fix(start-work): restore atlas handoff

Keep native /start-work resolvable on Sisyphus, but switch the work session back to Atlas when Atlas is registered. Stamp the outgoing agent with Atlas's actual list-display key so config→start-work execution resolves correctly and still falls back to Sisyphus when Atlas is unavailable.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

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")
+  })
+})