[upstream-sync] Port 21 upstream commits (2026-03-10): protocol v3, agent pre-selection, onListModels, session logging, new event types

[Copilot]

Resolves #

Ports 21 upstream commits from github/copilot-sdk (4e1499d..7235609).

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Before the change?

• SDK negotiated protocol v2 only — rejected any server reporting v3
• No way to supply a custom model list for BYOK scenarios without a running CLI server
• No way to pre-select a custom agent at session creation time
• No way to log messages into the session timeline from SDK code
• Protocol v3 event types (external_tool.requested, permission.requested, command.queued, etc.) were unknown/dropped

After the change?

Protocol v3 (backward-compatible)

• SdkProtocolVersion bumped to 3; range check accepts v2–v3 so existing deployments keep working

BYOK: Custom Model List (e478657)

• CopilotClientOptions.setOnListModels(Supplier<CompletableFuture<List<ModelInfo>>>) — called by listModels() instead of querying the CLI; results are cached; no client.start() required

var options = new CopilotClientOptions()
    .setOnListModels(() -> CompletableFuture.completedFuture(List.of(
        new ModelInfo().setId("my-model").setName("My Custom Model")
    )));

Agent pre-selection at session start (7766b1a)

• SessionConfig.setAgent(String) / ResumeSessionConfig.setAgent(String) — activates a named custom agent immediately on session creation, replacing a follow-up selectAgent() call

new SessionConfig()
    .setCustomAgents(List.of(reviewer))
    .setAgent("reviewer")   // activated immediately

Session logging (11dde6e)

• CopilotSession.log(String) and CopilotSession.log(String, SessionLogRequestLevel, Boolean) — writes to the session timeline via session.log RPC; supports INFO/WARNING/ERROR levels and ephemeral (non-persisted) messages

New protocol v3 event types (11dde6e, 396e8b3)

• 8 new event classes registered in AbstractSessionEvent and SessionEventParser: ExternalToolRequestedEvent, ExternalToolCompletedEvent, PermissionRequestedEvent, CommandQueuedEvent, CommandCompletedEvent, ExitPlanModeRequestedEvent, ExitPlanModeCompletedEvent, SystemNotificationEvent
• Events are observable via session.on(); SDK does not auto-respond to them because the current CLI sends both v2 RPCs and v3 broadcast events simultaneously — auto-handling caused double-response conflicts

Pull request checklist

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• mvn spotless:apply has been run to format the code
• mvn clean verify passes locally

Does this introduce a breaking change?

• Yes
• No

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[edburns]

I am reviewing this now, @brunoborges