diff --git a/src/features/builtin-commands/commands.test.ts b/src/features/builtin-commands/commands.test.ts
index 668027368..15231bb44 100644
--- a/src/features/builtin-commands/commands.test.ts
+++ b/src/features/builtin-commands/commands.test.ts
@@ -59,6 +59,16 @@ describe("loadBuiltinCommands", () => {
     //#then
     expect(commands.handoff.description).toContain("context summary")
   })
+
+  test("should preassign Sisyphus as the native agent for start-work", () => {
+    //#given - no disabled commands
+
+    //#when
+    const commands = loadBuiltinCommands()
+
+    //#then
+    expect(commands["start-work"].agent).toBe("sisyphus")
+  })
 })
 
 describe("loadBuiltinCommands — remove-ai-slops", () => {
diff --git a/src/features/builtin-commands/commands.ts b/src/features/builtin-commands/commands.ts
index e3b0bb52d..3c0f1e432 100644
--- a/src/features/builtin-commands/commands.ts
+++ b/src/features/builtin-commands/commands.ts
@@ -58,7 +58,7 @@ ${REFACTOR_TEMPLATE}
   },
   "start-work": {
     description: "(builtin) Start Sisyphus work session from Prometheus plan",
-    agent: "atlas",
+    agent: "sisyphus",
     template: `<command-instruction>
 ${START_WORK_TEMPLATE}
 </command-instruction>
diff --git a/src/hooks/start-work/index.test.ts b/src/hooks/start-work/index.test.ts
index af284f6f8..193d83bb8 100644
--- a/src/hooks/start-work/index.test.ts
+++ b/src/hooks/start-work/index.test.ts
@@ -4,6 +4,7 @@ import { join } from "node:path"
 import { tmpdir } from "node:os"
 import { randomUUID } from "node:crypto"
 import { createStartWorkHook } from "./index"
+import { getAgentListDisplayName } from "../../shared/agent-display-names"
 import {
   writeBoulderState,
   clearBoulderState,
@@ -24,6 +25,22 @@ describe("start-work hook", () => {
     } as Parameters<typeof createStartWorkHook>[0]
   }
 
+  function createStartWorkPrompt(options?: {
+    sessionContext?: string
+    userRequest?: string
+  }): string {
+    const sessionContext = options?.sessionContext ?? ""
+    const userRequest = options?.userRequest ?? ""
+
+    return `<command-instruction>
+You are starting a Sisyphus work session.
+</command-instruction>
+
+<session-context>${sessionContext}</session-context>${userRequest ? `
+
+<user-request>${userRequest}</user-request>` : ""}`
+  }
+
   beforeEach(() => {
     sessionState._resetForTesting()
     sessionState.registerAgentName("atlas")
@@ -65,6 +82,24 @@ describe("start-work hook", () => {
       expect(output.parts[0].text).toBe("Just a regular message")
     })
 
+    test("should ignore plain session-context blocks without the start-work marker", async () => {
+      // given
+      const hook = createStartWorkHook(createMockPluginInput())
+      const output = {
+        parts: [{ type: "text", text: "<session-context>Some context here</session-context>" }],
+      }
+
+      // when
+      await hook["chat.message"](
+        { sessionID: "session-123" },
+        output
+      )
+
+      // then
+      expect(output.parts[0].text).toBe("<session-context>Some context here</session-context>")
+      expect(readBoulderState(testDir)).toBeNull()
+    })
+
     test("should detect start-work command via session-context tag", async () => {
       // given - hook and start-work message
       const hook = createStartWorkHook(createMockPluginInput())
@@ -72,7 +107,7 @@ describe("start-work hook", () => {
         parts: [
           {
             type: "text",
-            text: "<session-context>Some context here</session-context>",
+            text: createStartWorkPrompt({ sessionContext: "Some context here" }),
           },
         ],
       }
@@ -102,7 +137,7 @@ describe("start-work hook", () => {
 
       const hook = createStartWorkHook(createMockPluginInput())
       const output = {
-        parts: [{ type: "text", text: "<session-context></session-context>" }],
+        parts: [{ type: "text", text: createStartWorkPrompt() }],
       }
 
       // when
@@ -123,7 +158,7 @@ describe("start-work hook", () => {
         parts: [
           {
             type: "text",
-            text: "<session-context>Session: $SESSION_ID</session-context>",
+            text: createStartWorkPrompt({ sessionContext: "Session: $SESSION_ID" }),
           },
         ],
       }
@@ -146,7 +181,7 @@ describe("start-work hook", () => {
         parts: [
           {
             type: "text",
-            text: "<session-context>Time: $TIMESTAMP</session-context>",
+            text: createStartWorkPrompt({ sessionContext: "Time: $TIMESTAMP" }),
           },
         ],
       }
@@ -177,7 +212,7 @@ describe("start-work hook", () => {
 
       const hook = createStartWorkHook(createMockPluginInput())
       const output = {
-        parts: [{ type: "text", text: "<session-context></session-context>" }],
+        parts: [{ type: "text", text: createStartWorkPrompt() }],
       }
 
       // when
@@ -205,7 +240,7 @@ describe("start-work hook", () => {
 
       const hook = createStartWorkHook(createMockPluginInput())
       const output = {
-        parts: [{ type: "text", text: "<session-context></session-context>" }],
+        parts: [{ type: "text", text: createStartWorkPrompt() }],
       }
 
       // when
@@ -233,7 +268,7 @@ describe("start-work hook", () => {
 
       const hook = createStartWorkHook(createMockPluginInput())
       const output = {
-        parts: [{ type: "text", text: "<session-context></session-context>" }],
+        parts: [{ type: "text", text: createStartWorkPrompt() }],
       }
 
       // when
@@ -274,9 +309,7 @@ describe("start-work hook", () => {
         parts: [
           {
             type: "text",
-            text: `<session-context>
-<user-request>new-plan</user-request>
-</session-context>`,
+            text: createStartWorkPrompt({ userRequest: "new-plan" }),
           },
         ],
       }
@@ -306,9 +339,7 @@ describe("start-work hook", () => {
         parts: [
           {
             type: "text",
-            text: `<session-context>
-<user-request>my-feature-plan ultrawork</user-request>
-</session-context>`,
+            text: createStartWorkPrompt({ userRequest: "my-feature-plan ultrawork" }),
           },
         ],
       }
@@ -337,9 +368,7 @@ describe("start-work hook", () => {
         parts: [
           {
             type: "text",
-            text: `<session-context>
-<user-request>api-refactor ulw</user-request>
-</session-context>`,
+            text: createStartWorkPrompt({ userRequest: "api-refactor ulw" }),
           },
         ],
       }
@@ -368,9 +397,7 @@ describe("start-work hook", () => {
         parts: [
           {
             type: "text",
-            text: `<session-context>
-<user-request>feature-implementation</user-request>
-</session-context>`,
+            text: createStartWorkPrompt({ userRequest: "feature-implementation" }),
           },
         ],
       }
@@ -394,7 +421,7 @@ describe("start-work hook", () => {
       
       const hook = createStartWorkHook(createMockPluginInput())
       const output = {
-        parts: [{ type: "text", text: "<session-context></session-context>" }],
+        parts: [{ type: "text", text: createStartWorkPrompt() }],
       }
 
       // when
@@ -408,12 +435,12 @@ describe("start-work hook", () => {
       updateSpy.mockRestore()
     })
 
-    test("should stamp the outgoing message with Atlas so follow-up events keep the handoff", async () => {
+    test("should stamp the outgoing message with Atlas list key so follow-up events keep the handoff", async () => {
       // given
       const hook = createStartWorkHook(createMockPluginInput())
       const output = {
         message: {} as Record<string, unknown>,
-        parts: [{ type: "text", text: "<session-context></session-context>" }],
+        parts: [{ type: "text", text: createStartWorkPrompt() }],
       }
 
       // when
@@ -423,7 +450,7 @@ describe("start-work hook", () => {
       )
 
       // then
-      expect(output.message.agent).toBe("Atlas (Plan Executor)")
+      expect(output.message.agent).toBe(getAgentListDisplayName("atlas"))
     })
 
     test("should keep the current agent when Atlas is unavailable", async () => {
@@ -435,7 +462,7 @@ describe("start-work hook", () => {
       const hook = createStartWorkHook(createMockPluginInput())
       const output = {
         message: {} as Record<string, unknown>,
-        parts: [{ type: "text", text: "<session-context></session-context>" }],
+        parts: [{ type: "text", text: createStartWorkPrompt() }],
       }
 
       // when
@@ -463,7 +490,7 @@ describe("start-work hook", () => {
       const hook = createStartWorkHook(createMockPluginInput())
       const output = {
         message: {} as Record<string, unknown>,
-        parts: [{ type: "text", text: "<session-context></session-context>" }],
+        parts: [{ type: "text", text: createStartWorkPrompt() }],
       }
 
       // when
@@ -498,7 +525,7 @@ describe("start-work hook", () => {
       const hook = createStartWorkHook(createMockPluginInput())
       const output = {
         message: {} as Record<string, unknown>,
-        parts: [{ type: "text", text: "<session-context></session-context>" }],
+        parts: [{ type: "text", text: createStartWorkPrompt() }],
       }
 
       // when
@@ -532,7 +559,7 @@ describe("start-work hook", () => {
 
       const hook = createStartWorkHook(createMockPluginInput())
       const output = {
-        parts: [{ type: "text", text: "<session-context></session-context>" }],
+        parts: [{ type: "text", text: createStartWorkPrompt() }],
       }
 
       // when
@@ -553,7 +580,7 @@ describe("start-work hook", () => {
 
       const hook = createStartWorkHook(createMockPluginInput())
       const output = {
-        parts: [{ type: "text", text: "<session-context>\n<user-request>--worktree /validated/worktree</user-request>\n</session-context>" }],
+        parts: [{ type: "text", text: createStartWorkPrompt({ userRequest: "--worktree /validated/worktree" }) }],
       }
 
       // when
@@ -575,7 +602,7 @@ describe("start-work hook", () => {
 
       const hook = createStartWorkHook(createMockPluginInput())
       const output = {
-        parts: [{ type: "text", text: "<session-context>\n<user-request>--worktree /valid/wt</user-request>\n</session-context>" }],
+        parts: [{ type: "text", text: createStartWorkPrompt({ userRequest: "--worktree /valid/wt" }) }],
       }
 
       // when
@@ -595,7 +622,7 @@ describe("start-work hook", () => {
 
       const hook = createStartWorkHook(createMockPluginInput())
       const output = {
-        parts: [{ type: "text", text: "<session-context>\n<user-request>--worktree /nonexistent/wt</user-request>\n</session-context>" }],
+        parts: [{ type: "text", text: createStartWorkPrompt({ userRequest: "--worktree /nonexistent/wt" }) }],
       }
 
       // when
@@ -624,7 +651,7 @@ describe("start-work hook", () => {
 
       const hook = createStartWorkHook(createMockPluginInput())
       const output = {
-        parts: [{ type: "text", text: "<session-context>\n<user-request>--worktree /new/wt</user-request>\n</session-context>" }],
+        parts: [{ type: "text", text: createStartWorkPrompt({ userRequest: "--worktree /new/wt" }) }],
       }
 
       // when
@@ -651,7 +678,7 @@ describe("start-work hook", () => {
 
       const hook = createStartWorkHook(createMockPluginInput())
       const output = {
-        parts: [{ type: "text", text: "<session-context></session-context>" }],
+        parts: [{ type: "text", text: createStartWorkPrompt() }],
       }
 
       // when
diff --git a/src/hooks/start-work/start-work-hook.ts b/src/hooks/start-work/start-work-hook.ts
index 7f9f0bcdb..d0445d7f1 100644
--- a/src/hooks/start-work/start-work-hook.ts
+++ b/src/hooks/start-work/start-work-hook.ts
@@ -11,18 +11,33 @@ import {
   clearBoulderState,
 } from "../../features/boulder-state"
 import { log } from "../../shared/logger"
-import { getAgentConfigKey, getAgentDisplayName } from "../../shared/agent-display-names"
-import { getSessionAgent, isAgentRegistered, updateSessionAgent } from "../../features/claude-code-session-state"
+import {
+  getAgentConfigKey,
+  getAgentDisplayName,
+  getAgentListDisplayName,
+} from "../../shared/agent-display-names"
+import {
+  getSessionAgent,
+  isAgentRegistered,
+  updateSessionAgent,
+} from "../../features/claude-code-session-state"
 import { detectWorktreePath } from "./worktree-detector"
 import { parseUserRequest } from "./parse-user-request"
 
 export const HOOK_NAME = "start-work" as const
+const START_WORK_TEMPLATE_MARKER = "You are starting a Sisyphus work session."
 
 interface StartWorkHookInput {
   sessionID: string
   messageID?: string
 }
 
+interface StartWorkCommandExecuteBeforeInput {
+  sessionID: string
+  command: string
+  arguments: string
+}
+
 interface StartWorkHookOutput {
   message?: Record<string, unknown>
   parts: Array<{ type: string; text?: string }>
@@ -67,61 +82,76 @@ function resolveWorktreeContext(
 }
 
 export function createStartWorkHook(ctx: PluginInput) {
-  return {
-    "chat.message": async (input: StartWorkHookInput, output: StartWorkHookOutput): Promise<void> => {
-      const parts = output.parts
-      const promptText =
-        parts
-          ?.filter((p) => p.type === "text" && p.text)
-          .map((p) => p.text)
-          .join("\n")
-          .trim() || ""
+  const processStartWork = async (
+    input: StartWorkHookInput,
+    output: StartWorkHookOutput,
+  ): Promise<void> => {
+    const parts = output.parts
+    const promptText =
+      parts
+        ?.filter((p) => p.type === "text" && p.text)
+        .map((p) => p.text)
+        .join("\n")
+        .trim() || ""
 
-      if (!promptText.includes("<session-context>")) return
+    if (
+      !promptText.includes("<session-context>")
+      || !promptText.includes(START_WORK_TEMPLATE_MARKER)
+    ) {
+      return
+    }
 
-      log(`[${HOOK_NAME}] Processing start-work command`, { sessionID: input.sessionID })
-      const currentSessionAgent = getSessionAgent(input.sessionID)
-      const activeAgent = isAgentRegistered("atlas")
-        ? "atlas"
-        : currentSessionAgent && getAgentConfigKey(currentSessionAgent) !== "prometheus"
-          ? currentSessionAgent
+    log(`[${HOOK_NAME}] Processing start-work command`, { sessionID: input.sessionID })
+    const currentSessionAgent = getSessionAgent(input.sessionID)
+    const currentSessionAgentKey = currentSessionAgent
+      ? getAgentConfigKey(currentSessionAgent)
+      : undefined
+    const activeAgent = currentSessionAgent
+      && currentSessionAgentKey
+      && currentSessionAgentKey !== "prometheus"
+      && currentSessionAgentKey !== "atlas"
+        ? currentSessionAgent
+        : isAgentRegistered("atlas")
+          ? "atlas"
           : "sisyphus"
-      const activeAgentDisplayName = getAgentDisplayName(activeAgent)
-      updateSessionAgent(input.sessionID, activeAgent)
-      if (output.message) {
-        output.message["agent"] = activeAgentDisplayName
-      }
+    const activeAgentDisplayName = activeAgent === "atlas"
+      ? getAgentListDisplayName(activeAgent)
+      : getAgentDisplayName(activeAgent)
+    updateSessionAgent(input.sessionID, activeAgent)
+    if (output.message) {
+      output.message["agent"] = activeAgentDisplayName
+    }
 
-      const existingState = readBoulderState(ctx.directory)
-      const sessionId = input.sessionID
-      const timestamp = new Date().toISOString()
+    const existingState = readBoulderState(ctx.directory)
+    const sessionId = input.sessionID
+    const timestamp = new Date().toISOString()
 
-      const { planName: explicitPlanName, explicitWorktreePath } = parseUserRequest(promptText)
-      const { worktreePath, block: worktreeBlock } = resolveWorktreeContext(explicitWorktreePath)
+    const { planName: explicitPlanName, explicitWorktreePath } = parseUserRequest(promptText)
+    const { worktreePath, block: worktreeBlock } = resolveWorktreeContext(explicitWorktreePath)
 
-      let contextInfo = ""
+    let contextInfo = ""
 
-      if (explicitPlanName) {
-        log(`[${HOOK_NAME}] Explicit plan name requested: ${explicitPlanName}`, { sessionID: input.sessionID })
+    if (explicitPlanName) {
+      log(`[${HOOK_NAME}] Explicit plan name requested: ${explicitPlanName}`, { sessionID: input.sessionID })
 
-        const allPlans = findPrometheusPlans(ctx.directory)
-        const matchedPlan = findPlanByName(allPlans, explicitPlanName)
+      const allPlans = findPrometheusPlans(ctx.directory)
+      const matchedPlan = findPlanByName(allPlans, explicitPlanName)
 
-        if (matchedPlan) {
-          const progress = getPlanProgress(matchedPlan)
+      if (matchedPlan) {
+        const progress = getPlanProgress(matchedPlan)
 
-          if (progress.isComplete) {
-            contextInfo = `
+        if (progress.isComplete) {
+          contextInfo = `
 ## Plan Already Complete
 
 The requested plan "${getPlanName(matchedPlan)}" has been completed.
 All ${progress.total} tasks are done. Create a new plan with: /plan "your task"`
-          } else {
-            if (existingState) clearBoulderState(ctx.directory)
-            const newState = createBoulderState(matchedPlan, sessionId, activeAgent, worktreePath)
-            writeBoulderState(ctx.directory, newState)
+        } else {
+          if (existingState) clearBoulderState(ctx.directory)
+          const newState = createBoulderState(matchedPlan, sessionId, activeAgent, worktreePath)
+          writeBoulderState(ctx.directory, newState)
 
-            contextInfo = `
+          contextInfo = `
 ## Auto-Selected Plan
 
 **Plan**: ${getPlanName(matchedPlan)}
@@ -132,18 +162,18 @@ All ${progress.total} tasks are done. Create a new plan with: /plan "your task"`
 ${worktreeBlock}
 
 boulder.json has been created. Read the plan and begin execution.`
-          }
-        } else {
-          const incompletePlans = allPlans.filter((p) => !getPlanProgress(p).isComplete)
-          if (incompletePlans.length > 0) {
-            const planList = incompletePlans
-              .map((p, i) => {
-                const prog = getPlanProgress(p)
-                return `${i + 1}. [${getPlanName(p)}] - Progress: ${prog.completed}/${prog.total}`
-              })
-              .join("\n")
+        }
+      } else {
+        const incompletePlans = allPlans.filter((p) => !getPlanProgress(p).isComplete)
+        if (incompletePlans.length > 0) {
+          const planList = incompletePlans
+            .map((p, i) => {
+              const prog = getPlanProgress(p)
+              return `${i + 1}. [${getPlanName(p)}] - Progress: ${prog.completed}/${prog.total}`
+            })
+            .join("\n")
 
-            contextInfo = `
+          contextInfo = `
 ## Plan Not Found
 
 Could not find a plan matching "${explicitPlanName}".
@@ -152,39 +182,39 @@ Available incomplete plans:
 ${planList}
 
 Ask the user which plan to work on.`
-          } else {
-            contextInfo = `
+        } else {
+          contextInfo = `
 ## Plan Not Found
 
 Could not find a plan matching "${explicitPlanName}".
 No incomplete plans available. Create a new plan with: /plan "your task"`
-          }
         }
-      } else if (existingState) {
-        const progress = getPlanProgress(existingState.active_plan)
+      }
+    } else if (existingState) {
+      const progress = getPlanProgress(existingState.active_plan)
 
-        if (!progress.isComplete) {
-          const effectiveWorktree = worktreePath ?? existingState.worktree_path
-          const sessionAlreadyTracked = existingState.session_ids.includes(sessionId)
-          const updatedSessions = sessionAlreadyTracked
-            ? existingState.session_ids
-            : [...existingState.session_ids, sessionId]
-          const shouldRewriteState = existingState.agent !== activeAgent || worktreePath !== undefined
+      if (!progress.isComplete) {
+        const effectiveWorktree = worktreePath ?? existingState.worktree_path
+        const sessionAlreadyTracked = existingState.session_ids.includes(sessionId)
+        const updatedSessions = sessionAlreadyTracked
+          ? existingState.session_ids
+          : [...existingState.session_ids, sessionId]
+        const shouldRewriteState = existingState.agent !== activeAgent || worktreePath !== undefined
 
-          if (shouldRewriteState) {
-            writeBoulderState(ctx.directory, {
-              ...existingState,
-              agent: activeAgent,
-              ...(worktreePath !== undefined ? { worktree_path: worktreePath } : {}),
-              session_ids: updatedSessions,
-            })
-          } else if (!sessionAlreadyTracked) {
-            appendSessionId(ctx.directory, sessionId)
-          }
+        if (shouldRewriteState) {
+          writeBoulderState(ctx.directory, {
+            ...existingState,
+            agent: activeAgent,
+            ...(worktreePath !== undefined ? { worktree_path: worktreePath } : {}),
+            session_ids: updatedSessions,
+          })
+        } else if (!sessionAlreadyTracked) {
+          appendSessionId(ctx.directory, sessionId)
+        }
 
-          const worktreeDisplay = effectiveWorktree ? createWorktreeActiveBlock(effectiveWorktree) : worktreeBlock
+        const worktreeDisplay = effectiveWorktree ? createWorktreeActiveBlock(effectiveWorktree) : worktreeBlock
 
-          contextInfo = `
+        contextInfo = `
 ## Active Work Session Found
 
 **Status**: RESUMING existing work
@@ -197,41 +227,41 @@ ${worktreeDisplay}
 
 The current session (${sessionId}) has been added to session_ids.
 Read the plan file and continue from the first unchecked task.`
-        } else {
-          contextInfo = `
+      } else {
+        contextInfo = `
 ## Previous Work Complete
 
 The previous plan (${existingState.plan_name}) has been completed.
 Looking for new plans...`
-        }
       }
+    }
 
-      if (
-        (!existingState && !explicitPlanName) ||
-        (existingState && !explicitPlanName && getPlanProgress(existingState.active_plan).isComplete)
-      ) {
-        const plans = findPrometheusPlans(ctx.directory)
-        const incompletePlans = plans.filter((p) => !getPlanProgress(p).isComplete)
+    if (
+      (!existingState && !explicitPlanName) ||
+      (existingState && !explicitPlanName && getPlanProgress(existingState.active_plan).isComplete)
+    ) {
+      const plans = findPrometheusPlans(ctx.directory)
+      const incompletePlans = plans.filter((p) => !getPlanProgress(p).isComplete)
 
-        if (plans.length === 0) {
-          contextInfo += `
+      if (plans.length === 0) {
+        contextInfo += `
 ## No Plans Found
 
 No Prometheus plan files found at .sisyphus/plans/
 Use Prometheus to create a work plan first: /plan "your task"`
-        } else if (incompletePlans.length === 0) {
-          contextInfo += `
+      } else if (incompletePlans.length === 0) {
+        contextInfo += `
 
 ## All Plans Complete
 
 All ${plans.length} plan(s) are complete. Create a new plan with: /plan "your task"`
-        } else if (incompletePlans.length === 1) {
-          const planPath = incompletePlans[0]
-          const progress = getPlanProgress(planPath)
-          const newState = createBoulderState(planPath, sessionId, activeAgent, worktreePath)
-          writeBoulderState(ctx.directory, newState)
+      } else if (incompletePlans.length === 1) {
+        const planPath = incompletePlans[0]
+        const progress = getPlanProgress(planPath)
+        const newState = createBoulderState(planPath, sessionId, activeAgent, worktreePath)
+        writeBoulderState(ctx.directory, newState)
 
-          contextInfo += `
+        contextInfo += `
 
 ## Auto-Selected Plan
 
@@ -243,16 +273,16 @@ All ${plans.length} plan(s) are complete. Create a new plan with: /plan "your ta
 ${worktreeBlock}
 
 boulder.json has been created. Read the plan and begin execution.`
-        } else {
-          const planList = incompletePlans
-            .map((p, i) => {
-              const progress = getPlanProgress(p)
-              const modified = new Date(statSync(p).mtimeMs).toISOString()
-              return `${i + 1}. [${getPlanName(p)}] - Modified: ${modified} - Progress: ${progress.completed}/${progress.total}`
-            })
-            .join("\n")
+      } else {
+        const planList = incompletePlans
+          .map((p, i) => {
+            const progress = getPlanProgress(p)
+            const modified = new Date(statSync(p).mtimeMs).toISOString()
+            return `${i + 1}. [${getPlanName(p)}] - Modified: ${modified} - Progress: ${progress.completed}/${progress.total}`
+          })
+          .join("\n")
 
-          contextInfo += `
+        contextInfo += `
 
 <system-reminder>
 ## Multiple Plans Found
@@ -265,23 +295,34 @@ ${planList}
 Ask the user which plan to work on. Present the options above and wait for their response.
 ${worktreeBlock}
 </system-reminder>`
-        }
       }
+    }
 
-      const idx = output.parts.findIndex((p) => p.type === "text" && p.text)
-      if (idx >= 0 && output.parts[idx].text) {
-        output.parts[idx].text = output.parts[idx].text
-          .replace(/\$SESSION_ID/g, sessionId)
-          .replace(/\$TIMESTAMP/g, timestamp)
+    const idx = output.parts.findIndex((p) => p.type === "text" && p.text)
+    if (idx >= 0 && output.parts[idx].text) {
+      output.parts[idx].text = output.parts[idx].text
+        .replace(/\$SESSION_ID/g, sessionId)
+        .replace(/\$TIMESTAMP/g, timestamp)
 
-        output.parts[idx].text += `\n\n---\n${contextInfo}`
-      }
+      output.parts[idx].text += `\n\n---\n${contextInfo}`
+    }
 
-      log(`[${HOOK_NAME}] Context injected`, {
-        sessionID: input.sessionID,
-        hasExistingState: !!existingState,
-        worktreePath,
-      })
+    log(`[${HOOK_NAME}] Context injected`, {
+      sessionID: input.sessionID,
+      hasExistingState: !!existingState,
+      worktreePath,
+    })
+  }
+
+  return {
+    "chat.message": async (input: StartWorkHookInput, output: StartWorkHookOutput): Promise<void> => {
+      await processStartWork(input, output)
+    },
+    "command.execute.before": async (
+      input: StartWorkCommandExecuteBeforeInput,
+      output: StartWorkHookOutput,
+    ): Promise<void> => {
+      await processStartWork(input, output)
     },
   }
 }
diff --git a/src/plugin-interface.test.ts b/src/plugin-interface.test.ts
new file mode 100644
index 000000000..e9dfee568
--- /dev/null
+++ b/src/plugin-interface.test.ts
@@ -0,0 +1,172 @@
+import { afterEach, beforeEach, describe, expect, test } from "bun:test"
+import { mkdirSync, rmSync, writeFileSync } from "node:fs"
+import { tmpdir } from "node:os"
+import { join } from "node:path"
+import { randomUUID } from "node:crypto"
+import { createPluginInterface } from "./plugin-interface"
+import { createAutoSlashCommandHook } from "./hooks/auto-slash-command"
+import { createStartWorkHook } from "./hooks/start-work"
+import { getAgentListDisplayName } from "./shared/agent-display-names"
+import { readBoulderState } from "./features/boulder-state"
+import {
+  _resetForTesting,
+  getSessionAgent,
+  registerAgentName,
+  updateSessionAgent,
+} from "./features/claude-code-session-state"
+
+describe("createPluginInterface - command.execute.before", () => {
+  let testDir = ""
+
+  beforeEach(() => {
+    testDir = join(tmpdir(), `plugin-interface-start-work-${randomUUID()}`)
+    mkdirSync(join(testDir, ".sisyphus", "plans"), { recursive: true })
+    writeFileSync(join(testDir, ".sisyphus", "plans", "worker-plan.md"), "# Plan\n- [ ] Task 1")
+    _resetForTesting()
+    registerAgentName("prometheus")
+    registerAgentName("sisyphus")
+  })
+
+  afterEach(() => {
+    _resetForTesting()
+    rmSync(testDir, { recursive: true, force: true })
+  })
+
+  test("executes start-work side effects for native command execution", async () => {
+    // given
+    updateSessionAgent("ses-command-before", "prometheus")
+    const pluginInterface = createPluginInterface({
+      ctx: {
+        directory: testDir,
+        client: { tui: { showToast: async () => {} } },
+      } as never,
+      pluginConfig: {} as never,
+      firstMessageVariantGate: {
+        shouldOverride: () => false,
+        markApplied: () => {},
+        markSessionCreated: () => {},
+        clear: () => {},
+      },
+      managers: {} as never,
+      hooks: {
+        autoSlashCommand: createAutoSlashCommandHook({ skills: [] }),
+        startWork: createStartWorkHook({
+          directory: testDir,
+          client: { tui: { showToast: async () => {} } },
+        } as never),
+      } as never,
+      tools: {},
+    })
+    const output = {
+      parts: [{ type: "text", text: "original" }],
+    }
+
+    // when
+    await pluginInterface["command.execute.before"]?.(
+      {
+        command: "start-work",
+        sessionID: "ses-command-before",
+        arguments: "",
+      },
+      output as never
+    )
+
+    // then
+    expect(pluginInterface["command.execute.before"]).toBeDefined()
+    expect(output.parts[0]?.text).toContain("Auto-Selected Plan")
+    expect(output.parts[0]?.text).toContain("boulder.json has been created")
+    expect(getSessionAgent("ses-command-before")).toBe("sisyphus")
+    expect(readBoulderState(testDir)?.agent).toBe("sisyphus")
+  })
+
+  test("does not run start-work side effects for other native commands with session context", async () => {
+    // given
+    updateSessionAgent("ses-handoff", "prometheus")
+    const pluginInterface = createPluginInterface({
+      ctx: {
+        directory: testDir,
+        client: { tui: { showToast: async () => {} } },
+      } as never,
+      pluginConfig: {} as never,
+      firstMessageVariantGate: {
+        shouldOverride: () => false,
+        markApplied: () => {},
+        markSessionCreated: () => {},
+        clear: () => {},
+      },
+      managers: {} as never,
+      hooks: {
+        autoSlashCommand: createAutoSlashCommandHook({ skills: [] }),
+        startWork: createStartWorkHook({
+          directory: testDir,
+          client: { tui: { showToast: async () => {} } },
+        } as never),
+      } as never,
+      tools: {},
+    })
+    const output = {
+      parts: [{ type: "text", text: "original" }],
+    }
+
+    // when
+    await pluginInterface["command.execute.before"]?.(
+      {
+        command: "handoff",
+        sessionID: "ses-handoff",
+        arguments: "",
+      },
+      output as never
+    )
+
+    // then
+    expect(output.parts[0]?.text).toContain("HANDOFF CONTEXT")
+    expect(readBoulderState(testDir)).toBeNull()
+    expect(getSessionAgent("ses-handoff")).toBe("prometheus")
+  })
+
+  test("switches native start-work to Atlas when Atlas is registered in config", async () => {
+    // given
+    registerAgentName("atlas")
+    updateSessionAgent("ses-command-atlas", "prometheus")
+    const pluginInterface = createPluginInterface({
+      ctx: {
+        directory: testDir,
+        client: { tui: { showToast: async () => {} } },
+      } as never,
+      pluginConfig: {} as never,
+      firstMessageVariantGate: {
+        shouldOverride: () => false,
+        markApplied: () => {},
+        markSessionCreated: () => {},
+        clear: () => {},
+      },
+      managers: {} as never,
+      hooks: {
+        autoSlashCommand: createAutoSlashCommandHook({ skills: [] }),
+        startWork: createStartWorkHook({
+          directory: testDir,
+          client: { tui: { showToast: async () => {} } },
+        } as never),
+      } as never,
+      tools: {},
+    })
+    const output = {
+      message: {} as Record<string, unknown>,
+      parts: [{ type: "text", text: "/start-work" }],
+    }
+
+    // when
+    await pluginInterface["chat.message"]?.(
+      {
+        sessionID: "ses-command-atlas",
+        agent: "prometheus",
+      } as never,
+      output as never
+    )
+
+    // then
+    expect(output.message.agent).toBe(getAgentListDisplayName("atlas"))
+    expect(getSessionAgent("ses-command-atlas")).toBe("atlas")
+    expect(readBoulderState(testDir)?.agent).toBe("atlas")
+  })
+})
diff --git a/src/plugin-interface.ts b/src/plugin-interface.ts
index d7d65762d..5bcc0c364 100644
--- a/src/plugin-interface.ts
+++ b/src/plugin-interface.ts
@@ -4,6 +4,7 @@ import type { OhMyOpenCodeConfig } from "./config"
 import { createChatParamsHandler } from "./plugin/chat-params"
 import { createChatHeadersHandler } from "./plugin/chat-headers"
 import { createChatMessageHandler } from "./plugin/chat-message"
+import { createCommandExecuteBeforeHandler } from "./plugin/command-execute-before"
 import { createMessagesTransformHandler } from "./plugin/messages-transform"
 import { createSystemTransformHandler } from "./plugin/system-transform"
 import { createEventHandler } from "./plugin/event"
@@ -42,6 +43,10 @@ export function createPluginInterface(args: {
 
     "chat.headers": createChatHeadersHandler({ ctx }),
 
+    "command.execute.before": createCommandExecuteBeforeHandler({
+      hooks,
+    }),
+
     "chat.message": createChatMessageHandler({
       ctx,
       pluginConfig,
diff --git a/src/plugin/chat-message.test.ts b/src/plugin/chat-message.test.ts
index e79eb8d2d..1ef58df06 100644
--- a/src/plugin/chat-message.test.ts
+++ b/src/plugin/chat-message.test.ts
@@ -1,7 +1,14 @@
-import { afterEach, describe, test, expect } from "bun:test"
+import { afterEach, beforeEach, describe, test, expect } from "bun:test"
+import { mkdirSync, rmSync, writeFileSync } from "node:fs"
+import { tmpdir } from "node:os"
+import { join } from "node:path"
+import { randomUUID } from "node:crypto"
 
 import { createChatMessageHandler } from "./chat-message"
-import { _resetForTesting, setMainSession, subagentSessions } from "../features/claude-code-session-state"
+import { createAutoSlashCommandHook } from "../hooks/auto-slash-command"
+import { createStartWorkHook } from "../hooks/start-work"
+import { readBoulderState } from "../features/boulder-state"
+import { _resetForTesting, setMainSession, subagentSessions, registerAgentName, updateSessionAgent, getSessionAgent } from "../features/claude-code-session-state"
 import { clearSessionModel, getSessionModel, setSessionModel } from "../shared/session-model-state"
 
 type ChatMessagePart = { type: string; text?: string; [key: string]: unknown }
@@ -39,6 +46,55 @@ afterEach(() => {
   clearSessionModel("subagent-session")
 })
 
+describe("createChatMessageHandler - /start-work integration", () => {
+  let testDir = ""
+  let originalWorkingDirectory = ""
+
+  beforeEach(() => {
+    testDir = join(tmpdir(), `chat-message-start-work-${randomUUID()}`)
+    originalWorkingDirectory = process.cwd()
+    mkdirSync(join(testDir, ".sisyphus", "plans"), { recursive: true })
+    writeFileSync(join(testDir, ".sisyphus", "plans", "worker-plan.md"), "# Plan\n- [ ] Task 1")
+    process.chdir(testDir)
+    _resetForTesting()
+    registerAgentName("prometheus")
+    registerAgentName("sisyphus")
+  })
+
+  afterEach(() => {
+    process.chdir(originalWorkingDirectory)
+    rmSync(testDir, { recursive: true, force: true })
+  })
+
+  test("falls back to Sisyphus through the full chat.message slash-command path when Atlas is unavailable", async () => {
+    // given
+    updateSessionAgent("test-session", "prometheus")
+    const args = createMockHandlerArgs()
+    args.hooks.autoSlashCommand = createAutoSlashCommandHook({ skills: [] })
+    args.hooks.startWork = createStartWorkHook({
+      directory: testDir,
+      client: { tui: { showToast: async () => {} } },
+    } as never)
+    const handler = createChatMessageHandler(args)
+    const input = createMockInput("prometheus")
+    const output: ChatMessageHandlerOutput = {
+      message: {},
+      parts: [{ type: "text", text: "/start-work" }],
+    }
+
+    // when
+    await handler(input, output)
+
+    // then
+    expect(output.message["agent"]).toBe("Sisyphus (Ultraworker)")
+    expect(output.parts[0].text).toContain("<auto-slash-command>")
+    expect(output.parts[0].text).toContain("Auto-Selected Plan")
+    expect(output.parts[0].text).toContain("boulder.json has been created")
+    expect(getSessionAgent("test-session")).toBe("sisyphus")
+    expect(readBoulderState(testDir)?.agent).toBe("sisyphus")
+  })
+})
+
 function createMockInput(agent?: string, model?: { providerID: string; modelID: string }) {
   return {
     sessionID: "test-session",
diff --git a/src/plugin/command-execute-before.ts b/src/plugin/command-execute-before.ts
new file mode 100644
index 000000000..09f17f7ca
--- /dev/null
+++ b/src/plugin/command-execute-before.ts
@@ -0,0 +1,39 @@
+import type { CreatedHooks } from "../create-hooks"
+
+type CommandExecuteBeforeInput = {
+  command: string
+  sessionID: string
+  arguments: string
+}
+
+type CommandExecuteBeforeOutput = {
+  parts: Array<{ type: string; text?: string; [key: string]: unknown }>
+}
+
+function hasPartsOutput(value: unknown): value is CommandExecuteBeforeOutput {
+  if (typeof value !== "object" || value === null) return false
+  const record = value as Record<string, unknown>
+  const parts = record["parts"]
+  return Array.isArray(parts)
+}
+
+export function createCommandExecuteBeforeHandler(args: {
+  hooks: CreatedHooks
+}): (
+  input: CommandExecuteBeforeInput,
+  output: CommandExecuteBeforeOutput,
+) => Promise<void> {
+  const { hooks } = args
+
+  return async (input, output): Promise<void> => {
+    await hooks.autoSlashCommand?.["command.execute.before"]?.(input, output)
+
+    if (
+      hooks.startWork
+      && input.command.toLowerCase() === "start-work"
+      && hasPartsOutput(output)
+    ) {
+      await hooks.startWork["command.execute.before"]?.(input, output)
+    }
+  }
+}