feat: add OPENCLAUDE_DISABLE_TOOL_REMINDERS env var to suppress hidden tool-output reminders (#837)

Gates three injection sites behind OPENCLAUDE_DISABLE_TOOL_REMINDERS:
- FileReadTool cyber-risk mitigation reminder (appended to every Read
  result when the model is not in MITIGATION_EXEMPT_MODELS)
- todo_reminder attachment for TodoWrite usage
- task_reminder attachment for TaskCreate/TaskUpdate usage

All three reminders are model-only side-channel instructions the user
cannot see today. Users who want full transparency over what the model
receives can now opt out without patching dist/cli.mjs on every upgrade.

Default behavior is unchanged when the flag is unset.

Closes #809

.env.example

@@ -272,6 +272,11 @@ ANTHROPIC_API_KEY=sk-ant-your-key-here
 # trigger "Extra required key ... supplied" errors from OpenAI-compatible endpoints
 # OPENCLAUDE_DISABLE_STRICT_TOOLS=1
 
+# Disable hidden <system-reminder> messages injected into tool output
+# Suppresses the file-read cyber-risk reminder and the todo/task tool nudges
+# Useful for users who want full transparency over what the model sees
+# OPENCLAUDE_DISABLE_TOOL_REMINDERS=1
+
 # Custom timeout for API requests in milliseconds (default: varies)
 # API_TIMEOUT_MS=60000
 

src/tools/FileReadTool/FileReadTool.ts

@@ -733,6 +733,9 @@ export const CYBER_RISK_MITIGATION_REMINDER =
 const MITIGATION_EXEMPT_MODELS = new Set(['claude-opus-4-6'])
 
 function shouldIncludeFileReadMitigation(): boolean {
+  if (isEnvTruthy(process.env.OPENCLAUDE_DISABLE_TOOL_REMINDERS)) {
+    return false
+  }
   const shortName = getCanonicalName(getMainLoopModel())
   return !MITIGATION_EXEMPT_MODELS.has(shortName)
 }

src/utils/messages.ts

@@ -75,6 +75,7 @@ import type {
 import { isAdvisorBlock } from './advisor.js'
 import { isAgentSwarmsEnabled } from './agentSwarmsEnabled.js'
 import { count } from './array.js'
+import { isEnvTruthy } from './envUtils.js'
 import {
   type Attachment,
   type HookAttachment,
@@ -3666,6 +3667,9 @@ Read the team config to discover your teammates' names. Check the task list peri
       ])
     }
     case 'todo_reminder': {
+      if (isEnvTruthy(process.env.OPENCLAUDE_DISABLE_TOOL_REMINDERS)) {
+        return []
+      }
       const todoItems = attachment.content
         .map((todo, index) => `${index + 1}. [${todo.status}] ${todo.content}`)
         .join('\n')
@@ -3686,6 +3690,9 @@ Read the team config to discover your teammates' names. Check the task list peri
       if (!isTodoV2Enabled()) {
         return []
       }
+      if (isEnvTruthy(process.env.OPENCLAUDE_DISABLE_TOOL_REMINDERS)) {
+        return []
+      }
       const taskItems = attachment.content
         .map(task => `#${task.id}. [${task.status}] ${task.subject}`)
         .join('\n')