diff --git a/haiku_rag_slim/haiku/rag/ingester/sources/http.py b/haiku_rag_slim/haiku/rag/ingester/sources/http.py
index b024c9f3..5ac20713 100644
--- a/haiku_rag_slim/haiku/rag/ingester/sources/http.py
+++ b/haiku_rag_slim/haiku/rag/ingester/sources/http.py
@@ -144,6 +144,13 @@ class HTTPSource:
             revision, _ = _extract_revision(head.headers)
             if revision is not None and snapshot.get(url) == revision:
                 kind = SourceEventKind.UNCHANGED
+            elif revision is None and url in known:
+                # Server provides no revision header (no ETag, no
+                # Last-Modified). We can't detect changes, but the URL was
+                # already ingested — skip rather than re-fetch every sweep. A
+                # real change is only picked up if the server starts returning
+                # revision headers or the operator forces a re-ingest.
+                kind = SourceEventKind.UNCHANGED
             else:
                 kind = SourceEventKind.UPSERT
 
diff --git a/haiku_rag_slim/haiku/rag/ingester/sources/s3.py b/haiku_rag_slim/haiku/rag/ingester/sources/s3.py
index f3c8a446..418dd62d 100644
--- a/haiku_rag_slim/haiku/rag/ingester/sources/s3.py
+++ b/haiku_rag_slim/haiku/rag/ingester/sources/s3.py
@@ -132,6 +132,8 @@ class S3Source:
 
                 if revision is not None and snapshot.get(uri) == revision:
                     kind = SourceEventKind.UNCHANGED
+                elif revision is None and uri in known:
+                    kind = SourceEventKind.UNCHANGED
                 else:
                     kind = SourceEventKind.UPSERT
 
diff --git a/haiku_rag_slim/haiku/rag/ingester/sources/webdav.py b/haiku_rag_slim/haiku/rag/ingester/sources/webdav.py
index 0bb512f8..1b9bd27e 100644
--- a/haiku_rag_slim/haiku/rag/ingester/sources/webdav.py
+++ b/haiku_rag_slim/haiku/rag/ingester/sources/webdav.py
@@ -282,6 +282,8 @@ class WebDAVSource:
             revision = entry.revision
             if revision is not None and snapshot.get(uri) == revision:
                 kind = SourceEventKind.UNCHANGED
+            elif revision is None and uri in known:
+                kind = SourceEventKind.UNCHANGED
             else:
                 kind = SourceEventKind.UPSERT
             yield SourceEvent(
diff --git a/tests/ingester/test_http_source.py b/tests/ingester/test_http_source.py
index 8673f2fa..a45f8a58 100644
--- a/tests/ingester/test_http_source.py
+++ b/tests/ingester/test_http_source.py
@@ -342,3 +342,38 @@ async def test_discover_propagates_non_transport_errors():
     with pytest.raises(TypeError, match="unexpected bug"):
         async for _ in src.discover():
             pass
+
+
+@pytest.mark.asyncio
+async def test_discover_emits_unchanged_for_known_url_without_revision():
+    """A server that returns no ETag or Last-Modified should not cause
+    re-ingestion every sweep once the URL has been ingested."""
+    transport = _transport(
+        {("HEAD", "https://example.com/a.md"): httpx.Response(200)}
+    )
+    src = HTTPSource(
+        source_id="x", urls=["https://example.com/a.md"], transport=transport
+    )
+    events = [
+        e
+        async for e in src.discover(
+            known_uris={"https://example.com/a.md"}
+        )
+    ]
+    assert len(events) == 1
+    assert events[0].kind is SourceEventKind.UNCHANGED
+    assert events[0].revision is None
+
+
+@pytest.mark.asyncio
+async def test_discover_emits_upsert_for_unknown_url_without_revision():
+    """A brand-new URL with no revision should still UPSERT on first sight."""
+    transport = _transport(
+        {("HEAD", "https://example.com/new.md"): httpx.Response(200)}
+    )
+    src = HTTPSource(
+        source_id="x", urls=["https://example.com/new.md"], transport=transport
+    )
+    events = [e async for e in src.discover()]
+    assert len(events) == 1
+    assert events[0].kind is SourceEventKind.UPSERT
diff --git a/tests/ingester/test_s3_source.py b/tests/ingester/test_s3_source.py
index 469a0600..1aec74f4 100644
--- a/tests/ingester/test_s3_source.py
+++ b/tests/ingester/test_s3_source.py
@@ -213,3 +213,28 @@ async def test_discover_respects_ignore_patterns(fake_s3_listing):
     )
     events = [e async for e in src.discover()]
     assert {e.uri for e in events} == {"s3://bucket/a.md"}
+
+
+@pytest.mark.asyncio
+async def test_discover_emits_unchanged_for_known_key_without_etag(fake_s3_listing):
+    """An S3 object with no ETag should not cause re-ingestion every sweep
+    once the key has been ingested."""
+    fake_s3_listing([[{"path": "file.md", "size": 0, "last_modified": None}]])
+    src = S3Source(uri="s3://bucket/", supported_extensions=[".md"])
+    events = [
+        e
+        async for e in src.discover(known_uris={"s3://bucket/file.md"})
+    ]
+    non_delete = [e for e in events if e.kind is not SourceEventKind.DELETE]
+    assert len(non_delete) == 1
+    assert non_delete[0].kind is SourceEventKind.UNCHANGED
+
+
+@pytest.mark.asyncio
+async def test_discover_emits_upsert_for_unknown_key_without_etag(fake_s3_listing):
+    """A brand-new S3 key with no ETag should UPSERT on first sight."""
+    fake_s3_listing([[{"path": "new.md", "size": 0, "last_modified": None}]])
+    src = S3Source(uri="s3://bucket/", supported_extensions=[".md"])
+    events = [e async for e in src.discover()]
+    assert len(events) == 1
+    assert events[0].kind is SourceEventKind.UPSERT
diff --git a/tests/ingester/test_webdav_source.py b/tests/ingester/test_webdav_source.py
index 682d6e03..7323bd8b 100644
--- a/tests/ingester/test_webdav_source.py
+++ b/tests/ingester/test_webdav_source.py
@@ -384,3 +384,53 @@ async def test_discover_url_decodes_href_path():
     assert [e.uri for e in events] == [
         "https://nc.example.com/dav/my docs/Hello World.md"
     ]
+
+
+@pytest.mark.asyncio
+async def test_discover_emits_unchanged_for_known_uri_without_revision():
+    """A WebDAV entry with no ETag or Last-Modified should not cause
+    re-ingestion every sweep once the URI has been ingested."""
+    multistatus = _multistatus(
+        {"href": "/dav/", "collection": True},
+        {"href": "/dav/norev.md", "content_type": "text/markdown"},
+    )
+
+    def handler(request: httpx.Request) -> httpx.Response:
+        return httpx.Response(207, content=multistatus)
+
+    src = WebDAVSource(
+        source_id="nc",
+        base_url="https://nc.example.com/dav/",
+        transport=_transport(handler),
+    )
+    events = [
+        e
+        async for e in src.discover(
+            known_uris={"https://nc.example.com/dav/norev.md"}
+        )
+    ]
+    non_delete = [e for e in events if e.kind is not SourceEventKind.DELETE]
+    assert len(non_delete) == 1
+    assert non_delete[0].kind is SourceEventKind.UNCHANGED
+
+
+@pytest.mark.asyncio
+async def test_discover_emits_upsert_for_unknown_uri_without_revision():
+    """A brand-new WebDAV entry with no revision should UPSERT on first sight."""
+    multistatus = _multistatus(
+        {"href": "/dav/", "collection": True},
+        {"href": "/dav/new.md", "content_type": "text/markdown"},
+    )
+
+    def handler(request: httpx.Request) -> httpx.Response:
+        return httpx.Response(207, content=multistatus)
+
+    src = WebDAVSource(
+        source_id="nc",
+        base_url="https://nc.example.com/dav/",
+        transport=_transport(handler),
+    )
+    events = [e async for e in src.discover()]
+    non_delete = [e for e in events if e.kind is not SourceEventKind.DELETE]
+    assert len(non_delete) == 1
+    assert non_delete[0].kind is SourceEventKind.UPSERT