fix(spec): refuse a whitespace-only reference on lookup/master_detail (#16920)

The #13632 refinement spelled its emptiness test as `reference === ''`, so a
whitespace-only target passed a door whose whole purpose is to name an object.
Measured on the built artifact: absent and `''` were refused while `'   '` and
`'\t\n'` were accepted, at both the field and the document level.

Apply the test to the trimmed value, so a blank target joins absent and `''`
under the same `custom` issue, the same `reference` path and the same message.
The notion of blank is `.trim()` — the same one `EvaluatedExpressionSchema`
applies to `source`, not a third one.

Trimming is for the TEST only: a target with surrounding whitespace is authored
and is still stored as written, and a non-string still answers `invalid_type`
from the base schema. Both boundaries are pinned.


Claude-Session: https://claude.ai/code/session_016N6xmWt5hYm94ffVEwGH8x

Co-authored-by: Claude <noreply@anthropic.com>

Author: claude[bot]

.changeset/field-reference-non-blank.md

@@ -0,0 +1,51 @@
+---
+"@objectstack/spec": minor
+---
+
+fix(spec): `FieldSchema` refuses a WHITESPACE-ONLY `reference` on `lookup` / `master_detail`
+
+**BREAKING** accept-set narrowing on `FieldSchema`, shipped as `minor` under the
+repo's launch-window convention for breaking changes — the same grade the nearest
+tightening precedents shipped with, including #13632, the narrowing this one
+finishes.
+
+#13632 closed the declared-but-unenforced gap on `FieldSchema.reference` in 17.3.0,
+but spelled its emptiness test as an equality against `''`, so a whitespace-only
+target (`reference: '   '`) passed a door whose whole purpose is to name an object.
+Measured on the built artifact before this change: absent and `''` were refused,
+`'   '` and `'\t\n'` were **accepted**, at both the field level (`FieldSchema`) and
+the document level (`ObjectSchema`), on `lookup` and `master_detail` alike.
+
+A blank target names no object either. The declared grammar for an object name is
+`/^[a-z_][a-z0-9_]*$/` (`ObjectSchema`'s own `fields` key schema), so no
+whitespace-bearing string can ever resolve to one, and all three consequences the
+existing refusal message lists hold verbatim for `'   '`: the record picker has no
+object to query, `$expand` has nothing to resolve, and no relationship index can be
+built. It is also the state a cleared target picker emits — `''` and `'   '` are one
+authoring gesture that was getting opposite verdicts.
+
+What newly gets rejected: `type: 'lookup'` or `type: 'master_detail'` whose
+`reference` is present but consists only of whitespace. It joins absent and `''`
+under the same `custom` issue, on the same `reference` path, with the same
+prescriptive message — no new message and no new error shape. The notion of blank
+is `.trim()`, the same one `EvaluatedExpressionSchema` applies to `source`, not a
+third one.
+
+Everything else is untouched. Trimming is applied to the TEST only, never to the
+stored value: a target with surrounding whitespace (`' company '`) is still accepted
+and still round-trips byte-identically. A non-string `reference` still answers
+`invalid_type` from the base schema, not the custom message — that distinction is
+deliberate and pinned. Non-relationship types never carried the requirement, and the
+`Field.lookup()` / `Field.masterDetail()` helpers take the target as their first
+positional argument, so helper-authored fields cannot produce this shape.
+
+The measured population of affected authored sources is zero: one repo-wide census
+over all tracked files found a single whitespace-only `reference` in the tree, an
+objectql test fixture cast past Zod on the documented `registerObject` path that
+skips schema validation by design — it does not reach this door, and it is green
+after the change. The census and its positive controls are recorded on the PR.
+Downstream, objectui's two metadata writers already refuse this shape with
+`reference.trim() !== ''`; upstream trimming turns their declared divergence into
+contract-following, and that note can now be retired.
+
+<!-- adr-0087: not-required (no-migration-prescription) A validity narrowing over an existing key: `reference` is not removed, renamed or re-shaped, so there is no tombstone and nothing mechanical for `objectstack migrate meta` to rewrite. The parse refusal is the channel that reaches an affected author, at the parse site, carrying the remedy; which target object a blank `lookup` / `master_detail` was meant to point at is authoring intent no migration entry can decide on an upgrader's behalf — and the measured population of affected sources is zero across all tracked files (census on the PR). Mirrors the disposition of #13632, whose emptiness test this completes. -->

packages/spec/src/data/field.test.ts

@@ -2278,6 +2278,78 @@ describe('Relationship target — `reference` required on lookup/master_detail (
     },
   );
 
+  // [#16126] A whitespace-only target is the same hole a third way: it names
+  // no object either (no whitespace-bearing string can match the declared
+  // object-name grammar), and it is what a cleared target picker emits when
+  // the value round-trips through an input. The notion of blank is `.trim()`,
+  // the same one `EvaluatedExpressionSchema` applies to `source`.
+
+  it.each(['lookup', 'master_detail'] as const)(
+    'refuses a %s whose reference is whitespace-only — same issue, same path, same message as `\'\'`',
+    (type) => {
+      const result = FieldSchema.safeParse({
+        name: 'company_id',
+        label: 'Company',
+        type,
+        reference: '   ',
+      });
+      expect(result.success).toBe(false);
+      const issue = result.error!.issues.find((i) => i.path.join('.') === 'reference');
+      expect(issue).toBeDefined();
+      expect(issue!.code).toBe('custom');
+      expect(issue!.message).toMatch(/non-empty `reference`/);
+      expect(issue!.message).toMatch(/target object/);
+    },
+  );
+
+  it.each(['\t', '\n', ' \t\n '] as const)(
+    'refuses a lookup whose reference is only whitespace (%j) — not just the space character',
+    (reference) => {
+      const result = FieldSchema.safeParse({
+        name: 'company_id', label: 'Company', type: 'lookup', reference,
+      });
+      expect(result.success).toBe(false);
+      expect(
+        result.error!.issues.find((i) => i.path.join('.') === 'reference')?.code,
+      ).toBe('custom');
+    },
+  );
+
+  it('refuses a whitespace-only reference at the DOCUMENT level too, located at the field', () => {
+    const result = ObjectSchema.safeParse({
+      name: 'acct_note',
+      label: 'Note',
+      fields: { rel: { name: 'rel', label: 'Rel', type: 'lookup', reference: '   ' } },
+    });
+    expect(result.success).toBe(false);
+    const issue = result.error!.issues.find(
+      (i) => i.path.join('.') === 'fields.rel.reference',
+    );
+    expect(issue).toBeDefined();
+    expect(issue!.code).toBe('custom');
+  });
+
+  it.each([42, null, {}] as const)(
+    'keeps a non-string reference (%j) answering `invalid_type`, not the custom message',
+    (reference) => {
+      const result = FieldSchema.safeParse({
+        name: 'company_id', label: 'Company', type: 'lookup', reference,
+      });
+      expect(result.success).toBe(false);
+      const issue = result.error!.issues.find((i) => i.path.join('.') === 'reference');
+      expect(issue!.code).toBe('invalid_type');
+      expect(issue!.message).not.toMatch(/non-empty `reference`/);
+    },
+  );
+
+  it('trims only to TEST — a name with surrounding whitespace is authored and is stored as written', () => {
+    const result = FieldSchema.safeParse({
+      name: 'company_id', label: 'Company', type: 'lookup', reference: ' company ',
+    });
+    expect(result.success).toBe(true);
+    if (result.success) expect(result.data.reference).toBe(' company ');
+  });
+
   it.each(['lookup', 'master_detail'] as const)(
     'accepts a %s with a non-empty reference (positive control: the check refuses only the hole)',
     (type) => {

packages/spec/src/data/field.zod.ts

@@ -1129,7 +1129,8 @@ export const FieldSchema = lazySchema(() => {
    * Used by `lookup` and `master_detail` field types to define cross-object references.
    * The `reference` property is **required** for these types — it identifies the target
    * object whose records this field links to, and the superRefine below enforces it:
-   * a `lookup` / `master_detail` whose `reference` is missing or empty is refused at
+   * a `lookup` / `master_detail` whose `reference` is missing, empty, or
+   * whitespace-only is refused at
    * parse time. The engine uses `reference` during $expand
    * post-processing to resolve foreign key IDs into full related objects via batch queries.
    * 
@@ -1822,9 +1823,23 @@ export const FieldSchema = lazySchema(() => {
   // measured as accepted before this check). `Field.lookup()` /
   // `Field.masterDetail()` take the target as their first positional
   // argument, so helper-authored fields cannot miss it.
+  //
+  // [#16126] The emptiness test is applied to the TRIMMED value, so a
+  // whitespace-only `reference` joins `undefined` and `''` under this one
+  // issue and this one message. It names no object either: the declared
+  // grammar for an object name is `/^[a-z_][a-z0-9_]*$/` (`ObjectSchema`'s
+  // own `fields` key schema), so no whitespace-bearing string can ever
+  // resolve to one, and all three consequences the message lists hold
+  // verbatim for `'   '`. It is also the state a cleared target picker
+  // emits: `''` and `'   '` are one authoring gesture that was getting
+  // opposite verdicts. The notion of blank is `.trim()` — the same one
+  // `EvaluatedExpressionSchema` applies to `source`, not a third one.
+  // Trimming is for the TEST only: a value with surrounding whitespace is
+  // authored and is still stored as written, and a non-string still
+  // answers `invalid_type` from the base schema before this runs.
   if (
     (field.type === 'lookup' || field.type === 'master_detail') &&
-    (field.reference === undefined || field.reference === '')
+    (field.reference === undefined || field.reference.trim() === '')
   ) {
     ctx.addIssue({
       code: 'custom',