feat(flashcard): support multi-tag drill headings + --tag-filter / --guid-salt

Craig wanted a curated "DeepSat Fundamentals" deck: the ~100 most fundamental cards out of the 465-card deepsat.org deck, marked with a second org tag (:fundamental:) so they stay grep-able in the source. Both flashcard-to-anki.py and flashcard-stats.py keyed a card on a heading ending in exactly :drill:, so adding any second tag turned the heading into :fundamental:drill:, which that anchor didn't match. The 100 tagged cards would have silently dropped from the full-deck apkg and been undercounted by stats. That's the passing-gate-skips-your-file failure.

CARD_RE now matches a trailing org tag block, and a heading is a card when drill is among its tags. The other tags ride along as Anki tags next to the section tag. Card bodies are bounded by any L1/L2 heading (HEADING_RE) rather than only a section or a drill heading. flashcard-to-anki.py gains --tag-filter <tag> (emit only cards carrying that org tag, the subset deck) and --guid-salt <s> (a distinct GUID space so the subset imports non-empty instead of colliding with the full deck on GUID and importing empty). No salt is unchanged, so the existing deck's GUIDs and SRS state are untouched. flashcard-stats.py gets the same CARD_RE/HEADING_RE broadening plus a drill-membership guard.

This is the rulesets-canonical reconcile of a stopgap the work project ran locally. I re-derived it against the current canonical rather than copying the preserved files, which predate the #+TITLE deck-name fix (060a938) and would have reverted it.

parse()'s third element is now the Anki-tag list rather than a single tag string. Only build() and the tests consumed it. The existing parse tests move to the list contract, and new tests cover multi-tag parsing, --tag-filter, the guid salt, and the stats count. A bats case guards that a :fundamental:drill: card still counts. The full deck's real 465/100 check needs the work deck and isn't runnable here. Verified end to end instead on a synthetic multi-tag deck (2 cards, --tag-filter fundamental returns 1) through the real genanki path.

1 files changed, 25 insertions, 0 deletions

diff --git a/.ai/scripts/tests/test_flashcard_stats.py b/.ai/scripts/tests/test_flashcard_stats.py
index 606f7c1..46deccc 100644
--- a/.ai/scripts/tests/test_flashcard_stats.py
+++ b/.ai/scripts/tests/test_flashcard_stats.py
@@ -217,6 +217,31 @@ def test_parse_cards_captures_body_without_drawer_planning_or_answer_header(stat
     assert c["body"] == "the real answer"
 
 
+def test_parse_cards_counts_a_multitag_heading_as_a_card(stats):
+    """A card multi-tagged :fundamental:drill: still counts; the front is clean."""
+    text = "* Sec\n** Q multi? :fundamental:drill:\nthe answer\n"
+    cards, _ = stats.parse_cards(text.splitlines())
+    assert len(cards) == 1
+    assert cards[0]["heading"] == "Q multi?"
+    assert cards[0]["body"] == "the answer"
+
+
+def test_parse_cards_ignores_a_tagged_heading_without_drill(stats):
+    """A tagged heading missing :drill: is not a drill card."""
+    text = "* Sec\n** Just a note :note:\nbody\n"
+    cards, _ = stats.parse_cards(text.splitlines())
+    assert cards == []
+
+
+def test_parse_cards_body_stops_at_next_multitag_card(stats):
+    """The body scan ends at the next L2 card even when it is multi-tagged."""
+    text = "** Q1? :a:drill:\nbody1\n** Q2? :drill:\nbody2\n"
+    cards, _ = stats.parse_cards(text.splitlines())
+    assert len(cards) == 2
+    assert cards[0]["body"] == "body1"
+    assert cards[1]["body"] == "body2"
+
+
 def test_find_duplicate_fronts_matches_normalized_headings(stats):
     cards = [
         {"heading": "What is LEO?"},