[Bug] acq run opencode fails on sbx: duplicate kit name "opencode" blocks sandbox create #593

Summary

acq run opencode <paths> fails at sbx create on the sbx backend whenever the pinned OpenCode agent kit is active. The sandbox is never created.

error: request failed: 400 Bad Request: kit_artifacts: compose: duplicate kit name "opencode" — each kit in a composition must have a unique name

Reported by a user on 2026-10-20 against quickstart main.

Root cause

Two independent mechanisms each contribute a kit named opencode to the same sbx create composition.

1. acq explicitly passes the pinned OpenCode agent kit. The patterns kit declares name: opencode and an agent: block with name: opencode / entrypoint: opencode. acq fetches it and forwards it via --kit:

acq: selected built-in agent kit: agent=opencode kit=opencode entrypoint=opencode install_owner=kit start_owner=kit apply=enabled

2. sbx synthesizes its own native opencode kit from the positional agent token. acq.backends/sbx.sh:561 forwards the user's opencode token through _stripped, and the image resolves to docker/sandbox-templates:opencode-docker. sbx builds a native kit for that agent variant on its own.

sbx then rejects the composition because both carry the same name. Current main has no mitigation: the pinned kit is passed as --kit alongside the positional opencode token, and nothing rewrites that token or suppresses the native kit.

Scope

• Backend: sbx only. msb does not synthesize native agent kits from the agent token, so the msb path is unaffected.
• Trigger: the pinned patterns OpenCode agent kit being active, which is the default on current bundles.
• Visibility: limited because msb is now the default backend. Users still pinned to sbx hit this on their first OpenCode create.

Reproduction

On the sbx backend with a current kit bundle:

acq backend set sbx
acq run opencode <any-path>

Create fails with the duplicate kit name "opencode" error above.

Workaround

Switch to the recommended default backend, which is unaffected:

acq backend set msb
acq run opencode <paths>

Relationship to existing work

The token-rewrite portion of #584 fixes exactly this. That PR's own description states it:

Use shell only as SBX's template-selection token for the generic default, preventing SBX from synthesizing a duplicate native opencode kit.

#584 is currently CHANGES_REQUESTED for three unrelated Major findings in its launch-mode record logic, none of which touch the duplicate-kit fix. This issue exists so the user-facing break is tracked independently of that PR's review cycle, and so it does not get closed implicitly if #584 is restructured.

See also ADR-0030 for the generic-base direction this sits inside.

Acceptance criteria

• acq run opencode <path> succeeds on the sbx backend with the pinned OpenCode agent kit active.
• Exactly one kit named opencode reaches the sbx create composition.
• Regression coverage asserts the create argv does not contain both an explicit pinned opencode kit and an agent token that causes sbx to synthesize a second one.
• The msb path is unchanged.
• Non-OpenCode agents on sbx are unchanged.