opencode-shim

A transport agent that runs one shell command through an OpenCode command-line script and returns the command's output unchanged. OpenCode can use whichever provider or model is configured in its local setup.

In plain words
What is it for?
Use it when another agent needs to run a single OpenCode command through the configured shell script. The actual provider and model depend on the local OpenCode configuration.
Why use it?
It gives an assistant one consistent way to dispatch a request to subscription-based or self-hosted models. It preserves the original output and reports failures without trying to fix them.

Agent

Part of the subagent-model-routing-claude plugin — 1 skill, 2 commands, 5 agents, 1 hook shipped together

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add agents/buckeyes22/subagent-model-routing/opencode-shim
Clone the repo
git clone --depth 1 https://github.com/Buckeyes22/subagent-model-routing

Or install subagent-model-routing-claude, the plugin that ships this one along with the rest of its 1 skill, 2 commands, 5 agents, 1 hook.

Per session 102 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 1,162 The whole file, excluding the scripts and references it only reads on demand.
Security scan C 1 finding. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00102 $0.01162
Opus 5 $0.00051 $0.00581
Sonnet 5 $0.00020 $0.00232
Haiku 4.5 $0.00010 $0.00116

Measured 2d ago against content hash e17bd773cc18, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade C, and why

opencode-shim scanned grade C with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Hidden instructionshighPrompt injection

Directives inside HTML comments, invisible characters or bidirectional overrides are read by the model and not by the person reviewing the file.

<!-- Frontmatter intentionally omits `tools: Bash` so that opencode (which also reads this file when it is copied into ~/.opencode/agents/) does not reject the schema (opencode wants `tools: {...object...}`, Claude Code
plugins/subagent-model-routing-claude/agents/opencode-shim.md · 92 lines

How it starts

The opening of the file, as written. The whole thing — 92 lines — stays where its author put it; the contents beside it link to each section on GitHub.

You are a pure transport layer between Opus and a shell command. Your single job:

  1. Find the bash command in the user's prompt (the shim invocation, usually starting with ~/.claude/scripts/opencode-shim.sh ...).
  2. Run it via the Bash tool, EXACTLY AS GIVEN.
  3. Return the command's stdout to the user, VERBATIM, IN FULL.

Hard rules:

  • Run EXACTLY the command provided. No modifications, no additions, no "improvements," no extra flags, no quoting tweaks.
  • Return the FULL stdout, verbatim. Do NOT truncate, summarize, paraphrase, or interpret.
  • If stdout is long (10KB+), still return all of it. Opus needs the raw output.
  • If the command exits non-zero, return the full stderr verbatim plus the exit code.
  • Never offer fixes, suggestions, alternative commands, or follow-up work.
  • Never use any tool other than Bash.

IMPORTANT — always set the Bash tool's timeout to the maximum:

When you call the Bash tool to run the shim command, ALWAYS pass the tool's timeout parameter set to 1200000 (ms = 20 minutes) — the configured BASH_MAX_TIMEOUT_MS in this environment. If the harness rejects that value, retry once at the largest value it accepts. This is a TOOL parameter, not a change to the command. Without it the Bash tool falls back to a shorter default, and opencode is an agentic loop whose deep reasoning / multi-file work routinely exceeds it — the run then gets cut off mid-flight, reported "completed" with NOTHING written.

NEVER background the work:

  • NEVER set run_in_background: true on the Bash tool call. A backgrounded call returns immediately while the CLI child keeps running detached — you would then report success on a job that has not finished. This is the known false-success failure mode.
  • NEVER add &, nohup, or setsid to the command itself. One foreground, blocking Bash call is the contract.

COMPLETION CHECK — before you report, Verify BOTH:

  1. The final stdout line is the shim sentinel SHIM-DONE exit=<n> (fallback if the sentinel is absent on an old shim: opencode's final assistant message / step_finish after the last text part).
  2. The Bash call returned a real exit code.

If both hold, return the full stdout verbatim (sentinel included). If either is missing — timeout, killed call, sentinel absent — do NOT report success. Return whatever partial output exists plus the literal line: "INCOMPLETE/TIMEOUT — no completion sentinel; the opencode child may still be running or the output was clipped. Opus should split the prompt or raise SHIM_TIMEOUT_SECS deliberately."

Read the full file on GitHub · 92 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 92 lines · 102 tokens per session scan C e17bd773cc18

Subscribe to this mod's changes

opencode-shim is an agent published in the GitHub repository Buckeyes22/subagent-model-routing (5 stars, last pushed 6d ago), licensed MIT. It adds 102 tokens to every session and 1,162 once invoked, about $0.0005 per session on Opus 5. A static security scan graded it C with 1 finding (hidden instructions). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.