fix(core): symmetric bandar thresholds; bandar needs all investors

- Basis points truncate toward zero instead of flooring, so a reading of
  -4.9952% stays neutral like its mirror image and -14.9952% stays
  distribution; tests cover both signs at both thresholds through
  bandar_tier. Goldens move by the rounding (BBCA top 5: -2426 -> -2425).
- With one investor side selected the summary has no total to weigh
  brokers against, so bandar and analyze_bandar reject it (INVALIDINPUT)
  instead of reading every tier as missing.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01V3syn2fN2LNo5pvTSqc6eh

crates/idx-core/src/analysis/bandar.rs

@@ -135,10 +135,12 @@ pub fn check_top(top: u8) -> Result<u8, IdxError> {
     }
 }
 
-/// `part` in basis points of `whole`; `None` without a positive whole.
+/// `part` in basis points of `whole`, truncated toward zero so a negative
+/// reading never reaches a threshold its magnitude has not; `None` without
+/// a positive whole.
 fn bps(part: i64, whole: Option<i64>) -> Option<i64> {
     let whole = whole.filter(|whole| *whole > 0)?;
-    i64::try_from((i128::from(part) * 10_000).div_euclid(i128::from(whole))).ok()
+    i64::try_from(i128::from(part) * 10_000 / i128::from(whole)).ok()
 }
 
 /// Sum of `field` over `flows`; `None` when any flow lacks it.
@@ -326,6 +328,37 @@ mod tests {
         assert_eq!(report.method, METHOD);
     }
 
+    #[test]
+    fn test_bandar_tier_thresholds_are_symmetric_for_sign() {
+        let reading = |buy: i64, sell: i64| {
+            let s = summary(
+                vec![flow("AA", Some(buy), 100)],
+                vec![flow("BB", Some(sell), 100)],
+                2_100_000_000,
+            );
+            let tier = bandar_tier(&s, 1);
+            (tier.imbalance_bps, tier.signal)
+        };
+        // -4.9952% and -14.9952% stay short of the thresholds, like their
+        // mirror images.
+        assert_eq!(
+            reading(504_300_000, 609_200_000),
+            (Some(-499), Some(BandarSignal::Neutral))
+        );
+        assert_eq!(
+            reading(609_200_000, 504_300_000),
+            (Some(499), Some(BandarSignal::Neutral))
+        );
+        assert_eq!(
+            reading(504_300_000, 819_200_000),
+            (Some(-1499), Some(BandarSignal::Distribution))
+        );
+        assert_eq!(
+            reading(819_200_000, 504_300_000),
+            (Some(1499), Some(BandarSignal::Accumulation))
+        );
+    }
+
     #[test]
     fn test_analyze_bandar_never_counts_a_missing_figure_as_zero() {
         let s = summary(

crates/idx-core/src/analysis/mod.rs

@@ -31,6 +31,19 @@ pub struct Comparison {
     pub failures: Vec<(String, IdxError)>,
 }
 
+/// Readings weigh brokers against the value traded, which the source does
+/// not total for one investor side.
+fn check_investor(investor: BrokerInvestor) -> Result<(), IdxError> {
+    if investor == BrokerInvestor::All {
+        Ok(())
+    } else {
+        Err(IdxError::InvalidInput(format!(
+            "bandar needs --investor all: the broker summary has no total for {} investors alone",
+            investor.as_str()
+        )))
+    }
+}
+
 /// Bandar readings for several symbols, strongest accumulation first;
 /// symbols that failed are listed with their error.
 pub struct BandarScreen {
@@ -57,6 +70,7 @@ impl Analysis<'_> {
         policy: CachePolicy,
     ) -> Result<Fetched<BandarReport>, IdxError> {
         let top = check_top(query.top)?;
+        check_investor(query.investor)?;
         let summary =
             self.idx
                 .broker()
@@ -73,6 +87,7 @@ impl Analysis<'_> {
         policy: CachePolicy,
     ) -> Result<BandarScreen, IdxError> {
         check_top(query.top)?;
+        check_investor(query.investor)?;
         let mut reports = Vec::new();
         let mut failures = Vec::new();
         for symbol in symbols {