fix(plugin): normalize event session ids

Handle OpenCode session events that carry the session ID under properties.info.id or properties.info.sessionID so background tasks and continuation hooks do not miss idle/error/delete events.

Add regression coverage for nested session.idle events completing background tasks and waking continuation hooks.

src/hooks/ralph-loop/index.test.ts

@@ -304,6 +304,25 @@ describe("ralph-loop", () => {
       expect(state?.iteration).toBe(2)
     })
 
+    test("should inject continuation when idle event carries session id in info", async () => {
+      // given - active loop state and nested session event shape
+      const hook = createRalphLoopHook(createMockPluginInput())
+      hook.startLoop("session-info-idle", "Build a feature", { maxIterations: 10 })
+
+      // when - session goes idle with id under info
+      await hook.event({
+        event: {
+          type: "session.idle",
+          properties: { info: { id: "session-info-idle" } },
+        },
+      })
+
+      // then - continuation should be injected for that session
+      expect(promptCalls.length).toBe(1)
+      expect(promptCalls[0].sessionID).toBe("session-info-idle")
+      expect(promptCalls[0].text).toContain("RALPH LOOP")
+    })
+
     test("should settle idle before injecting continuation", async () => {
       // given - active loop state with a configured idle settle delay
       const hook = createRalphLoopHook(createMockPluginInput(), { idleSettleMs: 25 })