Upstream sync: session.setModel() and built-in tool override support

[Copilot]

Ports two features from upstream github/copilot-sdk (bd98e3a, f843c80). Commits dcd86c1/51baa25/b380a82/7460798 are release/changelog automation — not ported.

CopilotSession.setModel(String) — mid-session model switching

Calls session.model.switchTo RPC. Conversation history is preserved; new model takes effect on the next message.

session.setModel("gpt-4.1").get();
// next sendAndWait() uses gpt-4.1

ToolDefinition — override built-in CLI tools

New overridesBuiltInTool field (JSON: omitted when null) and createOverride() factory. Signals to the CLI that a name collision with a built-in tool (e.g. grep, read_file) is intentional. Existing create() is backward-compatible.

var customGrep = ToolDefinition.createOverride("grep", "Project-aware search", schema, handler);

Tests & docs

• E2E test for built-in tool override using upstream snapshot tools/overrides_built_in_tool_with_custom_tool.yaml
• Closed-session guard test for setModel()
• Documentation in advanced.md for both features
• .lastmerge updated to dcd86c1

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• checkstyle.org
  • Triggering command: /opt/hostedtoolcache/CodeQL/2.24.2/x64/codeql/tools/linux64/java/bin/java /opt/hostedtoolcache/CodeQL/2.24.2/x64/codeql/tools/linux64/java/bin/java -jar /opt/hostedtoolcache/CodeQL/2.24.2/x64/codeql/xml/tools/xml-extractor.jar --fileList=/tmp/codeql-scratch-a0b8ba07f7cabbfc/dbs/java/working/files-to-index3919231755423702167.list --sourceArchiveDir=/tmp/codeql-scratch-a0b8ba07f7cabbfc/dbs/java/src --outputDir=/tmp/codeql-scratch-a0b8ba07f7cabbfc/dbs/java/trap/java which ot-sdk/test/harness/node_modules/@github/copilot-linux-x64/copilot h which va/copilot-sdk-j--show-toplevel ot-sdk/test/harness/node_modules/@github/copilot-linux-x64/copilot curl�� modules/tsx/dist/loader.mjs which 0/x64/lib/node_modules/npm/node_modules/@npmcli/run-script/lib/node-gyp-bin/sh .0.18-8/x64/bin/git which ava/target/copild78db830cbbf576f5e92ea5fc556c619a01461a0:src/test/java/com/github/copilot/sdk/ClosedSessionGuardTest.java node (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

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This section details on the original issue you should resolve

<issue_title>[upstream-sync] Upstream sync: 6 new commits (2026-03-03)</issue_title>
<issue_description>The upstream github/copilot-sdk has 6 new commits since the last sync.

Commit Range

• Last merged: b9f746a
• Upstream HEAD: dcd86c1
• Compare: b9f746a...dcd86c1

New Commits (most recent first)

• dcd86c1 Add changelog for v0.1.30 (#642)
• 51baa25 Improve changelog agent: prerelease support, formatting fixes, publish trigger (#641)
• b380a82 Improve changelog agent output formatting (#640)
• 7460798 Add release changelog agentic workflow (#638)
• f843c80 Support overriding built-in tools (#636)
• bd98e3a Add session.setModel() for mid-session model switching (#621)

Action Required

Please follow the agentic-merge-upstream prompt to port these changes into the Java SDK.

When done, create a Pull Request with the label upstream-sync.

Generated by Weekly Upstream Sync Agentic Workflow

• expires on Mar 9, 2026, 5:50 PM UTC

Comments on the Issue (you are @copilot in this section)

• Fixes [upstream-sync] Upstream sync: 6 new commits (2026-03-03) #161

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