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>

docs/concepts/session.md

@@ -60,6 +60,7 @@ the workspace is writable. See [Memory](/concepts/memory) and
 - Idle reset (optional): `idleMinutes` adds a sliding idle window. When both daily and idle resets are configured, **whichever expires first** forces a new session.
 - Legacy idle-only: if you set `session.idleMinutes` without any `session.reset`/`resetByType` config, Clawdbot stays in idle-only mode for backward compatibility.
 - Per-type overrides (optional): `resetByType` lets you override the policy for `dm`, `group`, and `thread` sessions (thread = Slack/Discord threads, Telegram topics, Matrix threads when provided by the connector).
+- Per-channel overrides (optional): `resetByChannel` overrides the reset policy for a channel (applies to all session types for that channel and takes precedence over `reset`/`resetByType`).
 - Reset triggers: exact `/new` or `/reset` (plus any extras in `resetTriggers`) start a fresh session id and pass the remainder of the message through. `/new <model>` accepts a model alias, `provider/model`, or provider name (fuzzy match) to set the new session model. If `/new` or `/reset` is sent alone, Clawdbot runs a short “hello” greeting turn to confirm the reset.
 - Manual reset: delete specific keys from the store or remove the JSONL transcript; the next message recreates them.
 - Isolated cron jobs always mint a fresh `sessionId` per run (no idle reuse).
@@ -109,6 +110,9 @@ Send these as standalone messages so they register.
       dm: { mode: "idle", idleMinutes: 240 },
       group: { mode: "idle", idleMinutes: 120 }
     },
+    resetByChannel: {
+      discord: { mode: "idle", idleMinutes: 10080 }
+    },
     resetTriggers: ["/new", "/reset"],
     store: "~/.clawdbot/agents/{agentId}/sessions/sessions.json",
     mainKey: "main",