feat(config): make thinking idle threshold configurable and lower default to 5min

Align with observed provider prompt-cache TTL (~5 min). Add
`context.gapThresholdMinutes` setting so users can tune the threshold
for providers with different cache TTLs.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/cli/src/config/settingsSchema.ts

@@ -914,6 +914,16 @@ const SETTINGS_SCHEMA = {
           },
         },
       },
+      gapThresholdMinutes: {
+        type: 'number',
+        label: 'Thinking Block Idle Threshold (minutes)',
+        category: 'Context',
+        requiresRestart: false,
+        default: 5,
+        description:
+          'Minutes of inactivity after which retained thinking blocks are cleared to free context tokens. Aligns with provider prompt-cache TTL.',
+        showInDialog: false,
+      },
     },
   },