diff --git a/.changeset/19311-form-section-collapse-describes.md b/.changeset/19311-form-section-collapse-describes.md
new file mode 100644
index 0000000000..eec9c7ea1f
--- /dev/null
+++ b/.changeset/19311-form-section-collapse-describes.md
@@ -0,0 +1,22 @@
+---
+"@objectstack/spec": patch
+---
+
+`FormSection.collapsible` / `FormSection.collapsed` — both keys now carry a `.describe()`, so the published reference page no longer prints two empty Description cells for two authorable booleans (#19311).
+
+They were the only keys in `FormSectionSchema` with no contract text at all, sitting between neighbours that have it, and the dependency between them was published nowhere. **Both** are described rather than only `collapsed`: the sibling silence is what made the gap ambiguous in the first place, and describing one of a pair recreates it one key over.
+
+Measured against the built package, `FormSectionSchema.safeParse` on one section:
+
+| authored on the section | `collapsible` after parse | `collapsed` after parse |
+| :--- | :--- | :--- |
+| neither | `false` | `false` |
+| `collapsible: true` | `true` | `false` |
+| `collapsed: true` | `false` | `true` |
+| `collapsed: true` + `collapsible: false` | `false` | `true` |
+| both `true` | `true` | `true` |
+| both `false` | `false` | `false` |
+
+- **Parse does NOT normalize the pair, in either direction.** `{ collapsed: true }` parses to `{ collapsible: false, collapsed: true }` verbatim, and `safeParseAsync` agrees. So the implication `collapsed` ⇒ `collapsible` — ruled 2026-09-18, letter A — is a **renderer** rule applied from the declaration, and the describes say exactly that rather than implying a fold the schema does not perform. A consumer reading the parsed `collapsible` is reading what the author typed, never whether a disclosure control renders.
+- **This is the opposite of the `ObjectFieldGroup` pair**, where a parse-time mapping really does fold the old booleans onto the ADR-0085 `collapse` enum. The two surfaces share key names and share nothing else; the describes say so.
+- **Text only.** No key is added, removed or re-typed, no accept set moves and no refinement changes: `check:authorable-surface` and `check:api-surface` are both green with no delta, and the wizard-step and `group` co-declaration refusals parse identically before and after (only `true` is refused in either place; `false` is accepted in both).
diff --git a/content/docs/references/ui/view.mdx b/content/docs/references/ui/view.mdx
index ea800bd3ae..b48d558ff2 100644
--- a/content/docs/references/ui/view.mdx
+++ b/content/docs/references/ui/view.mdx
@@ -331,8 +331,8 @@ View filter rule
 | **name** | `string` | optional | Stable section identifier for i18n lookup (snake_case) |
 | **label** | `string \| Record<string, string>` | optional | Display label — the default-language string, or an inline locale map (`{ en, "zh-CN" }`) resolved at render time |
 | **description** | `string` | optional | Optional description rendered under the section header. |
-| **collapsible** | `boolean` | optional (default: `false`) |  |
-| **collapsed** | `boolean` | optional (default: `false`) |  |
+| **collapsible** | `boolean` | optional (default: `false`) | Whether the section renders a disclosure control, so a reader can close it and open it again. Default `false`: a section declaring neither collapse key is always open and shows no control. ⚠️ `collapsed: true` IMPLIES this key — an explicit `collapsible: false` beside it does NOT take the control away (ruled 2026-09-18). The renderer resolves that from the DECLARATION; parse never rewrites the pair, so a parsed section still reports the `false` that was authored. Only `true` is refused on a wizard step and beside `group`; `false` is accepted in both, because it declares exactly what those surfaces already deliver. |
+| **collapsed** | `boolean` | optional (default: `false`) | Whether the section starts closed. Default `false`. ⚠️ `collapsed: true` IMPLIES `collapsible` and is sufficient ON ITS OWN — a section that starts closed always carries the disclosure control that reopens it, and it outranks an explicit `collapsible: false` (ruled 2026-09-18; refusing the combination at the declaration, and warning on it, were both rejected — nobody can depend on a section that cannot be opened). The implication is a renderer rule, never a parse-time rewrite: `{ collapsed: true }` still parses to `collapsible: false, collapsed: true`, so the parsed `collapsible` must never be read as "a control renders". Only `true` is refused on a wizard step (steps do not collapse) and beside `group`, whose field group declares the pair. |
 | **visibleWhen** | `string \| { dialect: Enum<'cel' \| 'cron' \| 'template'>; source: string; ast?: any; meta?: object }` | optional | Visibility predicate (CEL) — section shown only when TRUE. Root: `record` (+ `previous`, `parent`) in runtime forms, or `data` in metadata forms. `current_user` (and the ADR-0068 aliases `user` / `ctx.user` / `os.user`) resolves here too — CLIENT-SIDE only: nothing server-side evaluates a form-view section `visibleWhen`, so a role test here hides the controls and protects no data (declare permission-set field-level security for that), and on the public `/f/:slug` route no host publishes a scope, so the root is unbound and the predicate faults open. No `features.*` on ANY form-view predicate — refused at parse (ruled 2026-08-27): unbound on the standalone form routes, where the predicate would fault open. |
 | **visibleOn** | `string \| { dialect: Enum<'cel' \| 'cron' \| 'template'>; source: string; ast?: any; meta?: object }` | optional | [DEPRECATED → `visibleWhen`] Visibility predicate (CEL). Hides the whole section when false. Normalized to `visibleWhen` at parse. |
 | **columns** | `Enum<'1' \| '2' \| '3' \| '4'> \| 1 \| 2 \| 3 \| 4` | optional (default: `1`) |  |
@@ -463,8 +463,8 @@ Form-view select option — the object-field option shape minus the per-option `
 | **name** | `string` | optional | Stable section identifier for i18n lookup (snake_case) |
 | **label** | `string \| Record<string, string>` | optional | Display label — the default-language string, or an inline locale map (`{ en, "zh-CN" }`) resolved at render time |
 | **description** | `string` | optional | Optional description rendered under the section header. |
-| **collapsible** | `boolean` | optional (default: `false`) |  |
-| **collapsed** | `boolean` | optional (default: `false`) |  |
+| **collapsible** | `boolean` | optional (default: `false`) | Whether the section renders a disclosure control, so a reader can close it and open it again. Default `false`: a section declaring neither collapse key is always open and shows no control. ⚠️ `collapsed: true` IMPLIES this key — an explicit `collapsible: false` beside it does NOT take the control away (ruled 2026-09-18). The renderer resolves that from the DECLARATION; parse never rewrites the pair, so a parsed section still reports the `false` that was authored. Only `true` is refused on a wizard step and beside `group`; `false` is accepted in both, because it declares exactly what those surfaces already deliver. |
+| **collapsed** | `boolean` | optional (default: `false`) | Whether the section starts closed. Default `false`. ⚠️ `collapsed: true` IMPLIES `collapsible` and is sufficient ON ITS OWN — a section that starts closed always carries the disclosure control that reopens it, and it outranks an explicit `collapsible: false` (ruled 2026-09-18; refusing the combination at the declaration, and warning on it, were both rejected — nobody can depend on a section that cannot be opened). The implication is a renderer rule, never a parse-time rewrite: `{ collapsed: true }` still parses to `collapsible: false, collapsed: true`, so the parsed `collapsible` must never be read as "a control renders". Only `true` is refused on a wizard step (steps do not collapse) and beside `group`, whose field group declares the pair. |
 | **visibleWhen** | `string \| { dialect: Enum<'cel' \| 'cron' \| 'template'>; source: string; ast?: any; meta?: object }` | optional | Visibility predicate (CEL) — section shown only when TRUE. Root: `record` (+ `previous`, `parent`) in runtime forms, or `data` in metadata forms. `current_user` (and the ADR-0068 aliases `user` / `ctx.user` / `os.user`) resolves here too — CLIENT-SIDE only: nothing server-side evaluates a form-view section `visibleWhen`, so a role test here hides the controls and protects no data (declare permission-set field-level security for that), and on the public `/f/:slug` route no host publishes a scope, so the root is unbound and the predicate faults open. No `features.*` on ANY form-view predicate — refused at parse (ruled 2026-08-27): unbound on the standalone form routes, where the predicate would fault open. |
 | **visibleOn** | `string \| { dialect: Enum<'cel' \| 'cron' \| 'template'>; source: string; ast?: any; meta?: object }` | optional | [DEPRECATED → `visibleWhen`] Visibility predicate (CEL). Hides the whole section when false. Normalized to `visibleWhen` at parse. |
 | **columns** | `Enum<'1' \| '2' \| '3' \| '4'> \| 1 \| 2 \| 3 \| 4` | optional (default: `1`) |  |
@@ -479,8 +479,8 @@ Form-view select option — the object-field option shape minus the per-option `
 | **name** | `string` | optional | Stable section identifier for i18n lookup (snake_case) |
 | **label** | `string \| Record<string, string>` | optional | Display label — the default-language string, or an inline locale map (`{ en, "zh-CN" }`) resolved at render time |
 | **description** | `string` | optional | Optional description rendered under the section header. |
-| **collapsible** | `boolean` | optional (default: `false`) |  |
-| **collapsed** | `boolean` | optional (default: `false`) |  |
+| **collapsible** | `boolean` | optional (default: `false`) | Whether the section renders a disclosure control, so a reader can close it and open it again. Default `false`: a section declaring neither collapse key is always open and shows no control. ⚠️ `collapsed: true` IMPLIES this key — an explicit `collapsible: false` beside it does NOT take the control away (ruled 2026-09-18). The renderer resolves that from the DECLARATION; parse never rewrites the pair, so a parsed section still reports the `false` that was authored. Only `true` is refused on a wizard step and beside `group`; `false` is accepted in both, because it declares exactly what those surfaces already deliver. |
+| **collapsed** | `boolean` | optional (default: `false`) | Whether the section starts closed. Default `false`. ⚠️ `collapsed: true` IMPLIES `collapsible` and is sufficient ON ITS OWN — a section that starts closed always carries the disclosure control that reopens it, and it outranks an explicit `collapsible: false` (ruled 2026-09-18; refusing the combination at the declaration, and warning on it, were both rejected — nobody can depend on a section that cannot be opened). The implication is a renderer rule, never a parse-time rewrite: `{ collapsed: true }` still parses to `collapsible: false, collapsed: true`, so the parsed `collapsible` must never be read as "a control renders". Only `true` is refused on a wizard step (steps do not collapse) and beside `group`, whose field group declares the pair. |
 | **visibleWhen** | `string \| { dialect: Enum<'cel' \| 'cron' \| 'template'>; source: string; ast?: any; meta?: object }` | optional | Visibility predicate (CEL) — section shown only when TRUE. Root: `record` (+ `previous`, `parent`) in runtime forms, or `data` in metadata forms. `current_user` (and the ADR-0068 aliases `user` / `ctx.user` / `os.user`) resolves here too — CLIENT-SIDE only: nothing server-side evaluates a form-view section `visibleWhen`, so a role test here hides the controls and protects no data (declare permission-set field-level security for that), and on the public `/f/:slug` route no host publishes a scope, so the root is unbound and the predicate faults open. No `features.*` on ANY form-view predicate — refused at parse (ruled 2026-08-27): unbound on the standalone form routes, where the predicate would fault open. |
 | **visibleOn** | `string \| { dialect: Enum<'cel' \| 'cron' \| 'template'>; source: string; ast?: any; meta?: object }` | optional | [DEPRECATED → `visibleWhen`] Visibility predicate (CEL). Hides the whole section when false. Normalized to `visibleWhen` at parse. |
 | **columns** | `Enum<'1' \| '2' \| '3' \| '4'> \| 1 \| 2 \| 3 \| 4` | optional (default: `1`) |  |
diff --git a/packages/spec/src/ui/view.zod.ts b/packages/spec/src/ui/view.zod.ts
index ce2ae04cde..2ecea023f2 100644
--- a/packages/spec/src/ui/view.zod.ts
+++ b/packages/spec/src/ui/view.zod.ts
@@ -3312,8 +3312,56 @@ export const FormSectionSchema = lazySchema(() => strictObject({
   name: z.string().optional().describe('Stable section identifier for i18n lookup (snake_case)'),
   label: I18nLabelSchema.optional(),
   description: z.string().optional().describe('Optional description rendered under the section header.'),
-  collapsible: z.boolean().default(false),
-  collapsed: z.boolean().default(false),
+  /**
+   * ## The collapse pair, declared once for both members
+   *
+   * Two independent booleans, both `.default(false)`, and the dependency
+   * between them is a RENDERER rule rather than anything parse does — so it
+   * has to be stated on the declaration or it reaches nobody. `collapsed`
+   * IMPLIES `collapsible`: a section that starts closed always carries the
+   * disclosure control that reopens it, `collapsed: true` needs no
+   * `collapsible` beside it, and it outranks an explicit `collapsible: false`
+   * (maintainer ruling 2026-09-18, letter A). Letter B — refusing the
+   * combination at the declaration — and letter C — a dev-only warning — were
+   * both REFUSED, so ⛔ neither this schema nor a lint rule may grow one:
+   * `collapsed: true` alone is a CORRECT spelling of "collapsed by default",
+   * which is why the ruling made the renderer widen instead.
+   *
+   * ⚠️ The pair is NOT normalized at parse, in either direction — measured
+   * against the built package: `{ collapsed: true }` parses to
+   * `{ collapsible: false, collapsed: true }`, verbatim, and
+   * `safeParseAsync` agrees. So a consumer reading the parsed `collapsible`
+   * is reading what the author typed, NOT whether a control renders; it
+   * applies the implication itself, from the declaration and never from live
+   * collapse state (deriving it from the latter deletes the control the
+   * moment the reader opens the section). That is the opposite of the
+   * `fieldGroups` pair on `ObjectSchema`, which a parse-time mapping folds
+   * onto the `collapse` enum — ⛔ do not carry a reading across.
+   *
+   * Only `true` is refused on a wizard step and beside `group`; `false` is
+   * accepted in both, because it declares exactly what those surfaces already
+   * deliver (see `trueOnlyDerivedKeys` below and the FormViewSchema wizard
+   * refinement).
+   */
+  collapsible: z.boolean().default(false).describe(
+    'Whether the section renders a disclosure control, so a reader can close it and open it again. '
+    + 'Default `false`: a section declaring neither collapse key is always open and shows no control. '
+    + '⚠️ `collapsed: true` IMPLIES this key — an explicit `collapsible: false` beside it does NOT take '
+    + 'the control away (ruled 2026-09-18). The renderer resolves that from the DECLARATION; parse never '
+    + 'rewrites the pair, so a parsed section still reports the `false` that was authored. Only `true` is '
+    + 'refused on a wizard step and beside `group`; `false` is accepted in both, because it declares '
+    + 'exactly what those surfaces already deliver.',
+  ),
+  collapsed: z.boolean().default(false).describe(
+    'Whether the section starts closed. Default `false`. ⚠️ `collapsed: true` IMPLIES `collapsible` and is '
+    + 'sufficient ON ITS OWN — a section that starts closed always carries the disclosure control that '
+    + 'reopens it, and it outranks an explicit `collapsible: false` (ruled 2026-09-18; refusing the '
+    + 'combination at the declaration, and warning on it, were both rejected — nobody can depend on a '
+    + 'section that cannot be opened). The implication is a renderer rule, never a parse-time rewrite: '
+    + '`{ collapsed: true }` still parses to `collapsible: false, collapsed: true`, so the parsed '
+    + '`collapsible` must never be read as "a control renders". Only `true` is refused on a wizard step (steps do not '
+    + 'collapse) and beside `group`, whose field group declares the pair.',
+  ),
   /**
    * Conditional-visibility predicate (CEL) — the whole section is shown only
    * when TRUE (ADR-0089, canonical `*When` name). Same per-layer binding root as