fix(measurements,coach): restore the live-fallback spread band and the stream lifecycle

The tiered rollup read emits minValue/maxValue; readLiveDaily omitted them, so
on a rollup-cold account or a coverage miss the chart silently dropped the
min/max spread band for the same underlying data — contradicting the file's own
byte-for-byte parity claim. The live aggregate now selects MIN/MAX alongside the
average.

useSendCoachMessage never aborted its in-flight reader on unmount. The drawer
works around that through handleOpenChange, but the full-page /coach surface
passes no registerReset, so navigating away mid-stream left the SSE loop alive:
the provider kept generating and billing, and trailing setState fired on an
unmounted component.

Switching conversations reset every piece of local state except the send state,
so the previous thread's last assistant or error bubble rendered appended to the
newly selected thread until the next send.

The two lifecycle invariants are pinned structurally, not behaviourally — the
repo ships no renderHook. That is weaker, and the header says so; both defects
were a missing call, which is what a structural guard does catch.

src/lib/measurements/__tests__/daily-series-read-tiered.test.ts

@@ -175,6 +175,8 @@ describe("readDailySeries — rollup read throw falls back to live SQL (F-DB-2)"
         bucket_start: new Date("2026-06-10T00:00:00.000Z"),
         avg: 80.5,
         cnt: 2,
+        min_value: 79.8,
+        max_value: 81.2,
       },
     ]);
 
@@ -189,6 +191,10 @@ describe("readDailySeries — rollup read throw falls back to live SQL (F-DB-2)"
     // The read did NOT throw — it fell through to live SQL and served a row.
     expect(result).toHaveLength(1);
     expect(result[0]).toMatchObject({ type: "WEIGHT", value: 80.5, count: 2 });
+    // The live fallback must carry the min/max spread the rollup path emits —
+    // otherwise a rollup-cold account silently loses the chart's spread band
+    // for the same underlying data.
+    expect(result[0]).toMatchObject({ minValue: 79.8, maxValue: 81.2 });
     expect(mocks.queryRaw).toHaveBeenCalled();
   });
 

src/lib/measurements/daily-series-read.ts

@@ -253,7 +253,14 @@ async function readLiveDaily(opts: {
     buildSourceRankCase(priorityJson, 'm."type"', 'm."source"'),
   );
   const buckets = await prisma.$queryRaw<
-    Array<{ type: string; bucket_start: Date; avg: number; cnt: number }>
+    Array<{
+      type: string;
+      bucket_start: Date;
+      avg: number;
+      cnt: number;
+      min_value: number | null;
+      max_value: number | null;
+    }>
   >`
     WITH canon AS (
       SELECT DISTINCT ON (m."type", date_trunc(${truncUnitLiteral}, m."measured_at"))
@@ -272,7 +279,9 @@ async function readLiveDaily(opts: {
       m."type"::text AS type,
       date_trunc(${truncUnitLiteral}, m."measured_at") AS bucket_start,
       ${aggregator} AS avg,
-      COUNT(*)::int AS cnt
+      COUNT(*)::int AS cnt,
+      MIN(m."value") AS min_value,
+      MAX(m."value") AS max_value
     FROM measurements m
     JOIN canon c
       ON c.t = m."type"
@@ -296,5 +305,15 @@ async function readLiveDaily(opts: {
     value: Number(b.avg),
     measuredAt: b.bucket_start.toISOString(),
     count: Number(b.cnt),
+    // The rollup path emits these; the live fallback used to omit them, so a
+    // rollup-cold account silently lost the min/max spread band on the chart
+    // for the same underlying data — contradicting this file's own
+    // byte-for-byte parity claim.
+    minValue: b.min_value === null ? undefined : Number(b.min_value),
+    maxValue: b.max_value === null ? undefined : Number(b.max_value),
+    // The rollup path emits these; the live fallback used to omit them, so a
+    // rollup-cold account silently lost the min/max spread band on the chart
+    // for the same underlying data — contradicting this file's own
+    // byte-for-byte parity claim.
   }));
 }