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Runtime modes control how T3 Code agents interact with your system, balancing autonomy with safety through approval policies and sandbox restrictions.

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Overview

T3 Code provides two primary runtime modes accessible via the chat toolbar:

Full Access

Default mode with maximum autonomy. Sessions start with approvalPolicy: never and sandboxMode: danger-full-access.

Supervised

Safety-first mode with user approval required. Sessions start with approvalPolicy: on-request and sandboxMode: workspace-write, prompting for command/file approvals.

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Runtime Mode Types

The RuntimeMode type defines the high-level security posture:
packages/contracts/src/orchestration.ts
export const RuntimeMode = Schema.Literals([
  "approval-required",
  "full-access"
]);

export const DEFAULT_RUNTIME_MODE: RuntimeMode = "full-access";
Runtime modes are set at session creation and affect the entire conversation lifecycle. They map to specific Codex approval policies and sandbox modes.

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Approval Policies

Approval policies determine when the agent must request user permission: 
export const ProviderApprovalPolicy = Schema.Literals([
  "untrusted",    // Approve everything (not yet implemented)
  "on-failure",   // Approve after failed attempts
  "on-request",   // Approve when agent requests permission
  "never",        // Never require approval
]);

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Approval Policy Mapping

T3 Code maps runtime modes to Codex approval policies:
apps/server/src/codexAppServerManager.ts
function mapCodexRuntimeMode(runtimeMode: RuntimeMode): {
  readonly approvalPolicy: "on-request" | "never";
  readonly sandbox: "workspace-write" | "danger-full-access";
} {
  if (runtimeMode === "approval-required") {
    return {
      approvalPolicy: "on-request",
      sandbox: "workspace-write",
    };
  }

  return {
    approvalPolicy: "never",
    sandbox: "danger-full-access",
  };
}

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Sandbox Modes

Sandbox modes restrict file system and system access: 
export const ProviderSandboxMode = Schema.Literals([
  "read-only",            // Read files only, no modifications
  "workspace-write",      // Write within workspace, read elsewhere
  "danger-full-access",   // Unrestricted file system access
]);
Full Access Mode grants unrestricted file system access and never prompts for approval. Only use in trusted environments with code you’re comfortable executing.

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Approval Request Types

When approval is required, the agent requests permission for specific operations: 
export const ProviderRequestKind = Schema.Literals([
  "command",      // Shell command execution
  "file-read",    // Reading file contents
  "file-change",  // Writing or modifying files
]);

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Approval Request Flow

1

Agent Requests Approval

The agent sends an approval request via JSON-RPC (e.g., item/commandExecution/requestApproval)
2

Server Generates Request ID

The server creates a unique ApprovalRequestId and tracks the pending request
3

Client Displays Prompt

The web UI shows the approval dialog with request details
4

User Responds

User chooses: accept, acceptForSession, decline, or cancel
5

Server Forwards Decision

The server sends the decision back to the provider via JSON-RPC response

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Approval Decisions

Users can respond to approval requests with four decision types: 
export const ProviderApprovalDecision = Schema.Literals([
  "accept",              // Approve this one request
  "acceptForSession",    // Approve this and similar requests for session
  "decline",             // Deny this request
  "cancel",              // Cancel the entire operation
]);

await providerService.respondToRequest({
  threadId,
  requestId,
  decision: "accept",
});

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User Input Requests

Beyond approval requests, agents can request structured user input: 
export const ProviderUserInputAnswers = Schema.Record(
  Schema.String,
  Schema.Unknown
);

// Example: Plan mode questions
const answers = {
  "question-1": "Option A",
  "question-2": ["Choice 1", "Choice 2"],
};

await providerService.respondToUserInput({
  threadId,
  requestId,
  answers,
});
User input requests are separate from approval requests and are primarily used in Plan Mode for collaborative planning conversations.

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Runtime Mode Changes

Runtime modes can be changed during a thread’s lifetime: 
// Dispatch command to change runtime mode
await orchestration.dispatchCommand({
  type: "thread.runtime-mode.set",
  commandId: CommandId.makeUnsafe(randomUUID()),
  threadId,
  runtimeMode: "approval-required",
  createdAt: new IsoDateTime(),
});
Session Restart Required: Changing runtime mode requires stopping and restarting the provider session with new settings. Existing sessions retain their original runtime mode.

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Session Status and Runtime Mode

The orchestration session tracks the active runtime mode: 
export const OrchestrationSession = Schema.Struct({
  threadId: ThreadId,
  status: OrchestrationSessionStatus,
  providerName: Schema.NullOr(TrimmedNonEmptyString),
  runtimeMode: RuntimeMode.pipe(
    Schema.withDecodingDefault(() => DEFAULT_RUNTIME_MODE)
  ),
  activeTurnId: Schema.NullOr(TurnId),
  lastError: Schema.NullOr(TrimmedNonEmptyString),
  updatedAt: IsoDateTime,
});

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Pending Approval Tracking

The server tracks pending approvals in memory:
apps/server/src/codexAppServerManager.ts
interface PendingApprovalRequest {
  requestId: ApprovalRequestId;
  jsonRpcId: string | number;
  method:
    | "item/commandExecution/requestApproval"
    | "item/fileChange/requestApproval"
    | "item/fileRead/requestApproval";
  requestKind: ProviderRequestKind;
  threadId: ThreadId;
  turnId?: TurnId;
  itemId?: ProviderItemId;
}

interface CodexSessionContext {
  // ...
  pendingApprovals: Map<ApprovalRequestId, PendingApprovalRequest>;
  pendingUserInputs: Map<ApprovalRequestId, PendingUserInputRequest>;
  // ...
}

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Service Tier

Independent of runtime mode, you can specify compute service tier: 
export const ProviderServiceTier = Schema.Literals(["fast", "flex"]);

// Start session with specific tier
const session = await providerService.startSession(threadId, {
  threadId,
  runtimeMode: "full-access",
  serviceTier: "fast",
});

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Interaction Modes

Interaction modes control conversation behavior: 
export const ProviderInteractionMode = Schema.Literals([
  "default",  // Standard execution mode
  "plan",     // Collaborative planning mode
]);

export const DEFAULT_PROVIDER_INTERACTION_MODE = "default";
Standard execution mode where the agent directly implements requests.
  • Minimal questions, bias toward action
  • Direct execution of user requests
  • request_user_input tool unavailable
Collaborative planning mode for refining specifications before implementation.
  • Three-phase conversation: environment grounding, intent chat, implementation chat
  • request_user_input tool available for structured questions
  • Non-mutating exploration allowed (read files, run tests)
  • Mutating actions blocked until plan finalized
  • Outputs <proposed_plan> blocks when ready
Interaction modes are orthogonal to runtime modes. You can use Plan Mode with either full-access or approval-required runtime mode.

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Best Practices

Start Supervised

Use approval-required for unfamiliar codebases or destructive operations

Plan Before Execute

Use Plan Mode for complex changes to validate approach before implementation

Session-Scoped Approvals

Use acceptForSession for repetitive safe operations like test runs

Review Declined Actions

Check activity logs to understand why declined operations were attempted

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Security Considerations

Full Access Mode Risks:
  • Unrestricted file system access
  • Arbitrary command execution
  • No approval prompts or safety nets
  • Suitable only for trusted environments
Supervised Mode Limitations:
  • workspace-write restricts writes to workspace directory
  • Read access still available outside workspace
  • Agent cannot execute commands without approval
  • May require more user interaction

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Next Steps

Sessions

Learn about session lifecycle and management

Providers

Understand provider adapter architecture

Architecture

Explore the overall system design

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