harden schwab csv parsing in manner similar to fidelity

src/brokerage/schwab.zig

@@ -25,9 +25,11 @@
 //! 4. Rows with symbol "Cash & Cash Investments" are treated as cash.
 //!    The row with symbol "Positions Total" is skipped.
 //!
-//! 5. Hardcodes the expected column layout. If Schwab changes the CSV
-//!    format, this parser will break. The header row is not validated
-//!    beyond being skipped.
+//! 5. Hardcodes the expected column layout via fixed indices. The header
+//!    row is validated (see `validateHeader`) to confirm the columns the
+//!    parser reads are where it expects them, so a Schwab reorder/rename of
+//!    a read-column fails loudly as `error.UnexpectedHeader` instead of
+//!    silently mis-reading a value.
 //!
 //! ## Schwab summary - limitations
 //!
@@ -75,6 +77,47 @@ const Col = struct {
     const asset_type = 16;
 };
 
+/// Distinctive prefix for each column `parseCsv` reads, at its expected
+/// index, matched case-insensitively. `Price` is matched exactly (not by
+/// prefix) because its bare label is a prefix of the "Price Chng ..."
+/// columns, so a startsWith could not tell them apart on a reorder.
+///
+/// Only the columns the parser actually reads are validated: Schwab
+/// reordering, renaming, or adding a column we ignore is tolerated, while a
+/// change that would shift a value we depend on is rejected with
+/// `error.UnexpectedHeader` instead of silently mis-reading. Schwab labels
+/// use a "Short (Long)" form ("Qty (Quantity)"); older exports and the test
+/// fixtures use the short form ("Qty") - a prefix match accepts both. Keep
+/// in sync with `Col`.
+const ExpectedColumn = struct { idx: usize, prefix: []const u8, exact: bool = false };
+const expected_header = [_]ExpectedColumn{
+    .{ .idx = Col.symbol, .prefix = "Symbol" },
+    .{ .idx = Col.price, .prefix = "Price", .exact = true },
+    .{ .idx = Col.quantity, .prefix = "Qty" },
+    .{ .idx = Col.market_value, .prefix = "Mkt Val" },
+    .{ .idx = Col.cost_basis, .prefix = "Cost Basis" },
+    .{ .idx = Col.asset_type, .prefix = "Asset Type" },
+};
+
+/// Validate that the header carries the columns `parseCsv` indexes into,
+/// at their expected positions (case-insensitive). Reuses `splitCsvLine`
+/// so the surrounding quotes are stripped the same way as data rows. A
+/// missing/renamed/reordered read-column - or too few columns - fails with
+/// `error.UnexpectedHeader`; trailing or unused-column changes are
+/// tolerated. See `expected_header`.
+fn validateHeader(header: []const u8) error{UnexpectedHeader}!void {
+    var cols: [expected_columns][]const u8 = undefined;
+    const n = splitCsvLine(header, &cols);
+    if (n < expected_columns) return error.UnexpectedHeader;
+    inline for (expected_header) |c| {
+        const ok = if (c.exact)
+            std.ascii.eqlIgnoreCase(cols[c.idx], c.prefix)
+        else
+            std.ascii.startsWithIgnoreCase(cols[c.idx], c.prefix);
+        if (!ok) return error.UnexpectedHeader;
+    }
+}
+
 /// Split a Schwab CSV line on commas, stripping surrounding quotes from each field.
 /// Returns the number of columns parsed. Fields are slices into the input line.
 fn splitCsvLine(line: []const u8, cols: *[expected_columns][]const u8) usize {
@@ -147,8 +190,12 @@ pub fn parseCsv(allocator: std.mem.Allocator, data: []const u8) !CsvResult {
 
     // Line 2: blank (skip)
     _ = lines.next();
-    // Line 3: header row (skip)
-    _ = lines.next();
+    // Line 3: header row - validate the columns we read are where we expect,
+    // so a Schwab format change surfaces as UnexpectedHeader (and, in the
+    // flagless audit, a "could not parse" warning) rather than silently
+    // reading a shifted column.
+    const header_line = lines.next() orelse return error.UnexpectedHeader;
+    try validateHeader(std.mem.trimEnd(u8, header_line, &.{ '\r', ' ' }));
 
     // Data rows
     while (lines.next()) |line| {
@@ -346,6 +393,65 @@ test "parseCsv basic" {
     try std.testing.expect(parsed.positions[1].quantity == null);
 }
 
+test "parseCsv accepts the real Short (Long) header labels" {
+    // Real Schwab exports label columns "Qty (Quantity)", "Mkt Val (Market
+    // Value)", etc. (the fixtures above use the short form). The prefix-token
+    // header validation must accept both forms.
+    const csv =
+        "\"Positions for account Sample IRA ...1234 as of 10:00 AM ET, 2026/06/27\"\n" ++
+        "\n" ++
+        "\"Symbol\",\"Description\",\"Price Chng $ (Price Change $)\",\"Price Chng % (Price Change %)\",\"Price\",\"Qty (Quantity)\",\"Day Chng $ (Day Change $)\",\"Day Chng % (Day Change %)\",\"Mkt Val (Market Value)\",\"Cost Basis\",\"Gain $ (Gain/Loss $)\",\"Gain % (Gain/Loss %)\",\"Ratings\",\"Reinvest?\",\"Reinvest Capital Gains?\",\"% of Acct (% of Account)\",\"Asset Type\",\n" ++
+        "\"AMZN\",\"AMAZON.COM INC\",\"5.55\",\"2.38%\",\"239.20\",\"100\",\"$8.00\",\"2.38%\",\"$23,920.00\",\"$10,000.00\",\"$13,920.00\",\"139%\",\"C\",\"No\",\"N/A\",\"41.54%\",\"Equity\",\n";
+    const allocator = std.testing.allocator;
+    const parsed = try parseCsv(allocator, csv);
+    defer allocator.free(parsed.positions);
+
+    try std.testing.expectEqual(@as(usize, 1), parsed.positions.len);
+    try std.testing.expectEqualStrings("AMZN", parsed.positions[0].symbol);
+    try std.testing.expectApproxEqAbs(@as(f64, 100), parsed.positions[0].quantity.?, 0.01);
+    try std.testing.expectApproxEqAbs(@as(f64, 23920.00), parsed.positions[0].current_value.?, 0.01);
+    try std.testing.expectApproxEqAbs(@as(f64, 10000.00), parsed.positions[0].cost_basis.?, 0.01);
+}
+
+test "parseCsv rejects a header whose read-columns are reordered" {
+    // Symbol (idx 0) and Price (idx 4) are swapped. Positional parsing would
+    // read a price where a symbol belongs, so validateHeader must reject it.
+    const csv =
+        "\"Positions for account Sample IRA ...1234 as of 10:00 AM ET, 2026/06/27\"\n" ++
+        "\n" ++
+        "\"Price\",\"Description\",\"Price Chng $\",\"Price Chng %\",\"Symbol\",\"Qty\",\"Day Chng $\",\"Day Chng %\",\"Mkt Val\",\"Cost Basis\",\"Gain $\",\"Gain %\",\"Ratings\",\"Reinvest?\",\"Reinvest Capital Gains?\",\"% of Acct\",\"Asset Type\",\n" ++
+        "\"239.20\",\"AMAZON.COM INC\",\"5.55\",\"2.38%\",\"AMZN\",\"100\",\"$8.00\",\"2.38%\",\"$23,920.00\",\"$10,000.00\",\"$13,920.00\",\"139%\",\"C\",\"No\",\"N/A\",\"41.54%\",\"Equity\",\n";
+    const allocator = std.testing.allocator;
+    try std.testing.expectError(error.UnexpectedHeader, parseCsv(allocator, csv));
+}
+
+test "parseCsv tolerates reordering of columns it does not read" {
+    // The two Price-change columns (idx 2, 3) are swapped. Neither is read,
+    // so validation passes and the read-columns still resolve correctly.
+    const csv =
+        "\"Positions for account Sample IRA ...1234 as of 10:00 AM ET, 2026/06/27\"\n" ++
+        "\n" ++
+        "\"Symbol\",\"Description\",\"Price Chng % (Price Change %)\",\"Price Chng $ (Price Change $)\",\"Price\",\"Qty (Quantity)\",\"Day Chng $ (Day Change $)\",\"Day Chng % (Day Change %)\",\"Mkt Val (Market Value)\",\"Cost Basis\",\"Gain $ (Gain/Loss $)\",\"Gain % (Gain/Loss %)\",\"Ratings\",\"Reinvest?\",\"Reinvest Capital Gains?\",\"% of Acct (% of Account)\",\"Asset Type\",\n" ++
+        "\"AMZN\",\"AMAZON.COM INC\",\"2.38%\",\"5.55\",\"239.20\",\"100\",\"$8.00\",\"2.38%\",\"$23,920.00\",\"$10,000.00\",\"$13,920.00\",\"139%\",\"C\",\"No\",\"N/A\",\"41.54%\",\"Equity\",\n";
+    const allocator = std.testing.allocator;
+    const parsed = try parseCsv(allocator, csv);
+    defer allocator.free(parsed.positions);
+
+    try std.testing.expectEqual(@as(usize, 1), parsed.positions.len);
+    try std.testing.expectEqualStrings("AMZN", parsed.positions[0].symbol);
+    try std.testing.expectApproxEqAbs(@as(f64, 100), parsed.positions[0].quantity.?, 0.01);
+    try std.testing.expectApproxEqAbs(@as(f64, 23920.00), parsed.positions[0].current_value.?, 0.01);
+}
+
+test "parseCsv rejects a header with too few columns" {
+    const csv =
+        "\"Positions for account Sample IRA ...1234 as of 10:00 AM ET, 2026/06/27\"\n" ++
+        "\n" ++
+        "\"Symbol\",\"Description\",\"Price\"\n";
+    const allocator = std.testing.allocator;
+    try std.testing.expectError(error.UnexpectedHeader, parseCsv(allocator, csv));
+}
+
 test "parseSummary basic" {
     const data =
         \\Sample Roth