Discord: thread bindings idle + max-age lifecycle (#27845) (thanks @osolmaz)

* refactor discord thread bindings to idle and max-age lifecycle

* fix: migrate legacy thread binding expiry and reduce hot-path disk writes

* refactor: remove remaining thread-binding ttl legacy paths

* fix: harden thread-binding lifecycle persistence

* Discord: fix thread binding types in message/reply paths

* Infra: handle win32 unknown inode in file identity checks

* Infra: relax win32 guarded-open identity checks

* Config: migrate threadBindings ttlHours to idleHours

* Revert "Infra: relax win32 guarded-open identity checks"

This reverts commit de94126771.

* Revert "Infra: handle win32 unknown inode in file identity checks"

This reverts commit 96fc5ddfb3.

* Discord: re-read live binding state before sweep unbind

* fix: add changelog note for thread binding lifecycle update (#27845) (thanks @osolmaz)

---------

Co-authored-by: Onur Solmaz <onur@textcortex.com>

docs/gateway/configuration.md

@@ -184,7 +184,8 @@ When validation fails:
         dmScope: "per-channel-peer",  // recommended for multi-user
         threadBindings: {
           enabled: true,
-          ttlHours: 24,
+          idleHours: 24,
+          maxAgeHours: 0,
         },
         reset: {
           mode: "daily",
@@ -196,7 +197,7 @@ When validation fails:
     ```
 
     - `dmScope`: `main` (shared) | `per-peer` | `per-channel-peer` | `per-account-channel-peer`
-    - `threadBindings`: global defaults for thread-bound session routing (Discord supports `/focus`, `/unfocus`, `/agents`, and `/session ttl`).
+    - `threadBindings`: global defaults for thread-bound session routing (Discord supports `/focus`, `/unfocus`, `/agents`, `/session idle`, and `/session max-age`).
     - See [Session Management](/concepts/session) for scoping, identity links, and send policy.
     - See [full reference](/gateway/configuration-reference#session) for all fields.