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, 57 insertions, 4 deletions

diff --git a/.ai/scripts/tests/test_flashcard_to_anki.py b/.ai/scripts/tests/test_flashcard_to_anki.py
index 87008a8..fa38b64 100644
--- a/.ai/scripts/tests/test_flashcard_to_anki.py
+++ b/.ai/scripts/tests/test_flashcard_to_anki.py
@@ -158,17 +158,18 @@ Geostationary Earth Orbit.
 def test_parse_returns_front_back_tag_per_card(drill):
     cards = drill.parse(SECTIONED)
     assert len(cards) == 2
-    assert cards[0] == ("What is LEO?", "Low Earth Orbit.", "orbital-regimes")
+    # The section becomes the sole Anki tag (as a one-element list).
+    assert cards[0] == ("What is LEO?", "Low Earth Orbit.", ["orbital-regimes"])
     assert cards[1][0] == "What is GEO?"
 
 
 def test_parse_card_without_a_section_gets_the_drill_tag(drill):
-    assert drill.parse("** Lone card? :drill:\nbody\n") == [("Lone card?", "body", "drill")]
+    assert drill.parse("** Lone card? :drill:\nbody\n") == [("Lone card?", "body", ["drill"])]
 
 
 def test_parse_strips_properties_drawer_from_back(drill):
     text = "** Q? :drill:\n:PROPERTIES:\n:ID: abc\n:END:\nThe answer.\n"
-    assert drill.parse(text) == [("Q?", "The answer.", "drill")]
+    assert drill.parse(text) == [("Q?", "The answer.", ["drill"])]
 
 
 def test_parse_trims_leading_and_trailing_blank_body_lines(drill):
@@ -178,7 +179,59 @@ def test_parse_trims_leading_and_trailing_blank_body_lines(drill):
 
 def test_parse_card_with_only_a_drawer_has_empty_back(drill):
     text = "** Q? :drill:\n:PROPERTIES:\n:ID: x\n:END:\n"
-    assert drill.parse(text) == [("Q?", "", "drill")]
+    assert drill.parse(text) == [("Q?", "", ["drill"])]
+
+
+# --- multi-tag headings, --tag-filter, --guid-salt -------------------------
+
+MULTITAG = """* Fundamentals
+** What is LEO? :fundamental:drill:
+Low Earth Orbit.
+** What is GEO? :drill:
+Geostationary Earth Orbit.
+"""
+
+
+def test_parse_multitag_heading_is_a_card_when_drill_is_present(drill):
+    """A heading with a second org tag still parses when drill is among them."""
+    cards = drill.parse(MULTITAG)
+    assert len(cards) == 2
+    assert cards[0][0] == "What is LEO?"
+
+
+def test_parse_multitag_tags_ride_along_next_to_the_section_tag(drill):
+    """Non-drill org tags become Anki tags alongside the section tag."""
+    cards = drill.parse(MULTITAG)
+    assert cards[0][2] == ["fundamentals", "fundamental"]  # section slug + org tag
+    assert cards[1][2] == ["fundamentals"]                 # drill-only -> section only
+
+
+def test_parse_heading_without_drill_tag_is_not_a_card(drill):
+    """A tagged heading missing :drill: is not a card (e.g. :note:)."""
+    assert drill.parse("* S\n** Just a note :note:\nbody\n") == []
+
+
+def test_parse_tag_filter_returns_only_cards_with_that_org_tag(drill):
+    """--tag-filter narrows to cards carrying the given org tag."""
+    cards = drill.parse(MULTITAG, tag_filter="fundamental")
+    assert len(cards) == 1
+    assert cards[0][0] == "What is LEO?"
+
+
+def test_parse_body_bounded_by_any_l1_or_l2_heading(drill):
+    """A card body stops at the next L1/L2 heading, multi-tagged or not."""
+    text = "** Q1? :a:drill:\nbody1\n** Q2? :drill:\nbody2\n"
+    cards = drill.parse(text)
+    assert cards[0][1] == "body1"
+    assert cards[1][1] == "body2"
+
+
+def test_card_guid_salt_changes_the_guid(drill, monkeypatch):
+    """--guid-salt gives a subset deck its own GUID space; no salt is unchanged."""
+    monkeypatch.setattr(drill.genanki, "guid_for", lambda *a: ":".join(a), raising=False)
+    assert drill.card_guid("front", None) == "front"
+    assert drill.card_guid("front", "fundamentals") == "fundamentals:front"
+    assert drill.card_guid("front", None) != drill.card_guid("front", "fundamentals")
 
 
 def test_parse_joins_multiline_body_with_br(drill):