refactor(engines): thin the Anthropic adapter and DRY shared engine utilities

[Copilot]

The Anthropic adapter was using any[] for conversation history and unknown-typed manual type guards for content extraction, obscuring the SDK's own type contract. objectToolSchema and toolResultText were also duplicated verbatim between anthropic.ts and pi.ts.

anthropic.ts

• messages: any[] → messages: BetaMessageParam[]
• contentText(content: unknown) with 4-line structural guards → contentText(content: BetaMessage["content"]) using the SDK's BetaTextBlock discriminant:

// before
content
  .filter((block): block is { type: "text"; text: string } =>
    block !== null && typeof block === "object"
    && (block as { type?: unknown }).type === "text"
    && typeof (block as { text?: unknown }).text === "string")

// after
content.filter((block): block is BetaTextBlock => block.type === "text")

• system: agentOptions.systemMessage as any → as string | BetaTextBlockParam[] — matches the Anthropic API's actual system param type and satisfies exactOptionalPropertyTypes

engines/utils.ts (new)

Extracts objectToolSchema and toolResultText into a shared module; both anthropic.ts and pi.ts import from here.

[github-actions]

🧠 Matt Pocock Skills Reviewer has completed the skills-based review. ✅

[github-actions]

Skills-Based Review 🧠

Applied /tdd and /codebase-design — commenting with two non-blocking suggestions.

📋 Key Themes & Highlights

Key Themes

• Missing unit tests for the newly shared utils.ts functions — the branching logic in objectToolSchema and toolResultText deserves coverage now that two adapters depend on a single copy.
• Intentional dead-code removal in contentText — the old non-array guard is correctly dropped given the narrower SDK type, but a comment would prevent future reader confusion.

Positive Highlights

• ✅ Clean extraction of duplicated helpers into a well-named utils.ts — exactly the right seam.
• ✅ Improved return type Record<string, unknown> & { type: "object" } makes the post-check narrowing visible to callers.
• ✅ BetaTextBlock discriminant replaces four lines of manual structural guards — simpler and more maintainable.
• ✅ system cast as any → as string | BetaTextBlockParam[] correctly documents the Anthropic API contract.

🧠 Reviewed using Matt Pocock's skills by Matt Pocock Skills Reviewer · sonnet46 28.3 AIC · ⌖ 4.3 AIC · ⊞ 6.3K
_{Comment /matt to run again}

[github-actions]

[/tdd] Both exported functions have branching logic but no tests were added alongside them — the throw branch in objectToolSchema and the three-way dispatch in toolResultText are prime regression targets.

💡 Suggested tests

// src/rig.test.ts or a new engines/utils.test.ts
import { objectToolSchema, toolResultText } from './engines/utils.ts';

it('objectToolSchema returns parameters when type is object', () => {
  const tool = { name: 'x', parameters: { type: 'object', properties: {} } };
  expect(objectToolSchema(tool)).toMatchObject({ type: 'object' });
});

it('objectToolSchema throws for non-object schema', () => {
  const tool = { name: 'x', parameters: { type: 'array' } };
  expect(() => objectToolSchema(tool)).toThrow(TypeError);
});

it('toolResultText: string passthrough', () => expect(toolResultText('hi')).toBe('hi'));
it('toolResultText: undefined → empty string', () => expect(toolResultText(undefined)).toBe(''));
it('toolResultText: object → JSON', () => expect(toolResultText({ a: 1 })).toBe('{"a":1}'));

Extracting these into a shared module is the right call; pairing the move with a small test file locks the contract before two adapters depend on it.

[github-actions]

[/codebase-design] The removal of the non-array guard in contentText is correct — BetaMessage["content"] is always an array, so the old typeof content === "string" branch was dead code. Consider adding a brief inline comment so future readers don't re-introduce the guard thinking it was accidentally lost.

// BetaMessage["content"] is always an array — no plain-string path
function contentText(content: BetaMessage["content"]): string {