Reject a duration with characters outside its parts (closes #215)

parseDuration fell back to an unanchored search for number-and-unit
pieces when time.ParseDuration failed, and skipped everything in
between. 1.0y became 0, so `snapshot create --prune --keep-newer-than
1.0y` deleted every snapshot of the backed-up names, the new one
included. 2.1w became one week and 1,5y five years. The fallback now
requires the whole input to be whole-number-and-unit parts with nothing
between them. A bare number is rejected before time.ParseDuration sees
it, since Go reads 0 and +0 as zero with no unit.

Judgement call: a space between number and unit (`30 days`) was
accepted and is now an error, matching Go's own units.

Model: opus-5-5

TODO.md

@@ -22,6 +22,15 @@ the tag exists and is exercised; what is left is merging `next` to
 
 # Completed Steps
 
+- 2026-10-06: Made `--older-than` and `--keep-newer-than` reject a
+  duration with characters outside its number-and-unit parts
+  ([issue #215](https://git.eeqj.de/sneak/vaultik/issues/215)). The
+  parser picked out the parts it recognised and skipped the rest, so
+  `1.0y` became zero and `--prune --keep-newer-than 1.0y` deleted every
+  snapshot of the backed-up names, the new one included. `1.0y`,
+  `1,5y`, `30 days`, `x7d` and a bare `0` are now errors; decimals still
+  work in Go units such as `1.5h`.
+
 - 2026-10-06: Made a backup re-chunk a known file that lists a chunk no
   uploaded blob holds
   ([issue #214](https://git.eeqj.de/sneak/vaultik/issues/214)). File

internal/vaultik/helpers.go

@@ -140,24 +140,34 @@ func parseSnapshotName(snapshotID string) string {
 // parseDuration parses a duration string with support for human-friendly units:
 // d/day/days, w/week/weeks, mo/month/months, y/year/years, plus standard Go
 // duration units. Following Go, m is minutes and mo is months. A bare number,
-// an unknown unit, and a negative value are all rejected.
+// an unknown unit, and a negative value are all rejected. Outside the Go
+// units the input must be whole numbers each followed directly by a unit
+// (2w3d), so 1.0y and 30 days are errors; decimals work only in Go units
+// (1.5h).
 func parseDuration(s string) (time.Duration, error) {
 	if strings.HasPrefix(strings.TrimSpace(s), "-") {
 		return 0, errNegativeDuration
 	}
 
+	// A bare number has no unit, but time.ParseDuration accepts 0, which
+	// would put the cutoff at now and select every snapshot.
+	_, err := strconv.ParseFloat(s, 64)
+	if err == nil {
+		return 0, fmt.Errorf("%w: %q", errInvalidDuration, s)
+	}
+
 	d, err := time.ParseDuration(s)
 	if err == nil {
 		return d, nil
 	}
 
-	re := regexp.MustCompile(`(\d+)\s*([a-zA-Z]+)`)
-
-	matches := re.FindAllStringSubmatch(s, -1)
-	if len(matches) == 0 {
+	if !regexp.MustCompile(`^(\d+[a-zA-Z]+)+$`).MatchString(s) {
 		return 0, fmt.Errorf("%w: %q", errInvalidDuration, s)
 	}
 
+	re := regexp.MustCompile(`(\d+)([a-zA-Z]+)`)
+	matches := re.FindAllStringSubmatch(s, -1)
+
 	var total time.Duration
 
 	for _, match := range matches {

internal/vaultik/helpers_test.go

@@ -59,6 +59,7 @@ func TestParseDuration(t *testing.T) {
 		{"30s", 30 * time.Second, false},
 		{"6m", 6 * time.Minute, false},
 		{"1h", time.Hour, false},
+		{"1.5h", 90 * time.Minute, false},
 		// Extended calendar units.
 		{"30d", 30 * 24 * time.Hour, false},
 		{"3days", 3 * 24 * time.Hour, false},
@@ -73,11 +74,21 @@ func TestParseDuration(t *testing.T) {
 		{"1y6mo", 365*24*time.Hour + 180*24*time.Hour, false},
 		// Rejected inputs.
 		{"6", 0, true},   // bare number, no unit
+		{"0", 0, true},   // bare number; time.ParseDuration accepts it
+		{"+0", 0, true},  // bare number; time.ParseDuration accepts it
 		{"5x", 0, true},  // unknown unit
 		{"-5d", 0, true}, // negative, extended unit
 		{"-5h", 0, true}, // negative, Go unit
 		{"", 0, true},    // empty
 		{"garbage", 0, true},
+		// Characters outside the number-and-unit parts must not be
+		// skipped: 1.0y read as 0y would select every snapshot.
+		{"1.0y", 0, true},
+		{"2.1w", 0, true},
+		{"1,5y", 0, true},
+		{"30 days", 0, true},
+		{"30 days ago", 0, true},
+		{"x7d", 0, true},
 	}
 
 	for _, tt := range tests {