feat(session-notification): add ready notification content builder

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

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

src/hooks/session-notification-content.test.ts

@@ -0,0 +1,67 @@
+const { describe, expect, test } = require("bun:test")
+import { buildReadyNotificationContent } from "./session-notification-content"
+
+describe("buildReadyNotificationContent", () => {
+  describe("#given session metadata and messages exist", () => {
+    test("#when ready notification content is built, #then it includes session title, last user query, and last assistant line", async () => {
+      const ctx = {
+        directory: "/tmp/test",
+        client: {
+          session: {
+            get: async () => ({ data: { title: "Bugfix session" } }),
+            messages: async () => ({
+              data: [
+                {
+                  info: { role: "user" },
+                  parts: [{ type: "text", text: "Investigate\nthis flaky test" }],
+                },
+                {
+                  info: { role: "assistant" },
+                  parts: [{ type: "text", text: "First line\nFinal answer line" }],
+                },
+              ],
+            }),
+          },
+        },
+      }
+
+      const result = await buildReadyNotificationContent(ctx, {
+        sessionID: "ses_123",
+        baseTitle: "OpenCode",
+        baseMessage: "Agent is ready for input",
+      })
+
+      expect(result).toEqual({
+        title: "OpenCode · Bugfix session",
+        message: "Agent is ready for input\nUser: Investigate this flaky test\nAssistant: Final answer line",
+      })
+    })
+  })
+
+  describe("#given session APIs do not provide rich data", () => {
+    test("#when ready notification content is built, #then it falls back to session id and the base message", async () => {
+      const ctx = {
+        directory: "/tmp/test",
+        client: {
+          session: {
+            get: async () => ({ data: {} }),
+            messages: async () => ({ data: [] }),
+          },
+        },
+      }
+
+      const result = await buildReadyNotificationContent(ctx, {
+        sessionID: "ses_fallback",
+        baseTitle: "OpenCode",
+        baseMessage: "Agent is ready for input",
+      })
+
+      expect(result).toEqual({
+        title: "OpenCode · ses_fallback",
+        message: "Agent is ready for input",
+      })
+    })
+  })
+})
+
+export {}