feat(sdk,core): drop legacy chat stream-ID constants

Final Phase F cleanup — `CHAT_STREAM_KEY`, `CHAT_MESSAGES_STREAM_ID`,
and `CHAT_STOP_STREAM_ID` were meaningful only when chat.agent I/O
lived on run-scoped Redis streams. The Session migration moved all
chat I/O onto the backing Session's `.in` / `.out` channels, so these
constants stopped describing how anything is addressed months ago and
have been dead-weight re-exports since.

Dropped from the public surface:
- `@trigger.dev/core/v3/chat-client` no longer exports the three
  constants. The file keeps `ChatStoreChunk` + `applyChatStorePatch`
  (the chat.store primitive's shared types).
- `@trigger.dev/sdk/ai` no longer re-exports them via the
  `CHAT_STREAM_KEY` / `CHAT_MESSAGES_STREAM_ID` / `CHAT_STOP_STREAM_ID`
  aliases introduced by the migration commit.
- Deletes `packages/trigger-sdk/src/v3/chat-constants.ts` (the shim
  that bridged core's definitions to the SDK's public surface).

What stayed the same:
- `chat.stream.id` / `chat.messages.id` / `chat.stopSignal.id` still
  contain the literal strings `"chat"` / `"chat-messages"` /
  `"chat-stop"` — inlined as opaque breadcrumbs rather than
  user-consumable constants. Telemetry attrs keep the same values,
  so dashboards/spans don't shift.
- All runtime behavior is untouched. The `chatStream` / `messagesInput` /
  `stopInput` facades still delegate through the Session handle
  exactly as before; only the constant symbols are gone.

Migration note for external callers:
Anyone still importing the old constants should migrate to the
session primitives:
- `streams.writer(CHAT_STREAM_KEY, …)` → `sessions.open(sessionId).out.writer(…)`
- `streams.input(CHAT_MESSAGES_STREAM_ID)` → `sessions.open(sessionId).in.on(…)`
  (filtered by `chunk.kind === "message"`)
- `streams.input(CHAT_STOP_STREAM_ID)` → `sessions.open(sessionId).in.on(…)`
  (filtered by `chunk.kind === "stop"`)

Validated
- 86/86 SDK tests green.
- Webapp typecheck clean (core types used in SpanPresenter + AgentView
  are untouched).
- ai-chat UI smoke passes end-to-end: new chat → send "Say hi in
  three words." → first assistant text in 4.9s → sessionId + runId +
  lastEventId all set.

Author: ericallam

.changeset/drop-legacy-chat-stream-constants.md

@@ -0,0 +1,11 @@
+---
+"@trigger.dev/sdk": patch
+"@trigger.dev/core": patch
+---
+
+Drop the pre-Sessions chat stream-ID constants from the public surface:
+
+- `CHAT_STREAM_KEY`, `CHAT_MESSAGES_STREAM_ID`, `CHAT_STOP_STREAM_ID` are no longer exported from `@trigger.dev/sdk/ai` or `@trigger.dev/core/v3/chat-client`. Deletes `packages/trigger-sdk/src/v3/chat-constants.ts`.
+- The `chat.stream.id` / `chat.messages.id` / `chat.stopSignal.id` labels still contain the same string values (`"chat"` / `"chat-messages"` / `"chat-stop"`) — now inlined as opaque breadcrumbs rather than user-consumable constants. Behavior and telemetry attrs are unchanged.
+
+These constants only mattered before the chat.agent I/O moved onto the Session primitive — the SDK no longer writes to run-scoped `streams.writer(CHAT_STREAM_KEY, …)` / `streams.input(CHAT_*_STREAM_ID)` at all. Customers who still referenced them externally should migrate to `sessions.open(sessionId).out.writer(...)` / `sessions.open(sessionId).in.on(...)` — same primitives, now session-keyed.

packages/core/src/v3/chat-client.ts

@@ -1,17 +1,12 @@
 /**
- * Chat constants shared between backend (ai.ts) and frontend (chat.ts).
- * The ChatClient class lives in @trigger.dev/sdk/chat.
+ * Chat shared types used by backend (ai.ts) and frontend (chat.ts)
+ * code paths — primarily {@link ChatStoreChunk} + {@link applyChatStorePatch}
+ * for the `chat.store` primitive. Pre-Session transport also exported
+ * `CHAT_STREAM_KEY` / `CHAT_MESSAGES_STREAM_ID` / `CHAT_STOP_STREAM_ID`
+ * from here; those are gone — chat output and input both live on the
+ * backing Session now (see `@trigger.dev/sdk/sessions`).
  */
 
-/** The output stream key where UIMessageChunks are written. */
-export const CHAT_STREAM_KEY = "chat";
-
-/** Input stream ID for sending chat messages to the running task. */
-export const CHAT_MESSAGES_STREAM_ID = "chat-messages";
-
-/** Input stream ID for sending stop signals to abort the current generation. */
-export const CHAT_STOP_STREAM_ID = "chat-stop";
-
 // ─── chat.store chunk types ────────────────────────────────────────
 //
 // First-class chunk types for `chat.store` — bidirectional shared data

packages/trigger-sdk/src/v3/ai.ts

@@ -96,11 +96,6 @@ import { tracer } from "./tracer.js";
 
 /** Re-export for typing `ctx` in `chat.agent` hooks without importing `@trigger.dev/core`. */
 export type { TaskRunContext } from "@trigger.dev/core/v3";
-import {
-  CHAT_STREAM_KEY as _CHAT_STREAM_KEY,
-  CHAT_MESSAGES_STREAM_ID,
-  CHAT_STOP_STREAM_ID,
-} from "./chat-constants.js";
 import {
   applyChatStorePatch,
   type ChatStoreChunk,
@@ -145,9 +140,8 @@ const chatTurnContextKey = locals.create<ChatTurnContext>("chat.turnContext");
  * Per-run slot holding the Session handle that backs this chat's `.in` /
  * `.out` channels. Populated at the top of `chatAgent`'s run function from
  * `payload.sessionId`; read by every module-level helper (`chatStream`,
- * `messagesInput`, `stopInput`, `streams.writer(CHAT_STREAM_KEY, …)`
- * callers) so the chat.agent internals can remain the same module-level
- * shape they were when the I/O was run-scoped.
+ * `messagesInput`, `stopInput`) so the chat.agent internals can remain
+ * the same module-level shape they were when the I/O was run-scoped.
  * @internal
  */
 const chatSessionHandleKey = locals.create<SessionHandle>("chat.sessionHandle");
@@ -500,16 +494,6 @@ function createChatAccessToken<TTask extends AnyTask>(
 // Chat transport helpers — backend side
 // ---------------------------------------------------------------------------
 
-/**
- * The default stream key used for chat transport communication.
- * Both `TriggerChatTransport` (frontend) and `pipeChat`/`chatAgent` (backend)
- * use this key by default.
- */
-export const CHAT_STREAM_KEY = _CHAT_STREAM_KEY;
-
-// Re-export input stream IDs for advanced usage
-export { CHAT_MESSAGES_STREAM_ID, CHAT_STOP_STREAM_ID };
-
 /**
  * Typed chat output stream — `.writer()`, `.pipe()`, `.append()`, and
  * `.read()` methods pre-bound to this run's Session `.out` channel and
@@ -533,7 +517,12 @@ export { CHAT_MESSAGES_STREAM_ID, CHAT_STOP_STREAM_ID };
  * options on `.pipe()` are honoured as no-ops; the session is the target.
  */
 const chatStream: RealtimeDefinedStream<UIMessageChunk> = {
-  id: _CHAT_STREAM_KEY,
+  // Stable opaque label for the run-scoped `RealtimeDefinedStream` shape.
+  // `chatStream` is backed by the Session's `.out` channel — this id is
+  // not the real addressing key (the session is). Kept as a literal so
+  // the facade type stays satisfied without re-introducing a top-level
+  // constant; dashboards/telemetry that already read "chat" keep working.
+  id: "chat",
   pipe(value, options) {
     const { target: _target, ...sessionOptions } = (options ?? {}) as PipeStreamOptions;
     return getChatSession().out.pipe<UIMessageChunk>(
@@ -966,7 +955,7 @@ export type ChatTaskRunPayload<TClientData = unknown> = ChatTaskPayload<TClientD
 // lazily via `getChatSession()` so the module-level references stay
 // compatible with the pre-migration wiring.
 const messagesInput: RealtimeDefinedInputStream<ChatTaskWirePayload> = {
-  id: CHAT_MESSAGES_STREAM_ID,
+  id: "chat-messages",
   on(handler) {
     return getChatSession().in.on<ChatInputChunk>((chunk) => {
       if (chunk.kind === "message") {
@@ -1003,12 +992,12 @@ const messagesInput: RealtimeDefinedInputStream<ChatTaskWirePayload> = {
               [SemanticInternalAttributes.ENTITY_TYPE]: "input-stream",
               ...(runId
                 ? {
-                    [SemanticInternalAttributes.ENTITY_ID]: `${runId}:${CHAT_MESSAGES_STREAM_ID}`,
+                    [SemanticInternalAttributes.ENTITY_ID]: `${runId}:chat-messages`,
                   }
                 : {}),
-              streamId: CHAT_MESSAGES_STREAM_ID,
+              streamId: "chat-messages",
               ...accessoryAttributes({
-                items: [{ text: CHAT_MESSAGES_STREAM_ID, variant: "normal" }],
+                items: [{ text: "chat-messages", variant: "normal" }],
                 style: "codepath",
               }),
             },
@@ -1067,7 +1056,7 @@ const messagesInput: RealtimeDefinedInputStream<ChatTaskWirePayload> = {
 };
 
 const stopInput: RealtimeDefinedInputStream<{ stop: true; message?: string }> = {
-  id: CHAT_STOP_STREAM_ID,
+  id: "chat-stop",
   on(handler) {
     return getChatSession().in.on<ChatInputChunk>((chunk) => {
       if (chunk.kind === "stop") {
@@ -1105,12 +1094,12 @@ const stopInput: RealtimeDefinedInputStream<{ stop: true; message?: string }> =
               [SemanticInternalAttributes.ENTITY_TYPE]: "input-stream",
               ...(runId
                 ? {
-                    [SemanticInternalAttributes.ENTITY_ID]: `${runId}:${CHAT_STOP_STREAM_ID}`,
+                    [SemanticInternalAttributes.ENTITY_ID]: `${runId}:chat-stop`,
                   }
                 : {}),
-              streamId: CHAT_STOP_STREAM_ID,
+              streamId: "chat-stop",
               ...accessoryAttributes({
-                items: [{ text: CHAT_STOP_STREAM_ID, variant: "normal" }],
+                items: [{ text: "chat-stop", variant: "normal" }],
                 style: "codepath",
               }),
             },
@@ -3686,8 +3675,8 @@ function chatAgent<
       locals.set(chatAgentRunContextKey, ctx);
 
       // Bind the run to its backing Session so every module-level helper
-      // (chat.stream, chat.messages, streams.writer(CHAT_STREAM_KEY, …))
-      // resolves to this chat's `.in` / `.out` channels.
+      // (chat.stream, chat.messages, chat.stopSignal) resolves to this
+      // chat's `.in` / `.out` channels.
       //
       // The transport opens/creates the session with `externalId = chatId`
       // and threads its friendlyId through `payload.sessionId`. For legacy

packages/trigger-sdk/src/v3/chat-constants.ts

@@ -37,11 +37,6 @@ function isRunPatAuthError(error: unknown): boolean {
   const e = error as { name?: string; status?: number };
   return e.name === "TriggerApiError" && (e.status === 401 || e.status === 403);
 }
-// Stream-ID constants are no longer used — the transport writes a tagged
-// ChatInputChunk to the session's `.in` channel (append route) and reads
-// UIMessageChunks from `.out` (SSE subscribe). Kept imported from
-// chat-constants.js only for callers that still import them directly; the
-// legacy constants will be deleted in a follow-up cleanup.
 import { ChatTabCoordinator } from "./chat-tab-coordinator.js";
 
 const DEFAULT_STREAM_KEY = "chat";