@@ -33,6 +33,7 @@ Preserve the following contracts exactly across all language ports:
 **Wire format:**
 - Currency: integer minor units on the wire always. Float arithmetic for money is forbidden.
 - Pagination: `?limit=N&offset=N` — identical across all generated endpoints.
+- **Output form is a project setting, and the default is each language's own** (ADR-0019 Amendment 2): `wire` in `.metaobjects/config.json` (`decimals`: `native`|`string`; `nullMembers`: `native`|`emit`|`omit`), read by the same config reader as `naming` and carried on the loaded root. `native` means what that port's standard serializer writes. Never make a port's default match another port or a corpus. The corpora pin `{"decimals": "string", "nullMembers": "omit"}` in their own config, and a harness reads it from there. Input rules (W2, W3) hold in every mode. Shared cases: `fixtures/wire-conformance/`.
 - **Runtime return types**: a port's runtime `ObjectManager` returns **native in-process language types** (`field.decimal`→`BigDecimal`/`decimal`/`Decimal`, TS `string`; temporal→native; jsonb→native map). Wire canonicalization (the bullets above + `normalization.md`) is applied at the **serialization boundary**, never inside the runtime query path. See [ADR-0019](spec/decisions/ADR-0019-runtime-return-type-contract.md).
 
 **Grammar:**
 
@@ -72,7 +72,7 @@ PyPI has had no product change since `0.25.0` — nothing is broken.
 - **Kotlin** — `codegen-kotlin` (KotlinPoet on JVM): entity + Exposed table + Spring controller + payload + relations + filter allowlist + validator + stored-proc + output-parser generators. `integration-tests-kotlin` runs the persistence-conformance corpus through Exposed against Testcontainers Postgres.
 
 **Cross-port conformance corpora** (every port runs the shared corpus):
-- Metamodel: `fixtures/conformance/` (410 fixtures; 30 shared corpora in total — per-corpus counts + the corpus x port matrix live in `docs/CONFORMANCE.md`). TS / C# / Java / Python all green.
+- Metamodel: `fixtures/conformance/` (410 fixtures; 31 shared corpora in total — per-corpus counts + the corpus x port matrix live in `docs/CONFORMANCE.md`). TS / C# / Java / Python all green.
 - Render: `fixtures/render-conformance/`. TS / C# / Java / Kotlin / Python byte-identical.
 - Persistence: `fixtures/persistence-conformance/`. **Query** scenarios run on every port (TS / C# / Java / Kotlin / Python), each provisioning its test DB by executing the committed, TS-produced `canonical/schema.postgres.sql` (Postgres only — Derby dropped for the cross-port query corpus, ADR-0015; the FR-044 `report-*` scenarios also run on SQLite, MySQL and D1 where a port has the engine, see [docs/CONFORMANCE.md](docs/CONFORMANCE.md)). The **migration** scenarios are exercised by **TS only** (TS owns schema migrations). **The corpus now gates WRITES, not just reads (SP-H):** an `op: roundtrip` scenario type INSERTs through each port's runtime/ORM write codec (NOT raw SQL), reads the row back, and asserts the wire-normalized value. The `AllTypes` entity (`roundtrip-all-types.yaml`) carries one field of **every** persistable `field.*` subtype — string/int/long/double/float/decimal/boolean/date/time/timestamp(+tz)/currency/enum/uuid/object — plus an **array-of-VO** `field.object @isArray @storage:jsonb` column (`labels`, written as 2-element / empty-`[]` / single-element arrays across the three rows) — so every subtype write+read (incl. the array-of-value-object jsonb codec) round-trips through every port against Testcontainers PG. (`field.byte`/`field.short`/`field.class` were cut as non-functional registration-only stubs — the matrix tracks only genuinely-supported subtypes; see `fixtures/registry-conformance/README.md` → "Per-subtype write-round-trip matrix".)
 - API-contract: `fixtures/api-contract-conformance/`. TS / C# / Java / Kotlin / Python all green — each port runs **two lanes**: a hand-rolled reference server AND its **generated** API artifact booted over HTTP (the deployed controller/routes; TS+C# full-stack vs Testcontainers PG, Java/Kotlin/Python generated controller + in-memory repo behind the consumer seam). The generated fan-out found 10 real deployment bugs golden snapshots missed. Three sub-corpora run the **generated lane only, on all five ports** — `write-through/`, `projection/` (F22: a view-only `object.projection` serves GET list + GET by id and answers every write verb with `405 {"error": "method_not_allowed"}`) and `report/` (FR-044: a view-backed `object.report` serves GET list, answers `POST` with that same `405`, and mounts no `/{id}` route). That is deliberate, not a gap: what is under test is whether a port's GENERATOR emits those routes, and a hand-rolled reference server would answer every scenario by construction. The `m2m/` sub-corpus also gates **TPH x M:N together** (base-declared, subtype-declared, abstract-mid-declared, a non-subtype source onto a subtype TARGET, and the cross-subtype source id answering `200 []`) — the two corpora were originally built disjoint (`tph/` had no relationships, `m2m/` no discriminators), which is precisely how that defect class survived.
@@ -389,6 +389,8 @@ These are the load-bearing principles that have emerged through implementation.
 
 - **Expanding the metamodel vocabulary follows ONE decision procedure (ADR-0037) — driven by semantic behavior, not surface storage.** Don't ask "is X a string/number/date?"; ask "what does X *do*?" Ordered test: (0) **derivable** from existing subtype + attrs (`isArray`/`@maxLength`) + structure? → derive in codegen, add nothing; (1) **physical-only** (native type/meaning unchanged)? → the `@dbColumnType` escape hatch, not first-class vocab; (2) logical — **does X have its own native type, behavior, or attributes** (a *thing* that owns custom logic)? → **subtype** (the extension point: `field.uuid`, `field.uri`, `field.inet`); a **structural variant *within* a subtype** (changes generated shape, shares native type)? → **`@kind`** (the one chartered structural-variant axis: source table/view, uri url/urn — never a catch-all, never on a plain string); otherwise X just **modifies/validates/configures** an existing type → **attribute** (boolean flag `@localTime`; validation `@stringFormat` email/hostname; config `@maxLength`). The "string formats" set splits by behavior: url/uri→`field.uri`, ip→`field.inet` (native types + behavior), only email/hostname→`@stringFormat` (plain validated strings); uuid is already `field.uuid`. Self-documentation over economy; no same-name overloads (hence `@stringFormat`, not a third `@format`). Consult it every time. See [ADR-0037](spec/decisions/ADR-0037-metamodel-vocabulary-expansion-decision-framework.md).
 
+- **Each port defaults to its own language's standard behaviour; identical cross-port output is opt-in.** Generated code writes what that language's standard serializer writes: C# decimals as JSON numbers, a value object's null member as `null`. Do not standardize the ports for the convenience of our own conformance tests. A cross-port form, such as `"wire": { "decimals": "string", "nullMembers": "omit" }`, is a project setting that adopters choose. The corpora pin it explicitly in their own config and never decide a default. 1.1.0 broke this rule by making the decimal string and null omission the only output, and 1.1.2 put it back. See [ADR-0019 Amendment 2](spec/decisions/ADR-0019-runtime-return-type-contract.md).
+
 - **Pattern-derivable from metadata = codegen, never hand-code.** This is the metaobjects raison d'être. If you find yourself proposing that users hand-write something the metadata fully describes (FK references, basic CRUD, validator chains, type-safe finders, relations() blocks), stop. Codegen it. The only exception is what metadata genuinely cannot express (custom SQL views, regex patterns from outside metadata, business logic). When in doubt, generate.
 
 - **Study reference implementations for subtle pipeline behavior; don't re-derive from spec.** For complex orchestration (loader, parser, super resolution, overlay/override merging, registry lifecycle), the spec describes WHAT but the implementation captures HOW — including edge cases and error handling. When porting, read existing implementations first. First-principles reasoning produces subtly wrong behavior that breaks cross-language interop.
 
@@ -12,10 +12,49 @@ here.**
 
 ## [1.1.2] — unreleased
 
-_Fixes #455. A bug-fix release: no vocabulary or `metamodelVersion` change._
+_Fixes #454 and #455. A bug-fix release: no vocabulary or `metamodelVersion` change._
 
 ### Fixed
 
+- **Each port writes its language's standard JSON again by default, and the cross-port form is
+  a setting (#454).** 1.1.0 changed what every generated API writes, with no way back. Decimals
+  became canonical strings (`12.50` was sent as `"12.5"`), and C#, Java and Kotlin stopped
+  writing a value object's null members. On an upgrade within 1.x, that broke clients of live
+  APIs. The output form is now the project setting `wire` in `.metaobjects/config.json`, read by
+  every port's codegen the way `naming` is (ADR-0019 Amendment 2):
+
+  ```json
+  { "schema_version": 1, "wire": { "decimals": "native", "nullMembers": "native" } }
+  ```
+
+  Both keys default to `native`, meaning what the language's standard serializer writes. **C#,
+  Java and Kotlin** write a decimal as a JSON number again (`12.50`), and a value object's null
+  member as `null` with its key present: the 1.0.x output. **Python and TypeScript** write a
+  decimal as their standard string, which keeps its scale (`"12.50"`). That is a change from
+  1.1.1's `"12.5"`.
+  **To keep 1.1.0's output** in every port, declare
+  `"wire": { "decimals": "string", "nullMembers": "omit" }` and regenerate. `nullMembers` also
+  takes `"emit"`, which writes every declared member of a value object, `null` when unset,
+  including members the stored value lacks (Python and TypeScript; in C#, Java and Kotlin
+  `emit` is what `native` already writes). Input is unchanged in every mode: a decimal is
+  accepted as a string or a number, and garbage or a value past `@scale` or `@precision` is
+  `400 validation`, never rounded. An unknown key or value is refused when the config is read.
+  Every port's codegen drift gate says which `wire` block reproduces committed output generated
+  under a different setting, instead of telling you to regenerate. The conformance
+  corpora pin the portable form in their own config. The per-port table is in
+  `docs/features/api-contract.md`, "The wire setting".
+
+  **What to expect when you regenerate with no setting.** C# entity and value-object properties
+  carry `[DecimalWire.Number]` in place of the string converters, and lose
+  `[JsonIgnore(WhenWritingNull)]`. A non-required array member of a value object starts as an
+  empty list again. Java DTOs and records, and Kotlin data classes, lose the decimal serializer
+  annotation and `@JsonInclude(NON_NULL)`. Python and TypeScript routes stop canonicalizing
+  decimals on output.
+- **C#: two namespaces no longer collide on `DecimalWire.g.cs` and `MetaNetValidation.g.cs`.**
+  When the model's packages bound to more than one namespace, each namespace's copy of a helper
+  was named `DecimalWire.g.cs`, and `gen` refused the duplicate output path (`emitted by both
+  "entity" and "entity"`). With more than one namespace, each copy is now named after its
+  namespace (`DecimalWire.Acme.Billing.g.cs`). A single-namespace project keeps the plain name.
 - **C#: `MetaDataLoader.FromDirectory` (every overload, the registry overload included) now applies
   the project's `naming`**, as the JVM `fromDirectory` does. A host that composed its own registry
   and loaded with `FromDirectory(dir, registry, strict: true)` got `PhysicalNaming.Default`
 
@@ -166,7 +166,7 @@ A concrete report whose read source is `@kind: view` is served by every port's g
 - `<segment>` is the report name, snake_cased then pluralized, like any object: `InvoicesByMonth` is `/invoices_by_months`, `StoreTotals` is `/store_totals`. There is no report-specific spelling.
 - **Every derived field with filter operators is filterable and sortable**, dimension and measure alike, with its type's own operators. You cannot narrow that set: a report has no field to put `@filterable` on. A field of the `@from` entity that the report does not expose is refused with a `400`.
 - A time dimension at `day` or coarser is `YYYY-MM-DD`; a null measure is `null` with the key present (a measure with `@default` is never null); `currency` is integer minor units.
-- **A decimal (`avg`, a ratio, a `sum` of a decimal) is one canonical string in every port** (ADR-0019 Amendment 1: `12.5`, never `12.50` or an exponent). Display formatting is a view's job. Do not parse it as a float to compare.
+- **A decimal (`avg`, a ratio, a `sum` of a decimal) is written per the project's `wire` setting**: by default, the port's language-standard form (a JSON number in C#, Java and Kotlin; a string in Python and TypeScript), and under `"wire": { "decimals": "string" }` one canonical string in every port (`12.5`, never `12.50` or an exponent). Do not parse it as a float to compare.
 - `meta gen` writes a model page for every report (`docsFile()`; a sourceless one is marked "Not served") and an API page for a served one (`apiDocsFile()`) — each an ordinary entry in `generators`.
 
 The files each port generates are in the `metaobjects-codegen` skill's reference for that language ("Reports").
 
@@ -40,6 +40,7 @@ exact config, generator names and commands for this project; read it. The other
 | `references/choosing-layers.md` | the generated API does not fit, you need joined or derived data, or you are adopting onto existing code |
 | `references/template-or-code.md` | choosing between a code generator and a Mustache template |
 | `references/physical-names.md` | before you write a table, column or index name as a string |
+| `references/wire-format.md` | a generated API's JSON for decimals or null value-object members is not what a client expects, or you are about to edit a JSON converter or annotation |
 | `references/dependencies-and-shared-models.md` | the project consumes or publishes metadata across projects |
 | `references/typescript-document-store.md` | a TypeScript project on MongoDB, or any store MetaObjects does not manage, wanting a tested repository generator |
 | `references/typescript-mysql.md` | a TypeScript project on a MySQL database |
@@ -60,8 +61,11 @@ in order and every change that needs action.
   args are removed.
 - Documentation is a generator in the project's list, and the docs commands are removed. C#
   and Python also need a generator list (`dotnet meta init`; `metaobjects.config.yaml`).
-- A `field.decimal` crosses the API as one canonical string, and a fractional validator `@min`
-  or `@max` is refused (write an integer bound).
+- Upgrade to 1.1.2 or later. With no `wire` setting, each port writes its language's standard
+  JSON (C#, Java and Kotlin keep their 1.0.x decimals and null members). A project whose clients
+  expect 1.1.0's canonical decimal strings declares `"wire": { "decimals": "string",
+  "nullMembers": "omit" }`; see `references/wire-format.md`. A fractional validator `@min` or
+  `@max` is refused (write an integer bound).
 - **Resync the generators you own.** An ejected copy keeps the logic it was copied with, and a
   plain `gen` does not refresh it. `meta eject --list` (TypeScript; `metaobjects gen --list` in Python, which has no
   `eject --list`; `dotnet meta gen --list`; `mvn metaobjects:eject -Dlist=true` in Java and Kotlin)
@@ -389,6 +393,15 @@ names artifact (`<Entity>.names.ts`, `<Entity>Names.java`, …) — **but only w
 migration scripts and external mappings; prefer the ORM's typed column handle where one exists.
 Details: `references/physical-names.md`.
 
+## The JSON your API writes is a project setting
+
+Each port writes what its language's standard serializer writes: a C# decimal is a JSON
+number, a Python one `str(Decimal)`. Identical output across ports is opt-in, through `wire` in
+`.metaobjects/config.json` (`"decimals": "string"`, `"nullMembers": "omit"` or `"emit"`). Never
+change one port to match another or to match a conformance corpus, and never hand-edit a
+generated converter or annotation: change the setting and regenerate. Input rules hold in every
+mode. Details and the per-port table: `references/wire-format.md`.
+
 ## Dialects
 
 Generated DB schema/DDL targets a SQL **dialect**:
 
@@ -11,6 +11,7 @@ is **schema-migrations only** on the C# side (ADR-0015): `meta migrate` /
 - `MetaObjects.Codegen` generators
 - Docs — one more entry in `codegen/Generators.cs`
 - Persistence + routes are the deployed artifact
+- The JSON the API writes
 - Write your own generator
 - Scoping a generator to some objects
 - Extending the generators (open-for-extension, ADR-0002)
@@ -207,6 +208,18 @@ persistence layer (EF Core), and the minimal-API routes mount on your `WebApplic
 There is no runtime "ObjectManager" layer to wire — the generated EF Core code is
 what runs. (The other ports leave a repository seam; C# does not.)
 
+## The JSON the API writes
+
+With no `wire` setting, the generated API writes what System.Text.Json writes: a decimal is a
+JSON number with its scale (`12.50`, through `[DecimalWire.Number]`), and a value object's null
+member is `null` with its key present. That is the 1.0.x output. `"wire": { "decimals":
+"string", "nullMembers": "omit" }` in `.metaobjects/config.json` gives the cross-port form
+(`"12.5"`, null members left out). The input checks (a string or a number; `400` past `@scale`
+or `@precision`) hold in every mode. Never strip the attributes or delete `DecimalWire.g.cs` to
+change the output: set `wire` and regenerate. `dotnet meta verify --codegen` names the `wire`
+block that reproduces committed output generated under another setting. See
+`references/wire-format.md`.
+
 ## Write your own generator
 
 For any output the model describes and no reference emits, write an `IGenerator` in the
 
@@ -12,6 +12,7 @@ Maven plugin goal — there is no standalone `meta` binary on the Java side (the
 - When a generator's output is wrong — own the generator
 - Docs — the `api-docs` generator
 - `codegen-spring` generators
+- The JSON the API writes
 - Discriminator inheritance (TPH)
 - Serializing generated objects
 
@@ -307,6 +308,18 @@ Metadata lives wherever the plugin's `<loader><sourceDir>` points (the examples
 ports read — fused-key form, `source.rdb` + `@table`, `@column` for a renamed
 physical column.
 
+## The JSON the API writes
+
+With no `wire` setting, the generated records write what the host's Jackson `ObjectMapper` writes: a
+decimal is a JSON number (`12.50`; `1E-7` under Spring Boot's defaults), and a value object's
+null member is `null` with its key present. `"wire": { "decimals": "string", "nullMembers":
+"omit" }` in `.metaobjects/config.json` gives the cross-port form (`"12.5"`, null members left
+out): `string` adds the canonical decimal serializer, and `omit` adds `@JsonInclude(NON_NULL)` to
+each value-object type. The input checks (a string or a number; `400` past `@scale` or
+`@precision`) hold in every mode. Never strip those annotations from generated code to change
+the output: set `wire` and regenerate. `mvn metaobjects:verify` names the `wire` block that
+reproduces committed output generated under another setting. See `references/wire-format.md`.
+
 ## Discriminator inheritance (TPH)
 
 `codegen-spring` fully supports **table-per-hierarchy (TPH) inheritance**. `TphPlan`