test(import): a folder of only header-only files kept no record and refuses (improvise-8jk6.6)

After merging PR #314, a header-only file's seeded File proposal means the
category check alone no longer refuses an import that kept no record.
nothing_to_import does, and this pins it. The docs now name from_merge
(switched to from_csv in the merge) among the CSV entry points.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VdfEGXA7aJ6ftMsCc9PJze

context/code/formula-and-io.md

@@ -670,8 +670,10 @@ This is not caution for its own sake. When the parser first changed, eleven
 tests in four files failed. Every one handed parser output to
 `ImportPipeline::new`, the JSON constructor, which would read every column as
 text and propose `Revenue` as a Category. Production had the same shape at all
-three CSV entry points: `main.rs`'s single file and merge, and
-`ImportJsonHeadless`. Now that mistake does not compile. Two holes remain, and
+three CSV entry points: `main.rs`'s single file, `ImportPipeline::from_merge`
+(the merge path, from PR #314), and `ImportJsonHeadless`. `from_merge` merged
+in with `Self::new` and now calls `Self::from_csv`. Now that mistake does not
+compile. Two holes remain, and
 both take a deliberate step. `ImportPipeline::records` is still a public
 `Vec<Value>`, and a test helper once copied it out of a CSV pipeline into a
 JSON one. And `CsvRecords` derefs to a slice that `.to_vec()` will copy.
@@ -708,6 +710,14 @@ records were skipped as not JSON objects`, or `the source has no records`. The
 wizard asks it first on `ReviewProposals`, where another array path can still
 be chosen.
 
+One case meets PR #314's "a header-only file is still a file". A folder whose
+CSVs are **all** header-only has no records, only sources. Built from
+`from_merge`'s seeded proposals alone, it would save `File` items, empty
+columns and one empty records view per file. It is refused here, because it
+kept no record. A header-only file *beside* files with rows is unaffected,
+since some record was kept. Whether an all-header-only folder should instead
+save its structure is a question for the user on the PR.
+
 **A partial skip stays a warning.** Some records kept and some skipped still
 builds, exits 0, and warns with a count: `Skipped 1 of 3 records that were not
 JSON objects`. The argument: a non-object in an array of records is not a
@@ -717,7 +727,7 @@ trailing `null` or a stray scalar in a hand-edited file. Every record that
 Making it fatal would fail every import that carries one stray element.
 Making it a distinct non-zero exit that still writes gives a contract where
 `import … && next` stops even though the file was written. That is a question
-for the user (PR #TBD), and `an_import_that_skips_some_records_warns_with_a_count_and_still_writes`
+put to the user on the PR that fixed 8jk6.6, and `an_import_that_skips_some_records_warns_with_a_count_and_still_writes`
 pins the current answer so that changing it is a decision.
 
 ### A folder of CSVs is one sparse model, with a view per file (improvise-lpzu)

context/test-evidence/formula-and-io.md

@@ -1894,3 +1894,14 @@ improvise-8jk6.12 (4). A `region` of `"   "` is kept as a record with no
 predates this PR (improvise-ych), but the sparse-record rule now rests on it:
 without it the value becomes an item named `"   "`. Rival F4 (the reviewer's
 fault) fails it.
+
+### a_folder_of_only_header_only_files_keeps_no_record_and_refuses
+
+improvise-8jk6.6 meeting PR #314's rule that a header-only file is still a
+file. Written after merging `main` at `c91cc055`, where the two rules first
+met. The file seeds give the pipeline a `File` Category proposal even with no
+records. So without `nothing_to_import` the build succeeds and saves `File`
+items and empty views: the category check alone cannot refuse. The `setup`
+assertion proves that seeded proposal exists, so the test is not passing only
+because there was no category. **R7**, the check removed from the build, fails
+it. Whether this case should refuse is put to the user on the PR.

crates/improvise-io/src/import/wizard.rs

@@ -3338,6 +3338,16 @@ mod tests {
         assert_eq!(wb.model.get_cell(&key), Some(&CellValue::Number(5.0)));
     }
 
+    /// improvise-8jk6.6 meets lpzu's header-only rule: a folder of nothing but
+    /// headers kept no record. Evidence: `context/test-evidence/formula-and-io.md`.
+    #[test]
+    fn a_folder_of_only_header_only_files_keeps_no_record_and_refuses() {
+        let p = merged_pipeline(&[("m/a.csv", "entity,x\n"), ("m/b.csv", "entity,y\n")]);
+        assert!(p.proposals.iter().any(|f| f.field == "File"), "setup");
+        let msg = p.build_model().expect_err("refuses").to_string();
+        assert_eq!(msg, "Nothing to import: the source has no records");
+    }
+
     /// improvise-8jk6.6: the wizard asks on the review step, where another
     /// path can still be chosen. Evidence: the test-evidence doc.
     #[test]