diff --git a/src/adapters/openai-responses.ts b/src/adapters/openai-responses.ts
index 8bb40769a..9e9b46acc 100644
--- a/src/adapters/openai-responses.ts
+++ b/src/adapters/openai-responses.ts
@@ -538,6 +538,65 @@ function repairOrphanedInputItems(body: unknown, dropReasoning: boolean): unknow
   return changed ? { ...body, input: repaired } : body;
 }
 
+/**
+ * Make unambiguous Responses tool pairs adjacent for upstream parsers that require it.
+ *
+ * [Decision Log]
+ * - 목적과 의도: Keep Codex hook-injected developer context without letting it make a strict upstream reject the matching tool result.
+ * - 기존 구현 및 제약 조건: The orphan repair verifies only pair presence; globally reordering valid history would change tolerant providers unnecessarily.
+ * - 검토한 주요 대안: Reorder every Responses request, drop the intervening message, or gate a lossless reorder behind provider capability metadata.
+ * - 선택한 방식: Reorder only unique call/result pairs for providers that explicitly require adjacency, preserving every intervening item immediately after the result.
+ * - 다른 대안 대신 이 방식을 선택한 이유: The provider gate limits semantic blast radius, while refusing ambiguous duplicate ids avoids guessing which result belongs to which call.
+ * - 장점, 단점 및 영향: DeepSeek receives the adjacency its parser requires; tolerant providers stay byte/order equivalent. Ambiguous duplicate ids still fail upstream rather than being silently rewritten.
+ */
+function normalizeResponsesToolResultAdjacency(body: unknown): unknown {
+  if (!isPlainObject(body) || !Array.isArray(body.input)) return body;
+  const input = body.input;
+  const calls = new Map<string, number[]>();
+  const outputs = new Map<string, number[]>();
+
+  const appendIndex = (map: Map<string, number[]>, key: string, index: number): void => {
+    const existing = map.get(key);
+    if (existing) existing.push(index);
+    else map.set(key, [index]);
+  };
+
+  for (let index = 0; index < input.length; index += 1) {
+    const item = input[index];
+    if (!isPlainObject(item) || typeof item.call_id !== "string" || item.call_id.length === 0) continue;
+    if (item.type === "function_call" || item.type === "local_shell_call") {
+      appendIndex(calls, `function:${item.call_id}`, index);
+    } else if (item.type === "custom_tool_call") {
+      appendIndex(calls, `custom:${item.call_id}`, index);
+    } else if (item.type === "function_call_output") {
+      appendIndex(outputs, `function:${item.call_id}`, index);
+    } else if (item.type === "custom_tool_call_output") {
+      appendIndex(outputs, `custom:${item.call_id}`, index);
+    }
+  }
+
+  const movedOutputIndices = new Set<number>();
+  const outputAfterCall = new Map<number, unknown>();
+  for (const [key, callIndices] of calls) {
+    const outputIndices = outputs.get(key);
+    if (callIndices.length !== 1 || outputIndices?.length !== 1) continue;
+    const callIndex = callIndices[0]!;
+    const outputIndex = outputIndices[0]!;
+    if (outputIndex === callIndex + 1) continue;
+    movedOutputIndices.add(outputIndex);
+    outputAfterCall.set(callIndex, input[outputIndex]);
+  }
+  if (movedOutputIndices.size === 0) return body;
+
+  const normalized: unknown[] = [];
+  for (let index = 0; index < input.length; index += 1) {
+    if (movedOutputIndices.has(index)) continue;
+    normalized.push(input[index]);
+    if (outputAfterCall.has(index)) normalized.push(outputAfterCall.get(index));
+  }
+  return { ...body, input: normalized };
+}
+
 /**
  * Remove `previous_response_id` before forwarding. Two triggers:
  * - the proxy expanded the request into a full input replay (the id is now redundant), or
@@ -1158,6 +1217,9 @@ export function createResponsesPassthroughAdapter(provider: OcxProviderConfig):
       if (forward || stateless) {
         outBody = repairOrphanedInputItems(outBody, unexpandedMiss);
       }
+      if (provider.requiresAdjacentResponsesToolResults === true) {
+        outBody = normalizeResponsesToolResultAdjacency(outBody);
+      }
       if (forward) {
         outBody = stripUnsupportedForwardParams(outBody);
       } else {
diff --git a/src/config.ts b/src/config.ts
index b662959bd..57dc80646 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -613,6 +613,7 @@ const providerConfigSchema = z.object({
   apiKeyTransport: z.enum(["x-api-key", "bearer"]).optional(),
   responsesPath: z.string().min(1).optional(),
   statelessResponses: z.boolean().optional(),
+  requiresAdjacentResponsesToolResults: z.boolean().optional(),
   supportsServiceTier: z.boolean().optional(),
   preserveResponsesReasoningContent: z.boolean().optional(),
   allowPrivateNetwork: z.boolean().optional(),
diff --git a/src/providers/derive.ts b/src/providers/derive.ts
index c947c0b4f..db7287d18 100644
--- a/src/providers/derive.ts
+++ b/src/providers/derive.ts
@@ -152,6 +152,9 @@ export function providerConfigSeed(entry: ProviderRegistryEntry): OcxProviderCon
     ...(entry.promptCacheKey !== undefined ? { promptCacheKey: entry.promptCacheKey } : {}),
     ...(entry.responsesPath !== undefined ? { responsesPath: entry.responsesPath } : {}),
     ...(entry.statelessResponses !== undefined ? { statelessResponses: entry.statelessResponses } : {}),
+    ...(entry.requiresAdjacentResponsesToolResults !== undefined
+      ? { requiresAdjacentResponsesToolResults: entry.requiresAdjacentResponsesToolResults }
+      : {}),
     ...(entry.autoToolChoiceOnlyModels ? { autoToolChoiceOnlyModels: [...entry.autoToolChoiceOnlyModels] } : {}),
     ...(entry.preserveReasoningContentModels ? { preserveReasoningContentModels: [...entry.preserveReasoningContentModels] } : {}),
     ...(entry.reasoningSplitModels ? { reasoningSplitModels: [...entry.reasoningSplitModels] } : {}),
@@ -323,6 +326,9 @@ export function enrichProviderFromRegistry(name: string, prov: OcxProviderConfig
   // learned this route still gets backfilled.
   if (prov.responsesPath === undefined && seed.responsesPath !== undefined) prov.responsesPath = seed.responsesPath;
   if (prov.statelessResponses === undefined && seed.statelessResponses !== undefined) prov.statelessResponses = seed.statelessResponses;
+  if (prov.requiresAdjacentResponsesToolResults === undefined && seed.requiresAdjacentResponsesToolResults !== undefined) {
+    prov.requiresAdjacentResponsesToolResults = seed.requiresAdjacentResponsesToolResults;
+  }
   // Registry-only metadata (never seeded into saved config): backfill straight from
   // the entry so an explicit user value stays distinguishable from the default.
   if (prov.supportsServiceTier === undefined && entry.supportsServiceTier !== undefined) prov.supportsServiceTier = entry.supportsServiceTier;
diff --git a/src/providers/registry.ts b/src/providers/registry.ts
index 5856b6edf..a2ac24141 100644
--- a/src/providers/registry.ts
+++ b/src/providers/registry.ts
@@ -186,6 +186,11 @@ export interface ProviderRegistryEntry {
    * replay miss are repaired rather than forwarded.
    */
   statelessResponses?: boolean;
+  /**
+   * Responses parser requires a matched tool result directly after its call. This is
+   * seeded/backfilled like other fixed upstream wire-contract capabilities.
+   */
+  requiresAdjacentResponsesToolResults?: boolean;
   /**
    * Registry default for the provider's Responses `service_tier` support; see
    * `OcxProviderConfig.supportsServiceTier`. Registry-only: backfilled (never
@@ -1359,6 +1364,9 @@ export const PROVIDER_REGISTRY: readonly ProviderRegistryEntry[] = [
     // "The API is stateless: responses and conversations are not stored on the
     // server." https://api-docs.deepseek.com/api/create-response/
     statelessResponses: true,
+    // DeepSeek rejects a valid Codex continuation when hook-provided developer
+    // context is persisted between a call and its matching result (#1292).
+    requiresAdjacentResponsesToolResults: true,
     /* [Decision Log]
     - 목적: DeepSeek V4 thinking mode multi-turn/tool-call requests must replay prior assistant reasoning_content.
     - 대안 분석: Globally preserve reasoning_content for all OpenAI-compatible models; preserve it for legacy deepseek-reasoner too; mark only V4 thinking models in registry metadata.
diff --git a/src/router.ts b/src/router.ts
index ec1d5bb91..7dda3eef1 100644
--- a/src/router.ts
+++ b/src/router.ts
@@ -307,6 +307,10 @@ function routedProviderConfig(providerName: string, provider: OcxProviderConfig)
     ...(provider.responsesPath === undefined && registryEntry.responsesPath !== undefined
       ? { responsesPath: registryEntry.responsesPath }
       : {}),
+    ...(provider.requiresAdjacentResponsesToolResults === undefined
+      && registryEntry.requiresAdjacentResponsesToolResults !== undefined
+      ? { requiresAdjacentResponsesToolResults: registryEntry.requiresAdjacentResponsesToolResults }
+      : {}),
     ...(provider.supportsServiceTier === undefined && registryEntry.supportsServiceTier !== undefined
       ? { supportsServiceTier: registryEntry.supportsServiceTier }
       : {}),
diff --git a/src/types.ts b/src/types.ts
index 6e3054e19..510c073a2 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -1158,6 +1158,12 @@ export interface OcxProviderConfig {
    * forwarded to an upstream that cannot resolve their pair.
    */
   statelessResponses?: boolean;
+  /**
+   * Responses upstream whose parser requires each tool result to immediately follow
+   * its matching call. When enabled, only unambiguous matched pairs are reordered;
+   * intervening messages are preserved after the result instead of being dropped.
+   */
+  requiresAdjacentResponsesToolResults?: boolean;
   /**
    * Whether this provider's Responses route honours the OpenAI `service_tier`
    * parameter. Tri-state: `true` lets fast mode inject/remove the field (an unset
diff --git a/tests/deepseek-inbound-wire.test.ts b/tests/deepseek-inbound-wire.test.ts
index 426f9753c..e5a650a09 100644
--- a/tests/deepseek-inbound-wire.test.ts
+++ b/tests/deepseek-inbound-wire.test.ts
@@ -12,7 +12,7 @@
  * assert the captured upstream URL, which is externally observable.
  */
 import { afterEach, beforeEach, describe, expect, test } from "bun:test";
-import { providerConfigSeed } from "../src/providers/derive";
+import { enrichProviderFromRegistry, providerConfigSeed } from "../src/providers/derive";
 import { getProviderRegistryEntry, PROVIDER_REGISTRY } from "../src/providers/registry";
 import { createResponsesPassthroughAdapter as createResponsesPassthroughAdapterProduction } from "../src/adapters/openai-responses";
 import { resolveWireProtocolOverride } from "../src/server/adapter-resolve";
@@ -439,7 +439,45 @@ describe("stateless Responses upstreams get no stateful parameters", () => {
 
   test("the seed and backfill carry the capability, and only for declaring entries", () => {
     expect(providerConfigSeed(getProviderRegistryEntry("deepseek")!).statelessResponses).toBe(true);
+    expect(providerConfigSeed(getProviderRegistryEntry("deepseek")!).requiresAdjacentResponsesToolResults).toBe(true);
     expect(providerConfigSeed(getProviderRegistryEntry("cerebras")!).statelessResponses).toBeUndefined();
+    expect(providerConfigSeed(getProviderRegistryEntry("cerebras")!).requiresAdjacentResponsesToolResults).toBeUndefined();
+
+    const stale = deepseekProvider();
+    delete stale.requiresAdjacentResponsesToolResults;
+    enrichProviderFromRegistry("deepseek", stale);
+    expect(stale.requiresAdjacentResponsesToolResults).toBe(true);
+  });
+
+  test("DeepSeek makes a matched tool result adjacent without dropping injected developer context", () => {
+    const call = { type: "function_call", call_id: "call_plan", name: "shell_command", arguments: "{}" };
+    const injected = {
+      type: "message",
+      role: "developer",
+      content: [{ type: "input_text", text: "[planning-with-files] ACTIVE PLAN" }],
+    };
+    const output = { type: "function_call_output", call_id: "call_plan", output: "Exit code: 0" };
+    const tail = { type: "message", role: "user", content: [{ type: "input_text", text: "continue" }] };
+
+    const body = buildBody(deepseekProvider(), { input: [call, injected, output, tail] }) as { input: unknown[] };
+    expect(body.input).toEqual([call, output, injected, tail]);
+  });
+
+  test("tolerant Responses providers keep interleaved tool history unchanged", () => {
+    const provider: OcxProviderConfig = {
+      adapter: "openai-responses",
+      baseUrl: "https://api.openai.example/v1",
+      authMode: "key",
+      apiKey: "sk-test",
+    };
+    const input = [
+      { type: "function_call", call_id: "call_plan", name: "shell_command", arguments: "{}" },
+      { type: "message", role: "developer", content: [{ type: "input_text", text: "plan" }] },
+      { type: "function_call_output", call_id: "call_plan", output: "done" },
+    ];
+
+    const body = buildBody(provider, { input }) as { input: unknown[] };
+    expect(body.input).toEqual(input);
   });
 
   test("a replay miss does not forward an orphaned tool result", () => {