Fix OpenCode package file whitelist

[solanab]

What problem are you trying to solve?

OpenCode installs Superpowers from the git-backed npm package spec documented in docs/README.opencode.md:

{
  "plugin": ["superpowers@git+https://github.com/obra/superpowers.git"]
}

In a clean OpenCode 1.14.48 run using that plugin spec, the resolved package landed at:

~/.cache/opencode/packages/superpowers@git+https:/github.com/obra/superpowers.git/node_modules/superpowers

That package included repo and harness files that OpenCode does not need at runtime, including .github/, docs/, hooks/, scripts/, tests/, .claude-plugin/, .codex-plugin/, and .cursor-plugin/. npm pack --dry-run --json git+https://github.com/obra/superpowers.git reproduced the same issue and warned that no .npmignore was present, so npm fell back to .gitignore.

What does this PR change?

This PR adds a package.json files whitelist for the OpenCode npm package so only the plugin entrypoint, assets, and skills are packed. It also adds an OpenCode packaging regression test that rejects top-level repo/test/docs/hook/harness files while ensuring required runtime files and nested skill scripts remain present.

Is this change appropriate for the core library?

Yes. This is core packaging infrastructure for the documented OpenCode install path. It is not project-specific, does not add a new skill, and does not integrate a third-party service.

What alternatives did you consider?

I considered adding .npmignore, but that is easier to accidentally drift because it must blacklist every non-runtime path. A files whitelist is smaller and makes the intended runtime artifact explicit.

I also considered excluding all scripts/ paths, but that would break skill-owned scripts such as skills/brainstorming/scripts/server.cjs. The whitelist keeps skills/ intact and only removes top-level non-runtime paths.

Does this PR contain multiple unrelated changes?

No. The package whitelist and the regression test cover one packaging boundary issue.

Existing PRs

• I have reviewed all open AND closed PRs for duplicates or prior art
• Related PRs: none found for OpenCode package contents / npm pack whitelist

Searches reviewed included npmignore, npm pack, package size, package.json files, and opencode package files. Related-but-different OpenCode PRs included OpenCode plugin loading/caching/docs changes; they did not address package contents.

Environment tested

Harness (e.g. Claude Code, Cursor)	Harness version	Model	Model version/ID
OpenCode	1.14.48	OpenAI	gpt-5.4
npm	10.9.4	n/a	n/a

New harness support (required if this PR adds a new harness)

Not applicable. This does not add a new harness.

Clean-session transcript for "Let's make a react todo list"

Not applicable. This PR does not add a new harness.

Evaluation

• Initial prompt: compare what Superpowers installs for Codex and OpenCode, especially skills and hooks; then verify whether the OpenCode package bloat was reproducible.
• Eval sessions after the change: 3 packaging/runtime checks.
• Before: npm pack --dry-run --json git+https://github.com/obra/superpowers.git produced 145 entries and included top-level .github/, docs/, hooks/, scripts/, and tests/ paths. OpenCode also resolved the git plugin into cache with those same non-runtime paths.
• After: local npm pack --dry-run --json produces 52 entries: .opencode/plugins/superpowers.js, assets/, skills/, package.json, README.md, and LICENSE. OpenCode successfully loaded the local package path and initialized skills.

Verification run:

bash tests/opencode/test-package-files.sh
npm pack --dry-run --json
OPENCODE_CONFIG_DIR=/tmp/opencode/superpowers-pr-local opencode run --print-logs "Tell me about your superpowers"

Rigor

• If this is a skills change: I used superpowers:writing-skills and completed adversarial pressure testing (paste results below)
• This change was tested adversarially, not just on the happy path
• I did not modify carefully-tuned content (Red Flags table, rationalizations, "human partner" language) without extensive evals showing the change is an improvement

This is not a skills content change. The regression test includes negative checks for forbidden top-level paths and positive checks for required runtime files, including nested skill scripts.

Human review

• A human has reviewed the COMPLETE proposed diff before submission