Merge reference implementation SDK changes (2026-04-30)

[Copilot]

Ports 4 commits from github/copilot-sdk (dd2dcbc→e42b726).

Before the change?

• setForegroundSessionId() serialized its RPC request body as an ad-hoc Map.of("sessionId", ...), relying on Jackson's map handling rather than an explicit type
• E2ETestContext did not set COPILOT_HOME, diverging from the reference test harness
• scripts/codegen/package.json and pom.xml referenced @github/copilot@^1.0.39

After the change?

• SetForegroundSessionRequest record (json package): explicit DTO for the session.setForeground payload — mirrors the AOT-safe SetForegroundSessionRequest record added in reference impl commit c63feb2

• CopilotClient.setForegroundSessionId(): uses the new record instead of Map.of()

  // before
  .invoke("session.setForeground", Map.of("sessionId", sessionId), ...)
  // after
  .invoke("session.setForeground", new SetForegroundSessionRequest(sessionId), ...)

• E2ETestContext: adds COPILOT_HOME alongside XDG_CONFIG_HOME / XDG_STATE_HOME

• @github/copilot bumped to ^1.0.40-0 in package.json and pom.xml; generated Java RPC/event sources are already current (schemas unchanged at this version)

• .lastmerge updated to e42b726ca42bd1b2e099a956c9287ba9435ba3e5

Not ported: SessionFsTests path refactoring and MultiClientTests timing fix — no Java equivalents exist yet.

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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