chore(guardrails): add instructions and formatter config (8/8)

[terisuke]

Issue for this PR

Closes #116

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Completes the final 2 of 8 guardrails profile configuration items in opencode.json:

1. instructions: "Read and follow the rules in AGENTS.md at the profile root." — directs every session to load the co-located AGENTS.md rules.
2. formatter: { "enabled": true, "command": "npx prettier --write" } — enables Prettier auto-formatting.

Config completion: 8/8 ✅

Setting	Status
model	✅
small_model	✅
autoupdate	✅
dangerous ops deny	✅
.env protection	✅
git push control	✅
instructions	✅ (this PR)
formatter	✅ (this PR)

How did you verify your code works?

1. JSON validity verified (parsed with json.load)
2. $schema field remains first key
3. Typecheck: bun turbo typecheck — 13/13 pass

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[Copilot]

Pull request overview

Completes the last two Guardrails profile configuration items in packages/guardrails/profile/opencode.json, intending to (1) direct sessions to the profile’s rules and (2) enable automatic formatting.

Changes:

• Add an instructions entry to the Guardrails profile config.
• Add a formatter entry intended to run Prettier.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

instructions is defined in the config schema as an array of strings (instruction file paths / glob patterns / URLs), but this change sets it to a single string. With the current Zod schema (instructions: z.array(z.string())), this will cause config validation to fail and prevent the profile from loading. Change this to an array (e.g., include the profile’s AGENTS.md path/pattern such as "AGENTS.md").

Suggested change

	"instructions": "Read and follow the rules in AGENTS.md at the profile root.",
	"instructions": [
	"AGENTS.md"
	],

[Copilot]

formatter config shape here doesn’t match what OpenCode expects. The schema defines formatter as either false or a record keyed by formatter name, where each entry can set disabled, command (string array), environment, and extensions. The proposed { enabled: true, command: "npx prettier --write" } will fail validation (unknown keys, and command must be an array). Update to the record form (e.g., configure the prettier formatter entry with a string[] command, including $FILE substitution if needed).

Suggested change

	"enabled": true,
	"command": "npx prettier --write"
	"prettier": {
	"command": ["npx", "prettier", "--write", "$FILE"]
	}