diff --git a/changelog.d/fixes/1811-composer-space-sep.md b/changelog.d/fixes/1811-composer-space-sep.md
new file mode 100644
index 0000000000..856fab9e17
--- /dev/null
+++ b/changelog.d/fixes/1811-composer-space-sep.md
@@ -0,0 +1 @@
+- **fix(sse):** Cursor Composer/Auto tool calls that separate the arg name and value with a space instead of a newline (e.g. `path /Users/.../test`) no longer produce empty-valued, malformed argument keys, fixing silent no-op Write/tool calls. (thanks @way-art)
diff --git a/open-sse/utils/composerToolCalls.ts b/open-sse/utils/composerToolCalls.ts
index d688973ce3..916903a3ca 100644
--- a/open-sse/utils/composerToolCalls.ts
+++ b/open-sse/utils/composerToolCalls.ts
@@ -126,15 +126,28 @@ function parseInnerCall(body: string): { name: string; arguments: string } | nul
   const args: Record<string, unknown> = {};
   for (const seg of segments) {
     if (!seg) continue;
-    // Each segment is `arg_name\nvalue\n...`. The arg name is the first
-    // line; everything after the first newline is the value (verbatim,
-    // including additional newlines).
+    // Each segment is normally `arg_name\nvalue\n...`: the arg name is the
+    // first line, everything after the first newline is the value
+    // (verbatim, including additional newlines). Some live Composer/Auto
+    // captures instead separate the arg name and value with a single space
+    // on the same line (no newline at all in the segment) — fall back to
+    // splitting on the first whitespace boundary in that case so the value
+    // isn't swallowed into an empty-valued, space-containing "arg name".
     const idxNl = seg.indexOf("\n");
     let argName: string;
     let argValue: string;
     if (idxNl < 0) {
-      argName = seg.trim();
-      argValue = "";
+      const idxSp = seg.search(/\s/);
+      if (idxSp < 0) {
+        argName = seg.trim();
+        argValue = "";
+      } else {
+        argName = seg.slice(0, idxSp).trim();
+        // Unlike the newline-delimited form, a space-delimited value has no
+        // multi-line content to preserve — trim the trailing whitespace left
+        // over from the boundary with the next `<｜tool▁sep｜>` marker.
+        argValue = seg.slice(idxSp + 1).trim();
+      }
     } else {
       argName = seg.slice(0, idxNl).trim();
       argValue = seg.slice(idxNl + 1);
diff --git a/tests/unit/composer-tool-calls.test.ts b/tests/unit/composer-tool-calls.test.ts
index c1133f0513..5fba8abd3a 100644
--- a/tests/unit/composer-tool-calls.test.ts
+++ b/tests/unit/composer-tool-calls.test.ts
@@ -214,3 +214,27 @@ test("feedStreamingChunk: noop after done state", () => {
   assert.equal(out.safeDelta, "");
   assert.equal(out.ready, false);
 });
+
+// ─── Regression: space-separated arg name/value (9router#1811) ───────────────
+// Cursor's real Composer/Auto output has been observed using a single space
+// (instead of a newline) between the arg name and its value inside a
+// <｜tool▁sep｜> segment, e.g. "<｜tool▁sep｜>path /Users/.../test". The parser
+// must still extract {path: "/Users/.../test"} rather than treating the whole
+// segment as the (empty-valued) arg name.
+test("parseComposerToolCalls: parses args separated by a space instead of a newline (Cursor Composer live capture)", () => {
+  const text =
+    "<｜tool▁calls▁begin｜><｜tool▁call▁begin｜> Write " +
+    "<｜tool▁sep｜>path /Users/kabawagang/Desktop/Code/iOS_Review/test " +
+    "<｜tool▁sep｜>contents 22\n\n<｜tool▁call▁end｜><｜tool▁calls▁end｜>";
+
+  const result = parseComposerToolCalls(text);
+
+  assert.equal(result.toolCalls.length, 1);
+  const tc = result.toolCalls[0];
+  assert.equal(tc.function.name, "Write");
+  const args = JSON.parse(tc.function.arguments);
+  assert.deepEqual(args, {
+    path: "/Users/kabawagang/Desktop/Code/iOS_Review/test",
+    contents: 22,
+  });
+});