fix(scoring): parse underscores in fractional upstream constants

src/scoring/model.ts

@@ -150,13 +150,13 @@
   return stalenessWarning ? { ...snapshot, warnings: [...snapshot.warnings, stalenessWarning] } : snapshot;
 }
 
 export function parsePythonNumberConstants(source: string, options: { knownOnly?: boolean } = { knownOnly: true }): Record<string, number> {
   const constants: Record<string, number> = {};
   for (const line of source.split("\n")) {
-    // Match Python numeric literals including underscore separators (1_000_000), floats, and exponents
-    // (1e-9, 5.8e1). The previous /[-+]?\d+(?:\.\d+)?/ stopped at `_`/`e`, truncating 1_000_000 -> 1 and
-    // 1e-9 -> 1, which silently misparsed any such upstream constant and polluted the unmodeled list (#810).
-    const match = line.match(/^([A-Z][A-Z0-9_]+)\s*=\s*([-+]?(?:\d[\d_]*\.?\d*|\.\d+)(?:[eE][-+]?\d+)?)/);
+    // Match Python numeric literals including underscore separators in integer and fractional parts
+    // (1_000_000, 0.000_001, 3.14_15), floats, and exponents (1e-9, 5.8e1). The previous regex only
+    // allowed `_` in the integer part, truncating 0.000_001 -> 0 and 3.14_15 -> 3.14 (#992).
+    const match = line.match(/^([A-Z][A-Z0-9_]+)\s*=\s*([-+]?(?:\d[\d_]*\.?[\d_]*|\.\d[\d_]*)(?:[eE][-+]?\d+)?)/);
     if (!match) continue;
     const name = match[1]!;
     const raw = match[2]!;

test/unit/scoring.test.ts

@@ -83,9 +83,25 @@
     expect(parsed.CONTRIBUTION_SCORE_FOR_FULL_BONUS).toBe(1500000);
     expect(parsed.SRC_TOK_SATURATION_SCALE).toBe(58);
     expect(parsed.MERGED_PR_BASE_SCORE).toBe(1e-9);
     expect(parsed.OSS_EMISSION_SHARE).toBe(0.9);
   });
 
+  it("parses underscore separators in the fractional part of upstream constants (#992)", () => {
+    const parsed = parsePythonNumberConstants(
+      `
+RATE = 0.000_001
+SCALE = 3.14_15
+VAL = 1_000.000_5
+BARE = .5_0
+`,
+      { knownOnly: false },
+    );
+    expect(parsed.RATE).toBe(0.000001);
+    expect(parsed.SCALE).toBe(3.1415);
+    expect(parsed.VAL).toBe(1000.0005);
+    expect(parsed.BARE).toBe(0.5);
+  });
+
   it("flags only scoring snapshots older than the freshness window as stale (#810)", () => {
     const now = Date.parse("2026-06-21T12:00:00.000Z");
     const justFresh = new Date(now - SCORING_SNAPSHOT_STALE_MS + 60_000).toISOString();