[Bug] Hidden agents not registered: `Agent not found: "historian"` on OpenCode 1.14.41

[HaleTom]

Environment

• OpenCode Version: 1.14.41
• Plugin Version: 0.15.7 (latest)
• Platform: Linux

Description

The @cortexkit/opencode-magic-context plugin fails to register its hidden subagents (historian, historian-editor, dreamer, sidekick) through the plugin config hook, causing all subagent dispatches to fail with:

Agent not found: "historian". Available agents: build, explore, general, plan

Root Cause

The plugin registers agents in its config hook at dist/index.js:174059-174064:

config2.agent = {
  ...config2.agent ?? {},
  [DREAMER_AGENT]: buildHiddenAgentConfig(DREAMER_AGENT, ...),
  [HISTORIAN_AGENT]: buildHiddenAgentConfig(HISTORIAN_AGENT, ...),
  [HISTORIAN_EDITOR_AGENT]: buildHiddenAgentConfig(HISTORIAN_EDITOR_AGENT, ...),
  [SIDEKICK_AGENT]: buildHiddenAgentConfig(SIDEKICK_AGENT, ...)
};

However, OpenCode 1.14.41 does not propagate the agent field set/modified by plugin config hooks into the agent registry. When the plugin later tries to dispatch a child session via client.session.prompt({ agent: 'historian', ... }), SessionPrompt.resolveTools throws because "historian" is not a registered agent.

Steps to Reproduce

1. Fresh install OpenCode 1.14.41
2. Install @cortexkit/opencode-magic-context@latest
3. Open any file/project to trigger the session.created -> runHistorianPrompt flow
4. The error surface in:
   • Magic Context compaction when context hits the threshold
   • Background dream/discovery tasks dispatching dreamer or sidekick
   • Historian recovery on session load

Expected Behavior

The config hook’s mutation of config2.agent should be respected by OpenCode, or the plugin should use a supported mechanism to register agents that is compatible with OpenCode 1.14.x.

Workaround

Manually register the hidden agents in opencode.json:

{
  "$schema": "https://opencode.ai/config.json",
  "agent": {
    "historian": { "mode": "subagent", "hidden": true },
    "historian-editor": { "mode": "subagent", "hidden": true },
    "dreamer": { "mode": "subagent", "hidden": true },
    "sidekick": { "mode": "subagent", "hidden": true }
  }
}

Suggested Fix

1. Short-term: Document the minimum required OpenCode version that supports agent registration via config hook, and provide the workaround above.
2. Long-term: Update the plugin to register hidden agents through a supported mechanism (e.g., via the OpenCode SDK agent registration API if available, or by emitting a warning if the config hook is not honoured by the host OpenCode version).