fix(opencode): sanitize MCP tool schemas for Anthropic root combinators

[kvnloo]

Tip leaf (fork-only) — CLEAN

Maps to work-order issue #148. Upstream origin anomalyco#47542 (not touched / not promoted).

What: Sanitize MCP tool schemas for Anthropic root combinators so root-level anyOf/oneOf/allOf flatten (or fall back to a parameterless object).

Commit: 168e2d8c9d0e9564d7996e241a197604096b01be
Origin tip SHA: ab8cd4302da7

Proof: fail→pass on packages/opencode/test/provider/transform.test.ts -t "anthropic root combinators" (GREEN 7 / NEG 5 fail / RESTORE 7).

github_writes_origin: 0. Codex promote parked.

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[github-actions]

This PR doesn't fully meet our contributing guidelines and PR template.

What needs to be fixed:

• PR description is missing required template sections. Please use the PR template.

Please edit this PR description to address the above within 2 hours, or it will be automatically closed.

If you believe this was flagged incorrectly, please let a maintainer know.

[kvnloo]

READY_UPSTREAM

Rechecked before promotion:

• upstream PR fix(opencode): sanitize MCP tool schemas for Anthropic root combinators anomalyco/opencode#47542 is still open
• upstream head is exactly ab8cd4302da77ac7211a35e52d5acc6fe40b616f
• no prior kvnloo validation comment is present
• this fork leaf's fail → pass → restore evidence therefore still applies to the exact upstream head

GitHub App cannot write to anomalyco/opencode from this environment (403). Hermes/local-gh may post the evidence comment from this fork PR. Do not open a duplicate PR.