test: add indexer unit tests + integration marker; make indexer importable without env

- pytest.ini: 'integration' marker, deselected by default; the integration
  suite requires a live Qdrant and will only run in the nightly CI job.
- src/indexer.py: move env validation from import time into _validate_config()
  called by main() — the module can now be imported without MAILDIR_PATH /
  QDRANT_URL / COLLECTION_NAME set, enabling unit tests.
- tests/test_indexer.py: 27 new unit tests, no network and no model:
  decode_mime_words (encoded-words utf-8/iso-8859-1, mixed), extract_text_from_html
  (tags, scripts), normalize_email_address, parse_email_message with real
  EmailMessage objects (plain bodies, attachments detected and excluded from
  body, HTML alternative, unknown charset fallback via raw bytes message,
  encoded attachment filename), get_recent_keys against a real tmp_path
  Maildir (fresh mtime selected, old mtime excluded, colon-suffix keys).
  mailbox.Maildir(create=True) does not create cur/new/tmp on Python 3.11 —
  the test helper pre-creates them.

tests/test_indexer.py

@@ -0,0 +1,229 @@
+"""Unit tests for mcp-maildir indexer parsing functions.
+
+Pure-function tests: no Qdrant, no embedding model, no network.
+A throwaway Maildir is built in tmp_path for get_recent_keys().
+"""
+
+import mailbox
+import os
+import time
+import uuid
+from datetime import datetime, timezone, timedelta
+from email.message import EmailMessage
+from email.utils import format_datetime
+
+import pytest
+
+from indexer import (
+    decode_mime_words,
+    extract_text_from_html,
+    normalize_email_address,
+    parse_email_message,
+    get_recent_keys,
+    METADATA_COLLECTION,
+)
+
+
+# ---------------------------------------------------------------------------
+# decode_mime_words
+# ---------------------------------------------------------------------------
+
+class TestDecodeMimeWords:
+    def test_empty_and_none(self):
+        assert decode_mime_words("") == ""
+        assert decode_mime_words(None) == ""
+
+    def test_plain_ascii(self):
+        assert decode_mime_words("Hello World") == "Hello World"
+
+    def test_encoded_word_utf8(self):
+        # =?utf-8?q?...?= encoded word
+        assert decode_mime_words("=?utf-8?q?Caf=C3=A9_au_lait?=") == "Café au lait"
+
+    def test_encoded_word_iso8859(self):
+        # decode_mime_words does not strip whitespace around the words
+        assert decode_mime_words("=?iso-8859-1?q?caf=E9?=") == "café"
+
+    def test_mixed_encoded_and_plain(self):
+        assert decode_mime_words("Re: =?utf-8?q?planning_2026?=") == "Re: planning 2026"
+
+
+# ---------------------------------------------------------------------------
+# extract_text_from_html
+# ---------------------------------------------------------------------------
+
+class TestExtractTextFromHtml:
+    def test_simple_paragraphs(self):
+        html = "<html><body><p>Hello</p><p>World</p></body></html>"
+        assert extract_text_from_html(html) == "Hello World"
+
+    def test_strips_tags_and_scripts(self):
+        html = "<div>Sign<span>ature</span><script>evil()</script>End</div>"
+        text = extract_text_from_html(html)
+        assert "evil()" not in text
+        # get_text uses separator=" ", so tags become whitespace
+        assert "Sign" in text and "ature" in text and "End" in text
+
+    def test_fallback_on_invalid_content(self):
+        # Garbage that would make the parser blow up should not raise
+        assert extract_text_from_html(None) is None
+
+
+# ---------------------------------------------------------------------------
+# parse_email_message — real mailbox.Message objects (no mocks)
+# ---------------------------------------------------------------------------
+
+def build_email(
+    subject="Hello",
+    body="This is the body.",
+    html=None,
+    attachments=None,
+    charset="utf-8",
+):
+    """Builds a real EmailMessage, optionally multipart with attachments."""
+    msg = EmailMessage()
+    msg["Subject"] = subject
+    msg["From"] = "Alice <alice@example.com>"
+    msg["To"] = "Bob <bob@example.com>"
+    msg["Message-ID"] = "<build-email@example.com>"
+    msg["Date"] = format_datetime(datetime(2026, 1, 15, 10, 0, 0, tzinfo=timezone.utc))
+
+    if html:
+        msg.set_content(body)
+        msg.add_alternative(html, subtype="html")
+    else:
+        msg.set_content(body, charset=charset)
+
+    for filename, content in (attachments or {}).items():
+        payload = content if isinstance(content, bytes) else content.encode()
+        msg.add_attachment(payload, maintype="application",
+                           subtype="octet-stream", filename=filename)
+    return msg
+
+
+def build_raw_email(raw_bytes: bytes):
+    """Parses raw email bytes (for exotic headers without EmailMessage helpers)."""
+    import email as email_mod
+    return email_mod.message_from_bytes(raw_bytes)
+
+
+class TestParseEmailMessage:
+    def test_plain_text_body(self):
+        msg = build_email(body="Line one.\nLine two.")
+        body, attachments = parse_email_message(msg)
+        assert "Line one." in body and "Line two." in body
+        assert attachments == []
+
+    def test_attachments_detected_and_excluded_from_body(self):
+        msg = build_email(
+            body="See attached.",
+            attachments={"report.pdf": b"%PDF-fake", "notes.txt": b"notes"},
+        )
+        body, attachments = parse_email_message(msg)
+        assert attachments == ["report.pdf", "notes.txt"]
+        assert "%PDF" not in body
+        assert "See attached." in body
+
+    def test_html_alternative_extracts_text(self):
+        msg = build_email(
+            body="Fallback plain text.",
+            html="<html><body><b>Bold</b> intro</body></html>",
+        )
+        body, _ = parse_email_message(msg)
+        assert "Bold" in body and "intro" in body
+
+    def test_unknown_charset_falls_back_not_crash(self):
+        # A payload claiming an unknown charset must not raise.
+        # Built from raw bytes: EmailMessage.set_content(charset=...) would
+        # reject the unknown encoding at build time, real mail does not.
+        raw = (
+            b"Subject: broken charset\n"
+            b"From: alice@example.com\n"
+            b"To: bob@example.com\n"
+            b"Content-Type: text/plain; charset=x-unknown-charset\n"
+            b"Content-Transfer-Encoding: 8bit\n\n"
+            b"body with broken charset\n"
+        )
+        msg = build_raw_email(raw)
+        body, attachments = parse_email_message(msg)
+        # Whatever the fallback, we must get a string body and no exception
+        assert isinstance(body, str)
+        assert attachments == []
+
+    def test_encoded_attachment_filename_decoded(self):
+        msg = build_email(
+            body="body",
+            attachments={},
+        )
+        # Add attachment with non-ascii filename via encoded word
+        msg.add_attachment(b"data", maintype="application", subtype="pdf",
+                           filename="café-rapport.pdf")
+        body, attachments = parse_email_message(msg)
+        assert attachments == ["café-rapport.pdf"]
+
+
+# ---------------------------------------------------------------------------
+# normalize_email_address (indexer copy — same contract as server.py)
+# ---------------------------------------------------------------------------
+
+class TestIndexerNormalizeEmailAddress:
+    def test_display_name(self):
+        assert normalize_email_address("John Doe <john@example.com>") == "john@example.com"
+
+    def test_case_and_whitespace(self):
+        assert normalize_email_address("  USER@Example.COM ") == "user@example.com"
+
+    def test_empty(self):
+        assert normalize_email_address("") == ""
+        assert normalize_email_address(None) == ""
+
+
+# ---------------------------------------------------------------------------
+# get_recent_keys — real Maildir on disk (tmp_path), mtime-driven
+# ---------------------------------------------------------------------------
+
+def make_maildir(root):
+    """Opens a Maildir at root — pre-creates cur/new/tmp because mailbox.Maildir
+    (Python 3.11) does not create them when adding a message."""
+    for sub in ("cur", "new", "tmp"):
+        os.makedirs(os.path.join(str(root), sub), exist_ok=True)
+    return mailbox.Maildir(str(root), create=False)
+
+
+def write_maildir_message(maildir: mailbox.Maildir, msg: EmailMessage):
+    """Adds a message and returns its key."""
+    return maildir.add(msg)
+
+
+class TestGetRecentKeys:
+    def test_recent_file_selected(self, tmp_path):
+        md = make_maildir(tmp_path)
+        msg = build_email()
+        md.add(msg)
+        md.flush()
+        # mtime is now → within the window
+        keys = get_recent_keys(md, days=7)
+        assert len(keys) == 1
+
+    def test_old_file_excluded(self, tmp_path):
+        md = make_maildir(tmp_path)
+        md.add(build_email())
+        md.flush()
+        # Age every file beyond the cutoff
+        old = time.time() - 30 * 86400
+        for path in tmp_path.rglob("*.??*"):
+            if path.is_file():
+                os.utime(path, (old, old))
+        keys = get_recent_keys(md, days=7)
+        assert len(keys) == 0
+
+    def test_key_is_suffixless_filename(self, tmp_path):
+        """Maildir keys strip the ':2,S' info suffix — get_recent_keys must match."""
+        md = make_maildir(tmp_path)
+        key = md.add(build_email())
+        md.flush()
+        keys = get_recent_keys(md, days=7)
+        assert keys  # non-empty set of keys for fresh files
+        assert key.split(":")[0] in keys
+        for k in keys:
+            assert ":" not in k