UX: agent model config override — sticky last-used model survives session reload; wizard should warn + document workaround

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Problem

When opencode.json configures agent.build.model (or any agent model), OpenCode's last-used model per agent overrides the config default on session resume/reload. The config is loaded correctly — opencode debug config shows the right model — but the agent starts on whatever model was manually selected last, not the one in config.

Concrete case: set up the Zen fallback profile (wizard install + hand-written opencode.json with agent.build.model = opencode/claude-sonnet-4-6). On every session open, Build agent shows the previously-selected model (in this case Opus 4.8 max from the setup session) instead of Sonnet 4.6. User has to manually /models → pick the right model every time until the sticky selection matches config.

Root cause

This is OpenCode core behavior (anomalyco/opencode), not the wizard. The wizard can't fix it. But the wizard's post-install output and docs say nothing about it, so users hit it silently and assume the config is wrong.

What the wizard can do

1. Post-install note: add a line to the install summary — something like: "Note: OpenCode persists the last-used model per agent. On first open, use /models to select your configured model; it sticks after that."
2. SETUP profile docs: add the same note to the Zen profile recipe (and any profile that pins agent models).
3. Stretch: a pick --verify or opencode debug config step in the post-install flow that reminds users to confirm the active model matches config.

Workaround (for docs)

1. Open OpenCode after install.
2. For each primary agent (Tab to cycle), type /models and select the configured model explicitly.
3. Done — OpenCode now remembers it per-agent and it matches config on future sessions.

Environment

• OpenCode: 1.16.2
• opencode-sdlc-wizard: 0.13.4
• macOS 15.1 arm64