diff --git a/hermes_cli/dashboard_auth/native_refresh.py b/hermes_cli/dashboard_auth/native_refresh.py
new file mode 100644
index 0000000000..1578e8dd67
--- /dev/null
+++ b/hermes_cli/dashboard_auth/native_refresh.py
@@ -0,0 +1,78 @@
+"""Short-lived native refresh replay, scoped to the concrete provider and caller.
+
+A provider hint only orders discovery: it must neither split one rotating credential's
+lock nor let an unrelated provider reuse its result. Raw refresh tokens are never keys.
+"""
+from __future__ import annotations
+
+import hashlib
+import logging
+import threading
+import time
+from dataclasses import dataclass, field
+
+from hermes_cli.dashboard_auth.base import DashboardAuthProvider, RefreshExpiredError, Session
+from hermes_cli.dashboard_auth.request_utils import scan_session_providers
+
+_SUCCESS_TTL = 30.0
+_FAILURE_TTL = 5.0
+_MAX_ENTRIES = 256
+_guard = threading.Lock()
+
+
+@dataclass
+class _Flight:
+    lock: threading.Lock = field(default_factory=threading.Lock)
+    users: int = 0
+
+
+# Hold the provider itself while caching: replacement (including same-name scoped
+# registrations) invalidates identity, and Python cannot recycle its id under a live entry.
+_cache: dict[tuple[int, bytes], tuple[float, DashboardAuthProvider, Session | None]] = {}
+_flights: dict[tuple[int, bytes], _Flight] = {}
+
+
+def _prune(now: float) -> None:
+    for key, (expires, _, _) in list(_cache.items()):
+        if expires <= now:
+            del _cache[key]
+    while len(_cache) > _MAX_ENTRIES:
+        del _cache[min(_cache, key=lambda key: _cache[key][0])]
+
+
+def _refresh_provider(provider: DashboardAuthProvider, token: str, client_ip: str) -> Session | None:
+    digest = hashlib.sha256(client_ip.encode() + b"\0" + token.encode()).digest()
+    key = (id(provider), digest)
+    with _guard:
+        _prune(time.monotonic())
+        flight = _flights.setdefault(key, _Flight())
+        flight.users += 1
+    try:
+        with flight.lock:
+            with _guard:
+                cached = _cache.get(key)
+                if cached is not None and cached[0] > time.monotonic():
+                    return cached[2]
+            try:
+                session = provider.refresh_session(refresh_token=token)
+            except RefreshExpiredError:
+                session = None
+            # ProviderError and unexpected execution failures are deliberately not cached.
+            with _guard:
+                now = time.monotonic()
+                _cache[key] = (now + (_SUCCESS_TTL if session is not None else _FAILURE_TTL), provider, session)
+                _prune(now)
+            return session
+    finally:
+        with _guard:
+            flight.users -= 1
+            if flight.users == 0:
+                _flights.pop(key, None)
+
+
+def refresh_native_session(token: str, provider_hint: str, client_ip: str) -> Session | None:
+    """Preserve upstream provider fallback/503 behavior while coalescing each actual issuer."""
+    return scan_session_providers(
+        provider_hint, lambda provider: _refresh_provider(provider, token, client_ip),
+        phase="native refresh", log=logging.getLogger(__name__),
+    )
diff --git a/hermes_cli/dashboard_auth/routes.py b/hermes_cli/dashboard_auth/routes.py
index 553938f9ec..639dfef6f6 100644
--- a/hermes_cli/dashboard_auth/routes.py
+++ b/hermes_cli/dashboard_auth/routes.py
@@ -27,21 +27,23 @@ from urllib.parse import quote, unquote, urlencode, urlparse, urlunparse
 from fastapi import APIRouter, HTTPException, Request
 from fastapi.responses import HTMLResponse, JSONResponse, RedirectResponse
 from pydantic import BaseModel
+from starlette.concurrency import run_in_threadpool
 
 from hermes_cli.dashboard_auth import (
     get_provider, list_providers, list_session_providers, native_flow)
 from hermes_cli.dashboard_auth import prefix as _prefix_mod
 from hermes_cli.dashboard_auth.audit import AuditEvent, audit_log
 from hermes_cli.dashboard_auth.base import (
-    InvalidCodeError, InvalidCredentialsError, ProviderError, RefreshExpiredError, Session)
+    InvalidCodeError, InvalidCredentialsError, ProviderError, Session)
 from hermes_cli.dashboard_auth.cookies import (
     clear_pkce_cookie, clear_session_cookies, clear_sso_attempt_cookie, detect_https,
     parse_pkce_payload, read_pkce_cookie, read_session_cookies, set_pkce_cookie,
     set_session_cookies)
 from hermes_cli.dashboard_auth.login_page import (
     render_login_html, render_native_provider_choice_html)
+from hermes_cli.dashboard_auth.native_refresh import refresh_native_session
 from hermes_cli.dashboard_auth.request_utils import (
-    access_token_max_age, client_ip as _client_ip, is_safe_next_path, scan_session_providers)
+    access_token_max_age, client_ip as _client_ip, is_safe_next_path)
 
 _log = logging.getLogger(__name__)
 
@@ -499,9 +501,11 @@ async def auth_native_refresh(request: Request, body: _NativeRefreshBody):
     if not body.refresh_token:
         raise _http(400, "refresh_token required")
     try:
-        session = scan_session_providers(
-            body.provider, lambda p: p.refresh_session(refresh_token=body.refresh_token),
-            phase="native refresh", log=_log, swallow=(RefreshExpiredError,))
+        # Uvicorn validates trusted proxy peers before updating the ASGI client.
+        # Never split replay keys on caller-controlled X-Forwarded-For prefixes.
+        session = await run_in_threadpool(
+            refresh_native_session, body.refresh_token, body.provider,
+            request.client.host if request.client else "")
     except ProviderError as e:
         raise _http(503, f"Auth provider {str(e)!r} unreachable")
     if session is not None:
diff --git a/tests/hermes_cli/test_native_refresh_singleflight.py b/tests/hermes_cli/test_native_refresh_singleflight.py
new file mode 100644
index 0000000000..f841dbcd95
--- /dev/null
+++ b/tests/hermes_cli/test_native_refresh_singleflight.py
@@ -0,0 +1,154 @@
+"""Native HTTP replay boundaries and deterministic provider-level concurrency."""
+import threading
+import time
+from concurrent.futures import ThreadPoolExecutor
+
+import pytest
+from fastapi import FastAPI
+from fastapi.testclient import TestClient
+
+from hermes_cli.dashboard_auth import clear_providers, register_provider
+from hermes_cli.dashboard_auth import native_refresh as replay
+from hermes_cli.dashboard_auth.base import ProviderError, RefreshExpiredError, Session
+from hermes_cli.dashboard_auth.routes import router
+from tests.hermes_cli.conftest_dashboard_auth import StubAuthProvider
+
+
+class Provider(StubAuthProvider):
+    def __init__(self, name, outcome="success"):
+        super().__init__()
+        self.name = name
+        self.outcome = outcome
+        self.calls = 0
+        self.entered = threading.Event()
+        self.release = threading.Event()
+        self.release.set()
+
+    def refresh_session(self, *, refresh_token):
+        self.calls += 1
+        self.entered.set()
+        assert self.release.wait(5), "test provider timed out"
+        if self.outcome == "expired":
+            raise RefreshExpiredError("expired")
+        if self.outcome == "outage":
+            raise ProviderError("temporarily unavailable")
+        return Session(user_id=self.name, email="test@example.test", display_name=self.name,
+                       org_id="test", provider=self.name, expires_at=int(time.time()) + 3600,
+                       access_token=f"access-{self.name}", refresh_token=f"rotated-{self.name}")
+
+
+@pytest.fixture(autouse=True)
+def isolated_registry():
+    clear_providers()
+    with replay._guard:
+        replay._cache.clear()
+        replay._flights.clear()
+    yield
+    clear_providers()
+    with replay._guard:
+        assert not replay._flights
+        replay._cache.clear()
+
+
+@pytest.mark.parametrize("case", ["hint-fallback", "negative", "outage", "replacement", "client",
+                                      "ttl", "capacity", "independent", "xff"])
+def test_native_http_refresh_boundaries(case, monkeypatch):
+    owner = Provider("owner", "expired" if case == "negative" else "outage" if case == "outage" else "success")
+    other = Provider("other", "success" if case == "independent" else "expired")
+    register_provider(owner)
+    register_provider(other)
+    app = FastAPI()
+    app.include_router(router)
+    now = [100.0]
+    monkeypatch.setattr(replay.time, "monotonic", lambda: now[0])
+    with TestClient(app) as client:
+        def request(hint="owner", token="opaque-old-token", **kwargs):
+            return client.post("/auth/native/refresh", json={"refresh_token": token, "provider": hint}, **kwargs)
+
+        first = request()
+        assert first.status_code == (401 if case == "negative" else 503 if case == "outage" else 200)
+        if case in {"hint-fallback", "negative", "outage"}:
+            for hint in ("other", "", "unknown-a", "unknown-b", "owner"):
+                response = request(hint)
+                assert response.status_code == first.status_code
+                if first.status_code == 200:
+                    assert response.json() == first.json()
+            assert owner.calls == (6 if case == "outage" else 1)
+            assert other.calls == 1
+        elif case == "replacement":
+            clear_providers()
+            replacement = Provider("owner")
+            register_provider(replacement)
+            assert request().status_code == 200
+            assert replacement.calls == 1
+        elif case == "client":
+            with TestClient(app, client=("192.0.2.12", 2345)) as another_client:
+                assert another_client.post("/auth/native/refresh", json={"refresh_token": "opaque-old-token"}).status_code == 200
+            assert owner.calls == 2
+        elif case == "ttl":
+            assert request().json() == first.json()
+            now[0] += replay._SUCCESS_TTL
+            assert request().status_code == 200
+            assert owner.calls == 2
+        elif case == "capacity":
+            monkeypatch.setattr(replay, "_MAX_ENTRIES", 2)
+            for token in ("new-token-1", "new-token-2", "new-token-3"):
+                assert request(token=token).status_code == 200
+            assert len(replay._cache) == 2
+            assert all(isinstance(key[1], bytes) and len(key[1]) == 32 for key in replay._cache)
+        elif case == "independent":
+            response = request("other")
+            assert response.status_code == 200
+            assert response.json()["provider"] == "other"
+            assert first.json()["provider"] == "owner"
+            assert owner.calls == other.calls == 1
+        else:
+            for prefix in ("192.0.2.1", "192.0.2.2"):
+                assert request(headers={"x-forwarded-for": f"{prefix}, 192.0.2.100"}).status_code == 200
+            # Only the ASGI peer (validated by Uvicorn), never an arbitrary header, scopes replay.
+            assert owner.calls == 1
+
+
+@pytest.mark.parametrize("outcome, independent", [("success", False), ("expired", False),
+                                                  ("outage", False), ("success", True)])
+def test_concurrent_refresh_uses_concrete_provider_identity(outcome, independent):
+    owner = Provider("owner", outcome)
+    other = Provider("other", "success" if independent else "expired")
+    owner.release.clear()
+    if independent:
+        other.release.clear()
+    register_provider(owner)
+    register_provider(other)
+    with ThreadPoolExecutor(max_workers=3) as pool:
+        first = pool.submit(replay.refresh_native_session, "same-token", "owner", "client")
+        assert owner.entered.wait(3)
+        second = pool.submit(replay.refresh_native_session, "same-token", "other", "client")
+        try:
+            if independent:
+                assert other.entered.wait(3), "unrelated providers must not share a lock"
+            else:
+                deadline = time.monotonic() + 3
+                while time.monotonic() < deadline:
+                    with replay._guard:
+                        if any(key[0] == id(owner) and flight.users == 2 for key, flight in replay._flights.items()):
+                            break
+                    time.sleep(0.005)
+                else:
+                    pytest.fail("different hints did not converge on the concrete issuer lock")
+                assert owner.calls == 1
+        finally:
+            owner.release.set()
+            other.release.set()
+        if outcome == "outage":
+            for future in (first, second):
+                with pytest.raises(ProviderError):
+                    future.result(timeout=3)
+            assert owner.calls == 2
+        else:
+            results = [first.result(timeout=3), second.result(timeout=3)]
+            if outcome == "expired":
+                assert results == [None, None]
+            else:
+                assert [result.provider for result in results] == ["owner", "other" if independent else "owner"]
+            assert owner.calls == 1
+        assert not replay._flights