Bug Description

When running cron jobs with payload.kind: "agentTurn" and sessionTarget: "isolated", the tool call partialArgs field contains malformed JSON due to duplicate content concatenation.

Error Message

Unexpected non-whitespace character after JSON at position X (line 1 column Y)

Actual vs Expected Behavior

Expected (valid JSON):

"partialArgs": "{\"path\": \"/some/file.md\"}"

Actual (malformed JSON):

"partialArgs": "{\"path\": \"/some/file.md\"}{\"path\": \"/some/file.md\"}"

The same JSON object is being concatenated twice, creating invalid JSON.

Affected Versions

• 2026.1.30 (confirmed)
• 2026.3.23-2 (confirmed - latest stable)

Reproduction Steps

1. Create a cron job with:

   • sessionTarget: "isolated"
   • payload.kind: "agentTurn"
   • Any tool call (e.g., read, exec, sessions_history)

2. Wait for cron to trigger

3. Observe the error in the response

Example Cron Job That Triggers This

{
  "name": "Example research job",
  "schedule": {"kind": "cron", "expr": "0 9 * * *", "tz": "America/New_York"},
  "sessionTarget": "isolated",
  "payload": {
    "kind": "agentTurn",
    "message": "Read a file: read({\"path\": \"/some/file.md\"})",
    "model": "openrouter/moonshotai/kimi-k2.5",
    "timeoutSeconds": 120
  }
}

Observed Patterns

• Only affects agentTurn cron jobs with sessionTarget: "isolated"
• Does NOT affect systemEvent jobs or main session interactions
• Happens consistently across different tool types (read, exec, sessions_history)
• The duplication is identical - exact same JSON object appended to itself

Suspected Code Location

Based on error traces, likely in the gateway's tool call serialization for isolated sessions:

• File: gateway-cli-Dsd9gHBa.js (minified)
• Around line 12020 where partialJson is handled
• Possibly in RPC adapter or session isolation code path

Impact

• Cron jobs fail to execute tools properly
• Repeated error messages every time cron triggers
• Requires disabling affected cron jobs as workaround

Workaround

Disable agentTurn cron jobs with sessionTarget: "isolated" until fixed, or convert to systemEvent type jobs if they don't require isolated execution.