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1. opencode-agent commented on Oct 12, 2026

   

   opencode-agentBot

   on Oct 12, 2026 – with OpenCode Agent

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   Thanks for the detailed report, @osrt91!

   Some context first:

   • Session.Info in @opencode/schema/session does have model?: Model.Ref ({ providerID, id, variant? }), and ctx.session.get() returns it unchanged. It is only stored once a model has been picked explicitly for the session, through switchModel or session.create({ model }). A session running on its agent's model or the default model has no stored model, so you get undefined.
   • ctx.session.switchModel() does nothing if the session is already on that model (same provider, id and variant), so no event or extra switch happens. Calling it on every prompt only switches once, so a pin plugin like yours works today without the guard:

   await ctx.session.switchModel({ sessionID, model: { providerID: "anthropic", id: "claude-sonnet-4-5" } })

   The part that is really missing: a plugin can't read the model a session will actually use when none was picked explicitly. Today it would have to work that out itself, from session.model, then the agent's model, then ctx.model.default(). I've marked this as a feature request to expose that resolved model, e.g. on the prompt hook input or through a session method. Maintainers will consider it.

   Related issues:

   • prompt hook does not carry the agent id #54896: your report that the prompt hook doesn't carry the agent id
   • [FEATURE]: Five session capabilities that exist in core but are unreachable from a plugin #49389: other session capabilities plugins can't reach yet
   • TUI plugins cannot read the currently selected model/agent (only the last-sent server session value) #50315 / [FEATURE]: Expose the current TUI model to plugins #42817: TUI plugins can't read the live selected model
   • Model swap gets clobbered by model-less prompts (plugin reminders) #42893: how the session model is resolved and stored
2. osrt91 commented on Oct 12, 2026

   

   osrt91

   on Oct 12, 2026

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   Confirmed — my report was imprecise and this correction makes the report accurate.

   Session.Info does have model?: Model.Ref and ctx.session.get() returns it. It is only populated when a model was picked explicitly (switchModel or session.create({ model })), so a session running on its agent's model or the default model has no stored model. That is why the field reads undefined in our setup.

   That also explains the failure mode we hit. A pin plugin written as:

   const session = await ctx.session.get({ sessionID })
   if (!pin || !session?.model) return          // never true-safe
   await ctx.session.switchModel({ sessionID, model: pin })

   becomes a silent no-op on every prompt, with no error and no warning, because the guard trips forever. The fix is to drop the session?.model check and switch unconditionally — which is safe, since switchModel is a no-op when already on that model.

   So the gap is exactly as you framed it: a plugin cannot read the resolved model. It has to reconstruct it itself — session.model, else the agent's configured model, else ctx.model.default(). Exposing that resolved value on the prompt hook, or through a session method, would remove both the silent-no-op class of bug and that reconstruction.

   For reference, the resolved chain you described matches what we observe end to end: agents.*.model is read by the config layer but not applied on the run --agent path (tracked in #42561), which is what pushed us to a switchModel plugin in the first place.