feat(rules): show what an apply run changed, and which rule ran

Apply History listed only counts - '13 matches · 13 transactions' - which reads
identically whether the run renamed a merchant or split every transaction with
another participant. Revert is destructive, so that is not enough to decide on.

Two additions. Migration 0017 records rule_id, rule_name and source on each run:
rule_name is denormalised so history stays readable after a rule is edited or
deleted, and there is no FK so deleting a rule cannot cascade away the audit
trail. Both write paths now populate it - the condition-matched run and the
selection-based quick action.

And rows expand to show the run's snapshot set against current values: which
transactions were touched and what changed on each. Rows changed by something
else since the run are called out, because reverting restores the pre-run value
and would discard that later edit.

Runs recorded before this show 'Unknown rule' - the rule they came from is not
recoverable.

src/app/api/rules/runs/[id]/route.ts

@@ -0,0 +1,134 @@
+import { NextRequest, NextResponse } from "next/server";
+import { getCurrentUser } from "@/lib/auth";
+import { queryRaw } from "@/lib/db";
+
+/**
+ * What a rule run actually did — the before-state from its snapshot set against
+ * the values now.
+ *
+ * The run list only had counts, which is not enough to decide whether to revert:
+ * "13 matches · 13 transactions" reads the same whether it renamed a merchant or
+ * split your history with someone. Reverting is destructive, so the detail has
+ * to be visible before the button is pressed.
+ */
+
+interface SnapshotEntry {
+  transaction_id: number;
+  had_override: boolean;
+  prev_category_override: string | null;
+  prev_merchant_normalized: string | null;
+  prev_tag_ids: number[];
+  prev_splits: { participant_id: number; share_percent: number; settled: boolean }[];
+}
+
+export async function GET(
+  req: NextRequest,
+  { params }: { params: Promise<{ id: string }> }
+) {
+  const user = await getCurrentUser(req);
+  if (!user) return NextResponse.json({ error: "Unauthorized" }, { status: 403 });
+
+  const { id } = await params;
+  const runs = await queryRaw<{
+    id: number; applied_at: string; reverted_at: string | null;
+    split_from: string | null; matched: number; transactions_affected: number;
+    rule_id: number | null; rule_name: string | null; source: string | null;
+    snapshot: unknown;
+  }>(
+    `SELECT id, applied_at, reverted_at, split_from, matched, transactions_affected,
+            rule_id, rule_name, source, snapshot
+     FROM rule_apply_runs WHERE id = $1 AND owner_id = $2`,
+    [Number(id), user.id]
+  );
+  if (!runs.length) return NextResponse.json({ error: "Run not found" }, { status: 404 });
+
+  const run = runs[0];
+  const snapshot = (typeof run.snapshot === "string"
+    ? JSON.parse(run.snapshot) : run.snapshot) as SnapshotEntry[];
+  const byId = new Map(snapshot.map((s) => [s.transaction_id, s]));
+  const ids = snapshot.map((s) => s.transaction_id);
+
+  if (ids.length === 0) {
+    return NextResponse.json({ run: { ...run, snapshot: undefined }, transactions: [] });
+  }
+
+  const current = await queryRaw<{
+    id: number; transaction_date: string; description: string;
+    amount: number; amount_aud: number | null; bank_name: string;
+    category: string | null; category_override: string | null;
+    merchant_normalized: string | null; merchant_override: string | null;
+    merchant_name: string | null;
+    tag_ids: number[]; splits: { participant_id: number; share_percent: number }[];
+  }>(
+    `SELECT t.id, t.transaction_date::text, t.description, t.amount, t.amount_aud,
+       COALESCE(s.bank_name, 'Manual') as bank_name,
+       t.category, o.category_override,
+       t.merchant_normalized, o.merchant_normalized as merchant_override, t.merchant_name,
+       COALESCE((SELECT json_agg(tt.tag_id) FROM transaction_tags tt WHERE tt.transaction_id = t.id), '[]'::json) as tag_ids,
+       COALESCE((SELECT json_agg(json_build_object('participant_id', ts.participant_id, 'share_percent', ts.share_percent))
+                 FROM transaction_splits ts WHERE ts.transaction_id = t.id), '[]'::json) as splits
+     FROM transactions t
+     LEFT JOIN statements s ON s.id = t.statement_id
+     LEFT JOIN transaction_overrides o ON o.transaction_id = t.id
+     WHERE t.id = ANY($1::int[])
+     ORDER BY t.transaction_date DESC`,
+    [ids]
+  );
+
+  const parse = <T,>(v: unknown, fallback: T): T =>
+    (typeof v === "string" ? JSON.parse(v) : v) ?? fallback;
+
+  const transactions = current.map((t) => {
+    const prev = byId.get(t.id);
+    const nowTags: number[] = parse(t.tag_ids, []);
+    const nowSplits = parse<{ participant_id: number; share_percent: number }[]>(t.splits, []);
+    const prevTags = prev?.prev_tag_ids ?? [];
+    const prevSplits = prev?.prev_splits ?? [];
+
+    const nowCategory = t.category_override ?? t.category;
+    const prevCategory = prev?.prev_category_override ?? t.category;
+    const nowMerchant = t.merchant_override ?? t.merchant_normalized ?? t.merchant_name;
+    const prevMerchant = prev?.prev_merchant_normalized ?? t.merchant_normalized ?? t.merchant_name;
+
+    const changes: { field: string; from: string | null; to: string | null }[] = [];
+    if (nowCategory !== prevCategory) {
+      changes.push({ field: "category", from: prevCategory, to: nowCategory });
+    }
+    if (nowMerchant !== prevMerchant) {
+      changes.push({ field: "merchant", from: prevMerchant, to: nowMerchant });
+    }
+    const addedTags = nowTags.filter((x) => !prevTags.includes(x));
+    if (addedTags.length) {
+      changes.push({ field: "tags", from: null, to: addedTags.join(",") });
+    }
+    const fmtSplits = (arr: { participant_id: number; share_percent: number }[]) =>
+      arr.length ? arr.map((s) => `${s.participant_id}:${Number(s.share_percent)}%`).sort().join(" ") : null;
+    if (fmtSplits(nowSplits) !== fmtSplits(prevSplits)) {
+      changes.push({ field: "split", from: fmtSplits(prevSplits), to: fmtSplits(nowSplits) });
+    }
+
+    return {
+      id: t.id,
+      transaction_date: t.transaction_date,
+      description: t.description,
+      amount: t.amount,
+      amount_aud: t.amount_aud,
+      bank_name: t.bank_name,
+      merchant: nowMerchant,
+      changes,
+    };
+  });
+
+  return NextResponse.json({
+    run: {
+      id: run.id, applied_at: run.applied_at, reverted_at: run.reverted_at,
+      split_from: run.split_from, matched: run.matched,
+      transactions_affected: run.transactions_affected,
+      rule_id: run.rule_id, rule_name: run.rule_name, source: run.source,
+    },
+    // A reverted run still lists its transactions, but they will show no changes
+    // because the values are back where they started.
+    transactions,
+    still_changed: transactions.filter((t) => t.changes.length > 0).length,
+  });
+}