fix(docservice): 🐛 satisfy no-unused-vars on intentionally-unused catch

CI's ESLint config requires unused caught errors to be _-prefixed.
Six swallowed-error catch blocks used `err` without referencing it.

Assisted-by: ClaudeCode:claude-sonnet-5
Signed-off-by: James Manuel <moodyjmz@users.noreply.github.com>

Author: moodyjmz

DocService/sources/editorDataRedisPresence.js

@@ -83,7 +83,7 @@ function createPresenceStore(redis, prefix, ttlSeconds, memoryFallback) {
     await redis.presenceWriteScript(hashKey, expKey, userId, userInfo, expiresAt, ttlSeconds * NATIVE_TTL_MULTIPLIER * 1000);
     try {
       await docExpSweep.track(ctx.tenant, docId, expiresAt);
-    } catch (err) {
+    } catch (_err) {
       // The write above already landed and is genuinely live and
       // cross-replica-visible (and self-expires regardless, via the
       // PEXPIRE inside presenceWriteScript) - a failure here only means
@@ -104,7 +104,7 @@ function createPresenceStore(redis, prefix, ttlSeconds, memoryFallback) {
   async function failOpen(fn, fallback) {
     try {
       return await fn();
-    } catch (err) {
+    } catch (_err) {
       return fallback();
     }
   }
@@ -141,7 +141,7 @@ function createPresenceStore(redis, prefix, ttlSeconds, memoryFallback) {
         }
         try {
           await docExpSweep.track(ctx.tenant, docId, expiresAt);
-        } catch (err) {
+        } catch (_err) {
           // Same reasoning as writeAndTrack: the refresh itself already
           // landed in Redis - don't let a sweep-tracking failure alone
           // fall this call back to the memory backend.

DocService/sources/editorDataRedisSaveLock.js

@@ -68,7 +68,7 @@ function createSaveLockStore(redis, prefix) {
       const key = buildKey(keyPrefix, ctx.tenant, docId);
       const res = await redis.saveLockScript(key, userId, ttlToMs(ttl));
       return res === 1;
-    } catch (err) {
+    } catch (_err) {
       return false;
     }
   }
@@ -84,7 +84,7 @@ function createSaveLockStore(redis, prefix) {
       if (code === 1) return UNLOCK_RES.UNLOCKED;
       if (code === 0) return UNLOCK_RES.LOCKED;
       return UNLOCK_RES.EMPTY;
-    } catch (err) {
+    } catch (_err) {
       return UNLOCK_RES.LOCKED;
     }
   }
@@ -107,7 +107,7 @@ function createSaveLockStore(redis, prefix) {
           buildKey(lockSavePrefix, ctx.tenant, docId),
           buildKey(lockAuthPrefix, ctx.tenant, docId)
         );
-      } catch (err) {
+      } catch (_err) {
         // Intentionally swallowed - see above.
       }
     },