fix(plugin): harden metadata recovery and extraction

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

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

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

@@ -90,6 +90,17 @@ describe("extractSessionIdFromMetadata", () => {
     expect(result).toBe("ses_plugin_abc123")
   })
 
+  test("extracts legacy session aliases from tool metadata object", () => {
+    // given
+    const metadata = { sessionID: "ses_plugin_alias_123" }
+
+    // when
+    const result = extractSessionIdFromMetadata(metadata)
+
+    // then
+    expect(result).toBe("ses_plugin_alias_123")
+  })
+
   test("returns undefined for metadata without sessionId", () => {
     // given
     const metadata = { title: "some task" }