agent env: /tmp/opencode advertised as writable scratch but owned by another user

Summary

The agent environment banner advertises /tmp/opencode as "pre-created and approved for external access" and directs agents to prefer it over generic system temp dirs. On this host the directory exists but is owned by a different user than the session (uid 1000), so the agent cannot write to it:

$ printf 'probe' > /tmp/opencode/probe1.txt
/bin/bash: line 1: /tmp/opencode/probe1.txt: Permission denied

$ id
uid=1000(cunabu) ...
$ ls -ld /tmp/opencode
drwxrwxr-x 2 iconoclasta iconoclasta ...

(Verified 2026-08-24.)

Environment

• opencode version: opencode2 v0.0.0-beta-18050 (beta)
• OS: Linux 6.8.0-111-generic x86_64
• Shell: /bin/bash; Terminal: tmux

Expected Behavior

Either /tmp/opencode is owned/mode'd so the session user can write to it, or the banner stops claiming it is approved for access when it is not.

Actual Behavior

A sanctioned scratch location is unusable; agents are steered toward a path that fails, then must fall back to un-advertised locations.

Additional Context

Low priority and mostly host-provisioning, but it is an instruction-vs-reality mismatch in shipped surface text. If /tmp/opencode is created by harness/host tooling rather than by the user, it should be created with the session user as owner; if it is expected to be pre-existing, docs should say so and note the permission requirement.