[FEATURE]: TUI plugin API: session projection | session list adapters

[juanma91m]

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Summary

I'd like to propose a small extension to the TUI plugin API so plugins can influence:

1. the projection of the native session view
2. the projection of the native session switcher/list
   This is not a request to upstream a specific product feature.
   The goal is to expose generic host hooks so advanced plugins can work without requiring local host patches.

---

Problem

Today, plugins can inject some UI and commands, but they still lack a clean way to control session-aware behavior in the native TUI.
In practice, some advanced addons need to express things like:

• which session should be considered the active logical session
• which messages should be visible in the native session view
• whether the prompt should be visible for a given projected session state
• how the native session list should resolve the current highlighted session
• how session selection should map from a logical session to a concrete target session
  Without host hooks for this, the only alternatives are:
• fragile command shadowing
• duplicating native views
• or local host patches

---

Proposal

Add two optional plugin hooks with full native fallback:

1. Session projection adapter

Conceptually similar to:

• session.registerAdapter(...)
  This would let a plugin provide a partial projection policy for the native session view.
  Examples of responsibilities:
• resolve active session id
• resolve visible messages
• resolve prompt visibility
• resolve permission/question routing
• surface inspection state
  Important:
• core still renders the native session view
• plugin only provides policy
• default behavior stays unchanged when no adapter is registered

2. Session list adapter

Conceptually similar to:

• session.registerListAdapter(...)
  This would let a plugin provide a partial projection policy for the native session list/switcher.
  Examples of responsibilities:
• resolve current highlighted session
• resolve target session before navigation
• optional pre-navigation cleanup hook
  Important:
• native session list remains the host UI
• this avoids fragile command overrides

---

Why this should live in core

This is not feature-specific logic.
It is host-level TUI extensibility.
These hooks would help any plugin/addon that needs a logical session model on top of the native TUI, while preserving:

• native rendering
• native fallback behavior
• no runtime/server changes

---

Related issues

I reviewed the related items suggested by the bot, especially around plugin extensibility and TUI hooks.
This proposal is specifically about session-aware projection hooks for:

• native session
• native session list/switcher
  It is narrower than a general plugin extensibility umbrella, and more specific than generic UI injection points.

---

Success criteria

A successful outcome would be:

• advanced plugins can work against official OpenCode builds
• native session and session list remain the host UI
• no default UX regressions
• no feature-specific logic needs to live in core
• local host patching becomes unnecessary for this class of addons

---

Open question

Would maintainers prefer:

1. discussing this API shape first in an issue, then opening small PRs
2. or going directly to a focused PR for one adapter at a time?