docs(spec/ui): the object-tree titleField rationale is true at the pin again

At objectui 20c6d351a nothing reads a tree `titleField`: the renderer's
`getTreeConfig` rung went on objectui#8841, and the `case 'tree'` arm's
flatten rung went on objectui#6152 round 14 (objectui `3fd862510`), so
`ListView.tsx:3985` now reads `treeCfg.labelField || 'name'` and emits no
`titleField`. The OBJECT_TREE_FLAT_CONFIG_GUIDANCE docblock and the last
sentence of its prescription said the key was "only ever read as that
key's last fallback", a read that no longer exists.

The prose now says why the key stays in the set (for its prescription,
not for a read), and the prescription still names `tree.labelField`. The
flat key set and every schema shape are unchanged; keeping or dropping
`titleField` from the set is a schema decision outside this change. The
in-test note beside the key-set pin gains the same dated reading.

Claude-Session: https://claude.ai/code/session_01DhTqaEHqPVSVnAkjG3jywn
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude

packages/spec/src/ui/component.test.ts

@@ -4314,7 +4314,11 @@ describe('object-map / object-gantt / object-tree — key sets derived from the
     // still resolves `treeCfg.titleField` into `labelField` before emitting
     // (`ListView.tsx:3270` at this pin), so an authored `titleField` is still
     // only ever the block's `labelField`. What died is the renderer's own
-    // fallback, not the flatten's.
+    // fallback, not the flatten's. At `20c6d351a` the flatten's rung is gone
+    // too (objectui#6152 round 14, objectui `3fd862510`: `ListView.tsx:3985`
+    // reads `treeCfg.labelField || 'name'`), so no half reads `titleField`;
+    // it stays in the set for the prescription it carries, which names
+    // `tree.labelField` (see `OBJECT_TREE_FLAT_CONFIG_GUIDANCE`).
     expect(setFor('object-tree', 'OBJECT_TREE_FLAT_CONFIG_KEYS'))
       .toEqual([...Object.keys(TreeConfigSchema.shape), 'titleField'].sort());
   });

packages/spec/src/ui/component.zod.ts

@@ -8611,19 +8611,25 @@ export type ObjectGanttPropsParsed = z.infer<typeof ObjectGanttPropsSchema>;
  * uses above. The registration agrees: `plugin-tree/src/index.tsx` declares
  * `{ name: 'tree', type: 'object' }` and no flat input.
  *
- * `titleField` is in the set although no `tree` block key is spelled that way:
- * `ListView`'s flatten resolves `treeCfg.titleField` into `labelField` before
- * emitting (`ListView.tsx:3927`, `labelField: treeCfg.labelField ||
- * treeCfg.titleField || 'name'`), so the author's intent is always the block's
- * `labelField`, and the prescription below says so.
- *
- * ⚠️ The renderer's own half of that sentence is GONE, and it is a DELETED
- * read rather than a moved one: `getTreeConfig`'s `?? schema.titleField` rung
- * — the `:117` this record used to cite — was removed on objectui#8841
- * because it read the FLATTENED NODE and never the block, and the docblock at
+ * `titleField` is in the set although no `tree` block key is spelled that way,
+ * and at `20c6d351a` NOTHING reads it: both halves that once did are DELETED
+ * reads, not moved ones. The flatten half went on objectui#6152 round 14
+ * (objectui `3fd862510`): at `47b1f0bb7` the `case 'tree'` arm resolved
+ * `labelField: treeCfg.labelField || treeCfg.titleField || 'name'` (`:3927`);
+ * at `20c6d351a` it reads `labelField: treeCfg.labelField || 'name'`
+ * (`ListView.tsx:3985`) and emits no `titleField`. The renderer half went
+ * earlier: `getTreeConfig`'s `?? schema.titleField` rung — the `:117` this
+ * record used to cite — was removed on objectui#8841 because it read the
+ * FLATTENED NODE and never the block, and the docblock at
  * `ObjectTree.tsx:240-261` records the three measurements that retired it.
- * The flatten half above is what keeps the key in this set; ⛔ do not restore
- * the renderer half from this record's history.
+ * This paragraph is the correction the 2026-10-10 re-read above reported;
+ * ⛔ restore neither rung from this record's history.
+ *
+ * So `titleField` is in this set for its prescription, not for a read: an
+ * author who writes a flat `titleField` on an `object-tree` is naming the
+ * tree's label field, and the one key that does that is `tree.labelField`,
+ * which the prescription below says. Keeping or dropping `titleField` from
+ * the set is a schema decision this record does not make.
  */
 const OBJECT_TREE_FLAT_CONFIG_GUIDANCE: readonly KeySetGuidance[] = [
   ...COMPONENT_LEVEL_GUIDANCE,
@@ -8634,8 +8640,8 @@ const OBJECT_TREE_FLAT_CONFIG_GUIDANCE: readonly KeySetGuidance[] = [
     prescription:
       'Write this as a key of the `tree` config object instead — `tree: { parentField, labelField, fields, '
       + 'defaultExpandedDepth }`. The flat top-level spelling is the internal form `ObjectView`/`ListView` '
-      + 'produce when they flatten `options.tree`, not a second authoring spelling. A `titleField` is the '
-      + "block's `labelField`: it is only ever read as that key's last fallback.",
+      + 'produce when they flatten `options.tree`, not a second authoring spelling. A `titleField` names the '
+      + "tree's label field, which the `tree` block spells `labelField`: write `tree: { labelField }`.",
   },
 ];