feat(hooks): add start-work hook for Sisyphus workflow

Add hook for detecting /start-work command and triggering
orchestrator-sisyphus agent for plan execution.
Includes test coverage.

🤖 GENERATED WITH ASSISTANCE OF [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)

src/hooks/start-work/index.test.ts

@@ -0,0 +1,155 @@
+import { describe, expect, test, beforeEach, afterEach } from "bun:test"
+import { existsSync, mkdirSync, rmSync, writeFileSync } from "node:fs"
+import { join } from "node:path"
+import { tmpdir, homedir } from "node:os"
+import { createStartWorkHook } from "./index"
+import {
+  writeBoulderState,
+  clearBoulderState,
+} from "../../features/boulder-state"
+import type { BoulderState } from "../../features/boulder-state"
+
+describe("start-work hook", () => {
+  const TEST_DIR = join(tmpdir(), "start-work-test-" + Date.now())
+  const SISYPHUS_DIR = join(TEST_DIR, ".sisyphus")
+
+  function createMockPluginInput() {
+    return {
+      directory: TEST_DIR,
+      client: {},
+    } as Parameters<typeof createStartWorkHook>[0]
+  }
+
+  beforeEach(() => {
+    if (!existsSync(TEST_DIR)) {
+      mkdirSync(TEST_DIR, { recursive: true })
+    }
+    if (!existsSync(SISYPHUS_DIR)) {
+      mkdirSync(SISYPHUS_DIR, { recursive: true })
+    }
+    clearBoulderState(TEST_DIR)
+  })
+
+  afterEach(() => {
+    clearBoulderState(TEST_DIR)
+    if (existsSync(TEST_DIR)) {
+      rmSync(TEST_DIR, { recursive: true, force: true })
+    }
+  })
+
+  describe("chat.message handler", () => {
+    test("should ignore non-start-work commands", async () => {
+      // #given - hook and non-start-work message
+      const hook = createStartWorkHook(createMockPluginInput())
+      const output = {
+        parts: [{ type: "text", text: "Just a regular message" }],
+      }
+
+      // #when
+      await hook["chat.message"](
+        { sessionID: "session-123" },
+        output
+      )
+
+      // #then - output should be unchanged
+      expect(output.parts[0].text).toBe("Just a regular message")
+    })
+
+    test("should detect start-work command via session-context tag", async () => {
+      // #given - hook and start-work message
+      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 - output should be modified with context info
+      expect(output.parts[0].text).toContain("---")
+    })
+
+    test("should inject resume info when existing boulder state found", async () => {
+      // #given - existing boulder state with incomplete plan
+      const planPath = join(TEST_DIR, "test-plan.md")
+      writeFileSync(planPath, "# Plan\n- [ ] Task 1\n- [x] Task 2")
+
+      const state: BoulderState = {
+        active_plan: planPath,
+        started_at: "2026-01-02T10:00:00Z",
+        session_ids: ["session-1"],
+        plan_name: "test-plan",
+      }
+      writeBoulderState(TEST_DIR, state)
+
+      const hook = createStartWorkHook(createMockPluginInput())
+      const output = {
+        parts: [{ type: "text", text: "Start Sisyphus work session" }],
+      }
+
+      // #when
+      await hook["chat.message"](
+        { sessionID: "session-123" },
+        output
+      )
+
+      // #then - should show resuming status
+      expect(output.parts[0].text).toContain("RESUMING")
+      expect(output.parts[0].text).toContain("test-plan")
+    })
+
+    test("should replace $SESSION_ID placeholder", async () => {
+      // #given - hook and message with placeholder
+      const hook = createStartWorkHook(createMockPluginInput())
+      const output = {
+        parts: [
+          {
+            type: "text",
+            text: "Start Sisyphus work session\nSession: $SESSION_ID",
+          },
+        ],
+      }
+
+      // #when
+      await hook["chat.message"](
+        { sessionID: "ses-abc123" },
+        output
+      )
+
+      // #then - placeholder should be replaced
+      expect(output.parts[0].text).toContain("ses-abc123")
+      expect(output.parts[0].text).not.toContain("$SESSION_ID")
+    })
+
+    test("should replace $TIMESTAMP placeholder", async () => {
+      // #given - hook and message with placeholder
+      const hook = createStartWorkHook(createMockPluginInput())
+      const output = {
+        parts: [
+          {
+            type: "text",
+            text: "Start Sisyphus work session\nTime: $TIMESTAMP",
+          },
+        ],
+      }
+
+      // #when
+      await hook["chat.message"](
+        { sessionID: "session-123" },
+        output
+      )
+
+      // #then - placeholder should be replaced with ISO timestamp
+      expect(output.parts[0].text).not.toContain("$TIMESTAMP")
+      expect(output.parts[0].text).toMatch(/\d{4}-\d{2}-\d{2}T/)
+    })
+  })
+})