opencode loses its default agent (falls back to build) after the config folder is rewritten, when the worktree's opencode serve session is pinned to it #41275

What happens

Inside an Orca terminal running opencode, the agent in use flips from the configured default to
build, and it never recovers on its own.

Measured status lines inside the Orca terminal, opencode v2.2.7:

It loses the model too (local SGLang → built-in default), and restoring agents/ORACLE.md
afterwards does not bring the agent back.

It does not happen outside Orca

Same machine, same config, same act, plain opencode in a tmux session:

So the trigger needs Orca.

What Orca adds (read from the live process)

cmdline : /usr/local/bin/opencode serve --service
env     : ORCA_OPENCODE_PLUGIN_API=v2
          ORCA_AGENT_HOOK_ENDPOINT=/root/.config/orca/agent-hooks/endpoint.env
          ORCA_AGENT_HOOK_TOKEN=…
          ORCA_WORKTREE_ID=…::/work/proj
          ORCA_TERMINAL_HANDLE=term_…
          ORCA_APP_VERSION=1.4.255 (also reproduced on 1.4.256)

The terminal does not run a self-contained opencode: it attaches to a per-worktree
opencode serve --service that Orca starts and wraps with its plugin/hook layer. Hypothesis,
consistent with every observation: that service pins the agent for the session; when the config is
rewritten the pinned agent momentarily does not exist, the service falls back to build, and —
unlike a plain TUI, which re-resolves default_agent — it never re-resolves.

Minimal reproduction

mkdir -p ~/.config/opencode/agents
printf '{"$schema":"https://opencode.ai/config.json","default_agent":"ORACLE"}\n' \
  > ~/.config/opencode/opencode.json
printf -- '---\ndescription: stand-in\n---\n\nYou are ORACLE.\n' \
  > ~/.config/opencode/agents/ORACLE.md

# 1. open a worktree in Orca whose agent is opencode, and open its terminal
#    status line: ORACLE · <model>

# 2. rewrite the config folder while that terminal is open
rm -rf ~/.config/opencode/agents && mkdir -p ~/.config/opencode/agents
printf -- '---\ndescription: stand-in\n---\n\nYou are ORACLE.\n' \
  > ~/.config/opencode/agents/ORACLE.md
touch ~/.config/opencode/opencode.json

# 3. status line becomes: Build · ...       (and stays there)

This is not hypothetical: it is what an install-global-style deploy does on every update — two
rsync -a --delete --checksum passes over the live config folder.

Environment

• Orca 1.4.255 and 1.4.256 (both reproduced), Linux x86_64
• opencode v2.2.7, agent defined only in agents/*.md (the "agents" object in opencode.json
  is not read by the v2 schema, so the definition really does depend on that file)
• container: Debian bookworm, Orca server headless (orca serve), config mounted read-only from the
  host

What would help

Either the service re-resolving default_agent when a pinned agent disappears, or Orca re-selecting
the agent for a worktree whose pinned agent no longer exists (instead of silently staying on build).

Related upstream: anomalyco/opencode#62002 (default_agent reverts to build after a config rewrite).