feat(sessions): add channelIdleMinutes config for per-channel session idle durations (#1353)

* feat(sessions): add channelIdleMinutes config for per-channel session idle durations

Add new `channelIdleMinutes` config option to allow different session idle
timeouts per channel. For example, Discord sessions can now be configured
to last 7 days (10080 minutes) while other channels use shorter defaults.

Config example:
  sessions:
    channelIdleMinutes:
      discord: 10080  # 7 days

The channel-specific idle is passed as idleMinutesOverride to the existing
resolveSessionResetPolicy, integrating cleanly with the new reset policy
architecture.

* fix

* feat: add per-channel session reset overrides (#1353) (thanks @cash-echo-bot)

---------

Co-authored-by: Cash Williams <cashwilliams@gmail.com>
Co-authored-by: Peter Steinberger <steipete@gmail.com>

src/agents/pi-embedded-runner/run/attempt.test.ts

@@ -36,7 +36,9 @@ describe("injectHistoryImagesIntoMessages", () => {
     const didMutate = injectHistoryImagesIntoMessages(messages, new Map([[0, [image]]]));
 
     expect(didMutate).toBe(false);
-    expect((messages[0]?.content as unknown[]).length).toBe(2);
+    const content = messages[0]?.content as unknown[] | undefined;
+    expect(content).toBeDefined();
+    expect(content).toHaveLength(2);
   });
 
   it("ignores non-user messages and out-of-range indices", () => {