fix(opencode): drop skills emission to avoid provider 400 errors

[S1933]

OpenCode v1.x does not recognize skills as an agent field; the CLI forwards unknown top-level options to the LLM provider as payload fields. Strict providers (Pydantic additionalProperties: false, e.g. GLM-5.2) reject them with HTTP 400 Extra inputs are not permitted, which made every OpenCode-backed agent with a pivot agents[].skills binding unusable from providers with strict schemas.

Stop emitting skills from the OpenCode agent fragment. The pivot field is still consumed by the Claude Code adapter (frontmatter) and the Codex adapter (instruction hint). OpenCode agents are expected to reference their skills from the prompt body (e.g. an ## Available skills section) or rely on the opencode skill tool at runtime.

Tested:

• TestGenerateAgent, TestGenerateAgentSkills, TestGoldenOpenCodeJSON updated to assert the key is absent
• TestEndToEnd_SkillsRoundTrip updated to assert the OpenCode build agent has no skills key (Claude and native-only legacy-helper paths still validated)
• Golden file (expected_opencode.json) and init bootstrap fixture updated
• Docs (README, docs/SKILLS.md, docs/prd/shenron.md D9 + FR11) updated to describe the new policy

Summary by CodeRabbit

• Documentation

  • Clarified how per-agent skills are handled across Claude Code, Codex, and OpenCode.
  • Documented that OpenCode configurations omit the skills field, while Claude Code and Codex receive skill bindings through supported formats.
  • Updated installation and skill-binding guidance to reflect current behavior.

• Bug Fixes

  • Prevented unsupported skill fields from being included in OpenCode agent configurations, avoiding provider validation errors.

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 819c62c6-fa38-4285-8fa6-2f90ee4e6fc7

📥 Commits

Reviewing files that changed from the base of the PR and between 97825fe and 0dcd5b3.

📒 Files selected for processing (8)

• README.md
• docs/SKILLS.md
• docs/prd/shenron.md
• internal/adapter/opencode/adapter_test.go
• internal/adapter/opencode/agent.go
• internal/adapter/opencode/testdata/expected_opencode.json
• internal/cli/testdata/init/opencode/opencode.json
• internal/integration_test.go

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📝 Walkthrough

Walkthrough

The change removes per-agent skills from generated OpenCode agents, updates adapter fixtures and tests, and documents that Claude Code and Codex retain skill metadata through their respective output formats.

Changes

OpenCode skill handling

Layer / File(s)	Summary
Skill emission contract README.md, docs/SKILLS.md, docs/prd/shenron.md	Documentation specifies Claude Code frontmatter and Codex instructions for skills, while OpenCode output omits the skills key because strict providers may reject it.
OpenCode generation and validation internal/adapter/opencode/agent.go, internal/adapter/opencode/adapter_test.go, internal/adapter/opencode/testdata/..., internal/cli/testdata/..., internal/integration_test.go	OpenCode agent generation no longer emits agent.Skills; fixtures and adapter/integration tests now require the key to be absent.

Estimated code review effort: 2 (Simple) | ~10 minutes

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/opencode-drop-skills-emission

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