Give the food trend's figures, not only its rate

"Up about 40 g a week" is a rate with nothing to anchor it: it says the line
slopes without saying where it sits. The sentence now names both ends of the
fit — "roughly 280 g a day then, 400 g a day now" — which is the reading anyone
actually wants from a growth chart.

When the fit is not trustworthy it quotes the average instead, and says the
day-to-day variation is larger than any trend. That difference is the point.
The average is a measurement and survives the noise; the ends of the line are
the line's own output, and quoting them on a fit nobody should read would dress
a guess up as a reading. Everything rounds to 10 g for the same reason — "287 g
a day" would be false precision from four noisy points.

The wording moves into a pure foodTrendSentence() so those rules can be
checked, which is worth doing precisely because they are judgement rather than
arithmetic: the checks now pin that a clear climb gives both figures, a flat run
gives the average and no endpoints, a see-saw gives neither, and nothing is ever
quoted to the gram.

src/app.js

@@ -1713,30 +1713,43 @@
   // Says what the line means, and what it cannot mean. Kept in words under the
   // chart rather than as a figure on it: "up 40 g a week" is a claim, and it
   // needs the room to be qualified.
-  function renderFoodTrendNote(days, trend) {
-    const note = document.getElementById("grams-note");
-    if (!note) return;
-    const lines = [];
-    // The window comes from the 7/14/30 picker, and naming it is the only way
-    // the reader can tell that switching it changed the answer — the line
-    // itself often moves too little to notice.
-    const window = `the last ${chartDays()} days`;
-
+  // What the line is allowed to claim, in words. Separated from the drawing
+  // because this is where the judgement lives: a straight line through noisy
+  // points always has a slope, and stating it as a fact is how a chart starts
+  // lying. Kept pure so the rules can be checked.
+  //
+  // Figures are rounded to 10 g. The fitted endpoints are model output, not
+  // measurements — quoting "287 g" would dress a guess up as a reading.
+  function foodTrendSentence(trend, windowDays) {
+    const window = `the last ${windowDays} days`;
     if (!trend) {
       // Says why there is no line. Without this the chart looks broken on a
       // short window, or on one where most days are marked.
-      lines.push(`Not enough complete days in ${window} to draw a trend — it needs four, and today doesn't count until it's over.`);
-    } else {
-      const perWeek = Math.round(Math.abs(trend.perWeek));
-      // Under a twentieth of a typical day, a week apart, is not a trend
-      // anyone could act on, whatever the arithmetic says.
-      const slight = perWeek < 5 || perWeek < trend.mean * 0.05;
-      if (!trend.clear || slight) {
-        lines.push(`Over ${window}, daily intake is roughly steady — day-to-day variation is larger than any trend.`);
-      } else {
-        lines.push(`Over ${window}, daily intake is ${trend.perWeek > 0 ? "up" : "down"} about ${perWeek} g a week.`);
-      }
+      return `Not enough complete days in ${window} to draw a trend — it needs four, and today doesn't count until it's over.`;
     }
+    const round10 = (v) => Math.round(Math.max(0, v) / 10) * 10;
+    const perWeek = Math.round(Math.abs(trend.perWeek));
+    // Under a twentieth of a typical day, a week apart, is not a trend anyone
+    // could act on, whatever the arithmetic says.
+    const slight = perWeek < 5 || perWeek < trend.mean * 0.05;
+    if (!trend.clear || slight) {
+      // The average is a real measurement and survives the noise; the fitted
+      // endpoints would not, so they are not quoted here.
+      return `Over ${window}, daily intake is roughly steady, averaging about ` +
+        `${round10(trend.mean)} g a day — day-to-day variation is larger than any trend.`;
+    }
+    return `Over ${window}, daily intake is ${trend.perWeek > 0 ? "up" : "down"} about ` +
+      `${perWeek} g a week — roughly ${round10(trend.at(trend.first))} g a day then, ` +
+      `${round10(trend.at(trend.last))} g a day now.`;
+  }
+
+  function renderFoodTrendNote(days, trend) {
+    const note = document.getElementById("grams-note");
+    if (!note) return;
+    // The window comes from the 7/14/30 picker, and naming it is the only way
+    // the reader can tell that switching it changed the answer — the line
+    // itself often moves too little to notice.
+    const lines = [foodTrendSentence(trend, chartDays())];
 
     const missing = days.reduce((s, d) => s + (d.mealsMissingGrams || 0), 0);
     if (missing > 0) {
@@ -1745,7 +1758,7 @@
     }
 
     note.textContent = lines.join(" ");
-    note.hidden = lines.length === 0;
+    note.hidden = false; // there is always a sentence now, even if it is "no trend"
   }
 
   // Minutes walked per day. Hidden until there's a walk to show, like the