…-club#141) (systeminit#1205)

## Summary

- Fixes [swamp-club#141](https://swamp.club/lab/issues/141): extension
authors whose `_test.ts` imports the model source hit `TS7006` (implicit
`any` on execute parameters) under strict mode.
- Ships a type-only `ModelDefinition<TGlobalArgs>` in
`@systeminit/swamp-testing` that authors opt into via `satisfies
ModelDefinition<typeof Schema>` (or the `defineModel` function-form
alternative). The literal stays identical — only a trailing satisfies
and a type-only import are added.
- `context.globalArgs` narrows to the schema-inferred shape (verified by
probing an undeclared field → TS2339). This is a real type-safety
upgrade, not a TS7006 silencer.
- Default authoring experience is **unchanged** — unannotated execute
params remain the Quick Start. Existing extensions do not need to
migrate. The `: any` workaround keeps working for anyone already using
it.

## What's included

- `packages/testing/model_definition_types.ts` — new type-only file with
`ModelDefinition`, `MethodDefinition`, `CheckDefinition`,
`ResourceOutputSpec`, `FileOutputSpec`, `VersionUpgrade`, `CheckResult`,
and the `defineModel` helper.
- `packages/testing/types.ts` — `MethodContext<TGlobalArgs =
Record<string, unknown>>` (additive, backward compatible).
- `packages/testing/mod.ts` — new "Model authoring" export block.
- `packages/testing/model_definition_types_test.ts` — type-level
regression test asserting both `satisfies` and `defineModel` paths
narrow `globalArgs` under strict+noImplicitAny.
- `src/domain/models/testing_package_compat_test.ts` — extended to guard
drift between testing and canonical `ModelDefinition` /
`MethodDefinition`.
- `.claude/skills/swamp-extension-model/references/typing.md` — new
reference with before/after, "when not to use," and cross-links to the
compat test and issue systeminit#141.
- `.claude/skills/swamp-extension-model/SKILL.md` — Key Rule systeminit#5 points
at typing.md.
- `.claude/skills/swamp-extension-model/references/testing.md` —
cross-link banner at the top.
- `packages/testing/README.md` — new "Model authoring escape hatch"
subsection.
- `packages/testing/deno.json` — bumped 0.2.0 → 0.3.0.

## Author-facing usage

```typescript
import { z } from "npm:zod@4";
import type { ModelDefinition } from "jsr:@systeminit/swamp-testing";

const GlobalArgsSchema = z.object({ region: z.string() });

export const model = {
  type: "@myorg/my-model",
  version: "2026.04.21.1",
  globalArguments: GlobalArgsSchema,
  methods: {
    run: {
      description: "Run the model",
      arguments: z.object({ bucket: z.string() }),
      execute: async (_args, context) => {
        // context.globalArgs narrows to { region: string }
        return { dataHandles: [] };
      },
    },
  },
} satisfies ModelDefinition<typeof GlobalArgsSchema>;
```

## Why not a per-method args-narrowing helper

The plan's initial `defineModel` sketch intended per-method `args`
inference via mapped-intersection generics. Both the F-bounded recursive
constraint and the `Omit`-based override pattern failed contextual
typing during inference — per-method args narrowing for inline literals
requires a builder-style API (as used by tRPC / zod's own `.input()`
chain), which is out of scope here. Authors narrow `args` per method
with `MySchema.parse(args)` at runtime (the canonical Zod way).
`typing.md` documents this.

## Test plan

- [x] `deno check main.ts packages/testing/mod.ts` passes
- [x] `deno run test` — all 4505 existing tests pass; new 4 type-level +
smoke tests pass
- [x] `deno lint` clean
- [x] `deno fmt` applied
- [x] `deno run review-skills` — all skills pass the 90% threshold
- [x] Scratch-repo verification: reproduces TS7006 on the pre-fix shape;
compiles cleanly with `satisfies ModelDefinition<typeof Schema>` and
`defineModel({ ... })`; narrowing probe confirms
`context.globalArgs.region` is typed and
`context.globalArgs.undeclaredField` errors as expected.
- [x] Drift-guard verification: injecting `description: number` into
testing-side `MethodDefinition` immediately failed
`testing_package_compat_test.ts` as designed.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.7 (1M context) <[email protected]>