diff --git a/src/server/responses/collaboration.ts b/src/server/responses/collaboration.ts
index ab6a9b55c9..a7552adb86 100644
--- a/src/server/responses/collaboration.ts
+++ b/src/server/responses/collaboration.ts
@@ -152,6 +152,38 @@ export function buildToolBridgeMaps(parsed: OcxParsedRequest, budget?: Translato
       dottedAliasOwners.set(t.name, null);
     }
   }
+  // Bare echo alias (`name` with no namespace spelling, #4679): some providers — observed
+  // on the muse family via Command Code — echo a namespaced tool by its bare name. The
+  // bare spelling is only a safe alias while it names ONE tool and cannot be read as
+  // another identity's canonical or dotted spelling.
+  // Code-mode helper spellings never gain a bare alias (#4679 review): admitting bare
+  // `exec` into the declared set would authorize the unrelated helper normalization that
+  // the CODE_MODE_EXEC exception exists to contain.
+  const BARE_ECHO_EXCLUDED_NAMES = new Set([
+    "exec", "exec_command", "shell_command", "write_stdin", "apply_patch", "view_image",
+  ]);
+  const bareAliasOwners = new Map<string, string | null>();
+  for (const t of authorizedTools) {
+    // Bare (no-namespace) declarations participate as owners too: a namespaced tool whose
+    // bare name equals a bare-declared function must not gain the bare alias, mirroring how
+    // the tool_choice bare path refuses ambiguous owners across the whole request catalog.
+    const identity = JSON.stringify([t.namespace ?? null, t.name]);
+    const owner = bareAliasOwners.get(t.name);
+    if (owner === undefined) bareAliasOwners.set(t.name, identity);
+    else if (owner !== identity) bareAliasOwners.set(t.name, null);
+  }
+  for (const t of authorizedTools) {
+    const canonical = namespacedToolName(t.namespace, t.name);
+    const owner = bareAliasOwners.get(canonical);
+    if (owner !== undefined && owner !== JSON.stringify([t.namespace, t.name])) {
+      bareAliasOwners.set(canonical, null);
+    }
+    const dotted = dottedToolName(t.namespace, t.name);
+    const dottedOwner = bareAliasOwners.get(dotted);
+    if (dottedOwner !== undefined && dottedOwner !== JSON.stringify([t.namespace, t.name])) {
+      bareAliasOwners.set(dotted, null);
+    }
+  }
   for (const t of authorizedTools) {
     // Upstream output is untrusted: only restore calls for tools the caller authorized.
     const wireName = namespacedToolName(t.namespace, t.name);
@@ -175,6 +207,23 @@ export function buildToolBridgeMaps(parsed: OcxParsedRequest, budget?: Translato
         toolNsMap.set(dottedName, { namespace: t.namespace, name: t.name, ...(t.freeform ? { freeform: true } : {}) });
         if (t.parameters && typeof t.parameters === "object") toolParameterSchemas.set(dottedName, t.parameters);
       }
+      // Bare echo alias (`name` with no namespace spelling, #4679): same tool identity as
+      // the flattened wire name, so a provider that drops the namespace prefix still
+      // restores against this entry. Ambiguous bare names were resolved to null above;
+      // skipping them falls back to the spellings every provider can still echo.
+      // Code-mode helper spellings never gain a bare alias: admitting bare `exec` into the
+      // declared set would let normalizeDeclaredToolName authorize the unrelated helper
+      // names, the exact surface the CODE_MODE_EXEC exception exists to contain.
+      if (
+        bareAliasOwners.get(t.name) === JSON.stringify([t.namespace, t.name])
+        && !BARE_ECHO_EXCLUDED_NAMES.has(t.name)
+      ) {
+        budget?.chargeRetained(new TextEncoder().encode(t.name).byteLength, { kind: "retained_collectors" });
+        declaredToolNames.add(t.name);
+        budget?.chargeRetained(new TextEncoder().encode(JSON.stringify([t.name, t.namespace, t.name])).byteLength, { kind: "retained_collectors" });
+        toolNsMap.set(t.name, { namespace: t.namespace, name: t.name, ...(t.freeform ? { freeform: true } : {}) });
+        if (t.parameters && typeof t.parameters === "object") toolParameterSchemas.set(t.name, t.parameters);
+      }
     }
     if (t.freeform) {
       budget?.chargeRetained(new TextEncoder().encode(t.name).byteLength, { kind: "retained_collectors" });
diff --git a/src/server/responses/passthrough-dispatch.ts b/src/server/responses/passthrough-dispatch.ts
index f5c5b94694..6d612c9652 100644
--- a/src/server/responses/passthrough-dispatch.ts
+++ b/src/server/responses/passthrough-dispatch.ts
@@ -346,10 +346,13 @@ export async function preparePassthroughExchange(
     const declaredWireToolNames = new Set<string>();
     const declaredBareWireToolNames = new Set<string>();
     const declaredNamelessClientCallTypes = new Set<string>();
-    // `buildToolBridgeMaps` creates a bare alias only when the caller selected exactly one
-    // namespaced tool through a bare tool_choice. Restore that request-bounded identity before
-    // authorization checks instead of admitting the bare name into the declared set: for `exec`,
-    // the latter would also authorize the unrelated code-mode helper names.
+    // `buildToolBridgeMaps` adds each eligible bare alias to `declaredToolNames` and `toolNsMap`
+    // (one authorized identity claims the bare name). `refreshUndeclaredToolGuard` normally copies
+    // those entries into `declaredWireToolNames`, but passthrough restoration runs before the
+    // undeclared-tool guard, so restore that request-bounded identity here, before authorization
+    // checks. `exec` uses separate handling: its bridge alias is copied into the declared set only
+    // when the client itself declared bare `exec`, because otherwise code-mode normalization could
+    // authorize the unrelated code-mode helper names.
     const authorizedBareNamespaceToolAliases: RoutedNamespaceToolAliases = new Map(
       [...toolBridgeMaps.toolNsMap].flatMap(([alias, identity]) =>
         alias === identity.name
diff --git a/tests/responses/bare-echo-alias.test.ts b/tests/responses/bare-echo-alias.test.ts
new file mode 100644
index 0000000000..8b9c973971
--- /dev/null
+++ b/tests/responses/bare-echo-alias.test.ts
@@ -0,0 +1,125 @@
+import { describe, expect, test } from "bun:test";
+import { parseRequest } from "../../src/responses/parser";
+import { buildToolBridgeMaps } from "../../src/server/responses";
+
+function collabRequest(bareName: string) {
+  return parseRequest({
+    model: "meta/muse-spark-1.3-contributor",
+    input: [
+      { type: "additional_tools", role: "developer", tools: [
+        { type: "namespace", name: "collaboration", tools: [
+          { type: "function", name: bareName, description: bareName, strict: false, parameters: { type: "object", properties: {}, required: [] } },
+        ] },
+      ] },
+      { type: "message", role: "user", content: [{ type: "input_text", text: "run it" }] },
+    ],
+  } as any);
+}
+
+describe("bare echo alias for namespaced tools (#4679)", () => {
+  test("an unambiguous bare name is declared and restores to the namespaced identity", () => {
+    const maps = buildToolBridgeMaps(collabRequest("list_agents") as any);
+    expect(maps.declaredToolNames.has("list_agents")).toBe(true);
+    expect(maps.toolNsMap.get("list_agents")).toEqual({ namespace: "collaboration", name: "list_agents" });
+  });
+
+  test("a bare name claimed by two namespaces stays undeclared (no hijack)", () => {
+    const parsed = parseRequest({
+      model: "meta/muse-spark-1.3-contributor",
+      input: [
+        { type: "additional_tools", role: "developer", tools: [
+          { type: "namespace", name: "collaboration", tools: [
+            { type: "function", name: "list_agents", description: "a", strict: false, parameters: { type: "object", properties: {}, required: [] } },
+          ] },
+          { type: "namespace", name: "other__ns", tools: [
+            { type: "function", name: "list_agents", description: "b", strict: false, parameters: { type: "object", properties: {}, required: [] } },
+          ] },
+        ] },
+        { type: "message", role: "user", content: [{ type: "input_text", text: "run it" }] },
+      ],
+    } as any);
+    const maps = buildToolBridgeMaps(parsed as any);
+    expect(maps.declaredToolNames.has("list_agents")).toBe(false);
+    expect(maps.toolNsMap.has("list_agents")).toBe(false);
+    // Both canonical spellings remain declared.
+    expect(maps.declaredToolNames.has("collaboration__list_agents")).toBe(true);
+    expect(maps.declaredToolNames.has("other__ns__list_agents")).toBe(true);
+  });
+
+  test("a bare name that equals another tool's dotted spelling stays undeclared", () => {
+    const parsed = parseRequest({
+      model: "meta/muse-spark-1.3-contributor",
+      input: [
+        { type: "additional_tools", role: "developer", tools: [
+          { type: "namespace", name: "collaboration", tools: [
+            { type: "function", name: "list_agents", description: "a", strict: false, parameters: { type: "object", properties: {}, required: [] } },
+          ] },
+          { type: "namespace", name: "mcp__x", tools: [
+            { type: "function", name: "collaboration.list_agents", description: "b", strict: false, parameters: { type: "object", properties: {}, required: [] } },
+          ] },
+        ] },
+        { type: "message", role: "user", content: [{ type: "input_text", text: "run it" }] },
+      ],
+    } as any);
+    const maps = buildToolBridgeMaps(parsed as any);
+    // Tool B's bare name ("collaboration.list_agents") collides with tool A's dotted
+    // spelling, so that bare alias is poisoned; tool A's dotted spelling is poisoned in
+    // return by the pre-existing dotted rule. Tool B's own distinct dotted alias does not
+    // collide with anything and stays declared, as do both canonical spellings.
+    expect(maps.declaredToolNames.has("collaboration.list_agents")).toBe(false);
+    expect(maps.toolNsMap.has("collaboration.list_agents")).toBe(false);
+    expect(maps.declaredToolNames.has("mcp__x.collaboration.list_agents")).toBe(true);
+    expect(maps.toolNsMap.get("mcp__x.collaboration.list_agents")).toEqual({ namespace: "mcp__x", name: "collaboration.list_agents" });
+    expect(maps.declaredToolNames.has("collaboration__list_agents")).toBe(true);
+    expect(maps.declaredToolNames.has("mcp__x__collaboration.list_agents")).toBe(true);
+  });
+
+  test("a bare name that equals another tool's canonical spelling stays undeclared", () => {
+    const parsed = parseRequest({
+      model: "meta/muse-spark-1.3-contributor",
+      input: [
+        { type: "additional_tools", role: "developer", tools: [
+          { type: "namespace", name: "collaboration", tools: [
+            { type: "function", name: "list_agents", description: "a", strict: false, parameters: { type: "object", properties: {}, required: [] } },
+          ] },
+          { type: "namespace", name: "mcp__x", tools: [
+            { type: "function", name: "collaboration__list_agents", description: "b", strict: false, parameters: { type: "object", properties: {}, required: [] } },
+          ] },
+        ] },
+        { type: "message", role: "user", content: [{ type: "input_text", text: "run it" }] },
+      ],
+    } as any);
+    const maps = buildToolBridgeMaps(parsed as any);
+    // Tool B's bare name ("collaboration__list_agents") is also tool A's declared canonical
+    // spelling, so the bare alias is poisoned. The canonical spelling stays declared — but as
+    // tool A's wire name, never as an alias of tool B — so assert the identity via toolNsMap.
+    // Tool B's canonical and dotted spellings remain declared.
+    expect(maps.toolNsMap.get("collaboration__list_agents")).toEqual({ namespace: "collaboration", name: "list_agents" });
+    expect(maps.declaredToolNames.has("mcp__x__collaboration__list_agents")).toBe(true);
+    expect(maps.declaredToolNames.has("mcp__x.collaboration__list_agents")).toBe(true);
+    expect(maps.toolNsMap.get("mcp__x.collaboration__list_agents")).toEqual({ namespace: "mcp__x", name: "collaboration__list_agents" });
+  });
+
+  test("a bare-declared function owns its name and blocks the namespaced tool's bare alias", () => {
+    const parsed = parseRequest({
+      model: "meta/muse-spark-1.3-contributor",
+      input: [
+        { type: "additional_tools", role: "developer", tools: [
+          { type: "namespace", name: "collaboration", tools: [
+            { type: "function", name: "list_agents", description: "a", strict: false, parameters: { type: "object", properties: {}, required: [] } },
+          ] },
+          { type: "function", name: "list_agents", description: "b", strict: false, parameters: { type: "object", properties: {}, required: [] } },
+        ] },
+        { type: "message", role: "user", content: [{ type: "input_text", text: "run it" }] },
+      ],
+    } as any);
+    const maps = buildToolBridgeMaps(parsed as any);
+    // The bare-declared (no-namespace) function participates as an owner of "list_agents",
+    // mirroring the tool_choice bare path's whole-catalog counting, so the namespaced tool
+    // must not gain it as an echo alias. "list_agents" stays in declaredToolNames because the
+    // bare function's own wire name IS that spelling; the alias check is toolNsMap, which
+    // must never map the bare name to the namespaced identity.
+    expect(maps.toolNsMap.has("list_agents")).toBe(false);
+    expect(maps.declaredToolNames.has("collaboration__list_agents")).toBe(true);
+  });
+});