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Introduction

CLI-based code agents maintain internal session state that includes the conversation history, file context, and previous tool results. Agent-Ctrl exposes this session mechanism through two builder methods — continueSession() and resumeSession() — that work consistently across all supported agents. Session continuity is valuable when a task spans multiple steps. Rather than starting fresh each time and re-establishing context, you can continue an existing session so the agent remembers what was discussed and what actions were taken previously.

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How Sessions Work

Each agent manages sessions differently under the hood, but Agent-Ctrl normalizes the experience:
  • Claude Code stores sessions internally and exposes a session_id in its JSON stream output. Agent-Ctrl extracts this ID from the stream and makes it available via AgentResponse::sessionId().
  • Codex uses thread-based conversations and returns a thread ID in its response. Agent-Ctrl normalizes this into an AgentSessionId.
  • OpenCode maintains named sessions with their own session ID format. Agent-Ctrl extracts and normalizes these as well.
  • Pi maintains sessions with a session ID. It supports ephemeral mode (no session saved) and custom session directories. Agent-Ctrl normalizes the session ID into an AgentSessionId.
  • Gemini supports session resume by a session ID or the special value 'latest' for the most recent session. Agent-Ctrl normalizes these into an AgentSessionId.
Regardless of the agent, the flow is the same: execute a prompt, capture the session ID from the response, and pass it to a subsequent execution.

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Continuing the Most Recent Session

The simplest form of session continuity is continueSession(), which tells the agent to pick up where the last session left off. You do not need to know or store the session ID: 
use Cognesy\AgentCtrl\AgentCtrl;

// First execution starts a new session
$response = AgentCtrl::claudeCode()
    ->execute('Create an implementation plan for the payment module.');

echo $response->text();

// Second execution continues the most recent session
$response = AgentCtrl::claudeCode()
    ->continueSession()
    ->execute('Now implement the first item in the plan.');

echo $response->text();
// @doctest id="d9c2"
This approach works well for sequential, script-like workflows where each step builds on the previous one and there is no need to branch or revisit earlier sessions.

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Resuming a Specific Session

When you need to resume a particular session — for example, after a delay, from a different process, or to branch from a specific point — use resumeSession() with the session ID: 
use Cognesy\AgentCtrl\AgentCtrl;

// First execution: capture the session ID
$first = AgentCtrl::claudeCode()
    ->execute('Create a detailed plan for refactoring the UserService.');

$sessionId = $first->sessionId();

// Store $sessionId somewhere (database, cache, file, etc.)
// ...

// Later: resume the exact same session
if ($sessionId !== null) {
    $second = AgentCtrl::claudeCode()
        ->resumeSession((string) $sessionId)
        ->execute('Implement step 2 from the plan.');
}
// @doctest id="da85"
The resumeSession() method accepts a plain string. The AgentSessionId value object returned by sessionId() implements __toString(), so you can cast it directly.

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Reading the Session ID

AgentResponse::sessionId() returns an AgentSessionId value object or null. A null value means the agent did not expose a session identifier in its output — this can happen if the agent’s CLI version does not support sessions or if the execution failed before session data was emitted. 
$response = AgentCtrl::codex()->execute('Explain the test structure.');

$sessionId = $response->sessionId();

if ($sessionId !== null) {
    echo "Session ID: {$sessionId}\n";      // Uses __toString()
    echo "Session ID: " . (string) $sessionId . "\n"; // Explicit cast
} else {
    echo "No session ID available.\n";
}
// @doctest id="e116"
The AgentSessionId is an opaque value object (extending OpaqueExternalId) that wraps the raw string identifier. It provides type safety and prevents accidental mixing of session IDs with other string values.

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Session Management by Agent

Each agent’s builder exposes the same two methods, but the underlying behavior varies:

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Claude Code

// Continue most recent session
AgentCtrl::claudeCode()
    ->continueSession()
    ->execute('Continue the previous task.');

// Resume specific session
AgentCtrl::claudeCode()
    ->resumeSession('abc-123-def')
    ->execute('Pick up from where we left off.');
// @doctest id="43d7"
Claude Code passes --continue or --resume <session_id> to the claude CLI. Session IDs are extracted from the session_id field in the JSON stream output.

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Codex

// Continue most recent session
AgentCtrl::codex()
    ->continueSession()
    ->execute('Continue the previous task.');

// Resume specific session (uses Codex thread ID)
AgentCtrl::codex()
    ->resumeSession('thread_abc123')
    ->execute('Pick up from where we left off.');
// @doctest id="bb79"
Codex maps session management to its thread system. The session ID corresponds to the Codex thread ID.

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OpenCode

// Continue most recent session
AgentCtrl::openCode()
    ->continueSession()
    ->execute('Continue the previous task.');

// Resume specific session
AgentCtrl::openCode()
    ->resumeSession('session-xyz-789')
    ->execute('Pick up from where we left off.');
// @doctest id="0511"
OpenCode maintains its own session format with support for session titles and sharing.

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Pi

// Continue most recent session
AgentCtrl::pi()
    ->continueSession()
    ->execute('Continue the previous task.');

// Resume specific session
AgentCtrl::pi()
    ->resumeSession('session-abc-123')
    ->execute('Pick up from where we left off.');

// Ephemeral mode (session not saved)
AgentCtrl::pi()
    ->ephemeral()
    ->execute('Quick one-off task.');

// Custom session directory
AgentCtrl::pi()
    ->withSessionDir('/custom/sessions')
    ->execute('Work in a custom session location.');
// @doctest id="df80"
Pi supports continueSession(), resumeSession(), ephemeral() (no session saved), and withSessionDir() (custom session storage directory).

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Gemini

// Continue most recent session
AgentCtrl::gemini()
    ->continueSession()
    ->execute('Continue the previous task.');

// Resume specific session
AgentCtrl::gemini()
    ->resumeSession('session-xyz-789')
    ->execute('Pick up from where we left off.');
// @doctest id="73bd"
Gemini maps continueSession() to resuming the 'latest' session internally. resumeSession() accepts a session ID or index.

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Important Considerations

Session IDs are agent-specific. Do not attempt to resume a Claude Code session with the Codex bridge, or vice versa. Each agent’s session format is incompatible with the others. Session availability is not guaranteed. Some agent versions, configurations, or error scenarios may not produce a session ID. Always check for null before storing or reusing a session ID. Sessions persist on the agent’s side. Agent-Ctrl does not store or manage session state — it only passes session identifiers to the CLI. The actual session data (conversation history, file context, etc.) is managed by the agent’s own storage system. continueSession() and resumeSession() are mutually exclusive in intent. If you call both on the same builder, the behavior depends on the agent’s CLI — typically, the explicit session ID from resumeSession() takes precedence. For clarity, use only one per execution.

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Multi-Step Workflow Example

use Cognesy\AgentCtrl\AgentCtrl;

// Step 1: Create a plan
$plan = AgentCtrl::claudeCode()
    ->withTimeout(300)
    ->inDirectory('/projects/my-app')
    ->execute('Create a 3-step plan for adding rate limiting to the API.');

$sessionId = $plan->sessionId();
echo "Plan:\n" . $plan->text() . "\n";

if ($sessionId === null) {
    echo "No session available -- cannot continue.\n";
    exit(1);
}

// Step 2: Implement step 1
$step1 = AgentCtrl::claudeCode()
    ->withTimeout(300)
    ->inDirectory('/projects/my-app')
    ->resumeSession((string) $sessionId)
    ->execute('Implement step 1 from the plan.');

echo "\nStep 1 result:\n" . $step1->text() . "\n";

// Step 3: Implement step 2 (still using the same session)
$step2 = AgentCtrl::claudeCode()
    ->withTimeout(300)
    ->inDirectory('/projects/my-app')
    ->resumeSession((string) $sessionId)
    ->execute('Implement step 2 from the plan.');

echo "\nStep 2 result:\n" . $step2->text() . "\n";
// @doctest id="8b1a"