Report where the snap indicator is drawn, not just what it computed

Diagnostic mode proved the arithmetic: on a 30m chart every sample snapped to
the correct bar and to exactly that bar's low, while the user still saw the
indicator sitting off the bars. That leaves the half never measured in their
browser — whether the dot is drawn where the price says it should be.

The report now carries the cursor's y, the dot's rendered y, the y the snapped
price maps to, and the y coordinates of the snapped bar's high and low. A
correctly computed answer drawn in the wrong place and a wrong answer drawn
faithfully look identical on a screenshot; these four numbers separate them.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

app/api/routes.py

@@ -213,6 +213,15 @@ class SnapReport(BaseModel):
     last_bar_t: int | None = None
     tf: str | None = None
     chart_w: float | None = None
+    chart_h: float | None = None
+    cursor_y: float | None = None
+    # Where the indicator actually landed versus where the price says it should
+    # — the only way to tell a wrong answer from a correctly-computed one drawn
+    # in the wrong place.
+    dot_y: float | None = None
+    expected_y: float | None = None
+    bar_low_y: float | None = None
+    bar_high_y: float | None = None
     note: str | None = None
 
 

static/chart.js

@@ -642,6 +642,23 @@ class ConfluenceChart {
             bars_held: this.bars.length,
             first_bar_t: this.bars[0].t, last_bar_t: this.bars[this.bars.length - 1].t,
             chart_w: this.chartEl.clientWidth,
+            chart_h: this.chartEl.clientHeight,
+            cursor_y: Math.round(point.y),
+            dot_y: this.snapDot && !this.snapDot.hidden
+              ? Math.round(this.snapDot.getBoundingClientRect().top
+                  - this.chartEl.getBoundingClientRect().top) + 5
+              : null,
+            expected_y: Math.round(y),
+            bar_low_y: (() => {
+              const bar = this.bars.find(candle => candle.t === snapped.t);
+              const at = bar && this.candles.priceToCoordinate(bar.l);
+              return at == null ? null : Math.round(at);
+            })(),
+            bar_high_y: (() => {
+              const bar = this.bars.find(candle => candle.t === snapped.t);
+              const at = bar && this.candles.priceToCoordinate(bar.h);
+              return at == null ? null : Math.round(at);
+            })(),
             note: point.t == null
               ? 'coordinateToTime returned null'
               : `drift ${drift}s (${Math.round(drift / step)} bars), step ${step}s`,