test(backends): add engine contract test for all registered engines

[aaight]

Summary

• Adds tests/unit/backends/engine-contract.test.ts — a contract test that validates all 4 built-in engines against the AgentEngine interface
• Iterates over every registered engine using describe.each for consistent per-engine validation
• Validates getEngineCatalog() returns definitions for all registered engines

What is tested

• registerBuiltInEngines() successfully registers all 4 engines: llmist, claude-code, codex, opencode
• Each engine's definition has the required fields: id, label, description, capabilities (array), modelSelection, logLabel
• Each engine's definition.id matches its registry key
• execute is a function on each engine
• supportsAgentType() is a function that returns a boolean for known agent types (implementation, review, splitting)
• Optional resolveModel is a function if present (validates Story chore: update llmist and zangief dependencies #3 compliance)
• Optional beforeExecute/afterExecute are functions if present (validates Story feat: add UpdateChecklistItem gadget and improve agent workflow #5 compliance)
• getEngineCatalog() returns definitions for all registered engines and references the same objects as the registry

Test plan

• tests/unit/backends/engine-contract.test.ts exists and passes (49 tests)
• npm run typecheck passes
• npm run lint passes

Card: https://trello.com/c/69b57342a440fa1ff9a93706

🕵️ claude-code · claude-sonnet-4-6 · run details

[nhopeatall]

Summary

Clean, well-structured contract test that validates all 4 built-in engines against the AgentEngine interface. One duplicated test doesn't verify what its name claims.

Should Fix

tests/unit/backends/engine-contract.test.ts, lines 25-30 — The test "registers exactly the expected engines" is functionally identical to "registers all 4 built-in engines" (lines 17-22). Both iterate EXPECTED_ENGINE_IDS and assert each is contained in registeredIds:

// Test 1 (line 17): "registers all 4 built-in engines"
const registeredIds = getRegisteredEngines();
for (const id of EXPECTED_ENGINE_IDS) {
    expect(registeredIds).toContain(id);
}

// Test 2 (line 25): "registers exactly the expected engines"
const registeredIds = getRegisteredEngines();
for (const id of EXPECTED_ENGINE_IDS) {
    expect(registeredIds).toContain(id);
}

The name "exactly" implies it should also verify no unexpected engines are registered, but it doesn't. To make this test meaningful, add an assertion like:

expect(registeredIds).toHaveLength(EXPECTED_ENGINE_IDS.length);

Or remove the duplicate entirely.

🕵️ claude-code · claude-opus-4-6 · run details

[nhopeatall]

LGTM — Clean contract test that validates all 4 built-in engines against the AgentEngine interface. Test isolation is sound (vitest uses pool: 'forks', so the module-level registry state won't leak across test files). The describe.each pattern keeps per-engine validation DRY, optional member checks correctly guard with \!== undefined, and the hardcoded EXPECTED_ENGINE_IDS array will catch newly added engines via the length assertion. CI green.

🕵️ claude-code · claude-opus-4-6 · run details