sync-models user service fails from Nix store layout: resolves opencode config to /nix/.opencode/opencode.jsonc #591

Symptom

The sync-models systemd user service on amd (Framework laptop) fails on every run. Latest journal evidence (2026-10-22 00:44:49 CDT, journalctl --user -u sync-models):

[sync-models] Discovered 22 models from Antigravity Language Server
[sync-models] Discovering Codex models...
[sync-models] Discovered 9 models from Codex cache
[sync-models] Error: /nix/.opencode/opencode.jsonc does not exist!
sync-models.service: Main process exited, code=exited, status=1/FAILURE

Discovery works fine — the failure is purely in resolving the config file the script syncs models into.

Root cause

bin/sync-models.mjs resolves the config relative to its own location:

const ROOT_DIR = path.resolve(import.meta.dirname, '..');
const OPENCODE_CONFIG_PATH = path.join(ROOT_DIR, '.opencode/opencode.jsonc');

That assumption holds in a repo checkout (<repo>/bin → <repo>/.opencode/opencode.jsonc). But the home-manager unit (home/common/default.nix, systemd.user.services.sync-models) runs the file from the Nix store: node ${../../bin/sync-models.mjs} interpolates to a lone store file (/nix/store/<hash>-sync-models.mjs), so import.meta.dirname is /nix/store, ROOT_DIR becomes /nix, and the script looks for /nix/.opencode/opencode.jsonc — which never exists.

(POLICY_PATH has the same store-layout problem, but its loader already tolerates a missing file and falls back to empty defaults, so it degrades silently instead of failing.)

Fix

Resolve the config path in this order:

1. $OPENCODE_CONFIG_PATH env override, if set.
2. The repo-local .opencode/opencode.jsonc when it exists (in-checkout runs keep today's behavior).
3. The deployed user config ~/.config/opencode/opencode.jsonc — the file the service actually maintains, and the same file the opencode-config-normalize path unit already watches.

Acceptance

• Installed (store-layout) run no longer dies at the config-exists check; it targets ~/.config/opencode/opencode.jsonc.
• In-repo run behavior unchanged.
• Verified by a dry-run from a store-like layout (script copied alone into a bare directory) passing the config resolution step.