fix(interactive): resolve --label-column case-insensitively before pre-fill

internal/cli/interactive.go

@@ -625,22 +625,47 @@ func promptCategorySpecific(p *ui.Printer, pr prompter, a *runDataIngestArgs) (b
 // named "label" if present; otherwise — the header isn't readable yet — it falls
 // back to free text pre-filled with the supplied value so the flow never stalls.
 //
-// supplied is guarded through defaultInOptions before it reaches survey.Select:
-// a mistyped --label-column that is not one of the real headers would otherwise
-// abort the prompt on a TTY, the same default-not-in-options crash guarded
-// everywhere else in the guided flow.
+// supplied is resolved to the header's own spelling (canonicalHeader) and then
+// guarded through defaultInOptions before it reaches survey.Select: a mistyped
+// --label-column that is not one of the real headers would otherwise abort the
+// prompt on a TTY, the same default-not-in-options crash guarded everywhere
+// else in the guided flow.
 func promptLabelColumn(pr prompter, category, root, question, supplied string) (string, error) {
 	headers, err := push.PreviewLabelHeaders(category, root)
 	if err == nil && len(headers) > 0 {
 		ans, serr := pr.Select(question,
 			"pick the label/target column from your CSV header", headers,
-			defaultInOptions(supplied, headers, defaultLabelChoice(headers)))
+			defaultInOptions(canonicalHeader(supplied, headers), headers, defaultLabelChoice(headers)))
 		return strings.TrimSpace(ans), serr
 	}
 	ans, ierr := pr.Input(question, "the label/target column name", supplied, nil)
 	return strings.TrimSpace(ans), ierr
 }
 
+// canonicalHeader returns the header that matches want case-insensitively, so a
+// --label-column differing from the CSV only in case pre-selects the real column
+// instead of silently falling back to the header default.
+//
+// Why this is needed at all: defaultInOptions matches EXACTLY, and until #505 a
+// supplied --label-column skipped the prompt entirely, so its spelling was kept
+// verbatim and never had to agree with the header. Now that the question is
+// always asked, an unresolved value falls through to defaultLabelChoice — the
+// FIRST column when nothing is named "label" — and Enter accepts that wrong
+// column. Resolving here (rather than loosening defaultInOptions, which also
+// guards --intent and --label-policy against fixed vocabularies) keeps the
+// case-insensitivity where the options are user data.
+//
+// Returns want unchanged when nothing matches, leaving defaultInOptions to apply
+// the fallback: a genuine typo must still be caught, not case-folded into a hit.
+func canonicalHeader(want string, headers []string) string {
+	for _, h := range headers {
+		if strings.EqualFold(h, want) {
+			return h
+		}
+	}
+	return want
+}
+
 // defaultLabelChoice pre-highlights a column literally named "label"
 // (case-insensitive) when one exists, else the first column — a sensible
 // starting point for the SELECT.

internal/cli/interactive_test.go

@@ -700,7 +700,9 @@ func TestRunInteractive_SuppliedLabelColumnStillAsks(t *testing.T) {
 //
 // Mutation-proof: passing `supplied` straight to pr.Select (dropping the guard)
 // makes the "mistyped" row error under the strict fake; not threading the value
-// at all makes the "valid-supplied" row return the header default instead.
+// at all makes the "valid-supplied" row return the header default instead;
+// dropping canonicalHeader (resolving case) reddens the case-mismatch rows,
+// which resolve to "age" — the first column — exactly as the defect did.
 func TestPromptLabelColumn_SuppliedDefaultPrefillsAndGuards(t *testing.T) {
 	dir := tabularDir(t) // header: age,income,churned  (no column named "label")
 	const cat = "tabular_classification"
@@ -714,6 +716,14 @@ func TestPromptLabelColumn_SuppliedDefaultPrefillsAndGuards(t *testing.T) {
 		{"valid-supplied-is-preselected", "income", "income"},
 		{"empty-supplied-uses-header-default", "", "age"}, // defaultLabelChoice → first header
 		{"mistyped-supplied-falls-back", "incom", "age"},  // guarded, no crash
+
+		// Case-only differences must bind the HEADER's spelling, not fall back.
+		// Before the canonicalHeader resolve these landed on "age": the exact
+		// match failed, and with no column named "label" defaultLabelChoice
+		// returns the first column — which Enter then silently accepts as the
+		// label. That is the whole defect, so these rows are the regression.
+		{"case-mismatch-supplied-resolves", "Income", "income"},
+		{"case-mismatch-uppercase-resolves", "CHURNED", "churned"},
 	}
 	for _, tc := range cases {
 		t.Run(tc.name, func(t *testing.T) {