fix(node-sdk): protect hand-authored types from napi-rs regen churn

Before this commit, every `napi build` overwrote `index.d.ts` and
silently dropped the hand-added types (`ToolErrorKind`,
`VerificationStatus`, `VerificationCheck`, `VerificationReport`,
`ToolArtifact`). These types aren't generatable from Rust — they
describe JSON wire shapes whose field names must stay snake_case to
match the core's serialization, which napi-derive would auto-camelCase.

Reshape the SDK so generated and hand-authored types live in separate
files:

- napi build now writes to `generated.d.ts` (was `index.d.ts`).
- `extra-types.d.ts` holds the hand-authored types.
- `index.d.ts` becomes a small hand-authored aggregator that re-exports
  both. It is never touched by the build.
- `package.json` `files[]` ships all three .d.ts files; `types` field
  still points at `index.d.ts` so consumers' imports are unchanged.

Adds `test-types.ts` + `npm run test:types` as a tsc-based smoke check
that fails if the aggregator ever drops a type from either file.

Author: claude

sdk/node/extra-types.d.ts

@@ -0,0 +1,56 @@
+/**
+ * Hand-authored type declarations that complement the auto-generated
+ * `generated.d.ts`. These describe shapes that cross the SDK boundary as
+ * JSON (e.g. payloads inside `runs()`, `verificationReports()`,
+ * `errorKindJson` strings), not napi-bound objects.
+ *
+ * Keep field names matching the actual JSON wire format (snake_case where
+ * the Rust core serializes that way). Do not move these into Rust source —
+ * napi-derive would camelCase them and break consumers parsing the JSON.
+ */
+
+/**
+ * Parsed shape of `ToolResult.errorKindJson` / `AgentEvent.errorKindJson`.
+ *
+ * Use a discriminated union on the `type` field; new variants may be
+ * added in future minor releases — callers should match exhaustively on
+ * the kinds they care about and fall through to a default branch for
+ * unknown ones.
+ */
+export type ToolErrorKind =
+  | { type: 'version_conflict'; path: string; expected: string; actual: string | null }
+  | { type: 'remote_git_conflict'; code: string; message: string }
+  | { type: 'not_found'; path: string }
+  | { type: 'invalid_argument'; message: string }
+  | { type: 'unsupported'; message: string }
+  | { type: 'timeout'; op: string; duration_ms: number }
+
+export type VerificationStatus = 'passed' | 'failed' | 'needs_review' | 'skipped'
+
+export interface VerificationCheck {
+  id: string
+  kind: string
+  description: string
+  status: VerificationStatus
+  required?: boolean
+  suggested_tools?: Array<string>
+  evidence_uris?: Array<string>
+  residual_risk?: string
+}
+
+export interface VerificationReport {
+  schema: string
+  subject: string
+  status: VerificationStatus
+  checks: Array<VerificationCheck>
+  residual_risks?: Array<string>
+}
+
+export interface ToolArtifact {
+  artifact_id: string
+  artifact_uri: string
+  tool_name: string
+  content: string
+  original_bytes: number
+  shown_bytes: number
+}