feat(apiproxy): projection column on session.list — cold titles with zero log loads

SessionSummary grows an optional projections column (whole value per key,
same passthrough posture as the history-tail block): attached rows cut the
live registry watermark cache; cold rows view the persisted projection
cache's stored rows via the new registry viewCheckpoint face (version-
matching keys only, zero I/O) — the RFC's motivating scenario, every
session's title across a listing without loading one event log. The column
is fail-soft and absence-coded: no registry, no cache row, or a throwing
read serve the row without the column, never breaking the listing.

packages/host/apiproxy/package.json

@@ -47,6 +47,7 @@
     "@deepseek-ai/dsh-session": "workspace:^",
     "@deepseek-ai/dsh-session-persistence": "workspace:^",
     "@deepseek-ai/dsh-session-projection": "workspace:^",
+    "@deepseek-ai/dsh-session-projection-cache": "workspace:^",
     "@deepseek-ai/dsh-skill": "workspace:^",
     "@deepseek-ai/dsh-tools": "workspace:^",
     "@deepseek-ai/dsh-user-approval": "workspace:^",

packages/host/apiproxy/src/api-proxy.ts

@@ -29,7 +29,9 @@ import type {
   WorkspaceId, WorkspaceView,
 } from './api/index.ts'
 // Type-only: resolves `ctx.get('sessionProjections')` to the projection registry.
-import type {} from '@deepseek-ai/dsh-session-projection'
+import type { SessionProjectionMap } from '@deepseek-ai/dsh-session-projection'
+// Type-only: resolves `ctx.get('sessionProjectionCache')` (the cold listing column).
+import type {} from '@deepseek-ai/dsh-session-projection-cache'
 // Type-only edges: resolve `ctx.get('commands')`, the `commands/change` event, and `ctx.get('skills')`.
 import type {} from '@deepseek-ai/dsh-commands'
 import type {} from '@deepseek-ai/dsh-skill'
@@ -297,6 +299,26 @@ function projectionsFor(ctx: Context, agent: Agent): SessionProjectionsBlock | u
   return registry.snapshot(agent.session)
 }
 
+/**
+ * The projection column of one session.list row, fail-soft: attached
+ * sessions cut the registry's live watermark cache; cold sessions view the
+ * persisted projection cache's stored rows (zero log loads either way — the
+ * listing use case the cache exists for). Any failure — and an empty value
+ * set — yields an absent column: a listing without projections is degraded,
+ * never broken.
+ */
+function listProjectionsFor(ctx: Context, id: SessionId, session: Session | undefined): Partial<SessionProjectionMap> | undefined {
+  try {
+    const values = session !== undefined
+      ? ctx.get('sessionProjections')?.snapshot(session).values
+      : ctx.get('sessionProjectionCache')?.cachedValues(id)
+    return values !== undefined && Object.keys(values).length > 0 ? values : undefined
+  } catch (error) {
+    ctx.logger.warn(`session.list: projection column for "${id}" failed (serving the row without it): ${String(error)}`)
+    return undefined
+  }
+}
+
 /**
  * Thrown by the cold-resume path when the id names no servable session
  * (absent from the store, or a pre-project legacy log without a cwd).
@@ -654,13 +676,25 @@ export function createApiProxy(ctx: Context, defaults: ApiProxyDefaults): ApiPro
       async list(request) {
         const items = ctx.sessions.list().map((session) => {
           const agent = ctx.agents.get(session.id)
-          return summarize(session, agent?.status === 'running')
+          const projections = listProjectionsFor(ctx, session.id, session)
+          return {
+            ...summarize(session, agent?.status === 'running'),
+            ...projections === undefined ? {} : { projections },
+          }
         })
         const attached = new Set(items.map(item => item.sessionId))
         const persistence = ctx.get('sessionPersistence')
         if (persistence !== undefined) {
           const cold = (await persistence.list()).filter(meta => !attached.has(meta.id) && meta.cwd !== undefined)
-          items.push(...await Promise.all(cold.map(meta => summarizeCold(persistence, meta))))
+          items.push(...await Promise.all(cold.map(async (meta) => {
+            // Cold rows read the persisted projection cache only — never a
+            // log load; a session without a cache row simply has no column.
+            const projections = listProjectionsFor(ctx, meta.id, undefined)
+            return {
+              ...await summarizeCold(persistence, meta),
+              ...projections === undefined ? {} : { projections },
+            }
+          })))
         }
         items.sort((a, b) => b.updatedAt - a.updatedAt)
         return ok(request, { items })

packages/host/apiproxy/src/api/sessions.schema.ts

@@ -7,6 +7,7 @@
 
 import { z } from 'zod'
 import type { SessionEvent, SessionId } from '@deepseek-ai/dsh-session/types'
+import type { SessionProjectionMap } from '@deepseek-ai/dsh-session-projection/types'
 import type { RequestPayload, ResponseValue } from './rpc-map.ts'
 import type { Wire } from './rpc.schema.ts'
 import type {
@@ -37,6 +38,15 @@ export const sessionEventSchema = z.object({
   surfaceOp: z.unknown().optional(),
 }) as unknown as z.ZodType<SessionEvent>
 
+/**
+ * Projection-values passthrough (same posture as
+ * {@link sessionProjectionsBlockSchema}): each value already passed its
+ * unit's own schema on the host side; deep-validating here would import
+ * every domain's schema into the carrier.
+ */
+const projectionValuesSchema =
+  z.record(z.string(), z.unknown()) as unknown as z.ZodType<Partial<SessionProjectionMap>>
+
 /** SessionSummary row of session.list. */
 export const sessionSummarySchema = z.object({
   sessionId: sessionIdSchema,
@@ -45,6 +55,7 @@ export const sessionSummarySchema = z.object({
   blank: z.boolean(),
   parentSessionId: sessionIdSchema.optional(),
   cwd: z.string().optional(),
+  projections: projectionValuesSchema.optional(),
 }) satisfies z.ZodType<Wire<SessionSummary>>
 
 /** session.list request payload (cursor is a reserved seat, unimplemented in v1). */

packages/host/apiproxy/src/api/sessions.ts

@@ -143,6 +143,17 @@ export interface SessionSummary {
   parentSessionId?: SessionId
   /** Session working directory (header.cwd passthrough); absent when unrecorded. */
   cwd?: string
+  /**
+   * Whole current value per projection key, with zero log loads: attached
+   * sessions read the registry's live watermark cut; cold sessions read the
+   * persisted projection cache's stored rows — as stale as that session's
+   * last durable checkpoint, never wrong, superseded by the history tail
+   * baseline the moment the session is opened. Absent when no value is
+   * available (no registry, no cache row for a cold session, or a fail-soft
+   * cache read miss); a listing client treats absence as "no title yet",
+   * exactly like a blank session.
+   */
+  projections?: Partial<SessionProjectionMap>
 }
 
 /** Session-domain unary methods (the map keys session.* of RpcMethodMap). */

packages/host/apiproxy/tests/api-proxy-projections.spec.ts

@@ -13,7 +13,7 @@ import { z } from 'zod'
 import AgentRegistry from '@deepseek-ai/dsh-agent'
 import type { Agent } from '@deepseek-ai/dsh-agent'
 import { createUserMessage } from '@deepseek-ai/dsh-llm'
-import SessionStore from '@deepseek-ai/dsh-session'
+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 type { ProjectionDefinition } from '@deepseek-ai/dsh-session-projection'
@@ -125,6 +125,77 @@ describe('session.history projections block', () => {
   })
 })
 
+describe('session.list projections column', () => {
+  it('serves attached rows from the live registry cut', async () => {
+    const { ctx, session } = await harness(true)
+    ctx.sessionProjections.register(lastUserUnit())
+    seedMessages(session, 1)
+    const response = await api(ctx).sessions.list(request({}))
+    if (!response.result.ok) throw new Error('unreachable')
+    const row = response.result.value.items.find(item => item.sessionId === session.id)
+    expect(row?.projections?.['test/last-user']).toEqual({ text: 'm0' })
+  })
+
+  it('omits the column entirely when no registry is mounted', async () => {
+    const { ctx, session } = await harness(false)
+    seedMessages(session, 1)
+    const response = await api(ctx).sessions.list(request({}))
+    if (!response.result.ok) throw new Error('unreachable')
+    const row = response.result.value.items.find(item => item.sessionId === session.id)
+    expect(row).toBeDefined()
+    expect(row !== undefined && 'projections' in row).toBe(false)
+  })
+
+  it('serves cold rows from the persisted projection cache with zero log loads', async () => {
+    const { ctx } = await harness(true)
+    const coldId = SessionId('session-cold-listing')
+    const load = () => { throw new Error('list must not load event logs') }
+    ctx.provide('sessionPersistence', {
+      list: async () => [{ version: 0, id: coldId, createdAt: 5, cwd: '/tmp' }],
+      locate: () => undefined,
+      load,
+      inspect: load,
+      readFrom: load,
+    } as never)
+    ctx.provide('sessionProjectionCache', {
+      cachedValues: (id: unknown) => (id === coldId ? { 'test/last-user': { text: 'cached' } } : {}),
+    } as never)
+    const response = await api(ctx).sessions.list(request({}))
+    if (!response.result.ok) throw new Error('unreachable')
+    const row = response.result.value.items.find(item => item.sessionId === coldId)
+    expect(row?.running).toBe(false)
+    expect(row?.projections?.['test/last-user']).toEqual({ text: 'cached' })
+  })
+
+  it('cold rows without a cache plugin (or without a stored row) just lack the column', async () => {
+    const { ctx } = await harness(true)
+    const coldId = SessionId('session-cold-uncached')
+    ctx.provide('sessionPersistence', {
+      list: async () => [{ version: 0, id: coldId, createdAt: 5, cwd: '/tmp' }],
+      locate: () => undefined,
+    } as never)
+    const response = await api(ctx).sessions.list(request({}))
+    if (!response.result.ok) throw new Error('unreachable')
+    const row = response.result.value.items.find(item => item.sessionId === coldId)
+    expect(row).toBeDefined()
+    expect(row !== undefined && 'projections' in row).toBe(false)
+  })
+
+  it('a throwing column read degrades that row, never the listing', async () => {
+    const { ctx, session } = await harness(true)
+    ctx.sessionProjections.register({
+      ...lastUserUnit(),
+      view: () => { throw new Error('unit exploded') },
+    })
+    seedMessages(session, 1)
+    const response = await api(ctx).sessions.list(request({}))
+    if (!response.result.ok) throw new Error('unreachable')
+    const row = response.result.value.items.find(item => item.sessionId === session.id)
+    expect(row).toBeDefined()
+    expect(row !== undefined && 'projections' in row).toBe(false)
+  })
+})
+
 describe('session/projection push frame', () => {
   /** Drain frames until `count` session/projection frames arrived. */
   async function collect(iterable: AsyncIterable<RpcRequest<MuxFrame>>, count: number, abort: AbortController): Promise<MuxFrame[]> {

packages/host/apiproxy/tsconfig.json

@@ -35,6 +35,9 @@
     {
       "path": "../../session-projection/session-projection"
     },
+    {
+      "path": "../../session-projection/session-projection-cache"
+    },
     {
       "path": "../../skill/skill"
     },