Stream Manager — Reviewer Cluster

Scope

Intent

v1 was single-use IPC pipes. event.sender.send(chunk) per chunk; when the renderer window closed mid-stream the upstream cancel() cascaded back through Transport → Chat → useChat ref and aborted the LLM request. No persistence on Main. No reconnect after route change.

v2 turns streams into broker state. A topic owns an ActiveStream record; renderers subscribe instead of consume; persistence lives on Main behind a strategy interface; the manager is the single place that knows about status, grace-period cleanup, multi-model fan-out, mid-stream injection.

The architecture is fully described in docs/references/ai/stream-manager.md — this cluster doc focuses on what changed and what reviewers should check.

Key changes

Single dispatcher path (context/dispatch.ts)

dispatchStreamRequest(manager, request) is the only place that calls manager.send(...). Two callers feed it:

• Ai_Stream_Open IPC handler (renderer-driven submit/regenerate)
• Ai_ToolApproval_Respond IPC handler (synthetic continue-conversation after every approval on a turn decides)

Both shapes meet here as MainDispatchRequest. Providers (PersistentChatContextProvider / TemporaryChatContextProvider / AgentChatContextProvider) only produce a PreparedDispatch bundle; they never call manager.send directly.

Why: Providers were originally calling manager.send themselves, which duplicated the inject-vs-start logic per provider and made the multi-model fan-out contract hard to enforce in tests.

ChatContextProvider interface

interface ChatContextProvider {
  readonly name: string
  canHandle(topicId: string): boolean
  prepareDispatch(subscriber: StreamListener, req, ctx: DispatchContext)
    : Promise<PreparedDispatch>
}

PreparedDispatch carries { models, listeners, userMessage?, userMessageId?, siblingsGroupId?, isMultiModel, lifecycle? }. The dispatcher reads manager.activeStreams.get(topicId) to set DispatchContext.hasLiveStream so providers can shortcut persistence on the inject path.

Lifecycle strategy split

ChatStreamLifecycle (chat default) and PromptStreamLifecycle (translate / summarisation / model probes) differ in:

• Status broadcast — chat publishes topic.stream.statuses.<topicId> to shared cache; prompt-stream doesn't.
• Attach gating — chat allows attach during grace-period; prompt doesn't.
• Cleanup timing — chat holds the entry 30 s after terminal so a freshly-mounted renderer can still attach; prompt evicts immediately.

The split is on the lifecycle strategy, not on the manager — manager code branches only on stream.lifecycle.cleanup(...).

Persistence backends

PersistenceListener is storage-agnostic; it folds error parts into finalMessage.parts and calls the backend's persistAssistant / persistTranslate / etc. Stream-manager owns these built-in backends:

• MessageServiceBackend — persistent chats (SQLite tree).
• TemporaryChatBackend — temporary topics (in-memory).
• TranslationBackend — translate-on-main rows (see translate-on-main.md).

Agent session persistence is owned by agent-session/persistence, not by stream-manager.

pipeStreamLoop

Shared chunk-pipe primitive driven from AiStreamManager.runExecutionLoop — every execution runs through it, chat turns and ad-hoc prompt streams (streamPrompt) alike. Tees the broadcast reader from the readUIMessageStream accumulator. Behaviour contract is in the file header — focus check: never-throws, captures streamErrorText for in-stream chunk.type === 'error', returns threw for setup errors.

Invariants reviewers should check

1. Every manager.send call goes through dispatch.ts. Providers never import AiStreamManager directly to call methods on it.
2. A topic has exactly one ActiveStream. The inject path never spawns new StreamExecutions.
3. Terminal callbacks (onDone / onPaused / onError) fire exactly once per execution.
4. WebContentsListener survives window close — only the IPC send becomes a no-op; the stream and persistence continue.
5. Grace-period cleanup (ChatStreamLifecycle.cleanup) is cancellable by a new send on the same topic.

Validation

• __tests__/AiStreamManager.test.ts — 927-line suite, covers start/inject/abort/reconnect/persistence/multi-model.
• context/__tests__/TemporaryChatContextProvider.test.ts — temporary topic path.
• listeners/__tests__/WebContentsListener.test.ts — dead-listener removal.
• listeners/__tests__/PersistenceListener.test.ts — error-part folding, per-execution filtering.
• persistence/backends/__tests__/TranslationBackend.test.ts — translate row write path.
• __tests__/buildCompactReplay.test.ts — replay buffer compaction.

Follow-ups (out of scope)

• Stream resume across Main process restart (currently all in-memory).
• SSE listener: only used by the dev API server; can it move to the apiServer cluster? Decision deferred.