feat(ql3): establish 3.0 incubation baseline

back/runtime/domain/runtimeRollout.ts

@@ -0,0 +1,82 @@
+import {
+  EXECUTION_ORIGINS,
+  type ExecutionOrigin,
+  type ExecutionOwner,
+} from './run';
+
+export const COMPATIBILITY_MODES = ['off', 'shadow', 'primary'] as const;
+export type CompatibilityMode = (typeof COMPATIBILITY_MODES)[number];
+
+export interface RuntimeRolloutConfig {
+  defaultMode: CompatibilityMode;
+  origins: Partial<Record<ExecutionOrigin, CompatibilityMode>>;
+  allowLegacyFallbackBeforeStart: boolean;
+}
+
+export interface ExecutionOwnershipDecision {
+  origin: ExecutionOrigin;
+  mode: CompatibilityMode;
+  owner: ExecutionOwner;
+}
+
+const VALID_ORIGINS = new Set<ExecutionOrigin>(EXECUTION_ORIGINS);
+const VALID_MODES = new Set<CompatibilityMode>(COMPATIBILITY_MODES);
+
+function assertConfig(config: RuntimeRolloutConfig): void {
+  if (!VALID_MODES.has(config.defaultMode)) {
+    throw new TypeError('Runtime rollout defaultMode is invalid');
+  }
+  for (const [origin, mode] of Object.entries(config.origins)) {
+    if (!VALID_ORIGINS.has(origin as ExecutionOrigin)) {
+      throw new TypeError(`Runtime rollout origin is invalid: ${origin}`);
+    }
+    if (!VALID_MODES.has(mode as CompatibilityMode)) {
+      throw new TypeError(`Runtime rollout mode is invalid: ${String(mode)}`);
+    }
+  }
+}
+
+export class RuntimeRolloutPolicy {
+  private readonly config: RuntimeRolloutConfig;
+
+  constructor(config: RuntimeRolloutConfig) {
+    assertConfig(config);
+    this.config = {
+      defaultMode: config.defaultMode,
+      origins: { ...config.origins },
+      allowLegacyFallbackBeforeStart: config.allowLegacyFallbackBeforeStart,
+    };
+  }
+
+  modeFor(origin: ExecutionOrigin): CompatibilityMode {
+    return this.config.origins[origin] ?? this.config.defaultMode;
+  }
+
+  decide(origin: ExecutionOrigin): ExecutionOwnershipDecision {
+    const mode = this.modeFor(origin);
+    return {
+      origin,
+      mode,
+      owner: mode === 'primary' ? 'runtime' : 'legacy',
+    };
+  }
+
+  snapshot(): RuntimeRolloutConfig {
+    return {
+      defaultMode: this.config.defaultMode,
+      origins: { ...this.config.origins },
+      allowLegacyFallbackBeforeStart:
+        this.config.allowLegacyFallbackBeforeStart,
+    };
+  }
+}
+
+export function shadowOnlyRollout(
+  origins: readonly ExecutionOrigin[],
+): RuntimeRolloutPolicy {
+  return new RuntimeRolloutPolicy({
+    defaultMode: 'off',
+    origins: Object.fromEntries(origins.map((origin) => [origin, 'shadow'])),
+    allowLegacyFallbackBeforeStart: false,
+  });
+}