(bug) Runner's baked codex-acp version pin is bypassed when the container runs with a non-default uid or HOME

[mmabrouk]

The runner image pre-installs the Codex ACP adapter at build time to pin its version (decision D-005): Dockerfile.gh runs install-agent codex --agent-process-version 1.1.7 as user node with ENV HOME=/home/node, so the baked install lands in /home/node/.local/share/sandbox-agent.

When the container runs with a different uid and HOME, the sandbox-agent daemon looks in $HOME/.local/share/sandbox-agent, misses the baked pin, and installs the adapter from npm with the floating ^1.1.7 range. The local dev compose runs the runner as the host uid (1004:1004) with HOME=/tmp, so this happens on every fresh container: today that floating install resolved to codex-acp 1.7.0 (bundling @openai/codex 0.148.0) instead of the pinned 1.1.7 (@openai/codex 0.145.0).

The Dockerfile comment already names the hazard: "Without a fixed HOME an arbitrary runtime uid would miss the baked pin and reinstall." The fixed HOME does not survive a compose user: override.

Observed consequences (local OSS dev stack, 2026-09-01)

1. The unpinned 1.7.0 adapter's install-verify step (codex-acp --help) never exits. The first codex session after the runner restart hung forever in create_instance, and the session was stuck exactly as in (bug) An agent turn whose sandbox dies under it hangs for 30 minutes instead of failing #6418. Killing the hung --help process released a 15-minute-old create_instance call, and the turn then ran normally.
2. /tmp empties on every container replacement, so every deployment re-rolls the adapter version dice.

Verification snapshot

$ docker exec runner id; echo HOME=$HOME
uid=1004(agenta) gid=1004         HOME=/tmp
$ baked:   /home/node/.local/share/sandbox-agent/.../codex-acp/package.json -> "version": "1.1.7"
$ runtime: /tmp/.local/share/sandbox-agent/bin/agent_processes/codex/package.json -> "@agentclientprotocol/codex-acp": "^1.7.0"
$ ps: node .../codex/node_modules/.bin/codex-acp --help   (alive 15 min, stdin/stdout -> /dev/null)

Expected: the runtime daemon uses the baked, pinned adapter regardless of the uid and HOME the orchestrator assigns, or the runner refuses to fall back to a floating npm install.

[linear-code]

AGE-4237