Charge tuition automatically from attendance

Adds a per-student daily rate (students.daily_tuition_cents) and a trigger
that writes a tuition charge when a student is marked present or late.

Idempotency is the crux. The attendance UI upserts on (student_id, date)
and teachers toggle a status freely — present, absent, present again. A
naive "insert a charge on attendance" trigger bills the family once per
click. So each auto-charge is bound to the attendance row that caused it
via ledger_entries.attendance_id (UNIQUE), which turns the write into an
upsert, lets a change back to absent delete the charge, and cascades the
charge away if the attendance record is deleted.

Manual entries keep attendance_id NULL — Postgres allows unlimited NULLs
in a unique index — so hand-entered charges are untouched and the UI can
tell auto from manual.

A NULL rate (the default) means never auto-charge, so nothing begins
billing until a rate is deliberately set on a student. Existing
attendance is not backfilled: retroactively generating charges against
families' balances should be an explicit decision, not a side effect of
deploying a migration.

The trigger is SECURITY DEFINER because the writer is a teacher marking
attendance while ledger_entries is admin-write under RLS; teachers gain
no general ledger access, only this fixed attendance-derived write.

Verified against the live schema across all eight paths: charge on
present, reversal on absent, no duplicate on re-mark, late billable,
excused free, no rate means no charge, rate change on re-save, and
cascade on attendance delete.

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

src/routes/_authenticated/students.$id.tsx

@@ -18,6 +18,7 @@ import { createIntakeToken } from "@/lib/intake.functions";
 import { genTempPassword } from "@/lib/temp-password";
 import { StudentGradeReport } from "@/components/gradebook";
 import { StudentPlansTab } from "@/components/plans";
+import { money } from "@/lib/reports";
 
 export const Route = createFileRoute("/_authenticated/students/$id")({
   head: () => ({ meta: [{ title: "Student — School Portal" }] }),
@@ -167,7 +168,16 @@ function ProfileTab({ studentId, canEdit, isAdmin }: { studentId: string; canEdi
   // background refetch can never clobber in-progress input. Functional updates
   // avoid stale-closure races.
   const [form, setForm] = useState<Record<string, unknown>>({});
-  const startEdit = () => { setForm({ ...(s as Record<string, unknown>) }); setEditing(true); };
+  // daily_tuition_cents is stored in cents but edited in dollars, so it gets its
+  // own form key and is converted on save rather than going through the string
+  // field helpers below.
+  const startEdit = () => {
+    setForm({
+      ...(s as Record<string, unknown>),
+      tuition_rate_input: s?.daily_tuition_cents != null ? (s.daily_tuition_cents / 100).toFixed(2) : "",
+    });
+    setEditing(true);
+  };
   const c = (editing ? form : s) as Record<string, unknown> | null;
   const upd = (k: string, v: unknown) => setForm((f) => ({ ...f, [k]: v }));
   // Read date inputs straight from the DOM at save time (Safari doesn't reliably
@@ -193,6 +203,13 @@ function ProfileTab({ studentId, canEdit, isAdmin }: { studentId: string; canEdi
         const el = dateRefs.current[k];
         if (el) payload[k] = el.value || null;
       }
+      // Dollars -> cents. Blank clears the rate, which stops auto-charging.
+      const rate = String(c.tuition_rate_input ?? "").trim();
+      const rateNum = Number(rate);
+      if (rate !== "" && (!Number.isFinite(rateNum) || rateNum < 0)) {
+        throw new Error("Daily tuition rate must be a positive amount");
+      }
+      payload.daily_tuition_cents = rate === "" ? null : Math.round(rateNum * 100);
       const { error } = await supabase.from("students").update(payload as never).eq("id", studentId);
       if (error) throw error;
     },
@@ -235,6 +252,18 @@ function ProfileTab({ studentId, canEdit, isAdmin }: { studentId: string; canEdi
           <ViewRow label="Photo release" value={c.photo_release ? "Granted" : "Not granted"} />
           {isAdmin && <ViewRow label="Internal notes" value={val("notes")} />}
         </Section>
+        {isAdmin && (
+          <Section title="Tuition">
+            <ViewRow
+              label="Daily rate"
+              value={
+                c.daily_tuition_cents != null
+                  ? `${money(c.daily_tuition_cents as number)} — charged automatically when marked present or late`
+                  : "Not set — attendance does not create charges"
+              }
+            />
+          </Section>
+        )}
         <Section title="Agreement">
           <ViewRow label="Signed by" value={val("agreement_signed_by")} />
           <ViewRow label="Date" value={val("agreement_signed_date")} />
@@ -293,6 +322,23 @@ function ProfileTab({ studentId, canEdit, isAdmin }: { studentId: string; canEdi
         <div className="flex items-center justify-between max-w-sm"><Label className="text-xs">Photo release granted</Label><Switch checked={!!c.photo_release} onCheckedChange={(v) => upd("photo_release", v)} /></div>
         {isAdmin && A("notes", "Internal notes (staff only)")}
       </Section>
+      {isAdmin && (
+        <Section title="Tuition">
+          <Field label="Daily rate in dollars — leave blank for no automatic charging">
+            <Input
+              inputMode="decimal"
+              placeholder="e.g. 45.00"
+              value={(c.tuition_rate_input as string) ?? ""}
+              onChange={(e) => upd("tuition_rate_input", e.target.value)}
+            />
+          </Field>
+          <p className="text-xs text-muted-foreground">
+            When set, marking this student present or late adds a tuition charge for that day. Changing
+            a status to absent or excused removes the charge again. Existing attendance is not billed
+            retroactively.
+          </p>
+        </Section>
+      )}
       <Section title="Agreement">
         <div className="grid grid-cols-2 gap-3">{T("agreement_signed_by", "Signed by")}{D("agreement_signed_date", "Date")}</div>
       </Section>