@@ -69,7 +69,35 @@ code behind a grep hit; a "duplicate" validator's *divergence* is the finding.
   (ADR-0019); runtime reflection to resolve a type from FQN vs generated static imports /
   FQN registry (ADR-0001 / 0017); process-global registry vs per-loader (ADR-0014); code
   that **mutates the loaded metadata tree** (read-only after load); JVM/Kotlin missing
-  startup validator; writes not routed to the `@role: primary` source.
+  startup validator; writes not routed to the `@role: primary` source; **`own*()`
+  accessor reads of effective properties / own-only member iteration (ADR-0039 — see
+  the active check below).**
+
+- [ ] **G2. `own*()` accessor discipline (ADR-0039 — CORRECTNESS DEFECT, not advisory).**
+  In any custom generator, metamodel provider, or runtime path (NOT the sanctioned cases
+  below), **flag every read of a field/node's effective property, or own-only member
+  iteration, done through an own-only accessor** — it silently drops everything inherited
+  via `extends` (a super-reference, not a flatten), corrupting codegen and runtime. This
+  is exactly the class of bug that broke Kotlin's array-type derivation (a concrete field
+  inheriting an array flag from an abstract parent generated a scalar) and, per the audit,
+  is latent cross-port. Grep for the own-only accessors and verify each hit:
+  - **TS:** `ownAttr(`, `ownChildren(`, `ownFields(`, a raw `isArray` field flag read →
+    should be `attr(` / `children()` / `fields()` unless emitting a subclass's own members.
+  - **Python:** `own_children(`, `own_fields(`, and the **inverted** bare `attr(` (Python
+    `attr()` is OWN; the resolving form is `attrs().get(`) → flag `attr(` used to read an
+    effective value.
+  - **Java / Kotlin:** `getMetaAttr(name, false)` (the `,false` own overload), own-only
+    child walks (e.g. an own-only `filterIsInstance<…>()` source lookup that emits nothing
+    for an entity inheriting its source).
+  - **C#:** a native `IsArray` flag read, `OwnChildren()`, own attr reads.
+
+  **Sanctioned (do NOT flag):** (a) a generator emitting a generated **subclass** that
+  iterates `ownFields()` so inherited members aren't re-emitted (the generated base
+  declares them — the `class Sub extends Base` / TPH pattern); (b) the own-mode canonical
+  serializer + overlay-merge + super-resolution walks (library-internal); (c) the single
+  deliberately-own attribute `@dbColumnType` (a physical column-type override, never
+  inherited). Any own read that carries a comment naming one of these cases is fine; an
+  uncommented own read of an effective property is the defect.
 - [ ] **H. Authoring-correctness / ADR-conformance (deep).** Invented/unregistered
   `@`-attrs or post-bootstrap registration (ADR-0023 — custom attrs belong in a registered
   provider or `attr.properties`); retired source-v2 forms (`source.dbTable` / `@name` /
@@ -172,6 +200,7 @@ Per finding: `file:line` → what → generated-equivalent exists? → recommend
 4. **Drift-admitting comments** — grep: `"keep in sync with"` / `"mirrors the"` / `"matching the"`.
 5. **Runtime schema patching** (`ALTER TABLE … ADD COLUMN IF NOT EXISTS`, `_ensure_schema()`) — N schema owners.
 6. **N declarations of one shape** — same entity as Drizzle table + Zod schema + Pydantic model + hand dataclass; target is 1 + N generated.
+7. **`own*()` accessor read of an effective property** (ADR-0039) — `ownAttr` / `ownFields` / `own_children` / bare Python `attr(` / `getMetaAttr(name, false)` / native `IsArray` used to read a value or iterate members outside the sanctioned subclass-emit / own-serializer / `@dbColumnType` cases → silently drops `extends`-inherited values. A **correctness defect** (axis G2), not advisory.
 
 ---
 
 
@@ -540,6 +540,16 @@ Resolution facts:
 
 `abstract` and `extends` are **structural keys** (bare, no `@`).
 
+**Extends-inherited properties are real — consume metadata through the resolving
+accessors (ADR-0039).** If you write a custom generator or a metamodel provider that
+reads this metadata, a concrete field/entity's inherited attributes and members live
+on the parent it `extends`, not on the node itself (extends is a super-*reference*, not
+a flatten). Always read a property or iterate a member set via the **resolving/effective**
+accessor (TS `attr()`/`children()`/`fields()`, Python `attrs().get()`), **never an
+`own*()` accessor** — an own-only read silently drops everything inherited via `extends`
+and corrupts the generated code. See the `metaobjects-codegen` skill for the full
+per-port mapping.
+
 **`overlay` is a different concept.** `extends:` is an IS-A relationship between
 two distinct nodes. `overlay: true` re-opens the *same* named node to amend it
 across files (same `package` + same `name` → merged; last-writer-wins on attr
 
@@ -132,6 +132,44 @@ the `generators` array in `metaobjects.config.ts` next to the built-ins — it r
 the same pass, writes under the same target rules, and carries the `@generated`
 header so it round-trips like any other.
 
+### Never read metadata through an `own*()` accessor (ADR-0039) — top bug source
+
+When writing OR reviewing a generator, **read every field/node property and iterate
+every member set through the resolving/effective accessor — never the `own*()` form.**
+`extends` is a **super-reference, not a flatten**: a concrete field/entity that
+`extends` an abstract parent keeps its inherited attributes and members physically on
+the parent, reachable only through the *resolving* accessor. An `own*()` read of an
+effective property (`isArray`, `subType`, `maxLength`, `precision`/`scale`, `default`,
+the physical column name, `objectRef`, `storage`, `required`, …) or an own-only member
+iteration **silently drops everything inherited via `extends`** — the classic symptom
+was a concrete field that inherited `isArray: true` from an abstract parent generating
+a *scalar* column. These reads compile and pass every fixture that never exercises
+`extends`, so they are a latent, cross-port top bug source.
+
+**The one legitimate `own*()` use:** a generator emitting a generated **subclass** that
+`extends` a generated base iterates **own members** (`ownFields()`) so the inherited
+members are **not re-emitted** — the generated base class already declares them (the
+`class Sub extends Base` / TPH pattern). Everywhere else, resolve. (The own-mode
+canonical serializer and overlay-merge are the only other sanctioned own reads, and
+they are library-internal, not app-generator concerns.) The one deliberately-own
+attribute is `@dbColumnType` — a physical column-type override that is never inherited.
+
+**Per-port own↔resolving mapping** (reach for the resolving column; comment any
+`own*()` call with the sanctioned case it is):
+
+| Port | Resolving (default — use this) | Own-only (avoid unless emitting a subclass's own members) |
+|---|---|---|
+| TypeScript | `attr(name)`, `children()`, `fields()` | `ownAttr(name)`, `ownChildren()`, `ownFields()`, the raw `isArray` field flag |
+| Python | `attrs().get(name)`, `children()`, `fields()` | `attr(name)` **(own!)**, `own_children()`, `own_fields()` |
+| Java / Kotlin | `getMetaAttr(name)`, resolving `getChildren()` | `getMetaAttr(name, false)`, own-only child walks |
+| C# | resolving attr/`Children`/`Fields` accessors | `IsArray` native flag, `OwnChildren()`, own attr reads |
+
+**Naming inversion — the trap:** the *default-named* accessor is NOT consistently the
+safe one. **TS `attr()` RESOLVES; Python `attr()` is OWN** (own-only). In Python you
+must call `attrs().get(name)` to get the inherited value — a bare `attr(name)` is the
+own read that drops inheritance. When you review or port a generator, check the port's
+convention, not the method name.
+
 **Close but not exact?** You don't always need a new generator — a generated file is
 a normal source file. Copy it and customize the copy (three-way merge preserves your
 edits on regen), or customize the template a built-in renders from. Reach for a
 
@@ -69,7 +69,35 @@ code behind a grep hit; a "duplicate" validator's *divergence* is the finding.
   (ADR-0019); runtime reflection to resolve a type from FQN vs generated static imports /
   FQN registry (ADR-0001 / 0017); process-global registry vs per-loader (ADR-0014); code
   that **mutates the loaded metadata tree** (read-only after load); JVM/Kotlin missing
-  startup validator; writes not routed to the `@role: primary` source.
+  startup validator; writes not routed to the `@role: primary` source; **`own*()`
+  accessor reads of effective properties / own-only member iteration (ADR-0039 — see
+  the active check below).**
+
+- [ ] **G2. `own*()` accessor discipline (ADR-0039 — CORRECTNESS DEFECT, not advisory).**
+  In any custom generator, metamodel provider, or runtime path (NOT the sanctioned cases
+  below), **flag every read of a field/node's effective property, or own-only member
+  iteration, done through an own-only accessor** — it silently drops everything inherited
+  via `extends` (a super-reference, not a flatten), corrupting codegen and runtime. This
+  is exactly the class of bug that broke Kotlin's array-type derivation (a concrete field
+  inheriting an array flag from an abstract parent generated a scalar) and, per the audit,
+  is latent cross-port. Grep for the own-only accessors and verify each hit:
+  - **TS:** `ownAttr(`, `ownChildren(`, `ownFields(`, a raw `isArray` field flag read →
+    should be `attr(` / `children()` / `fields()` unless emitting a subclass's own members.
+  - **Python:** `own_children(`, `own_fields(`, and the **inverted** bare `attr(` (Python
+    `attr()` is OWN; the resolving form is `attrs().get(`) → flag `attr(` used to read an
+    effective value.
+  - **Java / Kotlin:** `getMetaAttr(name, false)` (the `,false` own overload), own-only
+    child walks (e.g. an own-only `filterIsInstance<…>()` source lookup that emits nothing
+    for an entity inheriting its source).
+  - **C#:** a native `IsArray` flag read, `OwnChildren()`, own attr reads.
+
+  **Sanctioned (do NOT flag):** (a) a generator emitting a generated **subclass** that
+  iterates `ownFields()` so inherited members aren't re-emitted (the generated base
+  declares them — the `class Sub extends Base` / TPH pattern); (b) the own-mode canonical
+  serializer + overlay-merge + super-resolution walks (library-internal); (c) the single
+  deliberately-own attribute `@dbColumnType` (a physical column-type override, never
+  inherited). Any own read that carries a comment naming one of these cases is fine; an
+  uncommented own read of an effective property is the defect.
 - [ ] **H. Authoring-correctness / ADR-conformance (deep).** Invented/unregistered
   `@`-attrs or post-bootstrap registration (ADR-0023 — custom attrs belong in a registered
   provider or `attr.properties`); retired source-v2 forms (`source.dbTable` / `@name` /
@@ -172,6 +200,7 @@ Per finding: `file:line` → what → generated-equivalent exists? → recommend
 4. **Drift-admitting comments** — grep: `"keep in sync with"` / `"mirrors the"` / `"matching the"`.
 5. **Runtime schema patching** (`ALTER TABLE … ADD COLUMN IF NOT EXISTS`, `_ensure_schema()`) — N schema owners.
 6. **N declarations of one shape** — same entity as Drizzle table + Zod schema + Pydantic model + hand dataclass; target is 1 + N generated.
+7. **`own*()` accessor read of an effective property** (ADR-0039) — `ownAttr` / `ownFields` / `own_children` / bare Python `attr(` / `getMetaAttr(name, false)` / native `IsArray` used to read a value or iterate members outside the sanctioned subclass-emit / own-serializer / `@dbColumnType` cases → silently drops `extends`-inherited values. A **correctness defect** (axis G2), not advisory.
 
 ---
 
 
@@ -540,6 +540,16 @@ Resolution facts:
 
 `abstract` and `extends` are **structural keys** (bare, no `@`).
 
+**Extends-inherited properties are real — consume metadata through the resolving
+accessors (ADR-0039).** If you write a custom generator or a metamodel provider that
+reads this metadata, a concrete field/entity's inherited attributes and members live
+on the parent it `extends`, not on the node itself (extends is a super-*reference*, not
+a flatten). Always read a property or iterate a member set via the **resolving/effective**
+accessor (TS `attr()`/`children()`/`fields()`, Python `attrs().get()`), **never an
+`own*()` accessor** — an own-only read silently drops everything inherited via `extends`
+and corrupts the generated code. See the `metaobjects-codegen` skill for the full
+per-port mapping.
+
 **`overlay` is a different concept.** `extends:` is an IS-A relationship between
 two distinct nodes. `overlay: true` re-opens the *same* named node to amend it
 across files (same `package` + same `name` → merged; last-writer-wins on attr
 
@@ -132,6 +132,44 @@ the `generators` array in `metaobjects.config.ts` next to the built-ins — it r
 the same pass, writes under the same target rules, and carries the `@generated`
 header so it round-trips like any other.
 
+### Never read metadata through an `own*()` accessor (ADR-0039) — top bug source
+
+When writing OR reviewing a generator, **read every field/node property and iterate
+every member set through the resolving/effective accessor — never the `own*()` form.**
+`extends` is a **super-reference, not a flatten**: a concrete field/entity that
+`extends` an abstract parent keeps its inherited attributes and members physically on
+the parent, reachable only through the *resolving* accessor. An `own*()` read of an
+effective property (`isArray`, `subType`, `maxLength`, `precision`/`scale`, `default`,
+the physical column name, `objectRef`, `storage`, `required`, …) or an own-only member
+iteration **silently drops everything inherited via `extends`** — the classic symptom
+was a concrete field that inherited `isArray: true` from an abstract parent generating
+a *scalar* column. These reads compile and pass every fixture that never exercises
+`extends`, so they are a latent, cross-port top bug source.
+
+**The one legitimate `own*()` use:** a generator emitting a generated **subclass** that
+`extends` a generated base iterates **own members** (`ownFields()`) so the inherited
+members are **not re-emitted** — the generated base class already declares them (the
+`class Sub extends Base` / TPH pattern). Everywhere else, resolve. (The own-mode
+canonical serializer and overlay-merge are the only other sanctioned own reads, and
+they are library-internal, not app-generator concerns.) The one deliberately-own
+attribute is `@dbColumnType` — a physical column-type override that is never inherited.
+
+**Per-port own↔resolving mapping** (reach for the resolving column; comment any
+`own*()` call with the sanctioned case it is):
+
+| Port | Resolving (default — use this) | Own-only (avoid unless emitting a subclass's own members) |
+|---|---|---|
+| TypeScript | `attr(name)`, `children()`, `fields()` | `ownAttr(name)`, `ownChildren()`, `ownFields()`, the raw `isArray` field flag |
+| Python | `attrs().get(name)`, `children()`, `fields()` | `attr(name)` **(own!)**, `own_children()`, `own_fields()` |
+| Java / Kotlin | `getMetaAttr(name)`, resolving `getChildren()` | `getMetaAttr(name, false)`, own-only child walks |
+| C# | resolving attr/`Children`/`Fields` accessors | `IsArray` native flag, `OwnChildren()`, own attr reads |
+
+**Naming inversion — the trap:** the *default-named* accessor is NOT consistently the
+safe one. **TS `attr()` RESOLVES; Python `attr()` is OWN** (own-only). In Python you
+must call `attrs().get(name)` to get the inherited value — a bare `attr(name)` is the
+own read that drops inheritance. When you review or port a generator, check the port's
+convention, not the method name.
+
 **Close but not exact?** You don't always need a new generator — a generated file is
 a normal source file. Copy it and customize the copy (three-way merge preserves your
 edits on regen), or customize the template a built-in renders from. Reach for a
 
@@ -69,7 +69,35 @@ code behind a grep hit; a "duplicate" validator's *divergence* is the finding.
   (ADR-0019); runtime reflection to resolve a type from FQN vs generated static imports /
   FQN registry (ADR-0001 / 0017); process-global registry vs per-loader (ADR-0014); code
   that **mutates the loaded metadata tree** (read-only after load); JVM/Kotlin missing
-  startup validator; writes not routed to the `@role: primary` source.
+  startup validator; writes not routed to the `@role: primary` source; **`own*()`
+  accessor reads of effective properties / own-only member iteration (ADR-0039 — see
+  the active check below).**
+
+- [ ] **G2. `own*()` accessor discipline (ADR-0039 — CORRECTNESS DEFECT, not advisory).**
+  In any custom generator, metamodel provider, or runtime path (NOT the sanctioned cases
+  below), **flag every read of a field/node's effective property, or own-only member
+  iteration, done through an own-only accessor** — it silently drops everything inherited
+  via `extends` (a super-reference, not a flatten), corrupting codegen and runtime. This
+  is exactly the class of bug that broke Kotlin's array-type derivation (a concrete field
+  inheriting an array flag from an abstract parent generated a scalar) and, per the audit,
+  is latent cross-port. Grep for the own-only accessors and verify each hit:
+  - **TS:** `ownAttr(`, `ownChildren(`, `ownFields(`, a raw `isArray` field flag read →
+    should be `attr(` / `children()` / `fields()` unless emitting a subclass's own members.
+  - **Python:** `own_children(`, `own_fields(`, and the **inverted** bare `attr(` (Python
+    `attr()` is OWN; the resolving form is `attrs().get(`) → flag `attr(` used to read an
+    effective value.
+  - **Java / Kotlin:** `getMetaAttr(name, false)` (the `,false` own overload), own-only
+    child walks (e.g. an own-only `filterIsInstance<…>()` source lookup that emits nothing
+    for an entity inheriting its source).
+  - **C#:** a native `IsArray` flag read, `OwnChildren()`, own attr reads.
+
+  **Sanctioned (do NOT flag):** (a) a generator emitting a generated **subclass** that
+  iterates `ownFields()` so inherited members aren't re-emitted (the generated base
+  declares them — the `class Sub extends Base` / TPH pattern); (b) the own-mode canonical
+  serializer + overlay-merge + super-resolution walks (library-internal); (c) the single
+  deliberately-own attribute `@dbColumnType` (a physical column-type override, never
+  inherited). Any own read that carries a comment naming one of these cases is fine; an
+  uncommented own read of an effective property is the defect.
 - [ ] **H. Authoring-correctness / ADR-conformance (deep).** Invented/unregistered
   `@`-attrs or post-bootstrap registration (ADR-0023 — custom attrs belong in a registered
   provider or `attr.properties`); retired source-v2 forms (`source.dbTable` / `@name` /
@@ -172,6 +200,7 @@ Per finding: `file:line` → what → generated-equivalent exists? → recommend
 4. **Drift-admitting comments** — grep: `"keep in sync with"` / `"mirrors the"` / `"matching the"`.
 5. **Runtime schema patching** (`ALTER TABLE … ADD COLUMN IF NOT EXISTS`, `_ensure_schema()`) — N schema owners.
 6. **N declarations of one shape** — same entity as Drizzle table + Zod schema + Pydantic model + hand dataclass; target is 1 + N generated.
+7. **`own*()` accessor read of an effective property** (ADR-0039) — `ownAttr` / `ownFields` / `own_children` / bare Python `attr(` / `getMetaAttr(name, false)` / native `IsArray` used to read a value or iterate members outside the sanctioned subclass-emit / own-serializer / `@dbColumnType` cases → silently drops `extends`-inherited values. A **correctness defect** (axis G2), not advisory.
 
 ---