feat(atlas): persist preferred task session reuse

src/hooks/atlas/subagent-session-id.test.ts

@@ -0,0 +1,53 @@
+import { describe, expect, test } from "bun:test"
+
+import { extractSessionIdFromOutput } from "./subagent-session-id"
+
+describe("extractSessionIdFromOutput", () => {
+  test("extracts Session ID blocks from background output", () => {
+    // given
+    const output = `Background task launched.\n\nSession ID: ses_bg_12345`
+
+    // when
+    const result = extractSessionIdFromOutput(output)
+
+    // then
+    expect(result).toBe("ses_bg_12345")
+  })
+
+  test("extracts session_id from task metadata blocks", () => {
+    // given
+    const output = `Task completed.\n\n<task_metadata>\nsession_id: ses_sync_12345\n</task_metadata>`
+
+    // when
+    const result = extractSessionIdFromOutput(output)
+
+    // then
+    expect(result).toBe("ses_sync_12345")
+  })
+
+  test("returns undefined when no session id is present", () => {
+    // given
+    const output = "Task completed without metadata"
+
+    // when
+    const result = extractSessionIdFromOutput(output)
+
+    // then
+    expect(result).toBeUndefined()
+  })
+
+  test("prefers the session id inside the trailing task_metadata block", () => {
+    // given
+    const output = `The previous attempt mentioned session_id: ses_wrong_body_123 but that was only context.
+
+<task_metadata>
+session_id: ses_real_metadata_456
+</task_metadata>`
+
+    // when
+    const result = extractSessionIdFromOutput(output)
+
+    // then
+    expect(result).toBe("ses_real_metadata_456")
+  })
+})