feature(1100): Discover .markdown posts and always log run summary

Extend the anniversary matcher to recursively scan both .md and
.markdown posts under _posts/blog, retaining the existing filename
validation and relative-path dedupe identifier so published-state
bookkeeping keeps working.

Drop the zero-counter short-circuit in log_run_summary so the
run_complete line is always emitted on a successful pass. Debug and
manual runs now clearly show that scanning completed and found
nothing instead of going silent.

Update matching, logging, and run-logging tests to cover the new
extension and always-emit contract, and refresh the logging
architecture doc accordingly.

tests/test_logging_setup.py

@@ -61,10 +61,19 @@ def test_log_run_summary_emits_one_line_with_counters() -> None:
     assert payload["posted_ids"] == ["x"]
 
 
-def test_log_run_summary_silent_when_no_matches() -> None:
+def test_log_run_summary_always_emits_summary_line_with_zero_counters() -> None:
     buf = _capture(logging.getLogger("tenbackward"))
     log_run_summary(0, 0, 0, 0, [])
-    assert buf.getvalue() == ""
+    lines = [line for line in buf.getvalue().splitlines() if line.strip()]
+    assert len(lines) == 1
+    payload = json.loads(lines[0])
+    assert payload["message"] == "run complete"
+    assert payload["event"] == "run_complete"
+    assert payload["scanned"] == 0
+    assert payload["matched"] == 0
+    assert payload["posted"] == 0
+    assert payload["skipped"] == 0
+    assert payload["posted_ids"] == []
 
 
 def test_log_startup_emits_single_info_line() -> None:

tests/test_matching.py

@@ -222,6 +222,48 @@ def test_missing_post_root_returns_empty(tmp_path: Path) -> None:
     assert find_anniversary_matches(tmp_path / "does-not-exist", SITE_URL, today=today) == []
 
 
+def test_markdown_extension_is_discovered(tmp_path: Path) -> None:
+    root = tmp_path / "_posts" / "blog"
+    _write_post(
+        root,
+        "2014/2014-08-04-foo.markdown",
+        body="---\ntitle: Foo\ndate: 2014-08-04\n---\nbody\n",
+    )
+
+    today = date(2024, 8, 4)
+    matches = find_anniversary_matches(root, SITE_URL, today=today)
+
+    assert len(matches) == 1
+    match = matches[0]
+    assert match.path == "2014/2014-08-04-foo.markdown"
+    assert match.title == "Foo"
+    assert match.date == date(2014, 8, 4)
+    assert match.url == "https://chaospott.de/2014/08/04/foo/"
+
+
+def test_markdown_and_md_are_discovered_together(tmp_path: Path) -> None:
+    root = tmp_path / "_posts" / "blog"
+    _write_post(
+        root,
+        "2014/2014-08-04-from-md.md",
+        body="---\ntitle: Md\ndate: 2014-08-04\n---\n",
+    )
+    _write_post(
+        root,
+        "2014/2014-08-04-from-markdown.markdown",
+        body="---\ntitle: Markdown\ndate: 2014-08-04\n---\n",
+    )
+
+    today = date(2024, 8, 4)
+    matches = find_anniversary_matches(root, SITE_URL, today=today)
+
+    paths = {m.path for m in matches}
+    assert paths == {
+        "2014/2014-08-04-from-md.md",
+        "2014/2014-08-04-from-markdown.markdown",
+    }
+
+
 def test_invalid_filename_is_skipped(tmp_path: Path) -> None:
     root = tmp_path / "_posts" / "blog"
     _write_post(root, "2014/not-a-date.md", body="---\ntitle: Bad\n---\n")

tests/test_run_logging.py

@@ -80,7 +80,7 @@ def test_run_emits_one_info_summary_on_success(env_setup, data_dir, capture_logg
     assert "already-1" in state
 
 
-def test_run_silent_when_no_matches(env_setup, data_dir, capture_logger, monkeypatch) -> None:
+def test_run_emits_zero_summary_when_no_matches(env_setup, data_dir, capture_logger, monkeypatch) -> None:
     monkeypatch.setenv("DATA_DIR", str(data_dir))
     monkeypatch.setattr(main_module, "ensure_repo", lambda *a, **kw: None)
     monkeypatch.setattr(main_module, "_iter_candidates", lambda config: [])
@@ -90,7 +90,13 @@ def test_run_silent_when_no_matches(env_setup, data_dir, capture_logger, monkeyp
 
     lines = _run_lines(capture_logger)
     summary = [line for line in lines if line.get("event") == "run_complete"]
-    assert summary == []
+    assert len(summary) == 1
+    payload = summary[0]
+    assert payload["scanned"] == 0
+    assert payload["matched"] == 0
+    assert payload["posted"] == 0
+    assert payload["skipped"] == 0
+    assert payload["posted_ids"] == []
 
 
 def test_run_returns_nonzero_on_pipeline_error(env_setup, data_dir, capture_logger, monkeypatch) -> None: