ) as typeof DEFAULT_WEIGHTS;
+  assert.equal(calculateScore(factors, weights), 1);
+});
+
+test("normalizeScoringWeights keeps independent UI values proportional", () => {
+  const normalized = normalizeScoringWeights({
+    ...DEFAULT_WEIGHTS,
+    cacheAffinity: 0.5,
+  });
+  const total = Object.values(normalized).reduce((sum, value) => sum + Number(value), 0);
+  assert.ok(Math.abs(total - 1) < 1e-9);
+  assert.ok((normalized.cacheAffinity ?? 0) > normalized.health);
+});
+
+test("normalizeScoringWeights does not inject hidden weights into saved configs", () => {
+  const normalized = normalizeScoringWeights({ health: 0.2, cacheAffinity: 0.5 });
+  assert.equal(normalized.connectionDensity, 0);
+  assert.equal(normalized.quota, 0);
+  assert.ok(Math.abs(normalized.health - 2 / 7) < 1e-9);
+  assert.ok(Math.abs((normalized.cacheAffinity ?? 0) - 5 / 7) < 1e-9);
+});
+
 test("calculateFactors — connectionDensity is clamped to [0,1] and NaN-safe", () => {
   // A large pool ((1000-1)/10 = 99.9) must not exceed 1 and skew the weighted score.
-  const big = calculateFactors(candidate({ connectionPoolSize: 1000 }), [candidate()], "default", () => 0.5);
+  const big = calculateFactors(
+    candidate({ connectionPoolSize: 1000 }),
+    [candidate()],
+    "default",
+    () => 0.5
+  );
   assert.ok(
     big.connectionDensity >= 0 && big.connectionDensity <= 1,
     `connectionDensity must be in [0,1], got ${big.connectionDensity}`
   );
   // A non-finite pool size must map to 0 (clamp01), not propagate NaN into the score.
-  const nan = calculateFactors(candidate({ connectionPoolSize: NaN }), [candidate()], "default", () => 0.5);
+  const nan = calculateFactors(
+    candidate({ connectionPoolSize: NaN }),
+    [candidate()],
+    "default",
+    () => 0.5
+  );
   assert.ok(
     Number.isFinite(nan.connectionDensity),
     `connectionDensity must be finite (clamp01 maps NaN→0), got ${nan.connectionDensity}`
diff --git a/tests/unit/combo-auto-config-split.test.ts b/tests/unit/combo-auto-config-split.test.ts
index dd755b3a10..2df3158949 100644
--- a/tests/unit/combo-auto-config-split.test.ts
+++ b/tests/unit/combo-auto-config-split.test.ts
@@ -2,12 +2,21 @@ import { test } from "node:test";
 import assert from "node:assert/strict";
 
 import { parseAutoConfig } from "@omniroute/open-sse/services/combo/autoConfig.ts";
-import { DEFAULT_WEIGHTS } from "@omniroute/open-sse/services/autoCombo/scoring.ts";
+import { DEFAULT_WEIGHTS, normalizeScoringWeights } from "@omniroute/open-sse/services/autoCombo/scoring.ts";
 import { MODE_PACKS } from "@omniroute/open-sse/services/autoCombo/modePacks.ts";
 
 // Split guard for Block J Task 2: parseAutoConfig was extracted verbatim from
 // handleComboChat's inline auto-strategy config block. These assertions pin the
 // pure derivation so the extraction stays behavior-identical.
+//
+// #8008 (prompt-cache affinity) added a `cacheAffinity` scoring factor and made
+// parseAutoConfig run configured/mode-pack weights through `normalizeScoringWeights()`
+// so independently-tuned UI weights always sum to a valid distribution and always
+// carry the new key. That is an intentional behavior change: `cfg.weights` is now a
+// freshly normalized object rather than a reference to `DEFAULT_WEIGHTS` /
+// `MODE_PACKS[...]` / the caller's raw weights object, so these assertions compare
+// against `normalizeScoringWeights(...)` (structural equality) instead of the
+// pre-#8008 reference-equality checks.
 
 const target = (provider: string, modelStr: string) =>
   ({ provider, modelStr, executionKey: `${provider}>${modelStr}` }) as never;
@@ -20,7 +29,7 @@ test("defaults: rules strategy, provider-derived pool, default weights", () => {
   ]);
   assert.equal(cfg.routingStrategy, "rules");
   assert.deepEqual(cfg.candidatePool, ["openai", "anthropic"]);
-  assert.equal(cfg.weights, DEFAULT_WEIGHTS);
+  assert.deepEqual(cfg.weights, normalizeScoringWeights(DEFAULT_WEIGHTS));
   assert.equal(cfg.explorationRate, 0.05);
   assert.equal(cfg.budgetCap, undefined);
   assert.equal(cfg.modePack, undefined);
@@ -42,7 +51,11 @@ test("routerStrategy takes precedence over routingStrategy/strategyName", () =>
 });
 
 test("explicit candidatePool, weights, exploration and budget are honored", () => {
-  const customWeights = { latency: 1 } as never;
+  // A well-formed ScoringWeights object (not an arbitrary key) — since #8008,
+  // configured weights are run through normalizeScoringWeights(), which only
+  // recognizes the real ScoringWeights keys and zeroes out/ignores anything else,
+  // then re-normalizes the distribution to sum to 1.
+  const customWeights = { ...DEFAULT_WEIGHTS, latencyInv: 1 } as never;
   const cfg = parseAutoConfig(
     {
       name: "c",
@@ -57,7 +70,7 @@ test("explicit candidatePool, weights, exploration and budget are honored", () =
     [target("ignored", "x")]
   );
   assert.deepEqual(cfg.candidatePool, ["glm", "openai"]);
-  assert.equal(cfg.weights, customWeights);
+  assert.deepEqual(cfg.weights, normalizeScoringWeights(customWeights));
   assert.equal(cfg.explorationRate, 0.3);
   assert.equal(cfg.budgetCap, 5);
   assert.equal(cfg.modePack, "coding");
@@ -76,7 +89,7 @@ test("valid modePack overrides configured weights for fallback scoring", () => {
   );
 
   assert.equal(cfg.modePack, "ship-fast");
-  assert.equal(cfg.weights, MODE_PACKS["ship-fast"]);
+  assert.deepEqual(cfg.weights, normalizeScoringWeights(MODE_PACKS["ship-fast"]));
 });
 
 test("config.auto is preferred over top-level config", () => {
diff --git a/tests/unit/combo-resolve-auto-strategy-split.test.ts b/tests/unit/combo-resolve-auto-strategy-split.test.ts
index 84c0fe114e..690c41c25f 100644
--- a/tests/unit/combo-resolve-auto-strategy-split.test.ts
+++ b/tests/unit/combo-resolve-auto-strategy-split.test.ts
@@ -87,6 +87,55 @@ test("all candidates quota-cutoff-blocked -> early 429 Response", async () => {
   }
 });
 
+test("cache affinity scores expanded auto account candidates directly", async () => {
+  const candidates = [
+    {
+      kind: "model",
+      stepId: "s1",
+      executionKey: "openai>gpt-4o@account-a",
+      modelStr: "gpt-4o",
+      provider: "openai",
+      model: "gpt-4o",
+      connectionId: "account-a",
+      quotaRemaining: 100,
+      quotaTotal: 100,
+      circuitBreakerState: "CLOSED",
+      costPer1MTokens: 1,
+      p95LatencyMs: 100,
+      latencyStdDev: 10,
+      errorRate: 0,
+    },
+    {
+      kind: "model",
+      stepId: "s1",
+      executionKey: "openai>gpt-4o@account-b",
+      modelStr: "gpt-4o",
+      provider: "openai",
+      model: "gpt-4o",
+      connectionId: "account-b",
+      quotaRemaining: 100,
+      quotaTotal: 100,
+      circuitBreakerState: "CLOSED",
+      costPer1MTokens: 1,
+      p95LatencyMs: 100,
+      latencyStdDev: 10,
+      errorRate: 0,
+    },
+  ];
+  const deps = baseDeps((async () => candidates) as never);
+  deps.orderedTargets = [target("openai", "gpt-4o")];
+  deps.body = { prompt_cache_key: "expanded-account-key", messages: [] };
+  deps.combo.autoConfig = {
+    candidatePool: ["openai"],
+    explorationRate: 0,
+    weights: { cacheAffinity: 1 },
+  };
+
+  await resolveAutoStrategyOrder(deps);
+
+  assert.deepEqual(candidates.map((candidate) => candidate.cacheAffinity).sort(), [0, 1]);
+});
+
 // #7008 follow-up: parseAutoConfig() (see combo-auto-config-split.test.ts) already
 // makes `weights` honor a combo's own STORED modePack. But resolveAutoStrategyOrder()
 // also supports a per-request `X-OmniRoute-Mode` override (relayOptions.mode) that can
diff --git a/tests/unit/combo-routing-engine.test.ts b/tests/unit/combo-routing-engine.test.ts
index a8f00c161e..41cda10850 100644
--- a/tests/unit/combo-routing-engine.test.ts
+++ b/tests/unit/combo-routing-engine.test.ts
@@ -15,6 +15,9 @@ const {
   resolveNestedComboModels,
   handleComboChat,
 } = await import("../../open-sse/services/combo.ts");
+const { resolveComboTargets } = await import("../../open-sse/services/combo/comboStructure.ts");
+const { applyPromptCacheAffinity } =
+  await import("../../open-sse/services/combo/promptCacheAffinity.ts");
 const { resolveReasoningBufferedMaxTokens } =
   await import("../../open-sse/services/reasoningTokenBuffer.ts");
 const { normalizeComboStep } = await import("../../src/lib/combos/steps.ts");
@@ -534,6 +537,50 @@ test("handleComboChat weighted strategy selects by weight and falls back in desc
   }
 });
 
+test("handleComboChat preserves the weighted primary before prompt-cache affinity reordering", async () => {
+  const combo = {
+    name: "weighted-cache-affinity-protection",
+    strategy: "weighted",
+    models: [
+      { model: "openai/gpt-4o-mini", weight: 1 },
+      { model: "claude/sonnet", weight: 9 },
+    ],
+    config: { maxRetries: 0 },
+  };
+  const resolvedTargets = resolveComboTargets(combo, null);
+  assert.equal(resolvedTargets.length, 2);
+
+  const cacheKey = Array.from({ length: 100 }, (_, index) => `weighted-cache-${index}`).find(
+    (key) =>
+      applyPromptCacheAffinity(resolvedTargets, { prompt_cache_key: key }).targets[0] !==
+      resolvedTargets[0]
+  );
+  assert.ok(cacheKey, "test fixture must exercise a different affinity winner");
+
+  const calls: string[] = [];
+  _setSecureRandomFloatSource(() => 0);
+  try {
+    const result = await handleComboChat({
+      body: { prompt_cache_key: cacheKey },
+      combo,
+      handleSingleModel: async (_body: Record<string, unknown>, modelStr: string) => {
+        calls.push(modelStr);
+        return okResponse();
+      },
+      isModelAvailable: async () => true,
+      log: createLog(),
+      settings: null,
+      relayOptions: null,
+      allCombos: null,
+    });
+
+    assert.equal(result.ok, true);
+    assert.deepEqual(calls, ["openai/gpt-4o-mini"]);
+  } finally {
+    _setSecureRandomFloatSource(null);
+  }
+});
+
 test("handleComboChat weighted strategy falls back to uniform random when all weights are zero", async () => {
   const calls: any[] = [];
   _setSecureRandomFloatSource(() => 0.75);
@@ -2011,6 +2058,57 @@ test("handleComboChat eval-driven routing prioritizes higher scoring evaluated t
   assert.deepEqual(calls, ["openai/eval-high"]);
 });
 
+test("cache-optimized preserves eval routing when no reusable cache key exists", async () => {
+  evalsDb.saveEvalRun({
+    suiteId: "cache-miss-routing",
+    suiteName: "Cache Miss Routing",
+    target: { type: "model", id: "openai/cache-low", label: "Model: openai/cache-low" },
+    summary: { total: 10, passed: 2, failed: 8, passRate: 20 },
+    avgLatencyMs: 100,
+    results: [],
+    createdAt: new Date().toISOString(),
+  });
+  evalsDb.saveEvalRun({
+    suiteId: "cache-miss-routing",
+    suiteName: "Cache Miss Routing",
+    target: { type: "model", id: "openai/cache-high", label: "Model: openai/cache-high" },
+    summary: { total: 10, passed: 10, failed: 0, passRate: 100 },
+    avgLatencyMs: 100,
+    results: [],
+    createdAt: new Date().toISOString(),
+  });
+
+  const calls: string[] = [];
+  const result = await handleComboChat({
+    body: { messages: [{ role: "user", content: "First turn without reusable prefix" }] },
+    combo: {
+      name: "cache-optimized-miss",
+      strategy: "cache-optimized",
+      models: ["openai/cache-low", "openai/cache-high"],
+      config: {
+        evalRouting: {
+          enabled: true,
+          suiteIds: ["cache-miss-routing"],
+          qualityWeight: 1,
+          latencyWeight: 0,
+        },
+      },
+    },
+    handleSingleModel: async (_body: any, modelStr: string) => {
+      calls.push(modelStr);
+      return okResponse();
+    },
+    isModelAvailable: async () => true,
+    log: createLog(),
+    settings: { promptCacheAffinityEnabled: false },
+    relayOptions: null as any,
+    allCombos: null,
+  });
+
+  assert.equal(result.ok, true);
+  assert.deepEqual(calls, ["openai/cache-high"]);
+});
+
 test("handleComboChat eval-driven routing ignores stale and undersized eval runs", async () => {
   evalsDb.saveEvalRun({
     suiteId: "routing-quality",
@@ -2583,7 +2681,7 @@ test("handleComboChat context cache protection pins the model and tags tool-call
     },
     isModelAvailable: async () => true,
     log: createLog(),
-    settings: null,
+    settings: { promptCacheAffinityEnabled: false },
     relayOptions: null as any,
     allCombos: null,
   });
diff --git a/tests/unit/prompt-cache-affinity.test.ts b/tests/unit/prompt-cache-affinity.test.ts
new file mode 100644
index 0000000000..4d9f8bc593
--- /dev/null
+++ b/tests/unit/prompt-cache-affinity.test.ts
@@ -0,0 +1,134 @@
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import {
+  applyPromptCacheAffinity,
+  calculatePromptCacheAffinityScores,
+  expandPromptCacheAffinityTargetsFromConnections,
+  promptCacheTargetIdentity,
+  resolvePromptCacheAffinityKey,
+} from "../../open-sse/services/combo/promptCacheAffinity.ts";
+import type { ResolvedComboTarget } from "../../open-sse/services/combo/types.ts";
+import { applyStrategyOrdering } from "../../open-sse/services/combo/applyStrategyOrdering.ts";
+
+function target(
+  executionKey: string,
+  connectionId: string,
+  modelStr = "codex/gpt-5"
+): ResolvedComboTarget {
+  return {
+    kind: "model",
+    stepId: executionKey,
+    executionKey,
+    modelStr,
+    provider: "codex",
+    providerId: connectionId,
+    connectionId,
+    weight: 1,
+    label: null,
+  };
+}
+
+test("uses explicit prompt_cache_key and never exposes it in the fingerprint", () => {
+  const body = { prompt_cache_key: "private-cache-key" };
+  const resolution = resolvePromptCacheAffinityKey(body);
+  assert.equal(resolution?.source, "explicit");
+  assert.notEqual(resolution?.fingerprint, body.prompt_cache_key);
+  assert.equal(resolution?.fingerprint?.length, 12);
+});
+
+test("derives a stable key from Responses input when explicit key is absent", () => {
+  const first = resolvePromptCacheAffinityKey({
+    input: [
+      { role: "system", content: "tools" },
+      { role: "user", content: "hello" },
+    ],
+  });
+  const second = resolvePromptCacheAffinityKey({
+    input: [
+      { role: "system", content: "tools" },
+      { role: "user", content: "hello" },
+    ],
+  });
+  assert.equal(first?.source, "prefix");
+  assert.deepEqual(first, second);
+});
+
+test("rendezvous ordering is deterministic and distinguishes same-model accounts", () => {
+  const targets = [target("step-a", "account-a"), target("step-b", "account-b")];
+  const body = { prompt_cache_key: "stable" };
+  const first = applyPromptCacheAffinity(targets, body);
+  const second = applyPromptCacheAffinity([...targets].reverse(), body);
+  assert.deepEqual(
+    first.targets.map((item) => item.connectionId),
+    second.targets.map((item) => item.connectionId)
+  );
+  assert.equal(first.applied, true);
+});
+
+test("disabled affinity and missing keys preserve the eligible order", () => {
+  const targets = [target("step-a", "account-a"), target("step-b", "account-b")];
+  assert.deepEqual(
+    applyPromptCacheAffinity(targets, { input: [{ role: "user", content: "hello" }] }, true)
+      .targets,
+    targets
+  );
+  assert.deepEqual(
+    applyPromptCacheAffinity([...targets], { prompt_cache_key: "stable" }, false).targets,
+    targets
+  );
+});
+
+test("auto scoring assigns the cache winner to exactly one account", () => {
+  const targets = [target("step-a", "account-a"), target("step-b", "account-b")];
+  const scores = calculatePromptCacheAffinityScores(targets, {
+    prompt_cache_key: "stable-auto-key",
+  });
+  assert.equal(scores.size, 2);
+  assert.equal(
+    targets.reduce((sum, item) => sum + (scores.get(promptCacheTargetIdentity(item)) ?? 0), 0),
+    1
+  );
+});
+
+test("expands unbound targets to active allowed accounts before cache routing", () => {
+  const unbound = { ...target("step-a", ""), connectionId: null };
+  const expanded = expandPromptCacheAffinityTargetsFromConnections(
+    [{ ...unbound, allowedConnectionIds: ["account-b"] }],
+    new Map([["codex", [{ id: "account-a" }, { id: "account-b" }, { id: "account-c" }]]])
+  );
+  assert.deepEqual(
+    expanded.map((item) => item.connectionId),
+    ["account-b"]
+  );
+  assert.equal(expanded[0].executionKey, "step-a@account-b");
+});
+
+test("expanded auto candidates receive exactly one concrete account cache score", () => {
+  const unbound = { ...target("step-a", ""), connectionId: null };
+  const expanded = expandPromptCacheAffinityTargetsFromConnections(
+    [unbound],
+    new Map([["codex", [{ id: "account-a" }, { id: "account-b" }]]])
+  );
+  const scores = calculatePromptCacheAffinityScores(expanded, {
+    prompt_cache_key: "expanded-auto-key",
+  });
+  assert.equal(
+    expanded.reduce((sum, item) => sum + (scores.get(promptCacheTargetIdentity(item)) ?? 0), 0),
+    1
+  );
+  assert.ok(expanded.every((item) => item.connectionId));
+});
+
+test("cache-optimized strategy routes a stable prompt key to the same account", async () => {
+  const targets = [target("step-a", "account-a"), target("step-b", "account-b")];
+  const deps = {
+    combo: { id: "cache-combo", name: "cache-combo" },
+    config: {},
+    body: { prompt_cache_key: "stable-strategy-key" },
+    log: { info() {}, warn() {} },
+    apiKeyAllowedConnections: null,
+  };
+  const first = await applyStrategyOrdering("cache-optimized", targets, deps);
+  const second = await applyStrategyOrdering("cache-optimized", [...targets].reverse(), deps);
+  assert.equal(first[0].connectionId, second[0].connectionId);
+});