Add span requirements for ABC rank

A requires ≥75% span, B ≥50%, C ≥25%. Prevents short arcs
(like Vogler 5/22 = 23%) from getting B rank.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: BirdInTheTree

src/tvplotlines/postprocess.py

@@ -157,25 +157,35 @@ def compute_ranks(
                 plotline.computed_rank = "B"
             fixed_ids.add(plotline.id)
 
-    # Phase 2: remaining plotlines sorted by event count
+    # Phase 2: remaining plotlines sorted by event count, filtered by span
+    n_episodes = len(episodes)
     remaining = [p for p in plotlines if p.id not in fixed_ids]
     remaining.sort(key=lambda p: (-event_counts.get(p.id, 0), p.id))
 
     logger.info(
         "Rank assignment order: %s",
-        [(p.id, event_counts.get(p.id, 0)) for p in remaining],
+        [(p.id, event_counts.get(p.id, 0), len(p.span)) for p in remaining],
     )
 
+    # Span requirements: A ≥ 75%, B ≥ 50%, C ≥ 25%
     for i, plotline in enumerate(remaining):
-        if i == 0 and not is_a_taken:
+        span_frac = len(plotline.span) / n_episodes if n_episodes else 0
+        if i == 0 and not is_a_taken and span_frac >= 0.75:
             plotline.computed_rank = "A"
             is_a_taken = True
-        elif i <= 1:
-            # Second plotline (or first when A is taken by case_of_the_week)
-            plotline.computed_rank = "B"
-        else:
+        elif i <= 1 and span_frac >= 0.50:
+            plotline.computed_rank = "B" if is_a_taken else "A"
+            if plotline.computed_rank == "A":
+                is_a_taken = True
+        elif span_frac >= 0.25:
             plotline.computed_rank = "C"
-        logger.info("  %s → %s (events=%d)", plotline.id, plotline.computed_rank, event_counts.get(plotline.id, 0))
+        else:
+            plotline.computed_rank = "C"  # low span but still serialized, not runner
+        logger.info(
+            "  %s → %s (events=%d, span=%d/%d=%.0f%%)",
+            plotline.id, plotline.computed_rank, event_counts.get(plotline.id, 0),
+            len(plotline.span), n_episodes, span_frac * 100,
+        )
 
 
 def validate_ranks(

tests/test_postprocess.py

@@ -147,12 +147,17 @@ def _make_plotline_no_rank(id: str, ptype: str = "serialized") -> Plotline:
 
 class TestComputeRanks:
     def test_serial_assigns_a_b_c(self):
-        """Most events → A, second → B, rest → C."""
+        """Most events → A, second → B, rest → C. Span must meet thresholds."""
         ctx = SeriesContext(format="serial", story_engine="x", genre="drama")
         lines = [_make_plotline_no_rank("big"), _make_plotline_no_rank("mid"), _make_plotline_no_rank("small")]
+        # 4 episodes so span fractions are: big=4/4=100%, mid=3/4=75%, small=2/4=50%
         episodes = [
-            _make_episode("S01E01", ["big", "big", "big", "mid", "mid", "small"]),
+            _make_episode("S01E01", ["big", "big", "mid", "small"]),
+            _make_episode("S01E02", ["big", "big", "mid", "small"]),
+            _make_episode("S01E03", ["big", "mid"]),
+            _make_episode("S01E04", ["big"]),
         ]
+        compute_span(lines, episodes)
         compute_ranks(lines, episodes, ctx)
         assert lines[0].computed_rank == "A"
         assert lines[1].computed_rank == "B"
@@ -163,6 +168,7 @@ def test_runner_gets_no_rank(self):
         runner = _make_plotline_no_rank("bg", ptype="runner")
         main = _make_plotline_no_rank("main")
         episodes = [_make_episode("S01E01", ["main", "main"])]
+        compute_span([runner, main], episodes)
         compute_ranks([runner, main], episodes, ctx)
         assert runner.computed_rank is None
         assert main.computed_rank == "A"
@@ -173,6 +179,7 @@ def test_procedural_case_of_week_gets_a(self):
         arc = _make_plotline_no_rank("arc")
         # arc has more events, but cotw is fixed at A for procedural
         episodes = [_make_episode("S01E01", ["arc", "arc", "arc", "case"])]
+        compute_span([cotw, arc], episodes)
         compute_ranks([cotw, arc], episodes, ctx)
         assert cotw.computed_rank == "A"
         assert arc.computed_rank == "B"
@@ -182,6 +189,7 @@ def test_hybrid_case_of_week_gets_b(self):
         cotw = _make_plotline_no_rank("case", ptype="case_of_the_week")
         arc = _make_plotline_no_rank("arc")
         episodes = [_make_episode("S01E01", ["arc", "case", "case"])]
+        compute_span([cotw, arc], episodes)
         compute_ranks([cotw, arc], episodes, ctx)
         assert cotw.computed_rank == "B"
         assert arc.computed_rank == "A"
@@ -203,6 +211,7 @@ def test_also_affects_counted_equally(self):
             ],
             theme="t",
         )
+        compute_span([main, side], [ep])
         compute_ranks([main, side], [ep], ctx)
         # main: 2 primary + 0 AA = 2. side: 1 primary + 2 AA = 3. side wins.
         assert side.computed_rank == "A"