diff --git a/src/adapters/zed-openai-stream.ts b/src/adapters/zed-openai-stream.ts
new file mode 100644
index 00000000000..02f98d0dc93
--- /dev/null
+++ b/src/adapters/zed-openai-stream.ts
@@ -0,0 +1,340 @@
+import type { AdapterEvent, OcxMessagePhase, OcxUsage } from "../types";
+import type { TranslatorBudget } from "../lib/translator-budget";
+import { decodeServerSentEvents } from "../lib/sse-decoder";
+
+function isRecord(value: unknown): value is Record<string, unknown> {
+  return !!value && typeof value === "object" && !Array.isArray(value);
+}
+
+function toolKey(tool: Record<string, unknown>): string | undefined {
+  if (typeof tool.type !== "string" || !tool.type) return undefined;
+  const name = typeof tool.name === "string" ? tool.name : "";
+  return tool.type + "\0" + name;
+}
+
+/**
+ * Zed's OpenAI Responses schema accepts message and call items, not Codex's private
+ * additional_tools wrapper. Drop every wrapper. Promote only wrappers at or after the
+ * replayed prefix: earlier ones are history, not the current turn's tool catalog.
+ * A non-array tools field is left untouched so a malformed catalog is not replaced
+ * by a partial promotion.
+ */
+export function liftZedAdditionalTools(providerRequest: Record<string, unknown>, replayPrefixLength: number): void {
+  if (!Array.isArray(providerRequest.input)) return;
+  if (providerRequest.tools !== undefined && !Array.isArray(providerRequest.tools)) return;
+
+  const currentTurnStart = Number.isFinite(replayPrefixLength)
+    ? Math.min(providerRequest.input.length, Math.max(0, Math.trunc(replayPrefixLength)))
+    : 0;
+  const input: unknown[] = [];
+  const promoted: unknown[] = [];
+  let changed = false;
+  for (const [index, item] of providerRequest.input.entries()) {
+    if (isRecord(item) && item.type === "additional_tools" && Array.isArray(item.tools)) {
+      changed = true;
+      if (index >= currentTurnStart) promoted.push(...item.tools);
+      continue;
+    }
+    input.push(item);
+  }
+  if (!changed) return;
+
+  const seen = new Set<string>();
+  const tools: unknown[] = [];
+  const existing = Array.isArray(providerRequest.tools) ? providerRequest.tools : [];
+  for (const tool of [...existing, ...promoted]) {
+    if (!isRecord(tool)) {
+      tools.push(tool);
+      continue;
+    }
+    const key = toolKey(tool);
+    if (key && seen.has(key)) continue;
+    if (key) seen.add(key);
+    tools.push(tool);
+  }
+  providerRequest.input = input;
+  providerRequest.tools = tools;
+}
+
+interface CallState {
+  key: string;
+  callId: string;
+  name: string;
+  args: string;
+  pendingFull?: string;
+  started: boolean;
+  ended: boolean;
+}
+
+function phaseOf(item: Record<string, unknown>): OcxMessagePhase | undefined {
+  return item.phase === "commentary" || item.phase === "final_answer" ? item.phase : undefined;
+}
+
+function messageText(item: Record<string, unknown>): string {
+  if (!Array.isArray(item.content)) return "";
+  return item.content
+    .filter((part): part is Record<string, unknown> => isRecord(part) && part.type === "output_text" && typeof part.text === "string")
+    .map(part => String(part.text))
+    .join("");
+}
+
+function usageFromResponse(response: unknown): OcxUsage | undefined {
+  if (!isRecord(response) || !isRecord(response.usage)) return undefined;
+  const usage = response.usage;
+  if (typeof usage.input_tokens !== "number" || typeof usage.output_tokens !== "number") return undefined;
+  const inputDetails = isRecord(usage.input_tokens_details) ? usage.input_tokens_details : undefined;
+  const outputDetails = isRecord(usage.output_tokens_details) ? usage.output_tokens_details : undefined;
+  return {
+    inputTokens: usage.input_tokens,
+    outputTokens: usage.output_tokens,
+    ...(typeof usage.total_tokens === "number" ? { totalTokens: usage.total_tokens } : {}),
+    ...(typeof inputDetails?.cached_tokens === "number"
+      ? { cachedInputTokens: inputDetails.cached_tokens, cacheReadInputTokens: inputDetails.cached_tokens }
+      : {}),
+    ...(typeof outputDetails?.reasoning_tokens === "number"
+      ? { reasoningOutputTokens: outputDetails.reasoning_tokens }
+      : {}),
+  };
+}
+
+function failureMessage(payload: Record<string, unknown>): string {
+  const source = isRecord(payload.response) ? payload.response : payload;
+  const err = source.error ?? payload.error;
+  if (typeof err === "string" && err) return err;
+  if (isRecord(err) && typeof err.message === "string" && err.message) return err.message;
+  if (typeof source.message === "string" && source.message) return source.message;
+  return "Zed OpenAI request failed";
+}
+
+function incompleteReason(payload: Record<string, unknown>): string {
+  const source = isRecord(payload.response) ? payload.response : payload;
+  const details = isRecord(source.incomplete_details) ? source.incomplete_details : undefined;
+  if (typeof details?.reason === "string" && details.reason) return details.reason;
+  return failureMessage(payload);
+}
+
+/**
+ * Translate Zed's OpenAI Responses SSE into adapter events.
+ *
+ * The shared Responses passthrough parser only keeps message text, because its other caller
+ * is compaction. Using it here drops function and custom calls, and Codex then stores the
+ * first sentence as final_answer and ends the turn. A later synthetic response.completed
+ * with empty output (Zed's stream-ended frame) must not wipe usage taken from the real
+ * completion, and completed output must not repeat text or calls that already streamed.
+ */
+export async function* translateZedOpenAiStream(
+  body: ReadableStream<Uint8Array> | null,
+  budget: TranslatorBudget,
+): AsyncGenerator<AdapterEvent> {
+  if (!body) {
+    yield { type: "error", message: "Zed OpenAI response had no body" };
+    return;
+  }
+
+  const calls = new Map<string, CallState>();
+  const phases = new Map<string, OcxMessagePhase>();
+  let streamedText = "";
+  let sawThinking = false;
+  let sawRawReasoning = false;
+  let usage: OcxUsage | undefined;
+  let terminal = false;
+
+  function* closeOpenCallsExcept(keep: CallState): Generator<AdapterEvent> {
+    for (const other of calls.values()) {
+      if (other !== keep && other.started && !other.ended) {
+        other.ended = true;
+        yield { type: "tool_call_end" };
+      }
+    }
+  }
+
+  function* startIfNeeded(state: CallState): Generator<AdapterEvent> {
+    if (state.started || state.ended || !state.name) return;
+    yield* closeOpenCallsExcept(state);
+    state.started = true;
+    yield { type: "tool_call_start", id: state.callId, name: state.name };
+    if (state.args) yield { type: "tool_call_delta", arguments: state.args };
+  }
+
+  function* appendArgs(state: CallState, fragment: string): Generator<AdapterEvent> {
+    if (!fragment || state.ended) return;
+    if (!state.started) {
+      if (!state.name) {
+        state.args += fragment;
+        return;
+      }
+      yield* startIfNeeded(state);
+    }
+    state.args += fragment;
+    yield { type: "tool_call_delta", arguments: fragment };
+  }
+
+  function rememberFull(state: CallState, full: unknown): void {
+    if (typeof full === "string" && full.length > 0) state.pendingFull = full;
+  }
+
+  function* finishCall(state: CallState): Generator<AdapterEvent> {
+    if (state.ended) return;
+    const full = state.pendingFull;
+    if (typeof full === "string" && full.length > state.args.length && full.startsWith(state.args)) {
+      yield* appendArgs(state, full.slice(state.args.length));
+    }
+    yield* startIfNeeded(state);
+    if (!state.started) return;
+    state.ended = true;
+    yield { type: "tool_call_end" };
+  }
+
+  function ensureCall(key: string, callId: string, name: string): CallState {
+    let state = calls.get(key);
+    if (!state) {
+      state = { key, callId, name, args: "", started: false, ended: false };
+      calls.set(key, state);
+      return state;
+    }
+    if (callId) state.callId = callId;
+    if (name) state.name = name;
+    return state;
+  }
+
+  function* emitNewText(text: string, phase?: OcxMessagePhase): Generator<AdapterEvent> {
+    if (!text) return;
+    if (!streamedText) {
+      streamedText = text;
+      yield { type: "text_delta", text, ...(phase ? { phase } : {}) };
+      return;
+    }
+    if (text === streamedText || streamedText.endsWith(text)) return;
+    if (text.startsWith(streamedText)) {
+      const tail = text.slice(streamedText.length);
+      streamedText = text;
+      if (tail) yield { type: "text_delta", text: tail };
+      return;
+    }
+    streamedText += text;
+    yield { type: "text_delta", text, ...(phase ? { phase } : {}) };
+  }
+
+  function* observeToolItem(item: Record<string, unknown>, done: boolean): Generator<AdapterEvent> {
+    if (item.type !== "function_call" && item.type !== "custom_tool_call") return;
+    const key = typeof item.id === "string" ? item.id : typeof item.call_id === "string" ? item.call_id : undefined;
+    if (!key) return;
+    const callId = typeof item.call_id === "string" ? item.call_id : key;
+    const name = typeof item.name === "string" ? item.name : "";
+    const state = ensureCall(key, callId, name);
+    rememberFull(state, item.type === "custom_tool_call" ? item.input : item.arguments);
+    if (done) yield* finishCall(state);
+    else yield* startIfNeeded(state);
+  }
+
+  function* emitReasoningItem(item: Record<string, unknown>): Generator<AdapterEvent> {
+    if (!sawThinking && Array.isArray(item.summary)) {
+      const text = item.summary
+        .filter((part): part is Record<string, unknown> => isRecord(part) && typeof part.text === "string")
+        .map(part => String(part.text))
+        .join("");
+      if (text) {
+        sawThinking = true;
+        yield { type: "thinking_delta", thinking: text };
+      }
+    }
+    if (!sawRawReasoning && Array.isArray(item.content)) {
+      const text = item.content
+        .filter((part): part is Record<string, unknown> => isRecord(part) && part.type === "reasoning_text" && typeof part.text === "string")
+        .map(part => String(part.text))
+        .join("");
+      if (text) {
+        sawRawReasoning = true;
+        yield { type: "reasoning_raw_delta", text };
+      }
+    }
+  }
+
+  function* consumeItem(item: Record<string, unknown>, done: boolean): Generator<AdapterEvent> {
+    if (item.type === "message") {
+      const phase = phaseOf(item);
+      if (typeof item.id === "string" && phase) phases.set(item.id, phase);
+      if (done) yield* emitNewText(messageText(item), phase);
+      return;
+    }
+    if (item.type === "function_call" || item.type === "custom_tool_call") {
+      yield* observeToolItem(item, done);
+      return;
+    }
+    if (done && item.type === "reasoning") yield* emitReasoningItem(item);
+  }
+
+  function* onPayload(payload: Record<string, unknown>): Generator<AdapterEvent> {
+    if (payload.type === "error" || payload.type === "response.failed") {
+      terminal = true;
+      yield { type: "error", message: failureMessage(payload) };
+      return;
+    }
+    if (payload.type === "response.incomplete") {
+      terminal = true;
+      for (const state of calls.values()) yield* finishCall(state);
+      yield { type: "incomplete", reason: incompleteReason(payload) };
+      return;
+    }
+    if (payload.type === "response.output_item.added" || payload.type === "response.output_item.done") {
+      if (isRecord(payload.item)) yield* consumeItem(payload.item, payload.type === "response.output_item.done");
+      return;
+    }
+    if (payload.type === "response.output_text.delta" && typeof payload.delta === "string" && payload.delta) {
+      const itemId = typeof payload.item_id === "string" ? payload.item_id : undefined;
+      const phase = itemId ? phases.get(itemId) : undefined;
+      streamedText += payload.delta;
+      yield { type: "text_delta", text: payload.delta, ...(phase ? { phase } : {}) };
+      return;
+    }
+    if (payload.type === "response.reasoning_summary_text.delta" && typeof payload.delta === "string" && payload.delta) {
+      sawThinking = true;
+      yield { type: "thinking_delta", thinking: payload.delta };
+      return;
+    }
+    if (payload.type === "response.reasoning_text.delta" && typeof payload.delta === "string" && payload.delta) {
+      sawRawReasoning = true;
+      yield { type: "reasoning_raw_delta", text: payload.delta };
+      return;
+    }
+    if (
+      (payload.type === "response.function_call_arguments.delta" || payload.type === "response.custom_tool_call_input.delta")
+      && typeof payload.delta === "string"
+    ) {
+      const key = typeof payload.item_id === "string" ? payload.item_id : undefined;
+      if (!key) return;
+      yield* appendArgs(ensureCall(key, key, ""), payload.delta);
+      return;
+    }
+    if (payload.type === "response.function_call_arguments.done" || payload.type === "response.custom_tool_call_input.done") {
+      const key = typeof payload.item_id === "string" ? payload.item_id : undefined;
+      if (!key) return;
+      const state = ensureCall(key, key, "");
+      rememberFull(state, payload.type === "response.custom_tool_call_input.done" ? payload.input : payload.arguments);
+      yield* finishCall(state);
+      return;
+    }
+    if (payload.type === "response.completed") {
+      const response = isRecord(payload.response) ? payload.response : undefined;
+      if (response && Array.isArray(response.output)) {
+        for (const item of response.output) {
+          if (isRecord(item)) yield* consumeItem(item, true);
+        }
+      }
+      const nextUsage = usageFromResponse(response);
+      if (nextUsage) usage = nextUsage;
+    }
+  }
+
+  for await (const event of decodeServerSentEvents(body, { translatorBudget: budget })) {
+    let payload: unknown;
+    try { payload = JSON.parse(event.data); } catch { continue; }
+    if (!isRecord(payload)) continue;
+    yield* onPayload(payload);
+    if (terminal) return;
+  }
+
+  for (const state of calls.values()) yield* finishCall(state);
+  yield { type: "done", ...(usage ? { usage } : {}) };
+}
+
diff --git a/src/adapters/zed.ts b/src/adapters/zed.ts
index 0004090896c..322e504f76a 100644
--- a/src/adapters/zed.ts
+++ b/src/adapters/zed.ts
@@ -5,6 +5,7 @@ import type { AnthropicCacheRetention } from "./anthropic/cache-retention";
 import { createGoogleAdapter } from "./google";
 import { createOpenAIChatAdapter } from "./openai-chat";
 import { createResponsesPassthroughAdapter } from "./openai-responses";
+import { liftZedAdditionalTools, translateZedOpenAiStream } from "./zed-openai-stream";
 import { createAdapterPhysicalSend } from "./physical-send";
 import type { AdapterEvent, OcxParsedRequest, OcxProviderConfig } from "../types";
 import { createTranslatorBudget, releaseTranslatedEvent, retainTranslatedEvent, type TranslatorBudget } from "../lib/translator-budget";
@@ -314,6 +315,12 @@ export function createZedAdapter(provider: OcxProviderConfig, cacheRetention?: A
           : item,
       );
     }
+    if (zedProvider === "open_ai") {
+      // Codex carries this turn's client tools in a private additional_tools input item.
+      // Zed rejects that variant, so promote the current turn and drop every wrapper
+      // before the built-in tool filter runs.
+      liftZedAdditionalTools(providerRequest, parsed._replayPrefixLen ?? 0);
+    }
     if (zedProvider === "open_ai" && Array.isArray(providerRequest.tools)) {
       // Zed's Responses decoder supports function/custom tools, not Codex's built-in web_search.
       const supported = (tool: unknown) => isRecord(tool) && (tool.type === "function" || tool.type === "custom");
@@ -410,7 +417,11 @@ export function createZedAdapter(provider: OcxProviderConfig, cacheRetention?: A
         headers: { "Content-Type": "text/event-stream" },
       });
       try {
-        yield* delegate.adapter.parseStream(translated, budget);
+        // The Responses passthrough parser only keeps compaction text. Zed is not a
+        // passthrough route, so function and custom calls have to be translated or
+        // Codex ends the turn on the first sentence.
+        if (delegate.provider === "open_ai") yield* translateZedOpenAiStream(translated.body, budget);
+        else yield* delegate.adapter.parseStream(translated, budget);
       } finally {
         // Some delegates only unlock their reader when a collector stops early.
         try { await translated.body?.cancel(); } catch { /* already closed/errored */ }
diff --git a/tests/providers/zed-hosted-provider.test.ts b/tests/providers/zed-hosted-provider.test.ts
index 7442777fba2..cb1c889edc9 100644
--- a/tests/providers/zed-hosted-provider.test.ts
+++ b/tests/providers/zed-hosted-provider.test.ts
@@ -362,6 +362,120 @@ describe("Zed OpenAI tool selection after filtering", () => {
   });
 });
 
+describe("Zed OpenAI tool relay", () => {
+  const provider: OcxProviderConfig = {
+    adapter: "zed",
+    baseUrl: "https://cloud.zed.dev",
+    authMode: "oauth",
+    apiKey: "access-token",
+  };
+
+  function catalogFetch(): void {
+    const responses = [
+      jsonResponse({ default_organization_id: "org-1" }),
+      jsonResponse({ token: "llm-token-1" }),
+      jsonResponse({ models: [{ id: "gpt-6.1-sol", provider: "open_ai" }] }),
+    ];
+    globalThis.fetch = (async () => {
+      const response = responses.shift();
+      if (!response) throw new Error("unexpected Zed catalog fetch");
+      return response;
+    }) as typeof globalThis.fetch;
+  }
+
+  test("promotes the current turn's additional_tools and drops replayed wrappers", async () => {
+    catalogFetch();
+    const already = { type: "function", name: "already", parameters: { type: "object", properties: {} } };
+    const parsed = parseRequest({
+      model: "gpt-6.1-sol",
+      input: [
+        { type: "additional_tools", tools: [{ type: "function", name: "old_tool", parameters: { type: "object", properties: {} } }] },
+        { type: "message", role: "user", content: [{ type: "input_text", text: "earlier" }] },
+        { type: "additional_tools", tools: [
+          { type: "function", name: "shell", parameters: { type: "object", properties: {} } },
+          { type: "web_search" },
+          already,
+        ] },
+        { type: "message", role: "user", content: [{ type: "input_text", text: "now" }] },
+      ],
+      tools: [already],
+      stream: true,
+    });
+    parsed._zedAuthContext = { userId: "user-1" };
+    parsed._replayPrefixLen = 2;
+    const adapter = withTestTranslatorBudget(createZedAdapter(provider));
+    const request = await adapter.buildRequest(parsed);
+    const body = JSON.parse(request.body).provider_request;
+    expect(body.input.map((item: { type: string }) => item.type)).toEqual(["message", "message"]);
+    expect(JSON.stringify(body.input)).not.toContain("old_tool");
+    expect(JSON.stringify(body.input)).not.toContain("additional_tools");
+    expect(body.tools).toEqual([
+      already,
+      { type: "function", name: "shell", parameters: { type: "object", properties: {} } },
+    ]);
+  });
+
+  async function relay(frames: unknown[]): Promise<unknown[]> {
+    catalogFetch();
+    const parsed = parseRequest({ model: "gpt-6.1-sol", input: "hello", stream: true });
+    parsed._zedAuthContext = { userId: "user-1" };
+    const adapter = withTestTranslatorBudget(createZedAdapter(provider));
+    await adapter.buildRequest(parsed);
+    const ndjson = frames.map(frame => JSON.stringify(frame)).join("\n") + "\n";
+    const events = [];
+    for await (const event of adapter.parseStream(new Response(ndjson))) events.push(event);
+    return events;
+  }
+
+  test("relays commentary text, function-call deltas, and usage across the synthetic completion", async () => {
+    const events = await relay([
+      { event: { type: "response.output_item.added", item: { id: "msg_1", type: "message", role: "assistant", phase: "commentary", content: [] } } },
+      { event: { type: "response.output_text.delta", item_id: "msg_1", delta: "Looking." } },
+      { event: { type: "response.output_item.added", item: { id: "fc_1", type: "function_call", call_id: "call_1", name: "shell", arguments: "" } } },
+      { event: { type: "response.function_call_arguments.delta", item_id: "fc_1", delta: "{\"cmd\":" } },
+      { event: { type: "response.function_call_arguments.delta", item_id: "fc_1", delta: "\"ls\"}" } },
+      { event: { type: "response.function_call_arguments.done", item_id: "fc_1", arguments: "{\"cmd\":\"ls\"}" } },
+      { event: { type: "response.completed", response: {
+        output: [
+          { type: "message", id: "msg_1", phase: "commentary", content: [{ type: "output_text", text: "Looking." }] },
+          { type: "function_call", id: "fc_1", call_id: "call_1", name: "shell", arguments: "{\"cmd\":\"ls\"}" },
+        ],
+        usage: { input_tokens: 11, output_tokens: 6 },
+      } } },
+      { status: "stream_ended" },
+    ]);
+    expect(events).toEqual([
+      { type: "text_delta", text: "Looking.", phase: "commentary" },
+      { type: "tool_call_start", id: "call_1", name: "shell" },
+      { type: "tool_call_delta", arguments: "{\"cmd\":" },
+      { type: "tool_call_delta", arguments: "\"ls\"}" },
+      { type: "tool_call_end" },
+      { type: "done", usage: { inputTokens: 11, outputTokens: 6 } },
+    ]);
+  });
+
+  test("relays a custom tool that arrives only in the completed output without repeating text", async () => {
+    const events = await relay([
+      { event: { type: "response.output_text.delta", delta: "hi" } },
+      { event: { type: "response.completed", response: {
+        output: [
+          { type: "message", id: "msg_1", phase: "commentary", content: [{ type: "output_text", text: "hi" }] },
+          { type: "custom_tool_call", id: "ctc_1", call_id: "call_c", name: "apply_patch", input: "patch body" },
+        ],
+        usage: { input_tokens: 3, output_tokens: 2 },
+      } } },
+      { status: "stream_ended" },
+    ]);
+    expect(events).toEqual([
+      { type: "text_delta", text: "hi" },
+      { type: "tool_call_start", id: "call_c", name: "apply_patch" },
+      { type: "tool_call_delta", arguments: "patch body" },
+      { type: "tool_call_end" },
+      { type: "done", usage: { inputTokens: 3, outputTokens: 2 } },
+    ]);
+  });
+});
+
 describe("Zed inference send accounting", () => {
   async function fixture(limit: number, full = false) {
     const catalog = [jsonResponse({ default_organization_id: "org-1" }),