feat(go): add --print-fio-table flag to fuj sync --dry-run

Prints an aligned tabwriter table of every Fio transaction in the
look-back window, with a STATUS column showing NEW (would be appended)
or DUP (already in sheet). Only fires when --dry-run is also set, so
it can't affect real syncs. Refactors Sync ID computation into a single
pre-pass shared by both the table printer and the row builder.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docs/plans/2026-05-07-1321-fuj-sync-print-fio-table.md

@@ -0,0 +1,29 @@
+# Add `--print-fio-table` debug flag to `fuj sync`
+
+## Context
+
+The Go port of `fuj sync --dry-run` currently prints only the **new**
+transactions — i.e. rows that will be appended to the payments sheet after
+deduping against existing Sync IDs (see [sync.go:125-129](../../go/internal/services/banksync/sync.go#L125-L129)).
+When debugging Fio sync issues ("why isn't transaction X showing up?",
+"is the dedup working?"), there's no way to see what Fio actually
+returned versus what got filtered as a duplicate.
+
+This change adds a `--print-fio-table` flag that, **only when combined
+with `--dry-run`**, prints an aligned table of every Fio transaction in
+the window with each row marked `NEW` (would be appended) or `DUP`
+(already in sheet, skipped). The flag is silently ignored without
+`--dry-run`, so it can't accidentally fire during a real sync.
+
+## Decisions
+
+- Flag name: `--print-fio-table` (specific, not generic `--verbose`).
+- Columns: `DATE | AMOUNT | SENDER | VS | MESSAGE | BANKID | STATUS`,
+  with MESSAGE truncated and STATUS = `NEW` / `DUP`.
+- Scope: only effective when `--dry-run` is also set.
+
+## Files modified
+
+- [go/cmd/fuj/main.go](../../go/cmd/fuj/main.go) — new flag + SyncOpts field
+- [go/internal/services/banksync/sync.go](../../go/internal/services/banksync/sync.go) — SyncOpts struct + refactored step 4
+- [go/internal/services/banksync/debug.go](../../go/internal/services/banksync/debug.go) — printFioTable helper (new)

go/cmd/fuj/main.go

@@ -135,8 +135,9 @@ func syncCmd(args []string) {
 	toStr := fs.String("to", "", "end date YYYY-MM-DD")
 	sort := fs.Bool("sort", true, "sort sheet by date after appending")
 	dryRun := fs.Bool("dry-run", false, "print planned writes without modifying the sheet")
+	printFioTable := fs.Bool("print-fio-table", false, "with --dry-run: print aligned table of every Fio transaction with NEW/DUP status")
 	fs.Usage = func() {
-		fmt.Fprintln(os.Stderr, "usage: fuj sync [--days N] [--from YYYY-MM-DD --to YYYY-MM-DD] [--sort] [--dry-run]")
+		fmt.Fprintln(os.Stderr, "usage: fuj sync [--days N] [--from YYYY-MM-DD --to YYYY-MM-DD] [--sort] [--dry-run] [--print-fio-table]")
 		fs.PrintDefaults()
 	}
 	if err := fs.Parse(args); err != nil {
@@ -154,7 +155,7 @@ func syncCmd(args []string) {
 	}
 	fioCli := fio.New(cfg.FioAPIToken, config.IBANAccountNum(cfg.BankAccount), nil)
 
-	opts := banksync.SyncOpts{Days: *days, Sort: *sort, DryRun: *dryRun}
+	opts := banksync.SyncOpts{Days: *days, Sort: *sort, DryRun: *dryRun, PrintFioTable: *printFioTable}
 	if *fromStr != "" && *toStr != "" {
 		opts.From, err = time.Parse("2006-01-02", *fromStr)
 		if err != nil {

go/internal/services/banksync/fio_table.go

@@ -0,0 +1,32 @@
+package banksync
+
+import (
+	"fmt"
+	"io"
+	"text/tabwriter"
+
+	"fuj-management/go/internal/io/fio"
+)
+
+func printFioTable(w io.Writer, txns []fio.Transaction, syncIDs []string, existing map[string]bool) {
+	tw := tabwriter.NewWriter(w, 0, 0, 2, ' ', 0)
+	fmt.Fprintln(tw, "DATE\tAMOUNT\tSENDER\tVS\tMESSAGE\tBANKID\tSTATUS")
+	for i, tx := range txns {
+		status := "NEW"
+		if existing[syncIDs[i]] {
+			status = "DUP"
+		}
+		fmt.Fprintf(tw, "%s\t%.2f\t%s\t%s\t%s\t%s\t%s\n",
+			tx.Date, tx.Amount, tx.Sender, tx.VS,
+			truncRunes(tx.Message, 40), tx.BankID, status)
+	}
+	_ = tw.Flush()
+}
+
+func truncRunes(s string, n int) string {
+	rs := []rune(s)
+	if len(rs) <= n {
+		return s
+	}
+	return string(rs[:n-1]) + "…"
+}

go/internal/services/banksync/sync.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"fuj-management/go/internal/domain/synch"
 	"fuj-management/go/internal/io/fio"
+	"os"
 	"strings"
 	"time"
 )
@@ -31,6 +32,7 @@ type SyncOpts struct {
 	From, To      time.Time // explicit window (overrides Days)
 	Sort          bool      // sort the sheet by Date after appending
 	DryRun        bool      // print planned writes without modifying the sheet
+	PrintFioTable bool      // with DryRun: print every fetched Fio txn with NEW/DUP status
 }
 
 // SyncToSheets fetches Fio transactions and appends new ones to the payments sheet.
@@ -92,14 +94,14 @@ func SyncToSheets(
 			from.Format("2006-01-02"), to.Format("2006-01-02"), len(txns))
 	}
 
-	// 4. Append new rows.
+	// 4a. Compute Sync IDs for every fetched txn (shared by table-print and row-build).
-	var newRows [][]any
+	syncIDs := make([]string, len(txns))
-	for _, tx := range txns {
+	for i, tx := range txns {
 		currency := tx.Currency
 		if currency == "" {
 			currency = "CZK"
 		}
-		id := synch.GenerateSyncID(synch.Transaction{
+		syncIDs[i] = synch.GenerateSyncID(synch.Transaction{
 			Date:     tx.Date,
 			Amount:   tx.Amount,
 			Currency: currency,
@@ -108,13 +110,23 @@ func SyncToSheets(
 			Message:  tx.Message,
 			BankID:   tx.BankID,
 		})
-		if existingIDs[id] {
+	}
+
+	// 4b. Optional debug table (dry-run only).
+	if opts.DryRun && opts.PrintFioTable {
+		printFioTable(os.Stdout, txns, syncIDs, existingIDs)
+	}
+
+	// 4c. Build new rows.
+	var newRows [][]any
+	for i, tx := range txns {
+		if existingIDs[syncIDs[i]] {
 			continue
 		}
 		newRows = append(newRows, []any{
 			tx.Date, tx.Amount,
 			"", "", "", "", // manual fix, Person, Purpose, Inferred Amount
-			tx.Sender, tx.VS, tx.Message, tx.BankID, id,
+			tx.Sender, tx.VS, tx.Message, tx.BankID, syncIDs[i],
 		})
 	}