analytics: your share of what someone else paid is your spend

Every spend analytic gated on `OWNER_SCOPE = $1` and scaled by `mySplitOf`
*within* that gate, so ownership was a precondition for an expense being
yours. Half a grocery shop Sonu paid for counted as zero — in monthly,
daily, merchants, subscriptions, fees and the budget page. 167 rows /
$3,210.91 across Jan-Jul 2026, worst in April (+$1,354.83, the Europe
trips), while getParticipantBalances booked the matching debt correctly.
The app could say you owed her for a shop while insisting you had not
spent anything on it.

New MY_SPEND_SCOPE(): owner = me OR I hold a split. OWNER_SCOPE stays on
the things that measure an *account* rather than a person — the income
and investment lines, and the statement-level fee rollup.

myShare had to change with it, and widening the gate alone would have
been worse than the bug: its `100 - everyone else` fallback is the
payer's remainder, so on someone else's unsplit row it returns 100 and
moves their whole bill onto you. It now branches on ownership — my row
resolves as before; their row takes an explicit split row only, absent
meaning 0. That 0 is what makes the wider gate safe.

my_share_percent is deliberately not read on someone else's row: one
unscoped column, writable by anyone who can see the row, so "my" can
only mean the owner's. All 402 rows carrying one today are owner-side.

MY_SHARE_PCT mirrors myShare for the transactions list, which has no
viewer-scoped ts join; a test asserts the two agree across seven fixture
shapes.

No historical restatement — every non-owner split is 2026-dated, and the
1,266 pre-2026 SplitMyExpenses splits are all on rows you own.

Also fixes a latent failure in the NATIVE_CURRENCY test, which inserted a
statement relying on participant id 1 existing (owner_id is NOT NULL
DEFAULT 1 with an FK) and only passed when a sibling file had left one
behind. It now owns its fixture.

15 new integration tests; 189 integration + 130 unit green.

CLAUDE.md

@@ -760,6 +760,50 @@ rather than hand-rolling them. Two failure modes they exist to prevent:
   Use the `EXCLUDE_NON_SPEND` fragment: a bare `category NOT IN (...)` evaluates
   to NULL for uncategorised rows and drops them from totals.
 
+### Spend is gated on MY_SPEND_SCOPE, not OWNER_SCOPE (2026-08-15)
+
+**Ownership is not a precondition for an expense being yours.** Every spend
+analytic used to gate on `OWNER_SCOPE = $1`, with `mySplitOf` scaling *within*
+that gate — so your half of a shop Sonu paid for counted as **zero**, in monthly,
+daily, merchants, subscriptions, fees and the budget page. 167 rows / **$3,210.91**
+across Jan–Jul 2026, worst in April (+$1,354.83, the Europe trips). Meanwhile
+`getParticipantBalances` booked the matching debt correctly, so the app could say
+you owed her for a shop while insisting you had not spent anything on it.
+
+Use `MY_SPEND_SCOPE()` — `owner = me OR I hold a split` — for anything measuring
+what *I* spent. `OWNER_SCOPE` is still right for anything measuring an **account**:
+the income and investment lines in `/analytics/monthly`, and the statement-level
+fee rollup in `/analytics/fees` (which reads `statements`, where splits are
+meaningless).
+
+**`myShare` had to change with it, and widening the gate alone would have been
+worse than the bug.** Its old third fallback, `100 - everyone else`, is the
+*payer's* remainder — on someone else's unsplit row it returns 100 and would have
+moved their entire bill onto you. It now branches on ownership:
+
+- **My row** — unchanged: explicit split, then `my_share_percent`, then the
+  remainder.
+- **Their row** — an explicit split row only; absent means **0**.
+
+`my_share_percent` is deliberately not consulted on someone else's row. It is one
+unscoped column on `transaction_overrides` writable by anyone who can see the row,
+so "my" can only mean the owner's. All 402 rows carrying one today are owner-side.
+
+That 0 is what makes the wider gate safe: admitting a row can never add more than
+the share actually held. Tested both ways in
+`src/__tests__/integration/analytics-sql.test.ts` — the discriminating cases are
+all ones where you hold **no** split on someone else's row, because that is the
+only place old and new disagree.
+
+`MY_SHARE_PCT` in `queries.ts` mirrors `myShare` in subselect form for the
+transactions list (which has no viewer-scoped `ts` join). A test asserts the two
+agree row for row across seven fixture shapes — keep it that way, since the list
+is the drill-down for these totals.
+
+**No historical restatement:** every non-owner split is 2026-dated. The 1,266
+pre-2026 SplitMyExpenses splits are all on rows you own, so nothing before the
+cutover moves.
+
 ### Statement types
 
 `statements.statement_type` is constrained to `credit_card | transaction |

src/__tests__/integration/analytics-sql.test.ts

@@ -1,11 +1,17 @@
-import { describe, it, expect } from "vitest";
+import { describe, it, expect, beforeAll } from "vitest";
 import { queryRaw, queryRow } from "../../lib/db";
 import {
   EXCLUDE_RECONCILED_SOURCE,
   NATIVE_CURRENCY,
   AMOUNT_UNCONVERTED,
   INVESTMENT_SIGNED,
+  MY_SPEND_SCOPE,
+  NET_SPEND_ROWS,
+  SPEND_SIGNED,
+  myShare,
+  mySplitOf,
 } from "../../lib/analytics-sql";
+import { MY_SHARE_PCT } from "../../lib/queries";
 
 /**
  * These fragments are the ones that drifted.
@@ -103,9 +109,17 @@ describe("NATIVE_CURRENCY", () => {
     // Opposite convention: on an AUD statement, `amount` is AUD and
     // foreign_currency_code merely notes what was originally charged. Reading
     // the foreign code here would mislabel an AUD row as USD.
+    // owner_id is NOT NULL DEFAULT 1 with an FK to participants, so this insert
+    // relied on a participant with id 1 already existing — true only when a
+    // sibling test file had seeded one and left it behind. On a freshly reset
+    // database it failed the FK. Own the fixture instead of inheriting it.
+    const owner = await queryRow<{ id: number }>(
+      `INSERT INTO participants (name) VALUES ('Analytics fixture — owner') RETURNING id`
+    );
     const stmt = await queryRow<{ id: number }>(
-      `INSERT INTO statements (bank_name, account_number, billing_end_date, currency, filename)
+      `INSERT INTO statements (bank_name, account_number, billing_end_date, currency, filename, owner_id)
-       VALUES ('Analytics Fixture Bank','0000','2026-03-31','AUD','analytics-fixture.pdf') RETURNING id`
+       VALUES ('Analytics Fixture Bank','0000','2026-03-31','AUD','analytics-fixture.pdf', $1) RETURNING id`,
+      [owner!.id]
     );
     const id = await scratchTxn(
       "transaction_date, description, amount, amount_aud, transaction_type, statement_id, foreign_currency_amount, foreign_currency_code",
@@ -183,3 +197,207 @@ describe("INVESTMENT_SIGNED", () => {
     expect(await signedValue(id)).toBe(-1500);
   });
 });
+
+/**
+ * Whose expense is it — the gate that decides, and the share that scales it.
+ *
+ * Both fragments changed together on 2026-08-15 and neither is safe alone.
+ * `OWNER_SCOPE = $1` was the gate on every spend analytic, with `mySplitOf`
+ * scaling within it, so a row someone else paid for contributed nothing to my
+ * spend no matter what share I held — 167 rows / $3,210.91 of my own share
+ * missing from Jan–Jul 2026, while the balance queries booked the debt
+ * correctly. Widening the gate without also fixing `myShare` is worse than
+ * leaving it: the old remainder fallback hands the viewer the PAYER's share on
+ * a row with no split of theirs, which on an unsplit row is the full amount.
+ *
+ * So the discriminating cases here are all ones where I hold NO split row on
+ * someone else's transaction. That is where old and new disagree, and it is the
+ * only place the widened gate could do damage.
+ */
+describe("MY_SPEND_SCOPE / myShare", () => {
+  let me = 0;
+  let them = 0;
+  let third = 0;
+
+  beforeAll(async () => {
+    const mk = async (name: string) =>
+      (await queryRow<{ id: number }>(
+        `INSERT INTO participants (name) VALUES ($1) RETURNING id`,
+        [name]
+      ))!.id;
+    me = await mk("Share fixture — viewer");
+    them = await mk("Share fixture — payer");
+    third = await mk("Share fixture — third party");
+  });
+
+  /** A transaction owned by `owner`, optionally split, optionally overridden. */
+  async function fixture(
+    label: string,
+    owner: number,
+    splits: [number, number][] = [],
+    myShareOverride?: number
+  ) {
+    const id = await scratchTxn(
+      "transaction_date, description, amount, transaction_type, category, owner_id",
+      `'2026-06-01', $1, 100.00, 'debit', 'groceries', $2`,
+      [`Share fixture — ${label}`, owner]
+    );
+    for (const [pid, pct] of splits) {
+      await queryRaw(
+        `INSERT INTO transaction_splits (transaction_id, participant_id, share_percent)
+         VALUES ($1, $2, $3)`,
+        [id, pid, pct]
+      );
+    }
+    if (myShareOverride !== undefined) {
+      await queryRaw(
+        `INSERT INTO transaction_overrides (transaction_id, my_share_percent) VALUES ($1, $2)`,
+        [id, myShareOverride]
+      );
+    }
+    return id;
+  }
+
+  const JOINS = `
+    FROM transactions t
+    LEFT JOIN statements s ON s.id = t.statement_id
+    LEFT JOIN transaction_overrides o ON o.transaction_id = t.id
+    LEFT JOIN transaction_splits ts ON ts.transaction_id = t.id AND ts.participant_id = $1`;
+
+  async function inScope(id: number, viewer: number): Promise<boolean> {
+    const rows = await queryRaw(
+      `SELECT t.id ${JOINS} WHERE t.id = $2 AND ${MY_SPEND_SCOPE()}`,
+      [viewer, id]
+    );
+    return rows.length === 1;
+  }
+
+  async function share(id: number, viewer: number): Promise<number> {
+    const row = await queryRow<{ v: string }>(
+      `SELECT (${myShare()})::numeric AS v ${JOINS} WHERE t.id = $2`,
+      [viewer, id]
+    );
+    return Number(row!.v);
+  }
+
+  /** What this row contributes to the viewer's net spend. */
+  async function spend(id: number, viewer: number): Promise<number> {
+    const row = await queryRow<{ v: string | null }>(
+      `SELECT SUM(${mySplitOf(SPEND_SIGNED)})::numeric(14,4) AS v ${JOINS}
+        WHERE t.id = $2 AND ${MY_SPEND_SCOPE()} AND ${NET_SPEND_ROWS}`,
+      [viewer, id]
+    );
+    return Number(row?.v ?? 0);
+  }
+
+  describe("the gate", () => {
+    it("admits a row someone else paid for that I hold a split on", async () => {
+      const id = await fixture("their shop, my half", them, [[me, 50], [them, 50]]);
+      expect(await inScope(id, me)).toBe(true);
+    });
+
+    it("still admits a row I paid for with no splits at all", async () => {
+      const id = await fixture("mine alone", me);
+      expect(await inScope(id, me)).toBe(true);
+    });
+
+    it("rejects a row someone else paid for that I have no split on", async () => {
+      const id = await fixture("not mine", them, [[them, 60], [third, 40]]);
+      expect(await inScope(id, me)).toBe(false);
+    });
+  });
+
+  describe("my share of someone else's row", () => {
+    it("is my split percent", async () => {
+      const id = await fixture("their shop, my quarter", them, [[me, 25], [them, 75]]);
+      expect(await share(id, me)).toBe(25);
+    });
+
+    it("is 0 with no split of mine — NOT the payer's remainder", async () => {
+      // The load-bearing case. An unsplit row someone else paid for has no
+      // `ts.share_percent`, so the old `100 - everyone else` fallback returned
+      // 100 and would have moved their entire grocery bill onto my spend the
+      // moment the gate widened.
+      const id = await fixture("entirely theirs", them);
+      expect(await share(id, me)).toBe(0);
+      expect(await spend(id, me)).toBe(0);
+    });
+
+    it("ignores my_share_percent, which can only mean the owner's share", async () => {
+      // One unscoped column per transaction, writable by anyone who can see the
+      // row. Reading it as the viewer's share on someone else's transaction
+      // would be a guess.
+      const id = await fixture("their row, their override", them, [], 30);
+      expect(await share(id, me)).toBe(0);
+    });
+  });
+
+  describe("my share of my own row is unchanged", () => {
+    it("prefers an explicit split row for me", async () => {
+      const id = await fixture("mine, split explicitly", me, [[me, 35], [them, 65]]);
+      expect(await share(id, me)).toBe(35);
+    });
+
+    it("falls back to the my_share_percent override", async () => {
+      const id = await fixture("mine, overridden", me, [], 80);
+      expect(await share(id, me)).toBe(80);
+    });
+
+    it("falls back to whatever is left after everyone else", async () => {
+      const id = await fixture("mine, remainder", me, [[them, 40]]);
+      expect(await share(id, me)).toBe(60);
+    });
+
+    it("is 0 when a row I paid for is allocated entirely to someone else", async () => {
+      const id = await fixture("mine, all theirs", me, [[them, 100]]);
+      expect(await share(id, me)).toBe(0);
+    });
+  });
+
+  describe("the regression it was written for", () => {
+    it("counts my half of a shop the other person paid for", async () => {
+      const id = await fixture("the grocery shop", them, [[me, 50], [them, 50]]);
+      expect(await spend(id, me)).toBe(50);
+    });
+
+    it("still counts my half of the same shop when I paid", async () => {
+      const id = await fixture("the same shop, my card", me, [[me, 50], [them, 50]]);
+      expect(await spend(id, me)).toBe(50);
+    });
+
+    it("counts my share whether or not the split is settled", async () => {
+      // `myShare` must not filter on `settled` — half a shop was my expense
+      // whether or not the other half was repaid. Same rule, payer-side.
+      const id = await fixture("settled shop", them, [[me, 50], [them, 50]]);
+      await queryRaw(`UPDATE transaction_splits SET settled = true WHERE transaction_id = $1`, [id]);
+      expect(await spend(id, me)).toBe(50);
+    });
+
+    it("never counts one row for both people at full value", async () => {
+      const id = await fixture("one shop, two people", them, [[me, 50], [them, 50]]);
+      expect(await spend(id, me) + await spend(id, them)).toBe(100);
+    });
+  });
+
+  describe("the transactions-list mirror agrees", () => {
+    it("MY_SHARE_PCT matches myShare on every fixture shape", async () => {
+      const shapes: [string, number, [number, number][], number | undefined][] = [
+        ["mirror A", them, [[me, 25], [them, 75]], undefined],
+        ["mirror B", them, [], undefined],
+        ["mirror C", them, [], 30],
+        ["mirror D", me, [[me, 35], [them, 65]], undefined],
+        ["mirror E", me, [], 80],
+        ["mirror F", me, [[them, 40]], undefined],
+        ["mirror G", me, [], undefined],
+      ];
+      for (const [label, owner, splits, override] of shapes) {
+        const id = await fixture(label, owner, splits, override);
+        const mirrored = await queryRow<{ v: string }>(
+          `SELECT (${MY_SHARE_PCT})::numeric AS v ${JOINS} WHERE t.id = $2`,
+          [me, id]
+        );
+        expect([label, Number(mirrored!.v)]).toEqual([label, await share(id, me)]);
+      }
+    });
+  });
+});

src/app/api/analytics/daily/route.ts

@@ -2,7 +2,7 @@ import { NextRequest, NextResponse } from "next/server";
 import { getCurrentUser } from "@/lib/auth";
 import { queryRaw } from "@/lib/db";
 import {
-  OWNER_SCOPE,
+  MY_SPEND_SCOPE,
   STATEMENTS_JOIN,
   EXCLUDE_NON_SPEND,
   EXCLUDE_RECONCILED_SOURCE,
@@ -57,7 +57,7 @@ export async function GET(req: NextRequest) {
     LEFT JOIN transaction_overrides o ON o.transaction_id = t.id
     LEFT JOIN transaction_splits ts ON ts.transaction_id = t.id AND ts.participant_id = $1
     ${STATEMENTS_JOIN}
-    WHERE ${OWNER_SCOPE} = $1
+    WHERE ${MY_SPEND_SCOPE()}
       AND ${NET_SPEND_ROWS}
       AND ${EXCLUDE_NON_SPEND}
       AND ${EXCLUDE_RECONCILED_SOURCE}

src/app/api/analytics/fees/route.ts

@@ -1,7 +1,7 @@
 import { NextRequest, NextResponse } from "next/server";
 import { getCurrentUser } from "@/lib/auth";
 import { queryRaw } from "@/lib/db";
-import { OWNER_SCOPE, STATEMENTS_JOIN, EXCLUDE_RECONCILED_SOURCE, mySplitOf, toDateStr } from "@/lib/analytics-sql";
+import { MY_SPEND_SCOPE, STATEMENTS_JOIN, EXCLUDE_RECONCILED_SOURCE, mySplitOf, toDateStr } from "@/lib/analytics-sql";
 
 /**
  * Fees and interest over an explicit window.
@@ -71,7 +71,7 @@ export async function GET(req: NextRequest) {
     LEFT JOIN transaction_overrides o ON o.transaction_id = t.id
     LEFT JOIN transaction_splits ts ON ts.transaction_id = t.id AND ts.participant_id = $1
     ${STATEMENTS_JOIN}
-    WHERE ${OWNER_SCOPE} = $1
+    WHERE ${MY_SPEND_SCOPE()}
       AND t.transaction_type IN ('fee', 'interest')
       AND ${EXCLUDE_RECONCILED_SOURCE}
       ${txnWindow}

src/app/api/analytics/merchants/[merchant]/route.ts

@@ -1,7 +1,7 @@
 import { NextRequest, NextResponse } from "next/server";
 import { getCurrentUser } from "@/lib/auth";
 import { queryRaw } from "@/lib/db";
-import { OWNER_SCOPE, STATEMENTS_JOIN, EXCLUDE_RECONCILED_SOURCE, EFFECTIVE_CATEGORY, mySplitOf } from "@/lib/analytics-sql";
+import { MY_SPEND_SCOPE, STATEMENTS_JOIN, EXCLUDE_RECONCILED_SOURCE, EFFECTIVE_CATEGORY, mySplitOf } from "@/lib/analytics-sql";
 import { bankLabel } from "@/lib/queries";
 
 const MY_AMOUNT = mySplitOf(`COALESCE(t.amount_aud, t.amount)`);
@@ -46,7 +46,7 @@ export async function GET(
     ${STATEMENTS_JOIN}
     LEFT JOIN transaction_overrides o ON o.transaction_id = t.id
     LEFT JOIN transaction_splits ts ON ts.transaction_id = t.id AND ts.participant_id = $1
-    WHERE ${OWNER_SCOPE} = $1
+    WHERE ${MY_SPEND_SCOPE()}
       AND t.transaction_type IN ('debit', 'fee', 'interest', 'refund', 'credit')
       AND COALESCE(o.merchant_normalized, t.merchant_normalized, t.merchant_name, t.description) = $2
       AND ${EXCLUDE_RECONCILED_SOURCE}

src/app/api/analytics/merchants/route.ts

@@ -1,7 +1,7 @@
 import { NextRequest, NextResponse } from "next/server";
 import { getCurrentUser } from "@/lib/auth";
 import { queryRaw } from "@/lib/db";
-import { OWNER_SCOPE, STATEMENTS_JOIN, EXCLUDE_NON_SPEND, EXCLUDE_RECONCILED_SOURCE, EFFECTIVE_CATEGORY, mySplitOf, toDateStr } from "@/lib/analytics-sql";
+import { MY_SPEND_SCOPE, STATEMENTS_JOIN, EXCLUDE_NON_SPEND, EXCLUDE_RECONCILED_SOURCE, EFFECTIVE_CATEGORY, mySplitOf, toDateStr } from "@/lib/analytics-sql";
 
 // Split-adjusted amount helper (positive for spend, negative for refunds)
 const MY_AMOUNT = mySplitOf(`COALESCE(t.amount_aud, t.amount)`);
@@ -65,7 +65,7 @@ export async function GET(req: NextRequest) {
     ${STATEMENTS_JOIN}
     LEFT JOIN transaction_overrides o ON o.transaction_id = t.id
     LEFT JOIN transaction_splits ts ON ts.transaction_id = t.id AND ts.participant_id = $1
-    WHERE ${OWNER_SCOPE} = $1
+    WHERE ${MY_SPEND_SCOPE()}
       AND t.transaction_type IN ('debit', 'fee', 'interest', 'refund', 'credit')
       AND t.transaction_date >= $2
       AND ${EXCLUDE_NON_SPEND}
@@ -91,7 +91,7 @@ export async function GET(req: NextRequest) {
       ${STATEMENTS_JOIN}
       LEFT JOIN transaction_overrides o ON o.transaction_id = t.id
       LEFT JOIN transaction_splits ts ON ts.transaction_id = t.id AND ts.participant_id = $1
-      WHERE ${OWNER_SCOPE} = $1
+      WHERE ${MY_SPEND_SCOPE()}
         AND t.transaction_type IN ('debit', 'fee', 'interest', 'refund', 'credit')
         AND t.transaction_date >= $2
         AND COALESCE(o.merchant_normalized, t.merchant_normalized, t.merchant_name, t.description) = ANY($3)

src/app/api/analytics/monthly/route.ts

@@ -3,6 +3,7 @@ import { getCurrentUser } from "@/lib/auth";
 import { queryRaw } from "@/lib/db";
 import {
   OWNER_SCOPE,
+  MY_SPEND_SCOPE,
   STATEMENTS_JOIN,
   EFFECTIVE_CATEGORY,
   EXCLUDE_NON_SPEND,
@@ -46,7 +47,7 @@ export async function GET(req: NextRequest) {
     LEFT JOIN transaction_overrides o ON o.transaction_id = t.id
     LEFT JOIN transaction_splits ts ON ts.transaction_id = t.id AND ts.participant_id = $1
     ${STATEMENTS_JOIN}
-    WHERE ${OWNER_SCOPE} = $1
+    WHERE ${MY_SPEND_SCOPE()}
       AND ${NET_SPEND_ROWS}
       AND ${EXCLUDE_NON_SPEND}
       AND ${EXCLUDE_RECONCILED_SOURCE}

src/app/api/analytics/subscriptions/route.ts

@@ -1,7 +1,7 @@
 import { NextRequest, NextResponse } from "next/server";
 import { getCurrentUser } from "@/lib/auth";
 import { queryRaw } from "@/lib/db";
-import { OWNER_SCOPE, STATEMENTS_JOIN, EXCLUDE_NON_SPEND, EXCLUDE_RECONCILED_SOURCE, EFFECTIVE_CATEGORY, mySplitOf } from "@/lib/analytics-sql";
+import { MY_SPEND_SCOPE, STATEMENTS_JOIN, EXCLUDE_NON_SPEND, EXCLUDE_RECONCILED_SOURCE, EFFECTIVE_CATEGORY, mySplitOf } from "@/lib/analytics-sql";
 
 export async function GET(req: NextRequest) {
   const user = await getCurrentUser(req);
@@ -28,7 +28,7 @@ export async function GET(req: NextRequest) {
       LEFT JOIN transaction_overrides o ON o.transaction_id = t.id
       LEFT JOIN transaction_splits ts ON ts.transaction_id = t.id AND ts.participant_id = $1
       ${STATEMENTS_JOIN}
-      WHERE ${OWNER_SCOPE} = $1
+      WHERE ${MY_SPEND_SCOPE()}
         AND t.transaction_type IN ('debit', 'fee')
         AND ${EXCLUDE_NON_SPEND}
         AND ${EXCLUDE_RECONCILED_SOURCE}

src/lib/analytics-sql.ts

@@ -129,10 +129,44 @@ export const SPEND_BASE = `CASE WHEN t.interest_amount IS NOT NULL THEN t.intere
 /** Effective category, honouring overrides. Never NULL. */
 export const EFFECTIVE_CATEGORY = `COALESCE(o.category_override, t.category, 'other')`;
 
+/**
+ * Rows whose cost is partly mine: ones I paid for, plus ones someone else paid
+ * for that I hold a split on.
+ *
+ * Every spend analytic used to gate on `${OWNER_SCOPE} = $1` alone, with
+ * `mySplitOf` scaling *within* that gate. Ownership was therefore a
+ * precondition for an expense being mine — which is backwards for a shared
+ * household. Half a grocery shop is my expense whether the card was mine or
+ * Sonu's; who owns the row says whose *account* the money left, a different
+ * question. It is the same principle the `settled` rule already states: my
+ * share is my expense regardless of who fronted it or whether it has since
+ * been repaid.
+ *
+ * Measured on 2026-08-15 the gate hid 167 rows / $3,210.91 of my own share
+ * (Jan–Jul 2026) from monthly, daily, merchants, subscriptions, fees and the
+ * budget page, while `getParticipantBalances` booked the matching debt
+ * correctly — so the app could tell you that you owed Sonu for a shop while
+ * insisting you had not spent anything on it. Worst month was April 2026
+ * (+$1,354.83), the Europe trips, where she paid for a lot.
+ *
+ * That figure is net of `EXCLUDE_NON_BUDGET_TAGS`: a further $456.50 of
+ * non-owned share in July is `family`-tagged and correctly stays out. Counting
+ * on transaction_type alone gives $3,667.41 and is the wrong comparison.
+ *
+ * Requires `transaction_splits ts` joined on `ts.participant_id =
+ * <participant>` and ${STATEMENTS_JOIN}. That join cannot multiply rows:
+ * `(transaction_id, participant_id)` is UNIQUE.
+ *
+ * Pair it with `myShare`, which returns 0 for a non-owned row with no split —
+ * so admitting a row here can never add more than the share actually held.
+ */
+export const MY_SPEND_SCOPE = (participant = "$1") =>
+  `(${OWNER_SCOPE} = ${participant} OR ts.participant_id IS NOT NULL)`;
+
 /**
  * My percentage share of a transaction, 0-100.
  *
- * Resolution order:
+ * On a row I paid for, resolution order:
  *   1. An explicit `transaction_splits` row for me.
  *   2. The `my_share_percent` override.
  *   3. Whatever is left after everyone else's shares.
@@ -142,17 +176,33 @@ export const EFFECTIVE_CATEGORY = `COALESCE(o.category_override, t.category, 'ot
  * they owe all of it, and there is no row for me to find. Those rows would
  * otherwise land in my spend at full value.
  *
- * Requires `transaction_splits ts` joined on `ts.participant_id = <participant>`
+ * On a row SOMEONE ELSE paid for, only an explicit split row counts, and its
- * and `transaction_overrides o` joined on the transaction.
+ * absence means 0. Both of the other two steps are meaningless there and one of
+ * them is actively wrong:
+ *
+ *  - `my_share_percent` is a single column on `transaction_overrides` with no
+ *    participant scoping, writable by anyone who can see the row. "My" can only
+ *    coherently mean the owner's. Reading it as the viewer's share on someone
+ *    else's transaction would be a guess, and all 402 rows carrying one today
+ *    are owner-side, so there is nothing to be gained by guessing.
+ *  - `100 - everyone else` is the *payer's* remainder by definition. Applied to
+ *    a row I did not pay for it would hand me the payer's share on top of my
+ *    own.
+ *
+ * Requires `transaction_splits ts` joined on `ts.participant_id = <participant>`,
+ * `transaction_overrides o` joined on the transaction, and ${STATEMENTS_JOIN}.
  */
-export const myShare = (participant = "$1") => `COALESCE(
+export const myShare = (participant = "$1") => `CASE
-    ts.share_percent,
+    WHEN ${OWNER_SCOPE} = ${participant} THEN COALESCE(
-    o.my_share_percent,
+      ts.share_percent,
-    100 - COALESCE((
+      o.my_share_percent,
-      SELECT SUM(x.share_percent) FROM transaction_splits x
+      100 - COALESCE((
-      WHERE x.transaction_id = t.id AND x.participant_id <> ${participant}
+        SELECT SUM(x.share_percent) FROM transaction_splits x
-    ), 0)
+        WHERE x.transaction_id = t.id AND x.participant_id <> ${participant}
-  )`;
+      ), 0)
+    )
+    ELSE COALESCE(ts.share_percent, 0)
+  END`;
 
 /** `base` scaled to my share. Use for every per-user spend total. */
 export const mySplitOf = (base: string, participant = "$1") =>

src/lib/queries.ts

@@ -160,6 +160,30 @@ interface TransactionFilters {
   trip_all_rows?: boolean;
 }
 
+/**
+ * `myShare` from analytics-sql.ts, in subselect form.
+ *
+ * Same resolution and the same ownership branch, spelled out inline because
+ * this query has no `transaction_splits ts` join scoped to the viewer — it
+ * already aggregates every participant's splits for display, and adding a
+ * second viewer-scoped join purely to reuse the fragment would be the more
+ * confusing of the two. Kept adjacent to its twin so a change to one is an
+ * obvious prompt to change the other; the mirror is covered by a test that
+ * asserts the two agree row for row.
+ */
+export const MY_SHARE_PCT = `CASE
+  WHEN COALESCE(t.owner_id, s.owner_id) = $1 THEN COALESCE(
+    (SELECT x.share_percent FROM transaction_splits x
+      WHERE x.transaction_id = t.id AND x.participant_id = $1),
+    o.my_share_percent,
+    100 - COALESCE((SELECT SUM(x.share_percent) FROM transaction_splits x
+                     WHERE x.transaction_id = t.id AND x.participant_id <> $1), 0)
+  )
+  ELSE COALESCE(
+    (SELECT x.share_percent FROM transaction_splits x
+      WHERE x.transaction_id = t.id AND x.participant_id = $1), 0)
+END`;
+
 export async function getTransactions(ownerId: number, filters: TransactionFilters) {
   // A real trip id, not "unassigned" — there is no trip to participate in for
   // rows that belong to none, so the owner scoping has to stand there.
@@ -297,23 +321,14 @@ export async function getTransactions(ownerId: number, filters: TransactionFilte
       ${NATIVE_CURRENCY} as currency,
       ${AMOUNT_UNCONVERTED} as amount_unconverted,
       -- My share, resolved the same way analytics does it (see myShare in
-      -- analytics-sql.ts): explicit split row, then override, then whatever is
+      -- analytics-sql.ts): on a row I paid for, explicit split row, then
-      -- left after everyone else. Computed here so the UI cannot drift from
+      -- override, then whatever is left after everyone else; on a row someone
-      -- the totals it is drilling into.
+      -- else paid for, only an explicit split row, absent meaning 0. Computed
-      COALESCE(
+      -- here so the UI cannot drift from the totals it is drilling into — this
-        (SELECT x.share_percent FROM transaction_splits x
+      -- list shows rows I merely hold a split on, and before MY_SPEND_SCOPE
-          WHERE x.transaction_id = t.id AND x.participant_id = $1),
+      -- those rows read as a share of a total that excluded them entirely.
-        o.my_share_percent,
+      ${MY_SHARE_PCT}::numeric(5,2) as my_share_pct,
-        100 - COALESCE((SELECT SUM(x.share_percent) FROM transaction_splits x
+      (COALESCE(t.amount_aud, t.amount) * ${MY_SHARE_PCT} / 100)::numeric(12,2) as my_amount,
-                         WHERE x.transaction_id = t.id AND x.participant_id <> $1), 0)
-      )::numeric(5,2) as my_share_pct,
-      (COALESCE(t.amount_aud, t.amount) * COALESCE(
-        (SELECT x.share_percent FROM transaction_splits x
-          WHERE x.transaction_id = t.id AND x.participant_id = $1),
-        o.my_share_percent,
-        100 - COALESCE((SELECT SUM(x.share_percent) FROM transaction_splits x
-                         WHERE x.transaction_id = t.id AND x.participant_id <> $1), 0)
-      ) / 100)::numeric(12,2) as my_amount,
       COALESCE(t.owner_id, s.owner_id) as owner_id,
       p.name as owner_name,
       COALESCE(src.created_at, t.created_at) as created_at,