[BambinoSK]

Fixes #1185.

Problem

OpenCode v2 pushes no config_option_update notifications: the full updated configOptions array is returned only as the session/set_config_option response echo, and the plugin discarded it everywhere. Session option state therefore went stale for the whole session (the Effort tick kept the pre-switch value after a model change reset the per-model effort), and agent switches were silent no-ops: the menu restarts the process expecting buildCommand to forward the selection, but OpenCodeClient never passes an agent flag, v2 removed session/set_model, and session/new silently ignores agent/modeId params, so every session kept running build. Wire evidence and step-by-step repros are in the issue.

What this PR does

• Apply the set_config_option echo to local option state. New shared AcpClient.applyConfigOptionEcho is attached to the request future in setConfigOption; the echoed array (including cross-effects such as effort resetting on a model switch) is merged through the same path as config_option_update notifications. Rejected options (-32602) complete exceptionally and leave state untouched.
• Capture model-switch cross-effects. OpenCodeClient.sendSetModel's v2 branch, which routes model changes through session/set_config_option (v2 removed session/set_model), attaches the same hook. The whenComplete runs before the blocking wait, so a late echo still applies after a timeout.
• Tick-mark the live value in the gear menu. New SessionOption.effectiveValue: the agent-reported live value wins, the locally stored pick is only the pre-session fallback, so the menu no longer keeps stale selections after agent-side resets.
• Switch agents live on v2. New AbstractClient.canSwitchAgentLive(slug). OpenCode v2 advertises its session modes (build, plan, plus custom agents from .opencode/agents/) as the mode config option's values, and session/set_config_option(mode) switches the live session, so OpenCodeClient overrides onAgentSlugChanged (live push) and onSessionCreated (deferred push of a selection stored before the session existed), guarded by the advertised values so invalid slugs are never sent and redundant switches are suppressed. The menu applies switchable slugs without a process restart, persists them for future sessions, and shows a status banner; non-switchable agents keep the restart flow and v1 keeps the legacy behavior.

Notes for reviewers

• The echo application is a no-op for agents that answer without a configOptions key or push notifications instead (same merge path, idempotent replace by id); agents whose options are static (no live initialValue) keep the stored-pick behavior in the menu. AcpClientEchoGuardTest pins these guards.
• The onAgentSlugChanged/onSessionCreated extension points and the deferred-then-applied selection flow follow the existing Kiro v3 pattern.
• 10 files changed, +612/-5, with tests: AcpClientEchoGuardTest, OpenCodeClientModelEchoTest, OpenCodeClientAgentSwitchTest, SessionOptionEffectiveValueTest.

Verification

• :plugin-core:test green on this branch for AcpClientEchoGuardTest, OpenCodeClientModelEchoTest, OpenCodeClientAgentSwitchTest, SessionOptionEffectiveValueTest, OpenCodeClientBehaviorTest, OpenCodeClientModelRoutingTest, AcpClientProtocolTest.
• Live-verified on OpenCode v2.0.27 (evidence in the issue): the Effort tick resets after a model switch; build/plan switches apply to the running session (the agent's self-reported mode changes in-session, same session id, no restart); a persisted selection is applied when a new session starts; a custom agent in .opencode/agents/ is listed, live-switchable, and runs with its own system prompt.

How to verify the interactive behavior

1. Connect OpenCode v2, open a session, set Effort to High, switch the model in the Model dropdown, reopen the gear menu: the tick is back on Default.
2. Ask the agent which mode it runs as, select Plan in the Agent menu (no restart happens), ask again: it answers plan. Select Build and ask again: build.
3. With Plan selected, start a fresh session: it begins in plan.

[github-actions]

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[codecov]

Codecov Report

❌ Patch coverage is 70.00000% with 15 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...afishen/agentbridge/client/acp/OpenCodeClient.java	72.41%	3 Missing and 5 partials ⚠️
...catatafishen/agentbridge/client/acp/AcpClient.java	72.22%	2 Missing and 3 partials ⚠️
...catatafishen/agentbridge/bridge/SessionOption.java	50.00%	0 Missing and 1 partial ⚠️
...atatafishen/agentbridge/client/AbstractClient.java	0.00%	1 Missing ⚠️

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