fix(occupancy): bound eigenvalue person-count to single-link max — #894

field_bridge::occupancy_or_fallback returned FieldModel::estimate_occupancy
unbounded (internal ceiling 10), while the perturbation fallback below it
and score_to_person_count both cap at 3 ("1-3 for single ESP32"). On noisy
or under-calibrated CSI the eigenvalue count inflated → "10 persons when 1
present" (#894, seen when --model fails to load → heuristic mode). Bound the
eigenvalue path to a shared MAX_SINGLE_LINK_OCCUPANCY const (3) so every
single-link estimator agrees. Genuine higher counts come from the
multistatic fusion path. Build clean, field_bridge tests pass.

v2/crates/wifi-densepose-sensing-server/src/field_bridge.rs

@@ -21,6 +21,15 @@ const ENERGY_THRESH_2: f64 = 12.0;
 /// Perturbation energy threshold for detecting a third person.
 const ENERGY_THRESH_3: f64 = 25.0;
 
+/// Maximum occupancy a single ESP32 link can plausibly resolve (#894).
+/// The score heuristic (`score_to_person_count`) and the perturbation-energy
+/// fallback below both cap here; the eigenvalue path is bounded to match,
+/// rather than leaking its internal `min(10)` ceiling on noisy / under-
+/// calibrated CSI (the "10 persons reported when 1 present" symptom).
+/// Resolving more than this from one link's subcarrier covariance is not
+/// reliable — genuine higher counts come from the multistatic fusion path.
+const MAX_SINGLE_LINK_OCCUPANCY: usize = 3;
+
 /// Create a FieldModelConfig for single-link mode (one ESP32 node = one link).
 /// This avoids the DimensionMismatch error when feeding single-frame observations.
 pub fn single_link_config() -> FieldModelConfig {
@@ -55,9 +64,15 @@ pub fn occupancy_or_fallback(
                 return score_to_person_count(smoothed_score, prev_count);
             }
 
-            // Try eigenvalue-based occupancy first (best accuracy).
+            // Try eigenvalue-based occupancy first (best accuracy). Bound it to
+            // the same single-link maximum the sibling estimators use — the
+            // perturbation fallback below and score_to_person_count both cap at
+            // MAX_SINGLE_LINK_OCCUPANCY. Without this, estimate_occupancy's
+            // internal min(10) ceiling leaks up to 10 persons on noisy / under-
+            // calibrated CSI (#894), while every other path on the same data
+            // would report ≤3.
             if let Ok(count) = field.estimate_occupancy(&frames) {
-                return count;
+                return count.min(MAX_SINGLE_LINK_OCCUPANCY);
             } // else fall through to perturbation energy
 
             // Fallback: perturbation energy thresholds.