[FEATURE]: REPL tool for isolated language-specific code execution separate from bash #20488

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Problem

OpenCode routes all code execution through the bash tool. When an agent wants to run a Python snippet, a Node.js expression, or a quick SQL query, it must:

1. Invoke bash with a full shell invocation (python3 -c "..." or node -e "...")
2. Handle shell escaping of the code content (single quotes, newlines, special chars)
3. Mix Python/JS exit codes with shell exit codes indistinguishably
4. Use DangerFullAccess permission even for trivial read-only calculations

claw-code implements a REPL tool that accepts a code string and language field, runs the code in an isolated subprocess, and returns structured stdout, stderr, and exit_code — cleanly separated from shell semantics.

Proposed solution

// packages/opencode/src/tool/repl.ts

export const REPLTool = Tool.define({
  name: "REPL",
  description: "Execute a code snippet in a language-specific subprocess. Prefer this over bash for Python, JavaScript, or SQL snippets to avoid shell-escaping issues and get clean per-language exit codes.",
  parameters: z.object({
    code: z.string(),
    language: z.enum(["python", "javascript", "typescript", "sql", "ruby", "shell"]),
    timeout_ms: z.number().int().min(1).max(60_000).optional()
  }),
  execute: async ({ code, language, timeout_ms }) => {
    const result = await executeREPL(code, language, timeout_ms ?? 10_000)
    return {
      language,
      stdout: result.stdout,
      stderr: result.stderr,
      exit_code: result.exitCode,
      duration_ms: result.durationMs
    }
  }
})

Language dispatch

Why this matters

• Eliminates shell-escaping bugs that cause agents to corrupt code containing quotes, backslashes, or newlines when passed through bash -c
• Produces clean, parseable stdout/stderr/exit_code without shell wrapper noise
• Particularly valuable for data science workflows running Python analysis snippets (DuckDB, pandas) inline without writing a temp file
• Permission model can be more nuanced: a python REPL that only does computation could be ReadOnly; only REPLs with filesystem access need WorkspaceWrite

Acceptance criteria

• REPL tool executes code in an isolated subprocess with configurable timeout
• stdout, stderr, and exit_code are returned as separate fields (not concatenated)
• Multiline code strings are handled without shell-escaping issues (passed via stdin pipe, not -c argument)
• timeout_ms kills the subprocess cleanly and returns a timeout error in stderr
• At minimum python and javascript/typescript are supported on first release; additional languages are additive

Related / cross-reference

• claw-code reference: https://github.com/instructkr/claw-code/tree/main/rust (REPL tool)
• Sub-agent tool-set isolation: [FEATURE]: Sub-agent tool-set isolation by role (Explore / Plan / Verification scopes) #20483
• Bash timeout kills background processes: Bash timeout kills background processes #20403
• Learnings from claude-code source: Lessons from claude-code-main? #20475