diff --git a/src/hooks/start-work/context-info-builder.test.ts b/src/hooks/start-work/context-info-builder.test.ts
new file mode 100644
index 000000000..ffc08978b
--- /dev/null
+++ b/src/hooks/start-work/context-info-builder.test.ts
@@ -0,0 +1,171 @@
+/// <reference types="bun-types" />
+
+import { afterEach, beforeEach, describe, expect, spyOn, test } from "bun:test"
+import { existsSync, mkdirSync, rmSync, writeFileSync } from "node:fs"
+import { randomUUID } from "node:crypto"
+import { join } from "node:path"
+import { tmpdir } from "node:os"
+import { buildStartWorkContextInfo } from "./context-info-builder"
+import {
+  addBoulderWork,
+  createBoulderState,
+  getBoulderFilePath,
+  getWorkByPlanName,
+  readBoulderState,
+  writeBoulderState,
+} from "../../features/boulder-state"
+import * as boulderState from "../../features/boulder-state"
+
+describe("buildStartWorkContextInfo", () => {
+  let testDirectory = ""
+
+  function createPluginInput() {
+    return {
+      directory: testDirectory,
+    } as never
+  }
+
+  function writePlan(planName: string, content: string): string {
+    const plansDirectory = join(testDirectory, ".sisyphus", "plans")
+    mkdirSync(plansDirectory, { recursive: true })
+    const planPath = join(plansDirectory, `${planName}.md`)
+    writeFileSync(planPath, content)
+    return planPath
+  }
+
+  function readExistingState() {
+    return readBoulderState(testDirectory)
+  }
+
+  beforeEach(() => {
+    testDirectory = join(tmpdir(), `context-info-builder-${randomUUID()}`)
+    mkdirSync(testDirectory, { recursive: true })
+  })
+
+  afterEach(() => {
+    if (existsSync(testDirectory)) {
+      rmSync(testDirectory, { recursive: true, force: true })
+    }
+  })
+
+  test("lists multiple active works and asks agent to choose resume vs new when no explicit plan", () => {
+    // given
+    const clearSpy = spyOn(boulderState, "clearBoulderState")
+    const planAPath = writePlan("plan-alpha", "## TODOs\n- [ ] 1. Alpha")
+    const planBPath = writePlan("plan-beta", "## TODOs\n- [ ] 1. Beta")
+    const initialState = createBoulderState(planAPath, "session-a", "atlas", "/tmp/worktree-a")
+    writeBoulderState(testDirectory, initialState)
+    addBoulderWork(testDirectory, {
+      planPath: planBPath,
+      sessionId: "session-b",
+      agent: "atlas",
+      worktreePath: "/tmp/worktree-b",
+    })
+
+    // when
+    const contextInfo = buildStartWorkContextInfo({
+      ctx: createPluginInput(),
+      explicitPlanName: null,
+      existingState: readExistingState(),
+      sessionId: "session-current",
+      timestamp: "2026-05-11T00:00:00.000Z",
+      activeAgent: "atlas",
+      worktreePath: undefined,
+      worktreeBlock: "",
+    })
+
+    // then
+    expect(contextInfo).toContain("plan-alpha")
+    expect(contextInfo).toContain("plan-beta")
+    expect(contextInfo).toContain("Use the Question tool")
+    expect(clearSpy).toHaveBeenCalledTimes(0)
+  })
+
+  test("auto-resumes when exactly one active work exists and no explicit plan", () => {
+    // given
+    const clearSpy = spyOn(boulderState, "clearBoulderState")
+    const planPath = writePlan("single-active-plan", "## TODOs\n- [ ] 1. Single task")
+    const initialState = createBoulderState(planPath, "session-a", "atlas", "/tmp/worktree-single")
+    writeBoulderState(testDirectory, initialState)
+
+    // when
+    const contextInfo = buildStartWorkContextInfo({
+      ctx: createPluginInput(),
+      explicitPlanName: null,
+      existingState: readExistingState(),
+      sessionId: "session-current",
+      timestamp: "2026-05-11T00:00:00.000Z",
+      activeAgent: "atlas",
+      worktreePath: undefined,
+      worktreeBlock: "",
+    })
+
+    // then
+    expect(contextInfo).toContain("RESUMING existing work")
+    expect(contextInfo).toContain("single-active-plan")
+    expect(contextInfo).not.toContain("Use the Question tool")
+    expect(clearSpy).toHaveBeenCalledTimes(0)
+  })
+
+  test("explicit plan selects matching work only and never clears boulder state", () => {
+    // given
+    const clearSpy = spyOn(boulderState, "clearBoulderState")
+    const planAPath = writePlan("explicit-plan-a", "## TODOs\n- [ ] 1. A")
+    const planBPath = writePlan("explicit-plan-b", "## TODOs\n- [ ] 1. B")
+    const initialState = createBoulderState(planAPath, "session-a", "atlas", "/tmp/worktree-a")
+    writeBoulderState(testDirectory, initialState)
+    addBoulderWork(testDirectory, {
+      planPath: planBPath,
+      sessionId: "session-b",
+      agent: "atlas",
+      worktreePath: "/tmp/worktree-b",
+    })
+
+    // when
+    const contextInfo = buildStartWorkContextInfo({
+      ctx: createPluginInput(),
+      explicitPlanName: "explicit-plan-a",
+      existingState: readExistingState(),
+      sessionId: "session-current",
+      timestamp: "2026-05-11T00:00:00.000Z",
+      activeAgent: "atlas",
+      worktreePath: "/tmp/worktree-a",
+      worktreeBlock: "",
+    })
+
+    // then
+    expect(contextInfo).toContain("explicit-plan-a")
+    expect(contextInfo).not.toContain("explicit-plan-b")
+    expect(clearSpy).toHaveBeenCalledTimes(0)
+
+    const selectedWork = getWorkByPlanName(testDirectory, "explicit-plan-a", { worktreePath: "/tmp/worktree-a" })
+    const nextState = readBoulderState(testDirectory)
+    expect(selectedWork).not.toBeNull()
+    expect(nextState?.active_work_id).toBe(selectedWork?.work_id)
+  })
+
+  test("falls back to auto-select latest plan when no works exist", () => {
+    // given
+    const clearSpy = spyOn(boulderState, "clearBoulderState")
+    const coldStartPlanPath = writePlan("cold-start-plan", "## TODOs\n- [ ] 1. Cold start")
+
+    // when
+    const contextInfo = buildStartWorkContextInfo({
+      ctx: createPluginInput(),
+      explicitPlanName: null,
+      existingState: null,
+      sessionId: "session-current",
+      timestamp: "2026-05-11T00:00:00.000Z",
+      activeAgent: "atlas",
+      worktreePath: undefined,
+      worktreeBlock: "",
+    })
+
+    // then
+    expect(contextInfo).toContain("Auto-Selected Plan")
+    expect(contextInfo).toContain("cold-start-plan")
+    expect(contextInfo).toContain(coldStartPlanPath)
+    expect(existsSync(getBoulderFilePath(testDirectory))).toBe(true)
+    expect(clearSpy).toHaveBeenCalledTimes(0)
+  })
+})
diff --git a/src/hooks/start-work/context-info-builder.ts b/src/hooks/start-work/context-info-builder.ts
index 4ad7859c0..5ea4d8fce 100644
--- a/src/hooks/start-work/context-info-builder.ts
+++ b/src/hooks/start-work/context-info-builder.ts
@@ -1,13 +1,17 @@
 import { statSync } from "node:fs"
 import {
   appendSessionId,
-  clearBoulderState,
+  addBoulderWork,
   createBoulderState,
   findPrometheusPlans,
+  getActiveWorks,
   getPlanName,
   getPlanProgress,
+  getWorkByPlanName,
+  getWorkResumeOptions,
   readBoulderState,
   resolveBoulderPlanPath,
+  selectActiveWork,
   writeBoulderState,
 } from "../../features/boulder-state"
 import { log } from "../../shared/logger"
@@ -99,9 +103,73 @@ Ask the user which plan to work on.`
  No incomplete plans available. Create a new plan using the Prometheus agent.`
 }
 
+function formatElapsedHuman(elapsedMs: number | undefined): string {
+  if (typeof elapsedMs !== "number" || elapsedMs <= 0) {
+    return "running"
+  }
+
+  const totalSeconds = Math.floor(elapsedMs / 1000)
+  const seconds = totalSeconds % 60
+  const totalMinutes = Math.floor(totalSeconds / 60)
+  const minutes = totalMinutes % 60
+  const hours = Math.floor(totalMinutes / 60)
+  if (hours > 0) {
+    return `${hours}h ${minutes}m ${seconds}s`
+  }
+  if (minutes > 0) {
+    return `${minutes}m ${seconds}s`
+  }
+  return `${seconds}s`
+}
+
+function buildMultipleActiveWorksContext(params: {
+  resumeOptions: ReturnType<typeof getWorkResumeOptions>
+  sessionId: string
+  timestamp: string
+}): string {
+  const { resumeOptions, sessionId, timestamp } = params
+  const optionList = resumeOptions
+    .map((option, index) => `${index + 1}. ${option.plan_name} - ${option.progress.completed}/${option.progress.total} (${option.progress.total === 0 ? 0 : Math.floor((option.progress.completed / option.progress.total) * 100)}%) - elapsed: ${formatElapsedHuman(option.elapsed_ms)} - worktree: ${option.worktree_path ?? "current directory"} - sessions: ${option.session_count}`)
+    .join("\n")
+
+  return `
+<system-reminder>
+## Multiple Active Works Found
+
+Current Time: ${timestamp}
+Session ID: ${sessionId}
+
+${optionList}
+
+Use the Question tool to ask the user which plan to resume.
+- If the user chooses one option, run /start-work {plan-name} for that plan.
+- If the user chooses to start a new plan, proceed with cold-start auto-selection flow.
+</system-reminder>`
+}
+
+function createNewWorkOrInitialize(params: {
+  directory: string
+  planPath: string
+  sessionId: string
+  activeAgent: string
+  worktreePath: string | undefined
+}): void {
+  const { directory, planPath, sessionId, activeAgent, worktreePath } = params
+  const created = addBoulderWork(directory, {
+    planPath,
+    sessionId,
+    agent: activeAgent,
+    worktreePath,
+  })
+
+  if (!created) {
+    const initializedState = createBoulderState(planPath, sessionId, activeAgent, worktreePath)
+    writeBoulderState(directory, initializedState)
+  }
+}
+
 function buildExplicitPlanContext(params: {
   explicitPlanName: string
-  existingState: ReturnType<typeof readBoulderState>
   sessionId: string
   timestamp: string
   activeAgent: string
@@ -109,9 +177,24 @@ function buildExplicitPlanContext(params: {
   worktreeBlock: string
   directory: string
 }): string {
-  const { explicitPlanName, existingState, sessionId, timestamp, activeAgent, worktreePath, worktreeBlock, directory } = params
+  const { explicitPlanName, sessionId, timestamp, activeAgent, worktreePath, worktreeBlock, directory } = params
   log(`[${HOOK_NAME}] Explicit plan name requested: ${explicitPlanName}`, { sessionID: sessionId })
 
+  const matchedWork = getWorkByPlanName(directory, explicitPlanName, { worktreePath })
+  if (matchedWork) {
+    const selectedState = selectActiveWork(directory, matchedWork.work_id)
+    if (selectedState) {
+      return buildExistingSessionContext({
+        existingState: selectedState,
+        sessionId,
+        activeAgent,
+        worktreePath,
+        worktreeBlock,
+        directory,
+      })
+    }
+  }
+
   const allPlans = findPrometheusPlans(directory)
   const matchedPlan = findPlanByName(allPlans, explicitPlanName)
   if (!matchedPlan) {
@@ -127,9 +210,13 @@ function buildExplicitPlanContext(params: {
  All ${progress.total} tasks are done. Create a new plan using the Prometheus agent.`
   }
 
-  if (existingState) {
-    clearBoulderState(directory)
-  }
+  createNewWorkOrInitialize({
+    directory,
+    planPath: matchedPlan,
+    sessionId,
+    activeAgent,
+    worktreePath,
+  })
 
   return buildAutoSelectedPlanContext({
     planPath: matchedPlan,
@@ -287,11 +374,48 @@ export function buildStartWorkContextInfo(params: {
 }): string {
   const { ctx, explicitPlanName, existingState, sessionId, timestamp, activeAgent, worktreePath, worktreeBlock } = params
 
+  const resumeOptions = getWorkResumeOptions(ctx.directory)
+    .filter((option) => option.status === "active" || option.status === "paused")
+
+  if (!explicitPlanName && resumeOptions.length > 1) {
+    return buildMultipleActiveWorksContext({
+      resumeOptions,
+      sessionId,
+      timestamp,
+    })
+  }
+
+  if (!explicitPlanName && resumeOptions.length === 1) {
+    const onlyOption = resumeOptions[0]
+    const selectedState = selectActiveWork(ctx.directory, onlyOption.work_id)
+    if (selectedState) {
+      return buildExistingSessionContext({
+        existingState: selectedState,
+        sessionId,
+        activeAgent,
+        worktreePath,
+        worktreeBlock,
+        directory: ctx.directory,
+      })
+    }
+  }
+
+  if (!explicitPlanName && resumeOptions.length === 0 && getActiveWorks(ctx.directory).length === 0) {
+    return buildPlanDiscoveryContext({
+      contextInfo: "",
+      sessionId,
+      timestamp,
+      activeAgent,
+      worktreePath,
+      worktreeBlock,
+      directory: ctx.directory,
+    })
+  }
+
   let contextInfo = ""
   if (explicitPlanName) {
     contextInfo = buildExplicitPlanContext({
       explicitPlanName,
-      existingState,
       sessionId,
       timestamp,
       activeAgent,