feat(sender): add outgoing Webmention pipeline

Scan generated h-entry documents for Webmention targets and track source
revisions and delivery state in the database.

Discover target endpoints, send Webmentions asynchronously, and reconcile
updated, removed, restored, and deleted sources across scans.

Add authenticated views for inspecting sent Webmentions and make the scanner
schedule configurable.

6 files changed, 2653 insertions, 425 deletions

diff --git a/tests/tasks/test_receiver.py b/tests/tasks/test_receiver.py
index 19630c3..811ab63 100644
--- a/tests/tasks/test_receiver.py
+++ b/tests/tasks/test_receiver.py
@@ -9,10 +9,7 @@ from flask import Flask
 
 from webmentions_ssg import DATABASE as db
 from webmentions_ssg.models import ReceivedWebmention
-from webmentions_ssg.url_security import (
-    AddressResolutionError,
-    NonPublicAddressError,
-)
+from webmentions_ssg.url_security import AddressResolutionError
 
 SOURCE_URL = "https://source.example/article"
 TARGET_URL = "https://dennisfink.me/blog/example/"
@@ -50,28 +47,16 @@ def create_webmention(
     return identifier
 
 
-def get_webmention_state(
-    app: Flask,
-    identifier: uuid.UUID,
-) -> tuple[str, str | None]:
+def get_webmention_state(app: Flask, identifier: uuid.UUID) -> tuple[str, str | None]:
     with app.app_context():
-        webmention = db.session.get(
-            ReceivedWebmention,
-            identifier,
-        )
+        webmention = db.session.get(ReceivedWebmention, identifier)
 
         assert webmention is not None
 
-        return (
-            webmention.status,
-            webmention.failure_reason,
-        )
+        return (webmention.status, webmention.failure_reason)
 
 
-def set_stream_response(
-    httpx_client: Mock,
-    response: httpx.Response,
-) -> Mock:
+def set_stream_response(httpx_client: Mock, response: httpx.Response) -> Mock:
     client = httpx_client.return_value.__enter__.return_value
     client.stream.return_value.__enter__.return_value = response
     return client
@@ -80,65 +65,25 @@ def set_stream_response(
 @pytest.mark.parametrize(
     ("body", "expected"),
     [
+        pytest.param(f'<a href="{TARGET_URL}">Reply</a>', True, id="a-href"),
+        pytest.param(f'<area href="{TARGET_URL}" alt="Target">', True, id="area-href"),
         pytest.param(
-            f'<a href="{TARGET_URL}">Reply</a>',
-            True,
-            id="a-href",
-        ),
-        pytest.param(
-            f'<area href="{TARGET_URL}" alt="Target">',
-            True,
-            id="area-href",
-        ),
-        pytest.param(
-            f'<link href="{TARGET_URL}" rel="alternate">',
-            True,
-            id="link-href",
-        ),
-        pytest.param(
-            f'<img src="{TARGET_URL}" alt="">',
-            True,
-            id="img-src",
-        ),
-        pytest.param(
-            f'<audio src="{TARGET_URL}"></audio>',
-            True,
-            id="audio-src",
-        ),
-        pytest.param(
-            f'<video src="{TARGET_URL}"></video>',
-            True,
-            id="video-src",
-        ),
-        pytest.param(
-            f'<audio><source src="{TARGET_URL}"></audio>',
-            True,
-            id="audio-source-src",
+            f'<link href="{TARGET_URL}" rel="alternate">', True, id="link-href"
         ),
+        pytest.param(f'<img src="{TARGET_URL}" alt="">', True, id="img-src"),
+        pytest.param(f'<audio src="{TARGET_URL}"></audio>', True, id="audio-src"),
+        pytest.param(f'<video src="{TARGET_URL}"></video>', True, id="video-src"),
         pytest.param(
-            f'<video><source src="{TARGET_URL}"></video>',
-            True,
-            id="video-source-src",
+            f'<audio><source src="{TARGET_URL}"></audio>', True, id="audio-source-src"
         ),
         pytest.param(
-            f'<iframe src="{TARGET_URL}"></iframe>',
-            True,
-            id="iframe-src",
+            f'<video><source src="{TARGET_URL}"></video>', True, id="video-source-src"
         ),
+        pytest.param(f'<iframe src="{TARGET_URL}"></iframe>', True, id="iframe-src"),
+        pytest.param(f'<embed src="{TARGET_URL}">', True, id="embed-src"),
+        pytest.param(f'<script src="{TARGET_URL}"></script>', True, id="script-src"),
         pytest.param(
-            f'<embed src="{TARGET_URL}">',
-            True,
-            id="embed-src",
-        ),
-        pytest.param(
-            f'<script src="{TARGET_URL}"></script>',
-            True,
-            id="script-src",
-        ),
-        pytest.param(
-            f'<video><track src="{TARGET_URL}"></video>',
-            True,
-            id="track-src",
+            f'<video><track src="{TARGET_URL}"></video>', True, id="track-src"
         ),
         pytest.param(
             f'<input type="image" src="{TARGET_URL}" alt="">',
@@ -155,51 +100,23 @@ def set_stream_response(
             True,
             id="blockquote-cite",
         ),
-        pytest.param(
-            f'<q cite="{TARGET_URL}">Quotation</q>',
-            True,
-            id="q-cite",
-        ),
-        pytest.param(
-            f'<ins cite="{TARGET_URL}">Addition</ins>',
-            True,
-            id="ins-cite",
-        ),
-        pytest.param(
-            f'<del cite="{TARGET_URL}">Removal</del>',
-            True,
-            id="del-cite",
-        ),
+        pytest.param(f'<q cite="{TARGET_URL}">Quotation</q>', True, id="q-cite"),
+        pytest.param(f'<ins cite="{TARGET_URL}">Addition</ins>', True, id="ins-cite"),
+        pytest.param(f'<del cite="{TARGET_URL}">Removal</del>', True, id="del-cite"),
         pytest.param(
             '<base href="https://dennisfink.me/blog/"><a href="example/">Reply</a>',
             True,
             id="base-url",
         ),
-        pytest.param(
-            f'<img cite="{TARGET_URL}" alt="">',
-            False,
-            id="img-cite-invalid",
-        ),
+        pytest.param(f'<img cite="{TARGET_URL}" alt="">', False, id="img-cite-invalid"),
         pytest.param(
             f'<blockquote src="{TARGET_URL}">Quote</blockquote>',
             False,
             id="blockquote-src-invalid",
         ),
-        pytest.param(
-            f'<a src="{TARGET_URL}">Reply</a>',
-            False,
-            id="a-src-invalid",
-        ),
-        pytest.param(
-            f'<div href="{TARGET_URL}"></div>',
-            False,
-            id="div-href-invalid",
-        ),
-        pytest.param(
-            f'<link src="{TARGET_URL}">',
-            False,
-            id="link-src-invalid",
-        ),
+        pytest.param(f'<a src="{TARGET_URL}">Reply</a>', False, id="a-src-invalid"),
+        pytest.param(f'<div href="{TARGET_URL}"></div>', False, id="div-href-invalid"),
+        pytest.param(f'<link src="{TARGET_URL}">', False, id="link-src-invalid"),
         pytest.param(
             f'<input type="text" src="{TARGET_URL}">',
             False,
@@ -210,51 +127,28 @@ def set_stream_response(
             False,
             id="picture-source-src-invalid",
         ),
+        pytest.param(f'<base href="{TARGET_URL}">', False, id="base-is-not-mention"),
         pytest.param(
-            f'<base href="{TARGET_URL}">',
-            False,
-            id="base-is-not-mention",
-        ),
-        pytest.param(
-            f'<a href="{TARGET_URL}more">Different page</a>',
-            False,
-            id="longer-url",
+            f'<a href="{TARGET_URL}more">Different page</a>', False, id="longer-url"
         ),
         pytest.param(
             f'<img cite="{TARGET_URL}" src="https://example.com/image.jpg" alt="">',
             False,
             id="invalid-cite-does-not-override-valid-src",
         ),
+        pytest.param(f"<p>{TARGET_URL}</p>", False, id="text-content"),
         pytest.param(
-            f"<p>{TARGET_URL}</p>",
-            False,
-            id="text-content",
-        ),
-        pytest.param(
-            '<a href="https://example.com/">Other site</a>',
-            False,
-            id="missing-target",
+            '<a href="https://example.com/">Other site</a>', False, id="missing-target"
         ),
     ],
 )
-def test_html_mentions_target(
-    receiver: ModuleType,
-    body: str,
-    expected: bool,
-) -> None:
+def test_html_mentions_target(receiver: ModuleType, body: str, expected: bool) -> None:
     assert (
-        receiver.html_mentions_target(
-            body.encode(),
-            SOURCE_URL,
-            TARGET_URL,
-        )
-        is expected
+        receiver.html_mentions_target(body.encode(), SOURCE_URL, TARGET_URL) is expected
     )
 
 
-def test_html_mentions_relative_target(
-    receiver: ModuleType,
-) -> None:
+def test_html_mentions_relative_target(receiver: ModuleType) -> None:
     assert receiver.html_mentions_target(
         b'<a href="../target/">Reply</a>',
         "https://source.example/posts/article/",
@@ -279,63 +173,14 @@ def test_html_mentions_relative_target(
     ],
 )
 def test_text_mentions_target(
-    receiver: ModuleType,
-    body: str,
-    target_url: str,
-    expected: bool,
+    receiver: ModuleType, body: str, target_url: str, expected: bool
 ) -> None:
     assert receiver.text_mentions_target(body, target_url) is expected
 
 
-@patch("webmentions_ssg.tasks.receiver.ensure_public_url")
-def test_ensure_public_request_accepts_public_url(
-    ensure_public_url: Mock,
-    receiver: ModuleType,
-) -> None:
-    receiver.ensure_public_request(httpx.Request("GET", SOURCE_URL))
-
-    ensure_public_url.assert_called_once_with(SOURCE_URL)
-
-
-@patch(
-    "webmentions_ssg.tasks.receiver.ensure_public_url",
-    side_effect=NonPublicAddressError("Non-public address"),
-)
-def test_ensure_public_request_rejects_non_public_address(
-    ensure_public_url: Mock,
-    receiver: ModuleType,
-) -> None:
-    with pytest.raises(
-        receiver.VerificationError,
-        match="Source resolves to a non-public address",
-    ):
-        receiver.ensure_public_request(httpx.Request("GET", SOURCE_URL))
-
-    ensure_public_url.assert_called_once_with(SOURCE_URL)
-
-
-@patch(
-    "webmentions_ssg.tasks.receiver.ensure_public_url",
-    side_effect=AddressResolutionError("Could not resolve hostname"),
-)
-def test_ensure_public_request_maps_dns_failure_to_temporary_error(
-    ensure_public_url: Mock,
-    receiver: ModuleType,
-) -> None:
-    with pytest.raises(
-        receiver.TemporaryFetchError,
-        match="Source hostname could not be resolved",
-    ):
-        receiver.ensure_public_request(httpx.Request("GET", SOURCE_URL))
-
-    ensure_public_url.assert_called_once_with(SOURCE_URL)
-
-
 @patch("webmentions_ssg.tasks.receiver.httpx.Client")
 def test_fetch_source_returns_response_and_body(
-    httpx_client: Mock,
-    app: Flask,
-    receiver: ModuleType,
+    httpx_client: Mock, app: Flask, receiver: ModuleType
 ) -> None:
     response = httpx.Response(
         200,
@@ -360,13 +205,10 @@ def test_fetch_source_returns_response_and_body(
     }
     assert options["follow_redirects"] is True
     assert options["max_redirects"] == app.config.get(
-        "WEBMENTIONS_SSG_MAX_REDIRECTS",
-        20,
+        "WEBMENTIONS_SSG_MAX_REDIRECTS", 20
     )
     assert options["trust_env"] is False
-    assert options["event_hooks"] == {
-        "request": [receiver.ensure_public_request],
-    }
+    assert options["event_hooks"] == {"request": [receiver.ensure_public_request]}
 
 
 @patch("webmentions_ssg.tasks.receiver.httpx.Client")
@@ -392,51 +234,34 @@ def test_fetch_source_maps_http_status_to_exception(
 ) -> None:
     set_stream_response(
         httpx_client,
-        httpx.Response(
-            status_code,
-            request=httpx.Request("GET", SOURCE_URL),
-        ),
+        httpx.Response(status_code, request=httpx.Request("GET", SOURCE_URL)),
     )
 
     exception_type = getattr(receiver, exception_name)
 
-    with (
-        app.app_context(),
-        pytest.raises(
-            exception_type,
-            match=f"HTTP {status_code}",
-        ),
-    ):
+    with app.app_context(), pytest.raises(exception_type, match=f"HTTP {status_code}"):
         receiver.fetch_source(SOURCE_URL)
 
 
 @patch("webmentions_ssg.tasks.receiver.httpx.Client")
 def test_fetch_source_propagates_network_error(
-    httpx_client: Mock,
-    app: Flask,
-    receiver: ModuleType,
+    httpx_client: Mock, app: Flask, receiver: ModuleType
 ) -> None:
     client = httpx_client.return_value.__enter__.return_value
     client.stream.side_effect = httpx.ConnectError(
-        "Connection refused",
-        request=httpx.Request("GET", SOURCE_URL),
+        "Connection refused", request=httpx.Request("GET", SOURCE_URL)
     )
 
     with (
         app.app_context(),
-        pytest.raises(
-            httpx.ConnectError,
-            match="Connection refused",
-        ),
+        pytest.raises(httpx.ConnectError, match="Connection refused"),
     ):
         receiver.fetch_source(SOURCE_URL)
 
 
 @patch("webmentions_ssg.tasks.receiver.httpx.Client")
 def test_fetch_source_rejects_declared_oversized_body(
-    httpx_client: Mock,
-    app: Flask,
-    receiver: ModuleType,
+    httpx_client: Mock, app: Flask, receiver: ModuleType
 ) -> None:
     app.config["WEBMENTIONS_SSG_MAX_SOURCE_BYTES"] = 10
 
@@ -444,10 +269,7 @@ def test_fetch_source_rejects_declared_oversized_body(
         httpx_client,
         httpx.Response(
             200,
-            headers={
-                "Content-Type": "text/html",
-                "Content-Length": "11",
-            },
+            headers={"Content-Type": "text/html", "Content-Length": "11"},
             content=b"x" * 11,
             request=httpx.Request("GET", SOURCE_URL),
         ),
@@ -455,19 +277,14 @@ def test_fetch_source_rejects_declared_oversized_body(
 
     with (
         app.app_context(),
-        pytest.raises(
-            receiver.VerificationError,
-            match="Source document is too large",
-        ),
+        pytest.raises(receiver.VerificationError, match="Source document is too large"),
     ):
         receiver.fetch_source(SOURCE_URL)
 
 
 @patch("webmentions_ssg.tasks.receiver.httpx.Client")
 def test_fetch_source_rejects_streamed_oversized_body(
-    httpx_client: Mock,
-    app: Flask,
-    receiver: ModuleType,
+    httpx_client: Mock, app: Flask, receiver: ModuleType
 ) -> None:
     app.config["WEBMENTIONS_SSG_MAX_SOURCE_BYTES"] = 10
 
@@ -488,10 +305,7 @@ def test_fetch_source_rejects_streamed_oversized_body(
 
     with (
         app.app_context(),
-        pytest.raises(
-            receiver.VerificationError,
-            match="Source document is too large",
-        ),
+        pytest.raises(receiver.VerificationError, match="Source document is too large"),
     ):
         receiver.fetch_source(SOURCE_URL)
 
@@ -537,10 +351,7 @@ def test_fetch_source_rejects_streamed_oversized_body(
             id="plain-text-invalid-byte",
         ),
         pytest.param(
-            "text/plain",
-            b"No target here.",
-            False,
-            id="plain-text-without-target",
+            "text/plain", b"No target here.", False, id="plain-text-without-target"
         ),
     ],
 )
@@ -600,24 +411,14 @@ def test_source_mentions_target_rejects_unsupported_media_type(
 
 @patch("webmentions_ssg.tasks.receiver.source_mentions_target")
 def test_verify_webmention_marks_row_verifying_before_check(
-    source_mentions_target: Mock,
-    app: Flask,
-    receiver: ModuleType,
+    source_mentions_target: Mock, app: Flask, receiver: ModuleType
 ) -> None:
     identifier = create_webmention(
-        app,
-        status="failed",
-        failure_reason="Earlier failure",
+        app, status="failed", failure_reason="Earlier failure"
     )
 
-    def verify_source(
-        source_url: str,
-        target_url: str,
-    ) -> bool:
-        webmention = db.session.get(
-            ReceivedWebmention,
-            identifier,
-        )
+    def verify_source(source_url: str, target_url: str) -> bool:
+        webmention = db.session.get(ReceivedWebmention, identifier)
 
         assert webmention is not None
         assert webmention.status == "verifying"
@@ -631,13 +432,7 @@ def test_verify_webmention_marks_row_verifying_before_check(
 
     receiver.verify_webmention.call_local(identifier)
 
-    assert get_webmention_state(
-        app,
-        identifier,
-    ) == (
-        "verified",
-        None,
-    )
+    assert get_webmention_state(app, identifier) == ("verified", None)
 
 
 @patch("webmentions_ssg.tasks.receiver.source_mentions_target")
@@ -678,28 +473,13 @@ def test_verify_webmention_persists_final_state(
 
     receiver.verify_webmention.call_local(identifier)
 
-    assert get_webmention_state(
-        app,
-        identifier,
-    ) == (
-        expected_status,
-        expected_reason,
-    )
+    assert get_webmention_state(app, identifier) == (expected_status, expected_reason)
 
 
 @patch("webmentions_ssg.tasks.receiver.source_mentions_target")
-@pytest.mark.parametrize(
-    "failure",
-    [
-        "temporary-http",
-        "network",
-    ],
-)
+@pytest.mark.parametrize("failure", ["temporary-http", "network"])
 def test_verify_webmention_persists_retryable_failure_and_reraises(
-    source_mentions_target: Mock,
-    app: Flask,
-    receiver: ModuleType,
-    failure: str,
+    source_mentions_target: Mock, app: Flask, receiver: ModuleType, failure: str
 ) -> None:
     identifier = create_webmention(app)
 
@@ -708,32 +488,21 @@ def test_verify_webmention_persists_retryable_failure_and_reraises(
             exception = receiver.TemporaryFetchError("Source returned HTTP 503")
         case "network":
             exception = httpx.ConnectError(
-                "Connection refused",
-                request=httpx.Request("GET", SOURCE_URL),
+                "Connection refused", request=httpx.Request("GET", SOURCE_URL)
             )
         case _:
             raise AssertionError(f"Unexpected failure: {failure}")
 
     source_mentions_target.side_effect = exception
 
-    with pytest.raises(
-        type(exception),
-        match=str(exception),
-    ):
+    with pytest.raises(type(exception), match=str(exception)):
         receiver.verify_webmention.call_local(identifier)
 
-    assert get_webmention_state(
-        app,
-        identifier,
-    ) == (
-        "failed",
-        str(exception),
-    )
+    assert get_webmention_state(app, identifier) == ("failed", str(exception))
 
 
 def test_verify_webmention_ignores_unknown_identifier(
-    receiver: ModuleType,
-    caplog: pytest.LogCaptureFixture,
+    receiver: ModuleType, caplog: pytest.LogCaptureFixture
 ) -> None:
     identifier = uuid.uuid7()
 
@@ -741,3 +510,52 @@ def test_verify_webmention_ignores_unknown_identifier(
         receiver.verify_webmention.call_local(identifier)
 
     assert f"Cannot verify unknown ReceivedWebmention {identifier}" in caplog.text
+
+
+@patch("webmentions_ssg.tasks.receiver.is_public_url", return_value=True)
+def test_ensure_public_request_accepts_public_url(
+    is_public_url: Mock, receiver: ModuleType
+) -> None:
+    receiver.ensure_public_request(httpx.Request("GET", SOURCE_URL))
+
+    is_public_url.assert_called_once_with(SOURCE_URL)
+
+
+@patch("webmentions_ssg.tasks.receiver.is_public_url", return_value=False)
+def test_ensure_public_request_rejects_non_public_address(
+    is_public_url: Mock, receiver: ModuleType
+) -> None:
+    with pytest.raises(
+        receiver.VerificationError, match="Source resolves to a non-public address"
+    ):
+        receiver.ensure_public_request(httpx.Request("GET", SOURCE_URL))
+
+    is_public_url.assert_called_once_with(SOURCE_URL)
+
+
+@patch(
+    "webmentions_ssg.tasks.receiver.is_public_url",
+    side_effect=AddressResolutionError("Could not resolve hostname"),
+)
+def test_ensure_public_request_maps_dns_failure_to_temporary_error(
+    is_public_url: Mock, receiver: ModuleType
+) -> None:
+    with pytest.raises(
+        receiver.TemporaryFetchError, match="Source hostname could not be resolved"
+    ):
+        receiver.ensure_public_request(httpx.Request("GET", SOURCE_URL))
+
+    is_public_url.assert_called_once_with(SOURCE_URL)
+
+
+@patch(
+    "webmentions_ssg.tasks.receiver.is_public_url",
+    side_effect=ValueError("No hostname was specified"),
+)
+def test_ensure_public_request_rejects_url_without_hostname(
+    is_public_url: Mock, receiver: ModuleType
+) -> None:
+    with pytest.raises(receiver.VerificationError, match="Source URL has no hostname"):
+        receiver.ensure_public_request(httpx.Request("GET", SOURCE_URL))
+
+    is_public_url.assert_called_once_with(SOURCE_URL)
diff --git a/tests/tasks/test_scanner.py b/tests/tasks/test_scanner.py
new file mode 100644
index 0000000..65031b4
--- /dev/null
+++ b/tests/tasks/test_scanner.py
@@ -0,0 +1,1558 @@
+from pathlib import Path
+from types import ModuleType
+from uuid import UUID
+
+import pytest
+import sqlalchemy as sa
+from bs4 import BeautifulSoup
+from flask import Flask
+from pytest import MonkeyPatch
+
+from webmentions_ssg import DATABASE as db
+from webmentions_ssg.models import SentWebmention, SentWebmentionStatus, Source
+
+BASE_URL = "https://dennisfink.me/blog/"
+SOURCE_URL = f"{BASE_URL}example/"
+
+
+@pytest.fixture
+def scanner_module(app: Flask) -> ModuleType:
+    # Importing scanner registers Huey tasks. The dependency on the
+    # app fixture guarantees that Huey has been initialized first.
+    _ = app
+
+    from webmentions_ssg.tasks import scanner
+
+    return scanner
+
+
+def run_scan(app: Flask, scanner_module: ModuleType) -> None:
+    with app.app_context():
+        scanner_module.scan_sources()
+
+
+def parse_html(html: str) -> BeautifulSoup:
+    return BeautifulSoup(html, "html5lib")
+
+
+def write_post(
+    root: Path,
+    slug: str,
+    content: str,
+    *,
+    canonical: str | None = None,
+    entry_url: str | None = None,
+) -> Path:
+    directory = root / slug
+    directory.mkdir(parents=True, exist_ok=True)
+
+    source_url = f"{BASE_URL}{slug}/"
+
+    if canonical is None:
+        canonical = source_url
+
+    if entry_url is None:
+        entry_url = source_url
+
+    path = directory / "index.html"
+    path.write_text(
+        f"""
+        <!doctype html>
+        <html>
+          <head>
+            <link
+              rel="canonical"
+              href="{canonical}"
+            >
+          </head>
+          <body>
+            <article class="h-entry">
+              <a
+                class="u-url"
+                href="{entry_url}"
+              >
+                Permalink
+              </a>
+
+              <div class="e-content">
+                {content}
+              </div>
+            </article>
+          </body>
+        </html>
+        """,
+        encoding="utf-8",
+    )
+
+    return path
+
+
+def configure_scanner(app: Flask, root: Path, *, base_url: str | None = None) -> None:
+    app.config["WEBMENTIONS_SSG_SOURCE_DIRECTORY"] = str(root)
+    app.config["WEBMENTIONS_SSG_SOURCE_BASE_URL"] = base_url
+
+
+# ---------------------------------------------------------------------------
+# Microformats parsing
+# ---------------------------------------------------------------------------
+
+
+def test_parse_entry_returns_microformats_entry(scanner_module: ModuleType) -> None:
+    document = parse_html(
+        f"""
+        <article class="h-entry">
+          <a class="u-url" href="{SOURCE_URL}">
+            Permalink
+          </a>
+
+          <div class="e-content">
+            Hello world
+          </div>
+        </article>
+        """
+    )
+
+    element = document.find(class_="h-entry")
+
+    assert element is not None
+
+    entry = scanner_module.parse_entry(element, SOURCE_URL)
+
+    assert "h-entry" in entry["type"]
+    assert entry["properties"]["url"] == [SOURCE_URL]
+
+
+def test_parse_entry_rejects_non_entry(scanner_module: ModuleType) -> None:
+    document = parse_html(
+        """
+        <article>
+          <p>Hello world</p>
+        </article>
+        """
+    )
+
+    element = document.find("article")
+
+    assert element is not None
+
+    with pytest.raises(
+        scanner_module.SourceScanError, match="Expected exactly one parsed h-entry"
+    ):
+        scanner_module.parse_entry(element, SOURCE_URL)
+
+
+def test_primary_entry_returns_source_entry(scanner_module: ModuleType) -> None:
+    document = parse_html(
+        f"""
+        <article class="h-entry" id="source">
+          <a class="u-url" href="{SOURCE_URL}">
+            Permalink
+          </a>
+
+          <p class="p-name">
+            Example post
+          </p>
+
+          <div class="e-content">
+            Hello world
+          </div>
+        </article>
+        """
+    )
+
+    element, entry = scanner_module.primary_entry(document, SOURCE_URL)
+
+    assert element["id"] == "source"
+    assert entry["properties"]["name"] == ["Example post"]
+    assert entry["properties"]["url"] == [SOURCE_URL]
+
+
+def test_primary_entry_rejects_missing_h_entry(scanner_module: ModuleType) -> None:
+    document = parse_html(
+        """
+        <main>
+          <p>No microformats here.</p>
+        </main>
+        """
+    )
+
+    with pytest.raises(
+        scanner_module.SourceScanError, match="Expected exactly one h-entry, found 0"
+    ):
+        scanner_module.primary_entry(document, SOURCE_URL)
+
+
+def test_primary_entry_rejects_multiple_h_entries(scanner_module: ModuleType) -> None:
+    document = parse_html(
+        f"""
+        <article class="h-entry">
+          <a class="u-url" href="{SOURCE_URL}">
+            First
+          </a>
+        </article>
+
+        <article class="h-entry">
+          <a
+            class="u-url"
+            href="https://example.com/other/"
+          >
+            Second
+          </a>
+        </article>
+        """
+    )
+
+    with pytest.raises(
+        scanner_module.SourceScanError, match="Expected exactly one h-entry, found 2"
+    ):
+        scanner_module.primary_entry(document, SOURCE_URL)
+
+
+def test_primary_entry_rejects_nested_h_entry(scanner_module: ModuleType) -> None:
+    document = parse_html(
+        f"""
+        <article class="h-entry">
+          <a class="u-url" href="{SOURCE_URL}">
+            Permalink
+          </a>
+
+          <div class="e-content">
+            <article class="h-entry">
+              <a
+                class="u-url"
+                href="https://example.com/nested/"
+              >
+                Nested
+              </a>
+            </article>
+          </div>
+        </article>
+        """
+    )
+
+    with pytest.raises(
+        scanner_module.SourceScanError, match="Expected exactly one h-entry, found 2"
+    ):
+        scanner_module.primary_entry(document, SOURCE_URL)
+
+
+def test_primary_entry_rejects_missing_u_url(scanner_module: ModuleType) -> None:
+    document = parse_html(
+        """
+        <article class="h-entry">
+          <div class="e-content">
+            Hello world
+          </div>
+        </article>
+        """
+    )
+
+    with pytest.raises(scanner_module.SourceScanError, match="does not match"):
+        scanner_module.primary_entry(document, SOURCE_URL)
+
+
+def test_primary_entry_rejects_nonmatching_u_url(scanner_module: ModuleType) -> None:
+    document = parse_html(
+        """
+        <article class="h-entry">
+          <a
+            class="u-url"
+            href="https://example.com/other/"
+          >
+            Other
+          </a>
+
+          <div class="e-content">
+            Hello world
+          </div>
+        </article>
+        """
+    )
+
+    with pytest.raises(scanner_module.SourceScanError, match="does not match"):
+        scanner_module.primary_entry(document, SOURCE_URL)
+
+
+# ---------------------------------------------------------------------------
+# e-content
+# ---------------------------------------------------------------------------
+
+
+def test_content_element_returns_e_content(scanner_module: ModuleType) -> None:
+    document = parse_html(
+        """
+        <article class="h-entry">
+          <div class="e-content" id="content">
+            Hello world
+          </div>
+        </article>
+        """
+    )
+
+    entry = document.find(class_="h-entry")
+
+    assert entry is not None
+
+    content = scanner_module.content_element(entry)
+
+    assert content["id"] == "content"
+
+
+def test_content_element_rejects_missing_e_content(scanner_module: ModuleType) -> None:
+    document = parse_html(
+        """
+        <article class="h-entry">
+          <p>Hello world</p>
+        </article>
+        """
+    )
+
+    entry = document.find(class_="h-entry")
+
+    assert entry is not None
+
+    with pytest.raises(
+        scanner_module.SourceScanError, match="Expected exactly one e-content, found 0"
+    ):
+        scanner_module.content_element(entry)
+
+
+def test_content_element_rejects_multiple_e_content(scanner_module: ModuleType) -> None:
+    document = parse_html(
+        """
+        <article class="h-entry">
+          <div class="e-content">
+            First
+          </div>
+
+          <div class="e-content">
+            Second
+          </div>
+        </article>
+        """
+    )
+
+    entry = document.find(class_="h-entry")
+
+    assert entry is not None
+
+    with pytest.raises(
+        scanner_module.SourceScanError, match="Expected exactly one e-content, found 2"
+    ):
+        scanner_module.content_element(entry)
+
+
+# ---------------------------------------------------------------------------
+# Canonical URLs
+# ---------------------------------------------------------------------------
+
+
+def test_canonical_url_returns_absolute_url(scanner_module: ModuleType) -> None:
+    document = parse_html(
+        f"""
+        <html>
+          <head>
+            <link
+              rel="canonical"
+              href="{SOURCE_URL}"
+            >
+          </head>
+        </html>
+        """
+    )
+
+    result = scanner_module.canonical_url(
+        document, relative_path=Path("example/index.html"), base_url=None
+    )
+
+    assert result == SOURCE_URL
+
+
+def test_canonical_url_returns_none_when_missing(scanner_module: ModuleType) -> None:
+    document = parse_html(
+        """
+        <html>
+          <head>
+            <title>Example</title>
+          </head>
+        </html>
+        """
+    )
+
+    result = scanner_module.canonical_url(
+        document, relative_path=Path("example/index.html"), base_url=None
+    )
+
+    assert result is None
+
+
+def test_canonical_url_resolves_relative_url_with_base_url(
+    scanner_module: ModuleType,
+) -> None:
+    document = parse_html(
+        """
+        <html>
+          <head>
+            <link
+              rel="canonical"
+              href="./canonical/"
+            >
+          </head>
+        </html>
+        """
+    )
+
+    result = scanner_module.canonical_url(
+        document, relative_path=Path("example/index.html"), base_url=BASE_URL
+    )
+
+    assert result == ("https://dennisfink.me/blog/example/canonical/")
+
+
+def test_relative_canonical_requires_base_url(scanner_module: ModuleType) -> None:
+    document = parse_html(
+        """
+        <html>
+          <head>
+            <link
+              rel="canonical"
+              href="./canonical/"
+            >
+          </head>
+        </html>
+        """
+    )
+
+    with pytest.raises(scanner_module.SourceScanError, match="relative canonical"):
+        scanner_module.canonical_url(
+            document, relative_path=Path("example/index.html"), base_url=None
+        )
+
+
+def test_empty_canonical_is_rejected(scanner_module: ModuleType) -> None:
+    document = parse_html(
+        """
+        <html>
+          <head>
+            <link
+              rel="canonical"
+              href=" "
+            >
+          </head>
+        </html>
+        """
+    )
+
+    with pytest.raises(scanner_module.SourceScanError, match="empty canonical URL"):
+        scanner_module.canonical_url(
+            document, relative_path=Path("example/index.html"), base_url=BASE_URL
+        )
+
+
+# ---------------------------------------------------------------------------
+# Target extraction
+# ---------------------------------------------------------------------------
+
+
+def test_scan_source_uses_canonical_without_base_url(
+    scanner_module: ModuleType, tmp_path: Path
+) -> None:
+    path = write_post(
+        tmp_path,
+        "example",
+        """
+        <a href="https://example.com/target">
+          Target
+        </a>
+        """,
+    )
+
+    scanned = scanner_module.scan_source_file(path, root=tmp_path, base_url=None)
+
+    assert scanned.path == "example/index.html"
+    assert scanned.url == SOURCE_URL
+    assert scanned.targets == frozenset({"https://example.com/target"})
+    assert len(scanned.content_hash) == 32
+
+
+def test_scan_source_falls_back_to_base_url(
+    scanner_module: ModuleType, tmp_path: Path
+) -> None:
+    directory = tmp_path / "example"
+    directory.mkdir()
+
+    path = directory / "index.html"
+    path.write_text(
+        """
+        <!doctype html>
+        <html>
+          <body>
+            <article class="h-entry">
+              <a class="u-url" href="./">
+                Permalink
+              </a>
+
+              <div class="e-content">
+                <a href="https://example.com/target">
+                  Target
+                </a>
+              </div>
+            </article>
+          </body>
+        </html>
+        """,
+        encoding="utf-8",
+    )
+
+    scanned = scanner_module.scan_source_file(path, root=tmp_path, base_url=BASE_URL)
+
+    assert scanned.url == SOURCE_URL
+    assert scanned.targets == frozenset({"https://example.com/target"})
+
+
+def test_scan_source_requires_canonical_or_base_url(
+    scanner_module: ModuleType, tmp_path: Path
+) -> None:
+    directory = tmp_path / "example"
+    directory.mkdir()
+
+    path = directory / "index.html"
+    path.write_text(
+        """
+        <!doctype html>
+        <html>
+          <body>
+            <article class="h-entry">
+              <a class="u-url" href="./">
+                Permalink
+              </a>
+
+              <div class="e-content">
+                <p>Hello world.</p>
+              </div>
+            </article>
+          </body>
+        </html>
+        """,
+        encoding="utf-8",
+    )
+
+    with pytest.raises(scanner_module.SourceScanError, match="no canonical URL"):
+        scanner_module.scan_source_file(path, root=tmp_path, base_url=None)
+
+
+def test_scan_source_extracts_only_content_links(
+    scanner_module: ModuleType, tmp_path: Path
+) -> None:
+    directory = tmp_path / "example"
+    directory.mkdir()
+
+    path = directory / "index.html"
+    path.write_text(
+        f"""
+        <!doctype html>
+        <html>
+          <head>
+            <link
+              rel="canonical"
+              href="{SOURCE_URL}"
+            >
+          </head>
+          <body>
+            <article class="h-entry">
+              <a class="u-url" href="{SOURCE_URL}">
+                Permalink
+              </a>
+
+              <a href="https://example.com/metadata">
+                Metadata link
+              </a>
+
+              <div class="e-content">
+                <a href="https://example.com/content">
+                  Content link
+                </a>
+              </div>
+            </article>
+          </body>
+        </html>
+        """,
+        encoding="utf-8",
+    )
+
+    scanned = scanner_module.scan_source_file(path, root=tmp_path, base_url=None)
+
+    assert scanned.targets == frozenset({"https://example.com/content"})
+
+
+def test_scan_source_extracts_relative_content_link(
+    scanner_module: ModuleType, tmp_path: Path
+) -> None:
+    path = write_post(
+        tmp_path,
+        "example",
+        """
+        <a href="../other/">
+          Other post
+        </a>
+        """,
+    )
+
+    scanned = scanner_module.scan_source_file(path, root=tmp_path, base_url=None)
+
+    assert scanned.targets == frozenset({"https://dennisfink.me/blog/other/"})
+
+
+@pytest.mark.parametrize(
+    "property_name", ("in-reply-to", "like-of", "repost-of", "bookmark-of")
+)
+def test_scan_source_extracts_reaction_properties(
+    scanner_module: ModuleType, tmp_path: Path, property_name: str
+) -> None:
+    directory = tmp_path / "example"
+    directory.mkdir()
+
+    target = f"https://example.com/{property_name}"
+
+    path = directory / "index.html"
+    path.write_text(
+        f"""
+        <!doctype html>
+        <html>
+          <head>
+            <link
+              rel="canonical"
+              href="{SOURCE_URL}"
+            >
+          </head>
+          <body>
+            <article class="h-entry">
+              <a class="u-url" href="{SOURCE_URL}">
+                Permalink
+              </a>
+
+              <a
+                class="u-{property_name}"
+                href="{target}"
+              >
+                Reaction target
+              </a>
+
+              <div class="e-content">
+                <p>Post content.</p>
+              </div>
+            </article>
+          </body>
+        </html>
+        """,
+        encoding="utf-8",
+    )
+
+    scanned = scanner_module.scan_source_file(path, root=tmp_path, base_url=None)
+
+    assert scanned.targets == frozenset({target})
+
+
+def test_scan_source_extracts_anchor_from_e_content(
+    scanner_module: ModuleType, tmp_path: Path
+) -> None:
+    path = write_post(
+        tmp_path,
+        "example",
+        """
+        <a href="https://example.com/target">
+          Target
+        </a>
+        """,
+    )
+
+    scanned = scanner_module.scan_source_file(path, root=tmp_path, base_url=None)
+
+    assert scanned.targets == frozenset({"https://example.com/target"})
+
+
+@pytest.mark.parametrize("tag", ("link", "area"))
+def test_scan_source_ignores_non_anchor_href_elements(
+    scanner_module: ModuleType, tmp_path: Path, tag: str
+) -> None:
+    path = write_post(
+        tmp_path,
+        "example",
+        f"""
+        <{tag} href="https://example.com/target">
+        """,
+    )
+
+    scanned = scanner_module.scan_source_file(path, root=tmp_path, base_url=None)
+
+    assert scanned.targets == frozenset()
+
+
+def test_scan_source_ignores_self_fragment(
+    scanner_module: ModuleType, tmp_path: Path
+) -> None:
+    path = write_post(
+        tmp_path,
+        "example",
+        """
+        <a href="#section">
+          Section
+        </a>
+
+        <a href="https://example.com/target">
+          Target
+        </a>
+        """,
+    )
+
+    scanned = scanner_module.scan_source_file(path, root=tmp_path, base_url=None)
+
+    assert scanned.targets == frozenset({"https://example.com/target"})
+
+
+# ---------------------------------------------------------------------------
+# Database reconciliation
+# ---------------------------------------------------------------------------
+
+
+def test_scan_creates_source_and_webmentions(
+    app: Flask, scanner_module: ModuleType, tmp_path: Path, monkeypatch: MonkeyPatch
+) -> None:
+    configure_scanner(app, tmp_path)
+
+    write_post(
+        tmp_path,
+        "example",
+        """
+        <a href="https://example.com/a">
+          A
+        </a>
+
+        <a href="https://example.com/b">
+          B
+        </a>
+        """,
+    )
+
+    queued: list[UUID] = []
+
+    monkeypatch.setattr(scanner_module, "send_webmention", queued.append)
+
+    run_scan(app, scanner_module)
+
+    with app.app_context():
+        source = db.session.scalar(sa.select(Source))
+
+        assert source is not None
+        assert source.path == "example/index.html"
+        assert source.url == SOURCE_URL
+        assert source.revision == 1
+        assert source.deleted_at is None
+        assert len(source.content_hash) == 32
+
+        webmentions = list(
+            db.session.scalars(
+                sa.select(SentWebmention).order_by(SentWebmention.target)
+            )
+        )
+
+        assert [webmention.target for webmention in webmentions] == [
+            "https://example.com/a",
+            "https://example.com/b",
+        ]
+
+        assert all(webmention.active for webmention in webmentions)
+        assert all(webmention.desired_revision == 1 for webmention in webmentions)
+        assert all(webmention.processed_revision is None for webmention in webmentions)
+
+        identifiers = {webmention.uuid for webmention in webmentions}
+
+    assert set(queued) == identifiers
+
+
+def test_unchanged_source_does_not_increment_revision(
+    app: Flask, scanner_module: ModuleType, tmp_path: Path, monkeypatch: MonkeyPatch
+) -> None:
+    configure_scanner(app, tmp_path)
+
+    write_post(
+        tmp_path,
+        "example",
+        """
+        <a href="https://example.com/a">
+          A
+        </a>
+        """,
+    )
+
+    queued: list[UUID] = []
+
+    monkeypatch.setattr(scanner_module, "send_webmention", queued.append)
+
+    run_scan(app, scanner_module)
+
+    with app.app_context():
+        webmention = db.session.scalar(sa.select(SentWebmention))
+
+        assert webmention is not None
+
+        webmention.processed_revision = 1
+        webmention.sent_revision = 1
+        webmention.status = SentWebmentionStatus.SENT
+
+        db.session.commit()
+
+    queued.clear()
+
+    run_scan(app, scanner_module)
+
+    with app.app_context():
+        source = db.session.scalar(sa.select(Source))
+
+        assert source is not None
+        assert source.revision == 1
+
+    assert queued == []
+
+
+def test_updated_source_increments_revision(
+    app: Flask, scanner_module: ModuleType, tmp_path: Path, monkeypatch: MonkeyPatch
+) -> None:
+    configure_scanner(app, tmp_path)
+
+    path = write_post(
+        tmp_path,
+        "example",
+        """
+        <p>Original content</p>
+
+        <a href="https://example.com/a">
+          A
+        </a>
+        """,
+    )
+
+    queued: list[UUID] = []
+
+    monkeypatch.setattr(scanner_module, "send_webmention", queued.append)
+
+    run_scan(app, scanner_module)
+
+    with app.app_context():
+        webmention = db.session.scalar(sa.select(SentWebmention))
+
+        assert webmention is not None
+
+        webmention.processed_revision = 1
+        webmention.sent_revision = 1
+        webmention.status = SentWebmentionStatus.SENT
+
+        db.session.commit()
+
+    queued.clear()
+
+    path.write_text(
+        f"""
+        <!doctype html>
+        <html>
+          <head>
+            <link
+              rel="canonical"
+              href="{SOURCE_URL}"
+            >
+          </head>
+          <body>
+            <article class="h-entry">
+              <a class="u-url" href="{SOURCE_URL}">
+                Permalink
+              </a>
+
+              <div class="e-content">
+                <p>Updated content</p>
+
+                <a href="https://example.com/a">
+                  A
+                </a>
+              </div>
+            </article>
+          </body>
+        </html>
+        """,
+        encoding="utf-8",
+    )
+
+    run_scan(app, scanner_module)
+
+    with app.app_context():
+        source = db.session.scalar(sa.select(Source))
+        webmention = db.session.scalar(sa.select(SentWebmention))
+
+        assert source is not None
+        assert webmention is not None
+
+        assert source.revision == 2
+
+        assert webmention.active
+        assert webmention.desired_revision == 2
+        assert webmention.processed_revision == 1
+        assert webmention.sent_revision == 1
+        assert webmention.pending
+
+        identifier = webmention.uuid
+
+    assert queued == [identifier]
+
+
+def test_new_target_is_added_on_update(
+    app: Flask, scanner_module: ModuleType, tmp_path: Path, monkeypatch: MonkeyPatch
+) -> None:
+    configure_scanner(app, tmp_path)
+
+    path = write_post(
+        tmp_path,
+        "example",
+        """
+        <p>No links yet.</p>
+        """,
+    )
+
+    queued: list[UUID] = []
+
+    monkeypatch.setattr(scanner_module, "send_webmention", queued.append)
+
+    run_scan(app, scanner_module)
+
+    assert queued == []
+
+    path.write_text(
+        f"""
+        <!doctype html>
+        <html>
+          <head>
+            <link
+              rel="canonical"
+              href="{SOURCE_URL}"
+            >
+          </head>
+          <body>
+            <article class="h-entry">
+              <a class="u-url" href="{SOURCE_URL}">
+                Permalink
+              </a>
+
+              <div class="e-content">
+                <a href="https://example.com/new">
+                  New
+                </a>
+              </div>
+            </article>
+          </body>
+        </html>
+        """,
+        encoding="utf-8",
+    )
+
+    run_scan(app, scanner_module)
+
+    with app.app_context():
+        source = db.session.scalar(sa.select(Source))
+        webmention = db.session.scalar(sa.select(SentWebmention))
+
+        assert source is not None
+        assert webmention is not None
+
+        assert source.revision == 2
+
+        assert webmention.target == ("https://example.com/new")
+        assert webmention.active
+        assert webmention.desired_revision == 2
+        assert webmention.processed_revision is None
+        assert webmention.sent_revision is None
+        assert webmention.pending
+
+        identifier = webmention.uuid
+
+    assert queued == [identifier]
+
+
+def test_removed_sent_target_is_queued_again(
+    app: Flask, scanner_module: ModuleType, tmp_path: Path, monkeypatch: MonkeyPatch
+) -> None:
+    configure_scanner(app, tmp_path)
+
+    path = write_post(
+        tmp_path,
+        "example",
+        """
+        <a href="https://example.com/sent">
+          Sent
+        </a>
+        """,
+    )
+
+    queued: list[UUID] = []
+
+    monkeypatch.setattr(scanner_module, "send_webmention", queued.append)
+
+    run_scan(app, scanner_module)
+
+    with app.app_context():
+        webmention = db.session.scalar(sa.select(SentWebmention))
+
+        assert webmention is not None
+
+        webmention.processed_revision = 1
+        webmention.sent_revision = 1
+        webmention.status = SentWebmentionStatus.SENT
+
+        identifier = webmention.uuid
+        db.session.commit()
+
+    queued.clear()
+
+    path.write_text(
+        f"""
+        <!doctype html>
+        <html>
+          <head>
+            <link
+              rel="canonical"
+              href="{SOURCE_URL}"
+            >
+          </head>
+          <body>
+            <article class="h-entry">
+              <a class="u-url" href="{SOURCE_URL}">
+                Permalink
+              </a>
+
+              <div class="e-content">
+                <p>The link is gone.</p>
+              </div>
+            </article>
+          </body>
+        </html>
+        """,
+        encoding="utf-8",
+    )
+
+    run_scan(app, scanner_module)
+
+    with app.app_context():
+        source = db.session.scalar(sa.select(Source))
+        webmention = db.session.scalar(sa.select(SentWebmention))
+
+        assert source is not None
+        assert webmention is not None
+
+        assert source.revision == 2
+
+        assert not webmention.active
+        assert webmention.desired_revision == 2
+        assert webmention.processed_revision == 1
+        assert webmention.sent_revision == 1
+        assert webmention.pending
+
+    assert queued == [identifier]
+
+
+def test_removed_unsent_target_is_not_queued(
+    app: Flask, scanner_module: ModuleType, tmp_path: Path, monkeypatch: MonkeyPatch
+) -> None:
+    configure_scanner(app, tmp_path)
+
+    path = write_post(
+        tmp_path,
+        "example",
+        """
+        <a href="https://example.com/unsent">
+          Unsent
+        </a>
+        """,
+    )
+
+    queued: list[UUID] = []
+
+    monkeypatch.setattr(scanner_module, "send_webmention", queued.append)
+
+    run_scan(app, scanner_module)
+
+    queued.clear()
+
+    path.write_text(
+        f"""
+        <!doctype html>
+        <html>
+          <head>
+            <link
+              rel="canonical"
+              href="{SOURCE_URL}"
+            >
+          </head>
+          <body>
+            <article class="h-entry">
+              <a class="u-url" href="{SOURCE_URL}">
+                Permalink
+              </a>
+
+              <div class="e-content">
+                <p>The link is gone.</p>
+              </div>
+            </article>
+          </body>
+        </html>
+        """,
+        encoding="utf-8",
+    )
+
+    run_scan(app, scanner_module)
+
+    with app.app_context():
+        source = db.session.scalar(sa.select(Source))
+        webmention = db.session.scalar(sa.select(SentWebmention))
+
+        assert source is not None
+        assert webmention is not None
+
+        assert source.revision == 2
+
+        assert not webmention.active
+        assert webmention.desired_revision == 2
+        assert webmention.processed_revision == 2
+        assert webmention.sent_revision is None
+        assert not webmention.pending
+
+    assert queued == []
+
+
+# ---------------------------------------------------------------------------
+# Source deletion/restoration
+# ---------------------------------------------------------------------------
+
+
+def test_deleted_source_queues_previously_sent_webmention(
+    app: Flask, scanner_module: ModuleType, tmp_path: Path, monkeypatch: MonkeyPatch
+) -> None:
+    configure_scanner(app, tmp_path)
+
+    path = write_post(
+        tmp_path,
+        "example",
+        """
+        <a href="https://example.com/a">
+          A
+        </a>
+        """,
+    )
+
+    queued: list[UUID] = []
+
+    monkeypatch.setattr(scanner_module, "send_webmention", queued.append)
+
+    run_scan(app, scanner_module)
+
+    with app.app_context():
+        webmention = db.session.scalar(sa.select(SentWebmention))
+
+        assert webmention is not None
+
+        webmention.processed_revision = 1
+        webmention.sent_revision = 1
+        webmention.status = SentWebmentionStatus.SENT
+
+        identifier = webmention.uuid
+        db.session.commit()
+
+    queued.clear()
+    path.unlink()
+
+    run_scan(app, scanner_module)
+
+    with app.app_context():
+        source = db.session.scalar(sa.select(Source))
+        webmention = db.session.scalar(sa.select(SentWebmention))
+
+        assert source is not None
+        assert webmention is not None
+
+        assert source.revision == 2
+        assert source.deleted_at is not None
+
+        assert not webmention.active
+        assert webmention.desired_revision == 2
+        assert webmention.processed_revision == 1
+        assert webmention.sent_revision == 1
+        assert webmention.pending
+
+    assert queued == [identifier]
+
+
+def test_deleted_source_does_not_queue_unsent_webmention(
+    app: Flask, scanner_module: ModuleType, tmp_path: Path, monkeypatch: MonkeyPatch
+) -> None:
+    configure_scanner(app, tmp_path)
+
+    path = write_post(
+        tmp_path,
+        "example",
+        """
+        <a href="https://example.com/a">
+          A
+        </a>
+        """,
+    )
+
+    queued: list[UUID] = []
+
+    monkeypatch.setattr(scanner_module, "send_webmention", queued.append)
+
+    run_scan(app, scanner_module)
+
+    queued.clear()
+    path.unlink()
+
+    run_scan(app, scanner_module)
+
+    with app.app_context():
+        source = db.session.scalar(sa.select(Source))
+        webmention = db.session.scalar(sa.select(SentWebmention))
+
+        assert source is not None
+        assert webmention is not None
+
+        assert source.revision == 2
+        assert source.deleted_at is not None
+
+        assert not webmention.active
+        assert webmention.desired_revision == 2
+        assert webmention.processed_revision == 2
+        assert webmention.sent_revision is None
+        assert not webmention.pending
+
+    assert queued == []
+
+
+def test_restored_source_creates_new_revision(
+    app: Flask, scanner_module: ModuleType, tmp_path: Path, monkeypatch: MonkeyPatch
+) -> None:
+    configure_scanner(app, tmp_path)
+
+    path = write_post(
+        tmp_path,
+        "example",
+        """
+        <a href="https://example.com/a">
+          A
+        </a>
+        """,
+    )
+
+    queued: list[UUID] = []
+
+    monkeypatch.setattr(scanner_module, "send_webmention", queued.append)
+
+    run_scan(app, scanner_module)
+
+    with app.app_context():
+        webmention = db.session.scalar(sa.select(SentWebmention))
+
+        assert webmention is not None
+
+        webmention.processed_revision = 1
+        webmention.sent_revision = 1
+        webmention.status = SentWebmentionStatus.SENT
+
+        db.session.commit()
+
+    path.unlink()
+    run_scan(app, scanner_module)
+
+    queued.clear()
+
+    write_post(
+        tmp_path,
+        "example",
+        """
+        <a href="https://example.com/a">
+          A
+        </a>
+        """,
+    )
+
+    run_scan(app, scanner_module)
+
+    with app.app_context():
+        source = db.session.scalar(sa.select(Source))
+        webmention = db.session.scalar(sa.select(SentWebmention))
+
+        assert source is not None
+        assert webmention is not None
+
+        assert source.revision == 3
+        assert source.deleted_at is None
+
+        assert webmention.active
+        assert webmention.desired_revision == 3
+        assert webmention.sent_revision == 1
+        assert webmention.pending
+
+        identifier = webmention.uuid
+
+    assert queued == [identifier]
+
+
+# ---------------------------------------------------------------------------
+# Queue recovery and invalid sources
+# ---------------------------------------------------------------------------
+
+
+def test_pending_webmention_is_requeued_on_next_scan(
+    app: Flask, scanner_module: ModuleType, tmp_path: Path, monkeypatch: MonkeyPatch
+) -> None:
+    configure_scanner(app, tmp_path)
+
+    write_post(
+        tmp_path,
+        "example",
+        """
+        <a href="https://example.com/a">
+          A
+        </a>
+        """,
+    )
+
+    queued: list[UUID] = []
+
+    monkeypatch.setattr(scanner_module, "send_webmention", queued.append)
+
+    run_scan(app, scanner_module)
+
+    assert len(queued) == 1
+
+    identifier = queued[0]
+    queued.clear()
+
+    run_scan(app, scanner_module)
+
+    assert queued == [identifier]
+
+
+def test_invalid_known_source_is_not_deleted(
+    app: Flask,
+    scanner_module: ModuleType,
+    tmp_path: Path,
+    monkeypatch: MonkeyPatch,
+    caplog: pytest.LogCaptureFixture,
+) -> None:
+    configure_scanner(app, tmp_path)
+
+    path = write_post(
+        tmp_path,
+        "example",
+        """
+        <p>Hello world.</p>
+        """,
+    )
+
+    monkeypatch.setattr(scanner_module, "send_webmention", lambda identifier: None)
+
+    run_scan(app, scanner_module)
+
+    path.write_text(
+        f"""
+        <!doctype html>
+        <html>
+          <head>
+            <link
+              rel="canonical"
+              href="{SOURCE_URL}"
+            >
+          </head>
+          <body>
+            <p>The h-entry disappeared.</p>
+          </body>
+        </html>
+        """,
+        encoding="utf-8",
+    )
+
+    run_scan(app, scanner_module)
+
+    with app.app_context():
+        source = db.session.scalar(sa.select(Source))
+
+        assert source is not None
+        assert source.revision == 1
+        assert source.deleted_at is None
+
+    assert "Could not scan source" in caplog.text
+    assert "Expected exactly one h-entry, found 0" in caplog.text
+
+
+def test_scan_sources_accepts_valid_base_url(
+    app: Flask, scanner_module: ModuleType, tmp_path: Path, monkeypatch: MonkeyPatch
+) -> None:
+    configure_scanner(app, tmp_path, base_url=BASE_URL)
+
+    directory = tmp_path / "example"
+    directory.mkdir()
+
+    path = directory / "index.html"
+    path.write_text(
+        """
+        <!doctype html>
+        <html>
+          <body>
+            <article class="h-entry">
+              <a class="u-url" href="./">
+                Permalink
+              </a>
+
+              <div class="e-content">
+                <p>Hello world.</p>
+              </div>
+            </article>
+          </body>
+        </html>
+        """,
+        encoding="utf-8",
+    )
+
+    monkeypatch.setattr(scanner_module, "send_webmention", lambda identifier: None)
+
+    run_scan(app, scanner_module)
+
+    with app.app_context():
+        source = db.session.scalar(sa.select(Source))
+
+        assert source is not None
+        assert source.url == SOURCE_URL
+
+
+def test_scan_sources_rejects_invalid_base_url(
+    app: Flask, scanner_module: ModuleType, tmp_path: Path
+) -> None:
+    configure_scanner(app, tmp_path, base_url="not-a-url")
+
+    with pytest.raises(RuntimeError, match="absolute HTTP or HTTPS URL"):
+        run_scan(app, scanner_module)
+
+
+@pytest.mark.parametrize(
+    "href",
+    (
+        "https://dennisfink.me/blog/other/",
+        "https://www.dennisfink.me/blog/other/",
+        "https://webmentions.dennisfink.me/endpoint",
+        "https://foo.bar.dennisfink.me/example",
+    ),
+)
+def test_scan_source_ignores_matching_hostname(
+    scanner_module: ModuleType, tmp_path: Path, href: str
+) -> None:
+    path = write_post(
+        tmp_path,
+        "example",
+        f"""
+        <a href="{href}">
+          Ignored
+        </a>
+
+        <a href="https://example.com/target">
+          External
+        </a>
+        """,
+    )
+
+    scanned = scanner_module.scan_source_file(
+        path,
+        root=tmp_path,
+        base_url=None,
+        ignored_hostnames=("dennisfink.me", "*.dennisfink.me"),
+    )
+
+    assert scanned.targets == frozenset({"https://example.com/target"})
+
+
+@pytest.mark.parametrize(
+    "href",
+    (
+        "https://notdennisfink.me/example",
+        "https://dennisfink.me.example.com/example",
+        "https://example.com/example",
+    ),
+)
+def test_scan_source_keeps_nonmatching_hostname(
+    scanner_module: ModuleType, tmp_path: Path, href: str
+) -> None:
+    path = write_post(
+        tmp_path,
+        "example",
+        f"""
+        <a href="{href}">
+          Target
+        </a>
+        """,
+    )
+
+    scanned = scanner_module.scan_source_file(
+        path,
+        root=tmp_path,
+        base_url=None,
+        ignored_hostnames=("dennisfink.me", "*.dennisfink.me"),
+    )
+
+    assert scanned.targets == frozenset({href})
+
+
+def test_scan_source_ignores_reaction_to_matching_hostname(
+    scanner_module: ModuleType, tmp_path: Path
+) -> None:
+    directory = tmp_path / "example"
+    directory.mkdir()
+
+    path = directory / "index.html"
+    path.write_text(
+        f"""
+        <!doctype html>
+        <html>
+          <head>
+            <link
+              rel="canonical"
+              href="{SOURCE_URL}"
+            >
+          </head>
+          <body>
+            <article class="h-entry">
+              <a
+                class="u-url"
+                href="{SOURCE_URL}"
+              >
+                Permalink
+              </a>
+
+              <a
+                class="u-in-reply-to"
+                href="https://www.dennisfink.me/blog/other/"
+              >
+                Reply target
+              </a>
+
+              <div class="e-content">
+                <p>Reply content.</p>
+              </div>
+            </article>
+          </body>
+        </html>
+        """,
+        encoding="utf-8",
+    )
+
+    scanned = scanner_module.scan_source_file(
+        path,
+        root=tmp_path,
+        base_url=None,
+        ignored_hostnames=("dennisfink.me", "*.dennisfink.me"),
+    )
+
+    assert scanned.targets == frozenset()
diff --git a/tests/tasks/test_sender.py b/tests/tasks/test_sender.py
new file mode 100644
index 0000000..86799f7
--- /dev/null
+++ b/tests/tasks/test_sender.py
@@ -0,0 +1,788 @@
+import logging
+import uuid
+from datetime import datetime, timezone
+from types import ModuleType
+from unittest.mock import MagicMock, Mock
+
+import httpx
+import pytest
+from flask import Flask
+
+from webmentions_ssg import DATABASE as db
+from webmentions_ssg.models import SentWebmention, SentWebmentionStatus, Source
+
+SOURCE_URL = "https://dennisfink.me/blog/example/"
+TARGET_URL = "https://example.com/post"
+ENDPOINT_URL = "https://example.com/webmention"
+STATUS_URL = "https://example.com/webmention/status/123"
+
+
+def create_sent_webmention(
+    app: Flask,
+    *,
+    active: bool = True,
+    desired_revision: int = 1,
+    processed_revision: int | None = None,
+    sent_revision: int | None = None,
+    status: SentWebmentionStatus | None = None,
+    failure_reason: str | None = None,
+    endpoint: str | None = None,
+    response_status: int | None = None,
+    status_url: str | None = None,
+) -> uuid.UUID:
+    now = datetime.now(timezone.utc)
+
+    with app.app_context():
+        source = Source(
+            path="example/index.html",
+            url=SOURCE_URL,
+            content_hash="0" * 32,
+            revision=desired_revision,
+            last_seen_at=now,
+            revised_at=now,
+        )
+
+        webmention = SentWebmention(
+            target=TARGET_URL,
+            active=active,
+            desired_revision=desired_revision,
+            processed_revision=processed_revision,
+            sent_revision=sent_revision,
+            status=status,
+            failure_reason=failure_reason,
+            endpoint=endpoint,
+            response_status=response_status,
+            status_url=status_url,
+        )
+
+        source.sent_webmentions.append(webmention)
+
+        db.session.add(source)
+        db.session.commit()
+
+        return webmention.uuid
+
+
+def mock_sender_requests(
+    sender_module: ModuleType,
+    monkeypatch: pytest.MonkeyPatch,
+    *,
+    endpoint: str | None = ENDPOINT_URL,
+    result: tuple[int, str | None] = (202, None),
+) -> tuple[Mock, Mock, Mock, Mock]:
+    httpx_client = MagicMock()
+    client = httpx_client.return_value.__enter__.return_value
+
+    discover = Mock(return_value=endpoint)
+    post = Mock(return_value=result)
+
+    monkeypatch.setattr(sender_module.httpx, "Client", httpx_client)
+    monkeypatch.setattr(sender_module, "discover_webmention_endpoint", discover)
+    monkeypatch.setattr(sender_module, "post_webmention", post)
+
+    return httpx_client, client, discover, post
+
+
+@pytest.fixture
+def sender_module(app: Flask) -> ModuleType:
+    # Importing sender registers Huey tasks. The dependency on the
+    # app fixture guarantees that Huey has been initialized first.
+    _ = app
+
+    from webmentions_ssg.tasks import sender
+
+    return sender
+
+
+@pytest.mark.parametrize(
+    ("value", "expected"),
+    (
+        (
+            '<https://example.com/webmention>; rel="webmention"',
+            ("https://example.com/webmention", {"webmention"}),
+        ),
+        (
+            "<https://example.com/webmention>; rel=webmention",
+            ("https://example.com/webmention", {"webmention"}),
+        ),
+        (
+            '<https://example.com/webmention>; rel="webmention alternate"',
+            ("https://example.com/webmention", {"webmention", "alternate"}),
+        ),
+        (
+            '<https://example.com/webmention>; REL="WebMention Alternate"',
+            ("https://example.com/webmention", {"webmention", "alternate"}),
+        ),
+        (
+            "<https://example.com/webmention>; "
+            'type="text/html"; rel="webmention"; title="Endpoint"',
+            ("https://example.com/webmention", {"webmention"}),
+        ),
+        (
+            '<https://example.com/stylesheet>; type="text/css"',
+            ("https://example.com/stylesheet", set()),
+        ),
+    ),
+)
+def test_parse_link_value(
+    sender_module: ModuleType, value: str, expected: tuple[str, set[str]]
+) -> None:
+    assert sender_module.parse_link_value(value) == expected
+
+
+@pytest.mark.parametrize(
+    "value", ("", "https://example.com/webmention", "<https://example.com/webmention")
+)
+def test_parse_link_value_rejects_malformed_value(
+    sender_module: ModuleType, value: str
+) -> None:
+    assert sender_module.parse_link_value(value) is None
+
+
+@pytest.mark.parametrize(
+    ("target", "headers", "html", "expected_endpoint"),
+    (
+        pytest.param(
+            "https://example.com/test/1",
+            (("Link", "</test/1/webmention?head=true>; rel=webmention"),),
+            "",
+            "https://example.com/test/1/webmention?head=true",
+            id="1-http-link-unquoted-rel-relative-url",
+        ),
+        pytest.param(
+            "https://example.com/test/2",
+            (
+                (
+                    "Link",
+                    "<https://example.com/test/2/webmention?head=true>; rel=webmention",
+                ),
+            ),
+            "",
+            "https://example.com/test/2/webmention?head=true",
+            id="2-http-link-unquoted-rel-absolute-url",
+        ),
+        pytest.param(
+            "https://example.com/test/3",
+            (),
+            """
+            <link
+              rel="webmention"
+              href="/test/3/webmention"
+            >
+            """,
+            "https://example.com/test/3/webmention",
+            id="3-html-link-relative-url",
+        ),
+        pytest.param(
+            "https://example.com/test/4",
+            (),
+            """
+            <link
+              rel="webmention"
+              href="https://example.com/test/4/webmention"
+            >
+            """,
+            "https://example.com/test/4/webmention",
+            id="4-html-link-absolute-url",
+        ),
+        pytest.param(
+            "https://example.com/test/5",
+            (),
+            """
+            <a
+              rel="webmention"
+              href="/test/5/webmention"
+            >
+              Endpoint
+            </a>
+            """,
+            "https://example.com/test/5/webmention",
+            id="5-html-a-relative-url",
+        ),
+        pytest.param(
+            "https://example.com/test/6",
+            (),
+            """
+            <a
+              rel="webmention"
+              href="https://example.com/test/6/webmention"
+            >
+              Endpoint
+            </a>
+            """,
+            "https://example.com/test/6/webmention",
+            id="6-html-a-absolute-url",
+        ),
+        pytest.param(
+            "https://example.com/test/7",
+            (
+                (
+                    "LinK",
+                    "<https://example.com/test/7/webmention?head=true>; rel=webmention",
+                ),
+            ),
+            "",
+            "https://example.com/test/7/webmention?head=true",
+            id="7-http-link-strange-casing",
+        ),
+        pytest.param(
+            "https://example.com/test/8",
+            (
+                (
+                    "Link",
+                    '<https://example.com/test/8/webmention?head=true>; rel="webmention"',
+                ),
+            ),
+            "",
+            "https://example.com/test/8/webmention?head=true",
+            id="8-http-link-quoted-rel",
+        ),
+        pytest.param(
+            "https://example.com/test/9",
+            (),
+            """
+            <link
+              rel="webmention somethingelse"
+              href="https://example.com/test/9/webmention"
+            >
+            """,
+            "https://example.com/test/9/webmention",
+            id="9-multiple-html-rel-values",
+        ),
+        pytest.param(
+            "https://example.com/test/10",
+            (
+                (
+                    "Link",
+                    "<https://example.com/test/10/webmention?head=true>; "
+                    'rel="webmention somethingelse"',
+                ),
+            ),
+            "",
+            "https://example.com/test/10/webmention?head=true",
+            id="10-multiple-link-header-rel-values",
+        ),
+        pytest.param(
+            "https://example.com/test/11",
+            (("Link", '</test/11/webmention>; rel="webmention"'),),
+            """
+            <link
+              rel="webmention"
+              href="/test/11/webmention/error"
+            >
+
+            <a
+              rel="webmention"
+              href="/test/11/webmention/error"
+            >
+              Wrong endpoint
+            </a>
+            """,
+            "https://example.com/test/11/webmention",
+            id="11-http-link-precedence",
+        ),
+        pytest.param(
+            "https://example.com/test/12",
+            (),
+            """
+            <link
+              rel="not-webmention"
+              href="/test/12/webmention/error"
+            >
+
+            <a
+              rel="webmention"
+              href="/test/12/webmention"
+            >
+              Correct endpoint
+            </a>
+            """,
+            "https://example.com/test/12/webmention",
+            id="12-exact-rel-match",
+        ),
+        pytest.param(
+            "https://example.com/test/13",
+            (),
+            """
+            <!--
+              <a
+                rel="webmention"
+                href="/test/13/webmention/error"
+              >
+                False endpoint
+              </a>
+            -->
+
+            <a
+              rel="webmention"
+              href="/test/13/webmention"
+            >
+              Correct endpoint
+            </a>
+            """,
+            "https://example.com/test/13/webmention",
+            id="13-endpoint-inside-html-comment",
+        ),
+        pytest.param(
+            "https://example.com/test/14",
+            (),
+            """
+            <code>
+              &lt;a
+                rel="webmention"
+                href="/test/14/webmention/error"
+              &gt;
+                False endpoint
+              &lt;/a&gt;
+            </code>
+
+            <a
+              rel="webmention"
+              href="/test/14/webmention"
+            >
+              Correct endpoint
+            </a>
+            """,
+            "https://example.com/test/14/webmention",
+            id="14-endpoint-in-escaped-html",
+        ),
+        pytest.param(
+            "https://example.com/test/15",
+            (),
+            """
+            <link
+              rel="webmention"
+              href=""
+            >
+            """,
+            "https://example.com/test/15",
+            id="15-empty-href",
+        ),
+        pytest.param(
+            "https://example.com/test/16",
+            (),
+            """
+            <a
+              rel="webmention"
+              href="/test/16/webmention"
+            >
+              First endpoint
+            </a>
+
+            <link
+              rel="webmention"
+              href="/test/16/webmention/error"
+            >
+            """,
+            "https://example.com/test/16/webmention",
+            id="16-a-before-link",
+        ),
+        pytest.param(
+            "https://example.com/test/17",
+            (),
+            """
+            <link
+              rel="webmention"
+              href="/test/17/webmention"
+            >
+
+            <a
+              rel="webmention"
+              href="/test/17/webmention/error"
+            >
+              Second endpoint
+            </a>
+            """,
+            "https://example.com/test/17/webmention",
+            id="17-link-before-a",
+        ),
+        pytest.param(
+            "https://example.com/test/18",
+            (
+                ("Link", '<https://example.com/test/18/webmention/error>; rel="other"'),
+                (
+                    "Link",
+                    "<https://example.com/test/18/webmention?head=true>; "
+                    'rel="webmention"',
+                ),
+            ),
+            "",
+            "https://example.com/test/18/webmention?head=true",
+            id="18-multiple-http-link-headers",
+        ),
+        pytest.param(
+            "https://example.com/test/19",
+            (
+                (
+                    "Link",
+                    "<https://example.com/test/19/webmention/error>; "
+                    'rel="other", '
+                    "<https://example.com/test/19/webmention?head=true>; "
+                    'rel="webmention"',
+                ),
+            ),
+            "",
+            "https://example.com/test/19/webmention?head=true",
+            id="19-single-header-multiple-values",
+        ),
+        pytest.param(
+            "https://example.com/test/20",
+            (),
+            """
+            <link rel="webmention">
+
+            <a
+              rel="webmention"
+              href="/test/20/webmention"
+            >
+              Correct endpoint
+            </a>
+            """,
+            "https://example.com/test/20/webmention",
+            id="20-link-without-href",
+        ),
+        pytest.param(
+            "https://example.com/test/21",
+            (),
+            """
+            <link
+              rel="webmention"
+              href="/test/21/webmention?query=yes"
+            >
+            """,
+            "https://example.com/test/21/webmention?query=yes",
+            id="21-endpoint-query-string",
+        ),
+        pytest.param(
+            "https://example.com/test/22",
+            (),
+            """
+            <link
+              rel="webmention"
+              href="22/webmention"
+            >
+            """,
+            "https://example.com/test/22/webmention",
+            id="22-endpoint-relative-to-path",
+        ),
+    ),
+)
+def test_discovery(
+    app: Flask,
+    sender_module: ModuleType,
+    target: str,
+    headers: tuple[tuple[str, str], ...],
+    html: str,
+    expected_endpoint: str,
+) -> None:
+    def handler(request: httpx.Request) -> httpx.Response:
+        if request.method == "HEAD":
+            return httpx.Response(200, headers=headers)
+
+        return httpx.Response(200, headers={"Content-Type": "text/html"}, text=html)
+
+    with (
+        app.app_context(),
+        httpx.Client(
+            transport=httpx.MockTransport(handler), follow_redirects=True
+        ) as client,
+    ):
+        endpoint = sender_module.discover_webmention_endpoint(client, target)
+
+    assert endpoint == expected_endpoint
+
+
+@pytest.mark.parametrize(
+    ("target", "responses", "expected_endpoint"),
+    (
+        pytest.param(
+            "https://example.com/test/23/page",
+            {
+                "/test/23/page": (302, {"Location": "page/redirect-key"}),
+                "/test/23/page/redirect-key": (
+                    200,
+                    {"Link": ("<webmention-endpoint/endpoint-key>; rel=webmention")},
+                ),
+            },
+            ("https://example.com/test/23/page/webmention-endpoint/endpoint-key"),
+            id="relative-endpoint-after-redirect",
+        ),
+    ),
+)
+def test_discovery_redirect(
+    app: Flask,
+    sender_module: ModuleType,
+    target: str,
+    responses: dict[str, tuple[int, dict[str, str]]],
+    expected_endpoint: str,
+) -> None:
+    def handler(request: httpx.Request) -> httpx.Response:
+        try:
+            status, headers = responses[request.url.path]
+        except KeyError:
+            raise AssertionError(f"Unexpected request: {request.url}") from None
+
+        return httpx.Response(status, headers=headers)
+
+    with (
+        app.app_context(),
+        httpx.Client(
+            transport=httpx.MockTransport(handler), follow_redirects=True
+        ) as client,
+    ):
+        endpoint = sender_module.discover_webmention_endpoint(client, target)
+
+    assert endpoint == expected_endpoint
+
+
+def test_discovery_stops_after_head(app: Flask, sender_module: ModuleType) -> None:
+    requests: list[httpx.Request] = []
+
+    def handler(request: httpx.Request) -> httpx.Response:
+        requests.append(request)
+
+        return httpx.Response(200, headers={"Link": "</webmention>; rel=webmention"})
+
+    with (
+        app.app_context(),
+        httpx.Client(
+            transport=httpx.MockTransport(handler), follow_redirects=True
+        ) as client,
+    ):
+        endpoint = sender_module.discover_webmention_endpoint(
+            client, "https://example.com/post"
+        )
+
+    assert endpoint == "https://example.com/webmention"
+    assert [request.method for request in requests] == ["HEAD"]
+
+
+def test_discovery_falls_back_to_get(app: Flask, sender_module: ModuleType) -> None:
+    requests: list[httpx.Request] = []
+
+    def handler(request: httpx.Request) -> httpx.Response:
+        requests.append(request)
+
+        if request.method == "HEAD":
+            return httpx.Response(200)
+
+        return httpx.Response(
+            200,
+            headers={"Content-Type": "text/html"},
+            text="""
+            <link
+              rel="webmention"
+              href="/webmention"
+            >
+            """,
+        )
+
+    with (
+        app.app_context(),
+        httpx.Client(
+            transport=httpx.MockTransport(handler), follow_redirects=True
+        ) as client,
+    ):
+        endpoint = sender_module.discover_webmention_endpoint(
+            client, "https://example.com/post"
+        )
+
+    assert endpoint == "https://example.com/webmention"
+    assert [request.method for request in requests] == ["HEAD", "GET"]
+
+
+def test_send_webmention_persists_success(
+    app: Flask, sender_module: ModuleType, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    identifier = create_sent_webmention(app)
+
+    _, client, discover, post = mock_sender_requests(
+        sender_module, monkeypatch, result=(201, STATUS_URL)
+    )
+
+    sender_module.send_webmention.call_local(identifier)
+
+    discover.assert_called_once_with(client, TARGET_URL)
+    post.assert_called_once_with(
+        client, endpoint=ENDPOINT_URL, source=SOURCE_URL, target=TARGET_URL
+    )
+
+    with app.app_context():
+        webmention = db.session.get(SentWebmention, identifier)
+
+        assert webmention is not None
+        assert webmention.processed_revision == 1
+        assert webmention.sent_revision == 1
+        assert webmention.status == SentWebmentionStatus.SENT
+        assert webmention.failure_reason is None
+        assert webmention.endpoint == ENDPOINT_URL
+        assert webmention.response_status == 201
+        assert webmention.status_url == STATUS_URL
+        assert webmention.last_attempted_at is not None
+        assert webmention.last_sent_at is not None
+        assert not webmention.pending
+
+
+def test_send_webmention_marks_unsupported_target_processed(
+    app: Flask, sender_module: ModuleType, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    identifier = create_sent_webmention(
+        app,
+        desired_revision=2,
+        processed_revision=1,
+        sent_revision=1,
+        status=SentWebmentionStatus.SENT,
+        endpoint="https://old.example/webmention",
+        response_status=201,
+        status_url="https://old.example/status/123",
+    )
+
+    _, client, discover, post = mock_sender_requests(
+        sender_module, monkeypatch, endpoint=None
+    )
+
+    sender_module.send_webmention.call_local(identifier)
+
+    discover.assert_called_once_with(client, TARGET_URL)
+    post.assert_not_called()
+
+    with app.app_context():
+        webmention = db.session.get(SentWebmention, identifier)
+
+        assert webmention is not None
+        assert webmention.processed_revision == 2
+        assert webmention.sent_revision == 1
+        assert webmention.status == SentWebmentionStatus.UNSUPPORTED
+        assert webmention.failure_reason == "No Webmention endpoint discovered"
+        assert webmention.endpoint is None
+        assert webmention.response_status is None
+        assert webmention.status_url is None
+        assert webmention.last_attempted_at is not None
+        assert not webmention.pending
+
+
+def test_send_webmention_persists_permanent_failure(
+    app: Flask, sender_module: ModuleType, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    identifier = create_sent_webmention(
+        app,
+        desired_revision=2,
+        processed_revision=1,
+        sent_revision=1,
+        status=SentWebmentionStatus.SENT,
+        status_url="https://old.example/status/123",
+    )
+
+    mock_sender_requests(sender_module, monkeypatch, result=(400, None))
+
+    sender_module.send_webmention.call_local(identifier)
+
+    with app.app_context():
+        webmention = db.session.get(SentWebmention, identifier)
+
+        assert webmention is not None
+        assert webmention.processed_revision == 2
+        assert webmention.sent_revision == 1
+        assert webmention.status == SentWebmentionStatus.FAILED
+        assert webmention.failure_reason == "Webmention endpoint returned HTTP 400"
+        assert webmention.endpoint == ENDPOINT_URL
+        assert webmention.response_status == 400
+        assert webmention.status_url is None
+        assert not webmention.pending
+
+
+def test_send_webmention_persists_temporary_failure_and_reraises(
+    app: Flask, sender_module: ModuleType, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    identifier = create_sent_webmention(
+        app,
+        desired_revision=2,
+        processed_revision=1,
+        sent_revision=1,
+        status=SentWebmentionStatus.SENT,
+        status_url="https://old.example/status/123",
+    )
+
+    mock_sender_requests(sender_module, monkeypatch, result=(503, None))
+
+    with pytest.raises(
+        sender_module.TemporarySenderError,
+        match="Webmention endpoint returned HTTP 503",
+    ):
+        sender_module.send_webmention.call_local(identifier)
+
+    with app.app_context():
+        webmention = db.session.get(SentWebmention, identifier)
+
+        assert webmention is not None
+        assert webmention.processed_revision == 1
+        assert webmention.sent_revision == 1
+        assert webmention.status == SentWebmentionStatus.FAILED
+        assert webmention.failure_reason == "Webmention endpoint returned HTTP 503"
+        assert webmention.endpoint == ENDPOINT_URL
+        assert webmention.response_status == 503
+        assert webmention.status_url is None
+        assert webmention.pending
+
+
+def test_send_webmention_ignores_processed_revision(
+    app: Flask, sender_module: ModuleType, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    identifier = create_sent_webmention(
+        app,
+        desired_revision=2,
+        processed_revision=2,
+        sent_revision=2,
+        status=SentWebmentionStatus.SENT,
+    )
+
+    httpx_client, _, discover, post = mock_sender_requests(sender_module, monkeypatch)
+
+    sender_module.send_webmention.call_local(identifier)
+
+    httpx_client.assert_not_called()
+    discover.assert_not_called()
+    post.assert_not_called()
+
+
+def test_send_webmention_ignores_result_for_superseded_revision(
+    app: Flask, sender_module: ModuleType, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    identifier = create_sent_webmention(app)
+
+    _, _, _, post = mock_sender_requests(sender_module, monkeypatch)
+
+    def supersede_revision(*args, **kwargs) -> tuple[int, None]:
+        webmention = db.session.get(SentWebmention, identifier)
+
+        assert webmention is not None
+
+        webmention.desired_revision = 2
+        db.session.commit()
+
+        return (202, None)
+
+    post.side_effect = supersede_revision
+
+    sender_module.send_webmention.call_local(identifier)
+
+    with app.app_context():
+        webmention = db.session.get(SentWebmention, identifier)
+
+        assert webmention is not None
+        assert webmention.desired_revision == 2
+        assert webmention.processed_revision is None
+        assert webmention.sent_revision is None
+        assert webmention.status is None
+        assert webmention.pending
+
+
+def test_send_webmention_ignores_unknown_identifier(
+    sender_module: ModuleType, caplog: pytest.LogCaptureFixture
+) -> None:
+    identifier = uuid.uuid7()
+
+    with caplog.at_level(logging.WARNING):
+        sender_module.send_webmention.call_local(identifier)
+
+    assert f"Cannot send unknown SentWebmention {identifier}" in caplog.text
diff --git a/tests/test_forms.py b/tests/test_forms.py
index 417c655..73c6ffc 100644
--- a/tests/test_forms.py
+++ b/tests/test_forms.py
@@ -10,83 +10,54 @@ VALID_SOURCE = "https://source.example/post"
 VALID_TARGET = "https://dennisfink.me/blog/example/"
 
 
-@patch(
-    "webmentions_ssg.forms.validators.ensure_public_url",
-    new=lambda url: None,
-)
+@patch("webmentions_ssg.forms.validators.is_public_url", new=lambda url: True)
 @pytest.mark.parametrize(
-    (
-        "form_data",
-        "invalid_field",
-        "expected_error",
-    ),
+    ("form_data", "invalid_field", "expected_error"),
     [
         pytest.param(
-            {
-                "target": VALID_TARGET,
-            },
+            {"target": VALID_TARGET},
             "source",
             "This field is required.",
             id="source-required",
         ),
         pytest.param(
-            {
-                "source": "not a URL",
-                "target": VALID_TARGET,
-            },
+            {"source": "not a URL", "target": VALID_TARGET},
             "source",
             "Invalid URL.",
             id="source-url",
         ),
         pytest.param(
-            {
-                "source": "ftp://source.example/post",
-                "target": VALID_TARGET,
-            },
+            {"source": "ftp://source.example/post", "target": VALID_TARGET},
             "source",
             "source must begin with http or https",
             id="source-scheme",
         ),
         pytest.param(
-            {
-                "source": VALID_TARGET,
-                "target": VALID_TARGET,
-            },
+            {"source": VALID_TARGET, "target": VALID_TARGET},
             "source",
             None,
             id="source-not-equal-to-target",
         ),
         pytest.param(
-            {
-                "source": VALID_SOURCE,
-            },
+            {"source": VALID_SOURCE},
             "target",
             "This field is required.",
             id="target-required",
         ),
         pytest.param(
-            {
-                "source": VALID_SOURCE,
-                "target": "not a URL",
-            },
+            {"source": VALID_SOURCE, "target": "not a URL"},
             "target",
             "Invalid URL.",
             id="target-url",
         ),
         pytest.param(
-            {
-                "source": VALID_SOURCE,
-                "target": "ftp://dennisfink.me/blog/example/",
-            },
+            {"source": VALID_SOURCE, "target": "ftp://dennisfink.me/blog/example/"},
             "target",
             "target must begin with http or https",
             id="target-scheme",
         ),
         pytest.param(
-            {
-                "source": VALID_SOURCE,
-                "target": "https://example.com/post",
-            },
+            {"source": VALID_SOURCE, "target": "https://example.com/post"},
             "target",
             None,
             id="target-allowed-hostname",
@@ -99,14 +70,8 @@ def test_endpoint_form_rejects_invalid_data(
     invalid_field: str,
     expected_error: str | None,
 ) -> None:
-    with app.test_request_context(
-        "/endpoint",
-        method="POST",
-    ):
-        form = EndpointForm(
-            formdata=MultiDict(form_data),
-            meta={"csrf": False},
-        )
+    with app.test_request_context("/endpoint", method="POST"):
+        form = EndpointForm(formdata=MultiDict(form_data), meta={"csrf": False})
 
         assert not form.validate()
         assert invalid_field in form.errors
@@ -115,24 +80,11 @@ def test_endpoint_form_rejects_invalid_data(
             assert expected_error in form.errors[invalid_field]
 
 
-@patch(
-    "webmentions_ssg.forms.validators.ensure_public_url",
-    new=lambda url: None,
-)
-def test_endpoint_form_accepts_valid_data(
-    app: Flask,
-) -> None:
-    with app.test_request_context(
-        "/endpoint",
-        method="POST",
-    ):
+@patch("webmentions_ssg.forms.validators.is_public_url", new=lambda url: True)
+def test_endpoint_form_accepts_valid_data(app: Flask) -> None:
+    with app.test_request_context("/endpoint", method="POST"):
         form = EndpointForm(
-            formdata=MultiDict(
-                {
-                    "source": VALID_SOURCE,
-                    "target": VALID_TARGET,
-                }
-            ),
+            formdata=MultiDict({"source": VALID_SOURCE, "target": VALID_TARGET}),
             meta={"csrf": False},
         )
 
diff --git a/tests/test_url_security.py b/tests/test_url_security.py
index b10e6ff..ffa0378 100644
--- a/tests/test_url_security.py
+++ b/tests/test_url_security.py
@@ -1,11 +1,9 @@
 from unittest.mock import Mock, patch
 
+import dns.resolver
 import pytest
 
-from webmentions_ssg.url_security import (
-    NonPublicAddressError,
-    ensure_public_url,
-)
+from webmentions_ssg.url_security import AddressResolutionError, is_public_url
 
 
 @patch("webmentions_ssg.url_security.dns.resolver.resolve_name")
@@ -21,14 +19,50 @@ from webmentions_ssg.url_security import (
         ("http://169.254.169.254/", ["169.254.169.254"]),
         ("http://localhost/", ["127.0.0.1", "::1"]),
         ("http://internal.example/", ["192.168.1.10"]),
+        ("https://example.com/", ["93.184.216.34", "192.168.1.10"]),
+    ],
+)
+def test_is_public_url_returns_false_for_non_public_addresses(
+    resolve_name: Mock, url: str, resolved_addresses: list[str]
+) -> None:
+    resolve_name.return_value.addresses.return_value = resolved_addresses
+
+    assert not is_public_url(url)
+
+
+@patch("webmentions_ssg.url_security.dns.resolver.resolve_name")
+@pytest.mark.parametrize(
+    ("url", "resolved_addresses"),
+    [
+        ("https://example.com/", ["93.184.216.34"]),
+        (
+            "https://example.com/",
+            ["93.184.216.34", "2606:2800:220:1:248:1893:25c8:1946"],
+        ),
     ],
 )
-def test_ensure_public_url_rejects_non_public_addresses(
-    resolve_name: Mock,
-    url: str,
-    resolved_addresses: list[str],
+def test_is_public_url_returns_true_for_public_addresses(
+    resolve_name: Mock, url: str, resolved_addresses: list[str]
 ) -> None:
     resolve_name.return_value.addresses.return_value = resolved_addresses
 
-    with pytest.raises(NonPublicAddressError):
-        ensure_public_url(url)
+    assert is_public_url(url)
+
+
+@patch(
+    "webmentions_ssg.url_security.dns.resolver.resolve_name",
+    side_effect=dns.resolver.NXDOMAIN(),
+)
+def test_is_public_url_raises_for_resolution_failure(resolve_name: Mock) -> None:
+    with pytest.raises(AddressResolutionError, match="Could not resolve hostname"):
+        is_public_url("https://nonexistent.example/")
+
+    resolve_name.assert_called_once_with("nonexistent.example")
+
+
+@patch("webmentions_ssg.url_security.dns.resolver.resolve_name")
+def test_is_public_url_raises_when_url_has_no_hostname(resolve_name: Mock) -> None:
+    with pytest.raises(ValueError, match="No hostname was specified"):
+        is_public_url("/relative/url")
+
+    resolve_name.assert_not_called()
diff --git a/tests/test_views.py b/tests/test_views.py
index 06e546c..aac281e 100644
--- a/tests/test_views.py
+++ b/tests/test_views.py
@@ -1,29 +1,89 @@
 import uuid
+from datetime import datetime, timezone
 from unittest.mock import Mock, call, patch
 
+import pytest
 import sqlalchemy as sa
 from flask import Flask
 from flask.testing import FlaskClient
 
 from webmentions_ssg import DATABASE as db
-from webmentions_ssg.models import ReceivedWebmention
+from webmentions_ssg.models import (
+    ReceivedWebmention,
+    SentWebmention,
+    SentWebmentionStatus,
+    Source,
+    User,
+)
 
 
-def test_endpoint_only_accepts_post(
-    client: FlaskClient,
-) -> None:
+def log_in(app: Flask, client: FlaskClient) -> None:
+    with app.app_context():
+        user = User(username="admin")
+
+        db.session.add(user)
+        db.session.commit()
+
+        user_id = user.id
+
+    with client.session_transaction() as session:
+        session["_user_id"] = str(user_id)
+        session["_fresh"] = True
+
+
+def create_sent_source(app: Flask) -> uuid.UUID:
+    now = datetime.now(timezone.utc)
+
+    with app.app_context():
+        source = Source(
+            path="blog/example/index.html",
+            url="https://dennisfink.me/blog/example/",
+            content_hash="0" * 32,
+            revision=2,
+            last_seen_at=now,
+            revised_at=now,
+        )
+
+        source.sent_webmentions.extend(
+            [
+                SentWebmention(
+                    target="https://example.com/b",
+                    active=True,
+                    desired_revision=2,
+                    processed_revision=2,
+                    sent_revision=2,
+                    status=SentWebmentionStatus.SENT,
+                    endpoint="https://example.com/webmention",
+                    response_status=202,
+                ),
+                SentWebmention(
+                    target="https://example.com/a",
+                    active=True,
+                    desired_revision=2,
+                    processed_revision=2,
+                    sent_revision=1,
+                    status=SentWebmentionStatus.FAILED,
+                    failure_reason="Webmention endpoint returned HTTP 400",
+                    endpoint="https://example.com/webmention",
+                    response_status=400,
+                ),
+            ]
+        )
+
+        db.session.add(source)
+        db.session.commit()
+
+        return source.uuid
+
+
+def test_endpoint_only_accepts_post(client: FlaskClient) -> None:
     response = client.get("/endpoint")
 
     assert response.status_code == 405
 
 
-@patch(
-    "webmentions_ssg.forms.validators.ensure_public_url",
-    new=lambda url: None,
-)
-def test_endpoint_returns_form_errors(
-    client: FlaskClient,
-) -> None:
+@patch("webmentions_ssg.forms.validators.is_public_url", new=lambda url: True)
+def test_endpoint_returns_form_errors(client: FlaskClient) -> None:
     response = client.post(
         "/endpoint",
         data={
@@ -40,26 +100,15 @@ def test_endpoint_returns_form_errors(
     assert "target" in errors
 
 
-@patch(
-    "webmentions_ssg.forms.validators.ensure_public_url",
-    new=lambda url: None,
-)
+@patch("webmentions_ssg.forms.validators.is_public_url", new=lambda url: True)
 @patch("webmentions_ssg.views.verify_webmention")
 def test_endpoint_creates_webmention(
-    verify_webmention: Mock,
-    app: Flask,
-    client: FlaskClient,
+    verify_webmention: Mock, app: Flask, client: FlaskClient
 ) -> None:
     source = "https://source.example/post"
     target = "https://dennisfink.me/blog/example/"
 
-    response = client.post(
-        "/endpoint",
-        data={
-            "source": source,
-            "target": target,
-        },
-    )
+    response = client.post("/endpoint", data={"source": source, "target": target})
 
     assert response.status_code == 201
 
@@ -78,29 +127,18 @@ def test_endpoint_creates_webmention(
     verify_webmention.assert_called_once_with(identifier)
 
 
-@patch(
-    "webmentions_ssg.forms.validators.ensure_public_url",
-    new=lambda url: None,
-)
+@patch("webmentions_ssg.forms.validators.is_public_url", new=lambda url: True)
 @patch("webmentions_ssg.views.verify_webmention")
 def test_endpoint_is_idempotent(
-    verify_webmention: Mock,
-    app: Flask,
-    client: FlaskClient,
+    verify_webmention: Mock, app: Flask, client: FlaskClient
 ) -> None:
     data = {
         "source": "https://source.example/post",
         "target": "https://dennisfink.me/blog/example/",
     }
 
-    first_response = client.post(
-        "/endpoint",
-        data=data,
-    )
-    second_response = client.post(
-        "/endpoint",
-        data=data,
-    )
+    first_response = client.post("/endpoint", data=data)
+    second_response = client.post("/endpoint", data=data)
 
     assert first_response.status_code == 201
     assert second_response.status_code == 201
@@ -120,21 +158,13 @@ def test_endpoint_is_idempotent(
 
         identifier = webmention.uuid
 
-    assert verify_webmention.call_args_list == [
-        call(identifier),
-        call(identifier),
-    ]
+    assert verify_webmention.call_args_list == [call(identifier), call(identifier)]
 
 
-@patch(
-    "webmentions_ssg.forms.validators.ensure_public_url",
-    new=lambda url: None,
-)
+@patch("webmentions_ssg.forms.validators.is_public_url", new=lambda url: True)
 @patch("webmentions_ssg.views.verify_webmention")
 def test_resending_resets_failure_state(
-    verify_webmention: Mock,
-    app: Flask,
-    client: FlaskClient,
+    verify_webmention: Mock, app: Flask, client: FlaskClient
 ) -> None:
     source = "https://source.example/post"
     target = "https://dennisfink.me/blog/example/"
@@ -153,24 +183,72 @@ def test_resending_resets_failure_state(
 
         identifier = existing.uuid
 
-    response = client.post(
-        "/endpoint",
-        data={
-            "source": source,
-            "target": target,
-        },
-    )
+    response = client.post("/endpoint", data={"source": source, "target": target})
 
     assert response.status_code == 201
 
     with app.app_context():
-        webmention = db.session.get(
-            ReceivedWebmention,
-            identifier,
-        )
+        webmention = db.session.get(ReceivedWebmention, identifier)
 
         assert webmention is not None
         assert webmention.status == "received"
         assert webmention.failure_reason is None
 
     verify_webmention.assert_called_once_with(identifier)
+
+
+@pytest.mark.parametrize("path", ["/sent", f"/sent/{uuid.uuid7()}"])
+def test_sent_views_require_login(client: FlaskClient, path: str) -> None:
+    response = client.get(path)
+
+    assert response.status_code == 302
+    assert "/login" in response.headers["Location"]
+
+
+def test_sent_lists_sources(app: Flask, client: FlaskClient) -> None:
+    log_in(app, client)
+    identifier = create_sent_source(app)
+
+    response = client.get("/sent")
+
+    assert response.status_code == 200
+
+    html = response.get_data(as_text=True)
+
+    assert "blog/example/index.html" in html
+    assert "https://dennisfink.me/blog/example/" in html
+    assert f"/sent/{identifier}" in html
+
+
+def test_sent_source_lists_webmentions(app: Flask, client: FlaskClient) -> None:
+    log_in(app, client)
+    identifier = create_sent_source(app)
+
+    response = client.get(f"/sent/{identifier}")
+
+    assert response.status_code == 200
+
+    html = response.get_data(as_text=True)
+
+    assert "blog/example/index.html" in html
+    assert "https://dennisfink.me/blog/example/" in html
+
+    first_target = "https://example.com/a"
+    second_target = "https://example.com/b"
+
+    assert first_target in html
+    assert second_target in html
+    assert html.index(first_target) < html.index(second_target)
+
+    assert "Webmention endpoint returned HTTP 400" in html
+    assert "https://example.com/webmention" in html
+
+
+def test_sent_source_returns_404_for_unknown_source(
+    app: Flask, client: FlaskClient
+) -> None:
+    log_in(app, client)
+
+    response = client.get(f"/sent/{uuid.uuid7()}")
+
+    assert response.status_code == 404