feat: title projection unit in dsh-session-title (key 'title', last-wins over session/title)

packages/session-title/session-title/tests/projection.spec.ts

@@ -0,0 +1,76 @@
+/**
+ * The `title` projection unit: mounting the title service beside the
+ * projection registry serves the current normalized title (last-wins over
+ * session/title events, the same events foldSessionTitle consumes) — null
+ * before the first title — through the registry snapshot and the change
+ * feed; compositions without the registry are unaffected; unmounting the
+ * service removes the key (HMR safety). The bespoke session/title mux frame
+ * is untouched by this unit (its retirement is the client value-store
+ * migration's concern).
+ */
+
+import { describe, expect, it } from 'vitest'
+import { Context } from 'cordis'
+import SessionStore, { SessionId } from '@deepseek-ai/dsh-session'
+import type { Session } from '@deepseek-ai/dsh-session'
+import SessionProjectionRegistry from '@deepseek-ai/dsh-session-projection'
+import SessionTitleService from '@deepseek-ai/dsh-session-title'
+
+const CONFIG = { fallbackMaxWords: 8, fallbackMaxBytes: 64, maxTitleBytes: 256 }
+
+async function harness(withTitleService: boolean): Promise<{ ctx: Context; session: Session }> {
+  const ctx = new Context()
+  await ctx.plugin(SessionStore)
+  await ctx.plugin(SessionProjectionRegistry)
+  if (withTitleService) await ctx.plugin(SessionTitleService, CONFIG)
+  return { ctx, session: ctx.sessions.create(SessionId('titled')) }
+}
+
+/** Append one session/title event directly (the replay-plane shape the unit folds). */
+function appendTitle(session: Session, title: string): number {
+  return session.append('session/title', { title, messageSeqs: [1], source: { kind: 'fallback' } }).seq
+}
+
+describe('title projection unit', () => {
+  it('serves null before the first title event', async () => {
+    const { ctx, session } = await harness(true)
+    const snapshot = ctx.sessionProjections.snapshot(session)
+    expect(snapshot.values.title).toBeNull()
+  })
+
+  it('serves the latest title last-wins and notifies the change feed with the causing seq', async () => {
+    const { ctx, session } = await harness(true)
+    const changes: { key: string; value: unknown; seq: number }[] = []
+    ctx.sessionProjections.onChanged((_session, key, value, seq) => {
+      changes.push({ key, value, seq })
+    })
+    const firstSeq = appendTitle(session, 'First title')
+    const secondSeq = appendTitle(session, 'Second title')
+    // Unrelated event: same-reference apply, no notification.
+    session.append('turn/start', { turn: 1, trigger: { kind: 'message', source: { kind: 'user' } } })
+    expect(changes).toEqual([
+      { key: 'title', value: 'First title', seq: firstSeq },
+      { key: 'title', value: 'Second title', seq: secondSeq },
+    ])
+    const snapshot = ctx.sessionProjections.snapshot(session)
+    expect(snapshot.values.title).toBe('Second title')
+    expect(snapshot.asOfSeq).toBe(session.seq - 1)
+  })
+
+  it('folds titles already in the log when the service mounts late (lazy cell build)', async () => {
+    const { ctx, session } = await harness(false)
+    appendTitle(session, 'Pre-mount title')
+    await ctx.plugin(SessionTitleService, CONFIG)
+    expect(ctx.sessionProjections.snapshot(session).values.title).toBe('Pre-mount title')
+  })
+
+  it('has no title key without the title service, and drops it when the service unloads (HMR safety)', async () => {
+    const { ctx, session } = await harness(false)
+    expect('title' in ctx.sessionProjections.snapshot(session).values).toBe(false)
+    const fiber = await ctx.plugin(SessionTitleService, CONFIG)
+    appendTitle(session, 'Ephemeral')
+    expect(ctx.sessionProjections.snapshot(session).values.title).toBe('Ephemeral')
+    await fiber.dispose()
+    expect('title' in ctx.sessionProjections.snapshot(session).values).toBe(false)
+  })
+})