feat(adapters): mock + recording + replay adapters [closes #119]

[EmersonBraun]

Summary

Phase 1 #119. Three testing primitives for adapters — write fast, deterministic tests without burning tokens.

import {
  mockAdapter, recordingAdapter, replayAdapter, inMemorySink,
} from '@agentskit/adapters'

mockAdapter — deterministic stub

Three call shapes:

// 1. Static chunks
mockAdapter({ response: [
  { type: 'text', content: 'hello' },
  { type: 'done' },
]})

// 2. Request-aware
mockAdapter({ response: req => [
  { type: 'text', content: 'echo: ' + req.messages[0].content },
  { type: 'done' },
]})

// 3. Sequenced — different output per call
mockAdapter({ response: [
  [{ type: 'text', content: 'first' },  { type: 'done' }],
  [{ type: 'text', content: 'second' }, { type: 'done' }],
]})

Conforms to ADR 0001 — auto-appends terminal done if the response doesn't include one, pure factory, abort-safe.

recordingAdapter + replayAdapter — capture once, replay forever

import { openai, recordingAdapter, replayAdapter, inMemorySink } from '@agentskit/adapters'

// Dev: record real sessions
const sink = inMemorySink()
const adapter = recordingAdapter(
  openai({ apiKey: KEY, model: 'gpt-4o' }),
  sink,
)
// ... run the agent ...
// sink.fixture is JSON-serializable — save to disk

// Test: replay
const replay = replayAdapter(savedFixture)

RecordedTurn includes recordedAt, original request, and every chunk yielded.

This is the substrate for the deterministic-replay feature tracked in #134 (Phase 2).

Use cases unlocked

• Unit-test agent flows without API keys or rate limits
• Snapshot-test prompts: record a real session, replay forever in CI
• Demo apps that need deterministic output for screenshots
• Cost-free CI runs of @agentskit/eval test suites

Tests

12 new cases — 75 / 75 passing on @agentskit/adapters (was 63):

• Static / request-aware / sequenced response shapes
• Auto-done append behavior
• Error termination (no double done)
• Pure factory invariant (no work until stream())
• Request history capture
• Abort cooperation
• recordingAdapter end-to-end
• replay determinism
• Empty fixture error

Test plan

• Build succeeds
• All 75 tests pass
• All exports threaded through src/index.ts
• No type leaks — RecordedTurn is JSON-serializable
• Reviewer: try recording a real session and replaying it

Refs #119 #134 #211