refactor(chat): route browser chat through one runtime (P3 Slice-Zero Task 5) (#1172)

Co-authored-by: shaggy <[email protected]>

apps/gateway/src/chat/chat-runtime.ts

@@ -0,0 +1,273 @@
+import type { ChannelAttachmentDto, RoutingDecisionInfo } from '@mosaicstack/types';
+
+/**
+ * The single chat execution strategy resolved by {@link ChatRuntimeRouter}.
+ *
+ * Exactly one runtime is live per process. There is no union that lets a
+ * `pi-rpc` deployment silently fall back to embedded execution: an unmet
+ * `pi-rpc` precondition is a typed startup failure, never a downgrade.
+ */
+export type ChatRuntimeMode = 'legacy' | 'pi-rpc';
+
+export type ChatRuntimeKind = 'embedded' | 'harness';
+
+/** The resolved runtime. Slice Zero exposes only its immutable {@link ChatRuntimeKind}. */
+export interface ChatRuntime {
+  readonly kind: ChatRuntimeKind;
+}
+
+/** Why the `pi-rpc` runtime could not be made ready. Both are hard startup failures. */
+export type ChatRuntimeUnavailableReason =
+  | 'adapter_unavailable'
+  | 'conversation_service_unavailable';
+
+/**
+ * Raised at module init when `pi-rpc` mode is selected but its preconditions are
+ * unmet. Carries only fixed, browser-safe text — never a raw exception message,
+ * stack, or provider detail — and reports the frozen ack code `runtime_unsupported`.
+ */
+export class ChatRuntimeUnavailableError extends Error {
+  readonly code = 'runtime_unsupported' as const;
+  readonly reason: ChatRuntimeUnavailableReason;
+
+  constructor(reason: ChatRuntimeUnavailableReason) {
+    super(
+      reason === 'adapter_unavailable'
+        ? 'The pi-rpc chat runtime is unavailable: no "pi" harness adapter is registered.'
+        : 'The pi-rpc chat runtime is unavailable: the harness conversation service is not bound.',
+    );
+    this.name = 'ChatRuntimeUnavailableError';
+    this.reason = reason;
+  }
+}
+
+/**
+ * Resolves the process-wide chat runtime mode from the environment. Anything other
+ * than the exact opt-in token `pi-rpc` keeps the legacy embedded runtime.
+ */
+export function resolveChatRuntimeMode(
+  env: Record<string, string | undefined> = process.env,
+): ChatRuntimeMode {
+  return env['CHAT_HARNESS_RUNTIME'] === 'pi-rpc' ? 'pi-rpc' : 'legacy';
+}
+
+// ---------------------------------------------------------------------------
+// Transitional embedded chat port (Task Five).
+//
+// The legacy embedded browser behaviour is moved behind this exact interface so
+// neither the controller nor the gateway retains AgentService, RoutingEngine,
+// session, `piSession`, metric, listener, or channel access. `EmbeddedChatRuntime`
+// implements the port; `ChatRuntimeRouter` exposes the same narrowly named
+// operations and returns `runtime_unsupported` before touching Embedded for legacy
+// browser operations when the mode is `pi-rpc`.
+//
+// The names are frozen (spec jarvis-brain@1c629b06). Legacy REST completion,
+// legacy Socket streaming, P3 harness turns, and verified Discord are distinct
+// transport/trust capabilities — there is deliberately no generic
+// `sendConversationTurn` nor an AgentService-shaped mirror on the router.
+// ---------------------------------------------------------------------------
+
+/**
+ * Phantom brand keeping {@link OwnedConversationContext} nominally distinct so browser
+ * DTOs are never structurally assignable to it. The factory that mints one may be called
+ * only after authentication with `scopeFromUser(...)`, never with payload authority fields.
+ */
+declare const ownedConversationContextBrand: unique symbol;
+
+/** Gateway-only ownership context. Embedded rechecks owner+tenant on every operation. */
+export interface OwnedConversationContext {
+  readonly [ownedConversationContextBrand]: true;
+  readonly conversationId: string;
+  readonly scope: Readonly<{ userId: string; tenantId: string }>;
+}
+
+/**
+ * Every non-`ok` legacy runtime outcome. Missing, foreign, and no-longer-owned
+ * conversations all collapse to `conversation_unavailable`. Ownership/mode/validation
+ * failures are total results and never throw.
+ */
+export type LegacyRuntimeFailure =
+  | { readonly ok: false; readonly code: 'runtime_unsupported'; readonly retryable: false }
+  | { readonly ok: false; readonly code: 'conversation_unavailable'; readonly retryable: false }
+  | { readonly ok: false; readonly code: 'request_invalid'; readonly retryable: false }
+  | {
+      readonly ok: false;
+      readonly code: 'thinking_level_invalid';
+      readonly retryable: false;
+      readonly availableThinkingLevels: readonly string[];
+    }
+  | { readonly ok: false; readonly code: 'runtime_unavailable'; readonly retryable: true }
+  | { readonly ok: false; readonly code: 'turn_already_dispatched'; readonly retryable: false }
+  | { readonly ok: false; readonly code: 'operation_failed'; readonly retryable: boolean }
+  | { readonly ok: false; readonly code: 'timeout'; readonly retryable: true };
+
+/** Total result: an `ok` value or one of the fixed {@link LegacyRuntimeFailure} codes. */
+export type LegacyRuntimeResult<T> =
+  | { readonly ok: true; readonly value: T }
+  | LegacyRuntimeFailure;
+
+/** User-facing session projection. Carries no session object, handle, or credential path. */
+export interface LegacySessionPresentation {
+  readonly provider: string;
+  readonly modelId: string;
+  readonly thinkingLevel: string;
+  readonly availableThinkingLevels: readonly string[];
+  readonly agentName?: string;
+  readonly routingDecision?: RoutingDecisionInfo;
+}
+
+/** Terminal usage stats, normalized by Embedded from AgentService metrics. */
+export interface LegacyUsage {
+  readonly provider: string;
+  readonly modelId: string;
+  readonly thinkingLevel: string;
+  readonly tokens: Readonly<{
+    input: number;
+    output: number;
+    cacheRead: number;
+    cacheWrite: number;
+    total: number;
+  }>;
+  readonly cost: number;
+  readonly context: Readonly<{ percent: number | null; window: number }>;
+}
+
+/**
+ * Normalized stream event. Exposes no `AgentSession`, `piSession`, native handle, raw
+ * exception, tool arguments, or credential-bearing path — the gateway sees only these.
+ */
+export type LegacyRuntimeEvent =
+  | { readonly type: 'started' }
+  | { readonly type: 'text_delta'; readonly text: string }
+  | { readonly type: 'thinking_delta'; readonly text: string }
+  | {
+      readonly type: 'tool_started';
+      readonly toolCallId: string;
+      readonly toolName: string;
+    }
+  | {
+      readonly type: 'tool_finished';
+      readonly toolCallId: string;
+      readonly toolName: string;
+      readonly isError: boolean;
+    }
+  | { readonly type: 'settled'; readonly usage?: LegacyUsage };
+
+/** Legacy browser message input. Authority fields are advisory only; scope comes from the context. */
+export interface LegacyBrowserMessagePayload {
+  readonly content: string;
+  readonly provider?: string;
+  readonly modelId?: string;
+  readonly agentId?: string;
+  readonly attachments?: readonly ChannelAttachmentDto[];
+}
+
+/** A prepared-but-not-yet-dispatched legacy socket turn. */
+export interface LegacySocketTurnLease {
+  readonly presentation: LegacySessionPresentation;
+  /**
+   * Atomically one-shot and scope-rechecking. A second call returns
+   * `turn_already_dispatched` and performs zero prompt/tool effects.
+   */
+  dispatch(): Promise<LegacyRuntimeResult<void>>;
+  /** Idempotent, non-throwing. Removes listener and channel, including partial setup. */
+  dispose(): Promise<void>;
+}
+
+/**
+ * Phantom brand for {@link VerifiedDiscordIngressContext}. Minted only after service-token
+ * auth plus signature, allowlist, binding, expected-route, replay, configured-agent,
+ * forced-scope, and attachment-normalization checks.
+ */
+declare const verifiedDiscordIngressContextBrand: unique symbol;
+
+/** Fully-verified Discord ingress. Contains no socket, envelope, signature, token, or escape hatch. */
+export interface VerifiedDiscordIngressContext {
+  readonly [verifiedDiscordIngressContextBrand]: true;
+  readonly conversationId: string;
+  readonly scope: Readonly<{ userId: string; tenantId: string }>;
+  readonly configuredAgent: Readonly<{ agentConfigId: string; instanceId: string }>;
+  readonly content: string;
+  readonly attachments?: readonly ChannelAttachmentDto[];
+  readonly correlationId: string;
+  readonly discordMessageId: string;
+  readonly discordUserId: string;
+}
+
+/** Verified-Discord turn lease. Same atomic one-shot dispatch and idempotent dispose rules. */
+export interface VerifiedDiscordTurnLease {
+  readonly presentation: LegacySessionPresentation;
+  dispatch(): Promise<LegacyRuntimeResult<void>>;
+  dispose(): Promise<void>;
+}
+
+/** Server-owned egress projection the runtime pushes normalized events into. */
+export interface LegacyRuntimeStream {
+  /** Server-derived, e.g. `websocket:<socket-id>`. Never client-supplied. */
+  readonly channelId: string;
+  onEvent(event: LegacyRuntimeEvent): void;
+}
+
+/**
+ * The exact transitional port. `EmbeddedChatRuntime` implements it; `ChatRuntimeRouter`
+ * mirrors the operation names and fails closed with `runtime_unsupported` for legacy
+ * browser operations under `pi-rpc`.
+ */
+export interface LegacyEmbeddedChatPort {
+  completeLegacyRestTurn(
+    context: OwnedConversationContext,
+    input: Readonly<{ content: string }>,
+  ): Promise<
+    LegacyRuntimeResult<Readonly<{ text: string; presentation: LegacySessionPresentation }>>
+  >;
+
+  prepareLegacySocketTurn(
+    context: OwnedConversationContext,
+    input: LegacyBrowserMessagePayload,
+    stream: LegacyRuntimeStream,
+  ): Promise<LegacyRuntimeResult<LegacySocketTurnLease>>;
+
+  setLegacyThinking(
+    context: OwnedConversationContext,
+    level: string,
+  ): LegacyRuntimeResult<LegacySessionPresentation>;
+
+  abortLegacyTurn(context: OwnedConversationContext): Promise<LegacyRuntimeResult<void>>;
+
+  applyLegacyModelOverride(
+    context: OwnedConversationContext,
+    modelId: string,
+  ): LegacyRuntimeResult<LegacySessionPresentation>;
+
+  readLegacySessionPresentation(
+    context: OwnedConversationContext,
+  ): LegacyRuntimeResult<LegacySessionPresentation>;
+
+  dispatchVerifiedDiscordIngress(
+    context: VerifiedDiscordIngressContext,
+    stream: LegacyRuntimeStream,
+  ): Promise<LegacyRuntimeResult<VerifiedDiscordTurnLease>>;
+}
+
+/**
+ * Mints an {@link OwnedConversationContext} from a server-derived scope. Callers must pass
+ * a scope produced by `scopeFromUser(...)` after authentication — never a client-supplied
+ * authority field. The brand is phantom, so this is the only way to obtain the branded type.
+ */
+export function ownConversation(
+  conversationId: string,
+  scope: Readonly<{ userId: string; tenantId: string }>,
+): OwnedConversationContext {
+  return { conversationId, scope } as unknown as OwnedConversationContext;
+}
+
+/**
+ * Mints a {@link VerifiedDiscordIngressContext}. Callers must have already completed every
+ * ingress check (service-token auth, signature, allowlist, binding, expected-route, replay,
+ * configured-agent, forced-scope, attachment normalization) before calling this.
+ */
+export function verifyDiscordIngress(
+  fields: Omit<VerifiedDiscordIngressContext, typeof verifiedDiscordIngressContextBrand>,
+): VerifiedDiscordIngressContext {
+  return { ...fields } as unknown as VerifiedDiscordIngressContext;
+}