Tool execute() receives operation=undefined for enum arg when value is large

Environment

• opencode version: 1.18.4
• Platform: linux

Bug

When calling a tool with an enum argument (operation) alongside a large value, the tool's execute() receives operation: undefined instead of the provided value (e.g. "write").

Reproduction

Tool definition (TypeScript, enum on operation):

args: {
  operation: tool.schema
    .enum(["write", "read", "forget", "list", "search", "stats"])
    .describe("..."),
  key: tool.schema.string(),
  value: tool.schema.string(),
  tags: tool.schema.string(),
}

Call (first time — second with short value worked):

{
  "operation": "write",
  "key": "session.save.2026-07-26",
  "value": "CRM 2026-07-26: Session complete. Final commit 96bca81. Single table cards (id + 15 optional fields), 4 sub-agent tools (search_cards, save_card, delete_card, list_cards), main chat with handle_client_request (1 tool). EntityDatabase replaced ClientDatabase. FastFlow works with 4 tool schemas. client_database.h/cpp removed.",
  "tags": "session,save,crm,cards"
}

Result

Error from argparse (Python script called by tool):

ERROR: memory.py: error: argument --operation: invalid choice: 'undefined' (choose from write, read, forget, list, search, stats, rag_store, rag_find)

The CLI received --operation=undefined meaning args.operation was undefined at template literal interpolation time.

Expected

args.operation should retain its provided value "write" regardless of other argument sizes.

Notes

• Second call with a short value (56 chars) worked correctly.
• This suggests the large "value" argument causes a serialization/deserialization issue in opencode's argument passing that corrupts or drops the enum argument.
• Workaround in the tool (guard + escape) applied locally, but the root cause is in opencode.