Third-party extension index

Replace mechanisms while preserving their public contracts.

These are replaceable framework mechanisms, not an exhaustive package index or a perpetual cross-version stability promise. Assemble extensions through explicit Python factories rather than arbitrary config-selected imports. The default lesson uses pure tools and a fake provider; client dependencies are listed in Installation.

Extension	Public entry	Contract to preserve
Provider	qitos.models.base.Model, ModelFactory; composition model_override	Model request/response, codec, continuation, typed failures; provider extra required only for that client
Tool	qitos.core.tool.BaseTool.execute, ToolRegistry	Schema, permission, effect declarations, ToolResult, cancellation and unknown outcome
Checkpoint store	qitos.checkpoint.store.CheckpointStore	Session capabilities, snapshot commit CAS, lineage, fork and durability; SQLite reference implementation
Event sink	qitos.tracing.sinks.EventSink	Privacy view, loss, required/optional failure policy, append/close contract
Sandbox	qitos.core.env.Env	Capability preflight, bounded tools, real isolation, artifacts, cleanup; publication is separately authorized
Evaluator	qitos.evaluate.base.TrajectoryEvaluator.evaluate	EvaluationContext to EvaluationResult, evidence, provenance and declared loss

Complete provider/context extension · API index

Provider stream lifecycle

Built-in native Chat, Responses and Anthropic streams validate provider termination before publishing success. Partial tool input, premature EOF and conflicting terminals fail closed. Usage-only trailing chunks are collected without duplicate charging; missing usage is unknown. chat_template_kwargs is relocated to extra_body for the OpenAI SDK. Explicit output limits are preserved.

Owned SDK clients and response iterators close on completion, failure and explicit close/aclose. Consumer callbacks propagate failure. Async cancellation cannot kill a running Python thread; AsyncEngine retains worker ownership until completion. Client construction is a proven unsent failure; transport failures remain conservatively possibly sent. Non-native LiteLLM, Gemini and local fallbacks emit one complete chunk and do not advertise token streaming.

Model history rereads preserve recorded tool completion order; declaration-order result views remain derived views. The offline installed consumer verifies this across three model requests.