feat(session-title): add fallback and model providers

packages/session-title/session-title-first-message-llm/README.md

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+# @deepseek-ai/dsh-session-title-first-message-llm
+
+Optional `ctx.sessionTitle` provider that summarizes the first eligible human message through `ctx.llm`. It registers the `first-message` cadence, runs automatically only when a fresh non-fork session first creates its fallback, and attributes the result to that message's exact seq. An automatic failure retains the fallback and is retried only through `ctx.sessionTitle.refresh()`.
+
+The plugin uses the complete required [shared LLM configuration](../session-title-llm/README.md#configuration). Omit both `provider` and `model` to inherit the exact route from the current logged main request, or set both to route title generation independently.
+
+## Model Experience
+
+### First-message title request
+
+#### What the model sees
+
+The title model receives the shared title instruction and a JSON array containing only the first eligible human message. Later prompts and inherited fork history do not trigger another automatic call.
+
+#### Token effect
+
+At most one automatic auxiliary request is made for a fresh session, bounded by `maxInputBytes` and `maxOutputTokens`; explicit refreshes may make additional calls. The main agent request gains zero tokens.
+
+#### KV Cache effect
+
+No main-request invalidation. The auxiliary request uses the configured or logged route and has provider-specific cache behavior.
+
+## Known Limitations and Deferred Work
+
+- The first message alone may cease to represent a long-running session; use the all-messages provider when later prompts should retitle it.
+- A fork keeps its inherited title and never runs this provider automatically, even when its seeded first message came from the parent.

packages/session-title/session-title-first-message-llm/package.json

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+{
+  "name": "@deepseek-ai/dsh-session-title-first-message-llm",
+  "description": "First-message LLM provider plugin for DeepSeek Harness session titles",
+  "version": "0.0.1",
+  "private": true,
+  "type": "module",
+  "main": "lib/index.js",
+  "types": "lib/types/index.d.ts",
+  "exports": {
+    ".": {
+      "types": "./lib/types/index.d.ts",
+      "default": "./lib/index.js"
+    },
+    "./package.json": "./package.json"
+  },
+  "files": ["lib/index.js", "lib/types/**/*.d.ts", "lib/types/**/*.d.ts.map", "src"],
+  "license": "BSD-3-Clause",
+  "peerDependencies": {
+    "@deepseek-ai/dsh-llm": "^0.0.1",
+    "@deepseek-ai/dsh-session-title": "^0.0.1",
+    "@deepseek-ai/dsh-session-title-llm": "^0.0.1",
+    "cordis": "^4.0.0-rc.7"
+  },
+  "dependencies": {
+    "schemastery": "^3.18.0"
+  },
+  "devDependencies": {
+    "@cordisjs/plugin-include": "workspace:^",
+    "@cordisjs/plugin-loader": "workspace:^",
+    "@deepseek-ai/dsh-llm": "workspace:^",
+    "@deepseek-ai/dsh-llm-deepseek": "workspace:^",
+    "@deepseek-ai/dsh-session": "workspace:^",
+    "@deepseek-ai/dsh-session-title": "workspace:^",
+    "@deepseek-ai/dsh-session-title-llm": "workspace:^",
+    "cordis": "^4.0.0-rc.7"
+  }
+}

packages/session-title/session-title-first-message-llm/src/index.ts

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+/** First-human-message model provider for `ctx.sessionTitle`. */
+
+import type { Context } from 'cordis'
+import z from 'schemastery'
+import {
+  registerSessionTitleLlmProvider,
+  SessionTitleLlmConfigFields,
+} from '@deepseek-ai/dsh-session-title-llm'
+import type { SessionTitleLlmConfig } from '@deepseek-ai/dsh-session-title-llm'
+
+export const name = 'session-title-first-message-llm'
+export const inject = ['sessionTitle', 'llm']
+
+/** Required LLM policy; this plugin adds no defaults. */
+export type Config = SessionTitleLlmConfig
+/** Loader schema shared with the all-messages provider. */
+/* jscpd:ignore-start -- Loader requires each plugin to export its own statically walkable schema; the field validators remain shared. */
+export const Config: z<Config> = z.object({
+  targetWords: SessionTitleLlmConfigFields.targetWords,
+  targetCjkCharacters: SessionTitleLlmConfigFields.targetCjkCharacters,
+  maxInputBytes: SessionTitleLlmConfigFields.maxInputBytes,
+  maxOutputTokens: SessionTitleLlmConfigFields.maxOutputTokens,
+  timeoutMs: SessionTitleLlmConfigFields.timeoutMs,
+  provider: SessionTitleLlmConfigFields.provider,
+  model: SessionTitleLlmConfigFields.model,
+})
+/* jscpd:ignore-end */
+
+/**
+ * Register the first-message model provider.
+ * @param ctx - context exposing session-title and LLM services.
+ * @param config - required route, target, byte, token, and timeout policy.
+ */
+export function apply(ctx: Context, config: Config): void {
+  registerSessionTitleLlmProvider(ctx, config, name, 'first-message', (messages) => {
+    const first = messages[0]
+    if (first === undefined) throw new Error('first-message title provider requires one human message')
+    return [first]
+  })
+}

packages/session-title/session-title-first-message-llm/tests/loader-composition.spec.ts

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+import { afterEach, describe, expect, it } from 'vitest'
+import { Context } from 'cordis'
+import Loader from '@cordisjs/plugin-loader'
+import Include from '@cordisjs/plugin-include'
+import { mkdtemp, rm, writeFile } from 'node:fs/promises'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { pathToFileURL } from 'node:url'
+import LlmService, { LlmAdapter } from '@deepseek-ai/dsh-llm'
+import type { GenerateOptions, StreamChunk } from '@deepseek-ai/dsh-llm'
+import SessionStore, { SessionId } from '@deepseek-ai/dsh-session'
+import SessionTitleService from '@deepseek-ai/dsh-session-title'
+import * as providerPlugin from '@deepseek-ai/dsh-session-title-first-message-llm'
+
+let root: string | undefined
+let context: Context | undefined
+
+class LoaderAdapter extends LlmAdapter {
+  readonly requests: GenerateOptions[] = []
+
+  override async * stream(options: GenerateOptions): AsyncIterable<StreamChunk> {
+    this.requests.push(options)
+    yield { type: 'text-delta', index: 0, text: 'Loader composed title' }
+    yield { type: 'finish', reason: { kind: 'stop' } }
+  }
+}
+
+afterEach(async () => {
+  await context?.fiber.dispose()
+  context = undefined
+  if (root !== undefined) await rm(root, { recursive: true, force: true })
+  root = undefined
+})
+
+async function loadComposition(): Promise<Context> {
+  root = await mkdtemp(join(tmpdir(), 'dsh-title-loader-'))
+  const configPath = join(root, 'cordis.yml')
+  await writeFile(configPath, [
+    "- name: '@deepseek-ai/dsh-llm'",
+    "- name: '@deepseek-ai/dsh-session'",
+    "- name: '@deepseek-ai/dsh-session-title'",
+    '  config:',
+    '    fallbackMaxWords: 5',
+    '    fallbackMaxBytes: 40',
+    '    maxTitleBytes: 80',
+    "- name: '@deepseek-ai/dsh-session-title-first-message-llm'",
+    '  config:',
+    '    targetWords: 5',
+    '    targetCjkCharacters: 10',
+    '    maxInputBytes: 1000',
+    '    maxOutputTokens: 32',
+    '    timeoutMs: 1000',
+    "    provider: 'title-route'",
+    "    model: 'title-model'",
+    '',
+  ].join('\n'))
+
+  context = new Context()
+  context.baseUrl = pathToFileURL(root).href + '/'
+  await context.plugin(Loader)
+  context.loader.builtins.include = Include
+  const modules = new Map<string, unknown>([
+    ['@deepseek-ai/dsh-llm', LlmService],
+    ['@deepseek-ai/dsh-session', SessionStore],
+    ['@deepseek-ai/dsh-session-title', SessionTitleService],
+    ['@deepseek-ai/dsh-session-title-first-message-llm', providerPlugin],
+  ])
+  context.loader.internal = {
+    version: 'v2',
+    async import(specifier: string) {
+      if (!modules.has(specifier)) throw new Error(`unexpected Loader import: ${specifier}`)
+      return modules.get(specifier)
+    },
+  } as unknown as NonNullable<typeof context.loader.internal>
+  await context.loader.create({
+    name: 'cordis:include',
+    config: { path: pathToFileURL(configPath).href },
+  })
+  await context.loader.await()
+  return context
+}
+
+describe('session-title Loader composition', () => {
+  it('loads the service and one model provider with required deployment policy', async () => {
+    const ctx = await loadComposition()
+    const unloaded = [...ctx.loader.entries()]
+      .filter(entry => entry.fiber === undefined && !entry.disabled)
+      .map(entry => entry.options.name)
+    expect(unloaded).toEqual([])
+
+    const adapter = new LoaderAdapter()
+    ctx.llm.registerAdapter(['title-route'], adapter)
+    const session = ctx.sessions.create(SessionId('loader-title'))
+    session.append('turn/start', {
+      turn: 1,
+      trigger: { kind: 'message', source: { kind: 'user' } },
+    })
+    const message = session.append('user/message', {
+      content: [{ type: 'text', text: 'Compose a title through Loader' }],
+      source: { kind: 'user' },
+    }, { surfaceOp: 'append' })
+    await new Promise(resolve => setTimeout(resolve, 0))
+    session.append('request/header', {
+      header: { config: { provider: 'main-route', model: 'main-model' } },
+      reason: 'initial',
+    })
+    await new Promise(resolve => setTimeout(resolve, 0))
+
+    expect(adapter.requests[0]).toMatchObject({ provider: 'title-route', model: 'title-model' })
+    expect(ctx.sessionTitle.get(session)).toMatchObject({
+      title: 'Loader composed title',
+      messageSeqs: [message.seq],
+      source: {
+        kind: 'provider',
+        provider: 'session-title-first-message-llm',
+        model: { provider: 'title-route', model: 'title-model' },
+      },
+    })
+  })
+})

packages/session-title/session-title-first-message-llm/tests/provider.e2e.ts

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+import { afterEach, describe, expect, it } from 'vitest'
+import { Context } from 'cordis'
+import LlmService from '@deepseek-ai/dsh-llm'
+import * as LlmDeepSeek from '@deepseek-ai/dsh-llm-deepseek'
+import SessionStore, { SessionId } from '@deepseek-ai/dsh-session'
+import SessionTitleService from '@deepseek-ai/dsh-session-title'
+import * as FirstMessageTitleProvider from '@deepseek-ai/dsh-session-title-first-message-llm'
+
+const contexts: Context[] = []
+
+afterEach(async () => {
+  await Promise.all(contexts.splice(0).map(ctx => ctx.fiber.dispose()))
+})
+
+describe.skipIf(!process.env.DEEPSEEK_API_KEY)('first-message title provider with real DeepSeek API', () => {
+  it('replaces the fallback with a short model title', async () => {
+    const ctx = new Context()
+    contexts.push(ctx)
+    await ctx.plugin(LlmService)
+    await ctx.plugin(LlmDeepSeek, { thinking: 'disabled' })
+    await ctx.plugin(SessionStore)
+    await ctx.plugin(SessionTitleService, {
+      fallbackMaxWords: 5,
+      fallbackMaxBytes: 40,
+      maxTitleBytes: 80,
+    })
+    await ctx.plugin(FirstMessageTitleProvider, {
+      targetWords: 5,
+      targetCjkCharacters: 10,
+      maxInputBytes: 4_096,
+      maxOutputTokens: 64,
+      timeoutMs: 60_000,
+      provider: 'deepseek',
+      model: 'deepseek-v4-flash',
+    })
+    const session = ctx.sessions.create(SessionId('real-title-provider'))
+    session.append('turn/start', {
+      turn: 1,
+      trigger: { kind: 'message', source: { kind: 'user' } },
+    })
+    const message = session.append('user/message', {
+      content: [{ type: 'text', text: 'Explain why append-only logs make session titles durable.' }],
+      source: { kind: 'user' },
+    }, { surfaceOp: 'append' })
+
+    const title = await ctx.sessionTitle.refresh(session)
+
+    expect(title).toMatchObject({
+      messageSeqs: [message.seq],
+      source: {
+        kind: 'provider',
+        provider: 'session-title-first-message-llm',
+        model: { provider: 'deepseek', model: 'deepseek-v4-flash' },
+      },
+    })
+    expect(title?.title.length).toBeGreaterThan(0)
+    expect(Buffer.byteLength(title?.title ?? '', 'utf8')).toBeLessThanOrEqual(80)
+  })
+})

packages/session-title/session-title-first-message-llm/tests/provider.spec.ts

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+import { Context } from 'cordis'
+import { describe, expect, it, vi } from 'vitest'
+import LlmService, { LlmAdapter } from '@deepseek-ai/dsh-llm'
+import type { GenerateOptions, StreamChunk } from '@deepseek-ai/dsh-llm'
+import SessionStore, { Session, SessionId } from '@deepseek-ai/dsh-session'
+import SessionTitleService, { type SessionTitleProvider } from '@deepseek-ai/dsh-session-title'
+import * as providerPlugin from '@deepseek-ai/dsh-session-title-first-message-llm'
+
+class RecordingAdapter extends LlmAdapter {
+  readonly requests: GenerateOptions[] = []
+
+  override async * stream(options: GenerateOptions): AsyncIterable<StreamChunk> {
+    this.requests.push(options)
+    yield { type: 'text-delta', index: 0, text: 'First-message model title' }
+    yield { type: 'finish', reason: { kind: 'stop' } }
+  }
+}
+
+const TITLE_CONFIG = { fallbackMaxWords: 5, fallbackMaxBytes: 40, maxTitleBytes: 80 } as const
+const LLM_CONFIG = {
+  targetWords: 5,
+  targetCjkCharacters: 10,
+  maxInputBytes: 1_000,
+  maxOutputTokens: 32,
+  timeoutMs: 1_000,
+  provider: 'title-route',
+  model: 'title-model',
+} as const
+
+async function settle(): Promise<void> {
+  await new Promise(resolve => setTimeout(resolve, 0))
+}
+
+describe('first-message LLM title provider', () => {
+  it('rejects an impossible empty provider request at its own boundary', async () => {
+    const ctx = new Context()
+    await ctx.plugin(LlmService)
+    await ctx.plugin(SessionStore)
+    await ctx.plugin(SessionTitleService, TITLE_CONFIG)
+    let registered: SessionTitleProvider | undefined
+    vi.spyOn(ctx.sessionTitle, 'register').mockImplementation((provider) => {
+      registered = provider
+      return () => undefined
+    })
+    providerPlugin.apply(ctx, LLM_CONFIG)
+
+    await expect(registered!.generate({
+      session: new Session(SessionId('empty-first-provider')),
+      messages: [],
+      signal: new AbortController().signal,
+    })).rejects.toThrow(/requires one human message/)
+  })
+
+  it('always selects only the first eligible human message, including explicit refresh', async () => {
+    const ctx = new Context()
+    await ctx.plugin(LlmService)
+    await ctx.plugin(SessionStore)
+    await ctx.plugin(SessionTitleService, TITLE_CONFIG)
+    const adapter = new RecordingAdapter()
+    ctx.llm.registerAdapter(['title-route'], adapter)
+    await ctx.plugin(providerPlugin, LLM_CONFIG)
+    const session = ctx.sessions.create(SessionId('first-plugin'))
+    session.append('turn/start', { turn: 1, trigger: { kind: 'message', source: { kind: 'user' } } })
+    const first = session.append('user/message', {
+      content: [{ type: 'text', text: 'first input' }], source: { kind: 'user' },
+    }, { surfaceOp: 'append' })
+    await settle()
+    session.append('request/header', {
+      header: { config: { provider: 'main', model: 'main-model' } }, reason: 'initial',
+    })
+    await settle()
+    session.append('user/message', {
+      content: [{ type: 'text', text: 'second input must be ignored' }], source: { kind: 'user' },
+    }, { surfaceOp: 'append' })
+
+    await ctx.sessionTitle.refresh(session)
+
+    expect(adapter.requests).toHaveLength(2)
+    for (const options of adapter.requests) {
+      const content = options.messages[0]?.content[0]
+      expect(content?.type === 'text' && content.text).toContain('first input')
+      expect(content?.type === 'text' && content.text).not.toContain('second input must be ignored')
+    }
+    expect(ctx.sessionTitle.get(session)).toMatchObject({ messageSeqs: [first.seq] })
+  })
+})

packages/session-title/session-title-first-message-llm/tsconfig.json

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+{
+  "extends": "../../../tsconfig.base.json",
+  "compilerOptions": { "rootDir": "src", "outDir": "lib/types" },
+  "include": ["src"],
+  "references": [
+    { "path": "../../../vendor/cosmokit" },
+    { "path": "../../../vendor/cordis" },
+    { "path": "../../../vendor/schemastery" },
+    { "path": "../../llm/llm" },
+    { "path": "../session-title" },
+    { "path": "../session-title-llm" }
+  ]
+}