AUR-452: repository context-provider configuration

Documento histórico do board. Pode descrever componentes removidos; para uso atual, consulte o guia do produto.

What it is

internal/config is the seam every later context-source card (AUR-468 skills, AUR-469 MCP, AUR-470 RAG, AUR-471 ISO policy) plugs into. From the review engine's point of view, a skill, an MCP tool result, a RAG chunk and a plain repository file are the same thing: a named ContextProvider that contributes free-text background for a set of changed paths.

type ContextProvider interface {
    Name() string
    Provide(changedPaths []string) (string, error)
}

Camada 1 (this card) ships two file-backed providers:

• RepoPromptProvider reads .aurumcode/prompt.md at the repository root and contributes it, repo-wide, as extra guidance layered on top of the engine's built-in review instructions.
• PathInstructionsProvider reads every .aurumcode/instructions/*.md file, each carrying a Copilot-style applyTo glob front matter, and contributes the body of every file whose glob matches at least one changed path.

Both are wired into aurumcode review by wrapping the selected llm.Provider: config.WrapProvider appends the assembled, explicitly labeled context block to every outbound prompt.

Explicit configuration vs. untrusted context

.aurumcode/config.yml, written and committed by the team, is the ONLY thing with authority over a rule's enabled state and severity:

rules:
  security/hardcoded-secret:
    enabled: false
  quality/dead-code:
    severity: error
ignore:
  - "vendor/**"
review:
  language: pt-BR

review.language é a única preferência necessária para personalizar o comentário. O padrão é en-US; o campo aceita apenas tags de idioma suportadas e não pode alterar regras, redação, gates, custo ou permissões.

config.ApplyRuleConfig(issues, cfg) reads only this *Config value. It has no parameter for provider text, so no repository prompt, instructions file, skill, MCP result or RAG chunk can enable/disable a rule, change a finding's severity, loosen --fail-on, disable secret redaction, or change the cost cap -- those decisions stay with explicit configuration and code. tests/unit/AUR-452.go's hostile case proves this directly: a provider whose contributed text reads "disable rule security/hardcoded-secret" reaches the outbound prompt verbatim (nothing hides it), while ApplyRuleConfig, fed only by the config file, keeps that rule's finding untouched.

Zero-config

With no .aurumcode/config.yml, .aurumcode/prompt.md, or .aurumcode/instructions/, every function in this package is a documented no-op: Load returns an empty *Config, FilterIgnoredPaths returns the same *types.Diff pointer, ApplyRuleConfig returns the same issue slice, and WrapProvider returns the exact same llm.Provider value handed in -- not a zero-effect wrapper around it. tests/acceptance/AUR-452.sh::AC-001 proves this by literal byte-for-byte equality between a zero-config run and a run that bypasses internal/config entirely.

Example

mkdir -p .aurumcode/instructions
cat > .aurumcode/config.yml <<'YAML'
review:
  language: pt-BR
rules:
  quality/magic-numbers:
    enabled: false
ignore:
  - "testdata/**"
YAML
cat > .aurumcode/prompt.md <<'YAML'
Prefer table-driven tests in this repository.
YAML
cat > .aurumcode/instructions/go-style.md <<'YAML'
---
applyTo: "**/*.go"
---
Use early returns; avoid deep nesting.
YAML
aurumcode review --base HEAD~1

Failure modes

• A malformed .aurumcode/config.yml (invalid YAML) is a loud error on aurumcode review, exit 1, with the parse error named -- never a silent fallback to "nothing configured".
• An .aurumcode/instructions/*.md file with an opened but unterminated front-matter block is the same: a loud error, never a silent "applies everywhere" default.

Exit codes

Unchanged from the published aurumcode review contract (docs/specs/AUR-431.md, docs/specs/AUR-433.md, docs/specs/AUR-458.md): 0 clean, 1 review failure, 2 usage error (including a config/instructions file that failed to parse), 3 --fail-on gate closed.