diff --git a/docs/PERF_BASELINE_PROTOCOL.md b/docs/PERF_BASELINE_PROTOCOL.md
index b526b50..b90e534 100644
--- a/docs/PERF_BASELINE_PROTOCOL.md
+++ b/docs/PERF_BASELINE_PROTOCOL.md
@@ -63,10 +63,12 @@ with the installed build's interpreter.
   version-probe result and timing, then a session-establishment attempt
   (fast failure versus hang matters more than the version answer), plus
   the resolved first rung and a no-emission `wtype ""` spawn cost as a
-  lower bound. End-to-end key-to-screen latency is deliberately not
-  taken here: emitting keystrokes into a live desktop from a background
-  run would disturb the session. It belongs to the hardware checklist
-  with a dedicated target window.
+  lower bound. On niri the portal probe is skipped, as the injector skips
+  it, and the report says so with `portal_skip_reason: "niri"` and
+  `portal_available: false`. End-to-end key-to-screen latency is
+  deliberately not taken here: emitting keystrokes into a live desktop
+  from a background run would disturb the session. It belongs to the
+  hardware checklist with a dedicated target window.
 - **Thresholds for the model ladder:** derive free-memory cutoffs from
   the maximum observed per-rung footprint (transcribe peak, not just
   load) plus explicit headroom for the compositor and other GPU
diff --git a/scripts/measure_perf_baseline.py b/scripts/measure_perf_baseline.py
index 2fb326a..ed1ad47 100644
--- a/scripts/measure_perf_baseline.py
+++ b/scripts/measure_perf_baseline.py
@@ -433,8 +433,11 @@ def cmd_inject_probe(args: argparse.Namespace) -> int:
 
     Never emits keystrokes: end-to-end key-to-screen latency would type
     into the live desktop, so it stays a hardware-checklist item (#32).
+
+    On niri the portal is skipped with the injector's own niri guard: the
+    injector never offers the portal there, so the report must not claim it.
     """
-    from vocalinux.text_injection.text_injector import TextInjector
+    from vocalinux.text_injection.text_injector import TextInjector, _is_niri_session
 
     probe_text = "the quick brown fox jumps over the lazy dog 0123456789"
     started = time.monotonic()
@@ -462,16 +465,20 @@ def cmd_inject_probe(args: argparse.Namespace) -> int:
                     env=host_env(),
                 )
                 wtype_roundtrips.append(time.monotonic() - begin)
-    try:
-        from vocalinux.text_injection.remote_desktop_portal import RemoteDesktopPortal
+    portal_available = False
+    portal_seconds = None
+    portal_skip_reason = "niri" if _is_niri_session() else None
+    if portal_skip_reason is None:
+        try:
+            from vocalinux.text_injection.remote_desktop_portal import RemoteDesktopPortal
 
-        portal_started = time.monotonic()
-        portal_available = RemoteDesktopPortal().probe()
-        portal_seconds = time.monotonic() - portal_started
-    except Exception as exc:  # noqa: BLE001 - probe must never fail the pass
-        portal_available = False
-        portal_seconds = None
-        print(f"portal probe raised: {exc}", file=sys.stderr)
+            portal_started = time.monotonic()
+            portal_available = RemoteDesktopPortal().probe()
+            portal_seconds = time.monotonic() - portal_started
+        except Exception as exc:  # noqa: BLE001 - probe must never fail the pass
+            portal_available = False
+            portal_seconds = None
+            print(f"portal probe raised: {exc}", file=sys.stderr)
     print(
         json.dumps(
             {
@@ -481,6 +488,7 @@ def cmd_inject_probe(args: argparse.Namespace) -> int:
                 "wtype_empty_roundtrip_stats": describe(wtype_roundtrips),
                 "portal_available": portal_available,
                 "portal_probe_seconds": portal_seconds,
+                "portal_skip_reason": portal_skip_reason,
             },
             indent=2,
             sort_keys=True,
diff --git a/tests/test_perf_baseline_protocol.py b/tests/test_perf_baseline_protocol.py
index c09bfa2..eab4bce 100644
--- a/tests/test_perf_baseline_protocol.py
+++ b/tests/test_perf_baseline_protocol.py
@@ -7,7 +7,10 @@ helpers tested here. Tests run offline with fixture text only and never
 touch audio hardware, the GPU, or the network.
 """
 
+import argparse
 import importlib.util
+import json
+import shutil
 from pathlib import Path
 
 import pytest
@@ -134,3 +137,90 @@ DBUS_TOGGLE_LOG = """\
 def test_parse_wake_latencies_pairs_dbus_toggle_starts_only() -> None:
     """Only IDLE toggles open capture; a stop toggle never borrows the next run."""
     assert PROTOCOL.parse_wake_latencies(DBUS_TOGGLE_LOG) == pytest.approx([0.146, 0.649])
+
+
+#: Session variables the injector's niri guard reads, plus Wayland; cleared so
+#: the host's own session (this machine runs niri) cannot leak into a test.
+_SESSION_ENV = (
+    "NIRI_SOCKET",
+    "XDG_CURRENT_DESKTOP",
+    "XDG_SESSION_DESKTOP",
+    "DESKTOP_SESSION",
+    "WAYLAND_DISPLAY",
+)
+
+
+class _FakeInjector:
+    """Stands in for TextInjector: a Wayland session that selected wtype."""
+
+    wayland_mode = True
+    wayland_tool = "wtype"
+
+
+def _run_inject_probe(
+    monkeypatch: pytest.MonkeyPatch,
+    capsys: pytest.CaptureFixture[str],
+    session_env: dict[str, str],
+    portal_answers: bool,
+) -> tuple[dict, list[bool]]:
+    """Run inject-probe under a fake session; return its report and portal probe calls."""
+    from vocalinux.text_injection import remote_desktop_portal, text_injector
+
+    probes: list[bool] = []
+
+    class _SpyPortal:
+        def probe(self) -> bool:
+            probes.append(True)
+            return portal_answers
+
+    for name in _SESSION_ENV:
+        monkeypatch.delenv(name, raising=False)
+    for name, value in session_env.items():
+        monkeypatch.setenv(name, value)
+    monkeypatch.setattr(text_injector, "TextInjector", _FakeInjector)
+    monkeypatch.setattr(remote_desktop_portal, "RemoteDesktopPortal", _SpyPortal)
+    monkeypatch.setattr(shutil, "which", lambda _name: None)
+    assert PROTOCOL.cmd_inject_probe(argparse.Namespace()) == 0
+    return json.loads(capsys.readouterr().out), probes
+
+
+@pytest.mark.parametrize(
+    "session_env",
+    [
+        {"XDG_CURRENT_DESKTOP": "niri"},
+        {"NIRI_SOCKET": "/run/user/1000/niri.wayland-1.1.sock"},
+    ],
+)
+def test_inject_probe_never_probes_portal_on_niri(
+    monkeypatch: pytest.MonkeyPatch,
+    capsys: pytest.CaptureFixture[str],
+    session_env: dict[str, str],
+) -> None:
+    """The injector never offers the portal on niri, so the probe must not claim it.
+
+    Both niri signals are covered: the probe reuses the injector's guard, so a
+    session the injector treats as niri is reported the same way here.
+    """
+    report, probes = _run_inject_probe(
+        monkeypatch, capsys, session_env=session_env, portal_answers=True
+    )
+    assert probes == []
+    assert report["portal_available"] is False
+    assert report["portal_probe_seconds"] is None
+    assert report["portal_skip_reason"] == "niri"
+
+
+def test_inject_probe_reports_portal_answer_off_niri(
+    monkeypatch: pytest.MonkeyPatch,
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    """Off niri the portal is probed and its answer is reported unchanged."""
+    report, probes = _run_inject_probe(
+        monkeypatch,
+        capsys,
+        session_env={"XDG_CURRENT_DESKTOP": "GNOME"},
+        portal_answers=True,
+    )
+    assert probes == [True]
+    assert report["portal_available"] is True
+    assert report["portal_skip_reason"] is None