fix(sessions): name relay handoffs deterministically

.changeset/relay-session-names.md

@@ -0,0 +1,5 @@
+---
+"@jmfederico/pi-web": patch
+---
+
+Name Relay handoff sessions deterministically from their relay name and leg number.

src/server/sessions/piSessionService.ts

@@ -24,7 +24,7 @@ import { SessionArchiveStore, type ArchivedSessionRecord, type ArchiveSessionInp
 import { findArchiveCandidateByIdOrPrefix, planSessionArchiveTree, type SessionArchiveTreeCandidate } from "./sessionArchiveTree.js";
 import type { ActiveSession } from "./sessionRuntimeStore.js";
 import type { AuthChange } from "./authService.js";
-import { fallbackSessionName, generateShortSessionName } from "./sessionNameGenerator.js";
+import { deterministicSessionName, fallbackSessionName, generateShortSessionName } from "./sessionNameGenerator.js";
 import { computeEditPreview, type EditPreviewResult } from "./editPreview.js";
 import { createPiSessionManagerGateway } from "./piSessionManagerGateway.js";
 import { attachmentsToInlineImages, saveAttachmentsToWorkspace } from "./attachmentService.js";
@@ -1706,6 +1706,13 @@ export class PiSessionService {
 
   private maybeGenerateSessionName(session: PiAgentSession, firstMessage: string): void {
     if (session.sessionName !== undefined || session.messages.length !== 0 || session.isStreaming || session.isCompacting) return;
+
+    const deterministicName = deterministicSessionName(firstMessage);
+    if (deterministicName !== undefined) {
+      this.applyGeneratedSessionName(session, deterministicName);
+      return;
+    }
+
     const model = session.model;
     if (model === undefined) return;
 

src/server/sessions/sessionNameGenerator.test.ts

@@ -2,7 +2,7 @@ import type { Api, AssistantMessage, Model } from "@earendil-works/pi-ai";
 import { createAssistantMessageEventStream } from "@earendil-works/pi-ai";
 import type { StreamFn } from "@earendil-works/pi-agent-core";
 import { describe, expect, it } from "vitest";
-import { cleanSessionName, fallbackSessionName, generateShortSessionName } from "./sessionNameGenerator.js";
+import { cleanSessionName, deterministicSessionName, fallbackSessionName, generateShortSessionName } from "./sessionNameGenerator.js";
 
 function fakeModel(): Model<Api> {
   return { id: "fake-model", name: "Fake Model", api: "anthropic-messages", provider: "anthropic", baseUrl: "https://example.test", reasoning: false, input: ["text"], cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 }, contextWindow: 1000, maxTokens: 100 };
@@ -69,6 +69,21 @@ describe("sessionNameGenerator", () => {
     expect(cleanSessionName('Title: "Fix Session Naming."\nextra')).toBe("Fix Session Naming");
   });
 
+  it("builds deterministic names for relay handoff prompts", () => {
+    expect(deterministicSessionName('Relay "handoff-check" leg 2 begins now.\n\nYou are the next runner.'))
+      .toBe("Relay handoff-check leg 2");
+  });
+
+  it("preserves the relay leg when truncating deterministic relay names", () => {
+    expect(deterministicSessionName('Relay "very-long-relay-name-that-would-otherwise-push-the-leg-number-out-of-view" leg 42 begins now.'))
+      .toBe("Relay very-long-relay-name-that-would-otherwise-push leg 42");
+  });
+
+  it("does not build deterministic names for non-canonical relay prompts", () => {
+    expect(deterministicSessionName('You are continuing Relay "handoff-check" under the Relay method.'))
+      .toBeUndefined();
+  });
+
   it("builds a concise fallback from the first request", () => {
     expect(fallbackSessionName("Seems like auto name for sessions is not working, I still get the first message as a name."))
       .toBe("Seems like auto name for sessions");

src/server/sessions/sessionNameGenerator.ts

@@ -5,6 +5,13 @@ const SESSION_NAME_TIMEOUT_MS = 10_000;
 const SESSION_NAME_MAX_INPUT_CHARS = 4_000;
 const SESSION_NAME_MAX_LENGTH = 60;
 const FALLBACK_SESSION_NAME_MAX_WORDS = 6;
+const RELAY_HANDOFF_FIRST_LINE = /^Relay\s+"([^"\n]+)"\s+leg\s+(\d+)\s+begins now\.?\s*(?:\n|$)/;
+
+export function deterministicSessionName(firstMessage: unknown): string | undefined {
+  if (typeof firstMessage !== "string") return undefined;
+
+  return relayHandoffSessionName(firstMessage.trimStart());
+}
 
 export async function generateShortSessionName<TApi extends Api>(streamFn: StreamFn, model: Model<TApi>, firstMessage: string): Promise<string | undefined> {
   const stream = await streamFn(
@@ -59,6 +66,31 @@ export function cleanSessionName(value: string): string | undefined {
   return title === "" ? undefined : title;
 }
 
+function relayHandoffSessionName(firstMessage: string): string | undefined {
+  const match = RELAY_HANDOFF_FIRST_LINE.exec(firstMessage);
+  if (match === null) return undefined;
+
+  const relayName = match[1]?.replace(/\s+/g, " ").trim();
+  const legNumber = match[2];
+  if (relayName === undefined || relayName === "" || legNumber === undefined) return undefined;
+
+  return cleanSessionName(formatRelaySessionName(relayName, legNumber));
+}
+
+function formatRelaySessionName(relayName: string, legNumber: string): string {
+  const prefix = "Relay ";
+  const suffix = ` leg ${legNumber}`;
+  const maxRelayNameLength = Math.max(1, SESSION_NAME_MAX_LENGTH - prefix.length - suffix.length);
+  const displayedRelayName = truncateRelayName(relayName, maxRelayNameLength);
+  return `${prefix}${displayedRelayName}${suffix}`;
+}
+
+function truncateRelayName(relayName: string, maxLength: number): string {
+  if (relayName.length <= maxLength) return relayName;
+  const truncated = relayName.slice(0, maxLength).replace(/[\s._-]+$/g, "").trim();
+  return truncated === "" ? relayName.slice(0, maxLength).trim() : truncated;
+}
+
 function textFromAssistant(message: AssistantMessage): string {
   return message.content
     .filter((part) => part.type === "text")