build(opencode): shrink single-file executable size

[Hona]

Summary

• enable Bun standalone splitting and minify in the opencode build script
• keep the executable build on ESM format explicitly
• reduce the current Windows single-file build from 158.19 MiB to 131.74 MiB (-16.72%) in the --skip-embed-web-ui build we measured

Testing

• bun script/build.ts --single --skip-install --skip-embed-web-ui
• dist/opencode-windows-x64/bin/opencode --version

[Copilot]

Pull request overview

Adds a compatibility shim for GitHub Copilot (and similar OpenAI-compatible gateways) so compaction/requests with prior tool-call history don’t fail when no active tools are enabled, plus a targeted regression test and build output-size optimizations for Bun standalone binaries.

Changes:

• Inject a stub _noop tool when sending requests to LiteLLM proxies or @ai-sdk/github-copilot and the message history contains tool calls but the active tool set is empty.
• Add a session LLM test that exercises the GitHub Copilot request shape for the above compatibility path.
• Enable format: "esm", minify: true, and splitting: true in the Bun standalone build to reduce single-file binary size.

Reviewed changes

Copilot reviewed 1 out of 1 changed files in this pull request and generated no comments.

File	Description
packages/opencode/src/session/llm.ts	Extends existing “dummy tool injection” compatibility behavior to also cover GitHub Copilot’s OpenAI-compatible gateway.
packages/opencode/test/session/llm.test.ts	Adds a regression test ensuring _noop is included in the outgoing request tools when history contains tool calls and active tools are empty.
packages/opencode/script/build.ts	Turns on ESM output, minification, and splitting for Bun compile builds to reduce binary size.

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