User Story

As an adopter running ApexYard against a domain-specific codebase, I want Rex to load domain-specific review notes when a PR touches files in that domain, so that reviews catch domain-specific gotchas that pure code-and-ticket context misses (e.g. GitHub EMU migration scripts must handle private-fork access; Stripe webhook handlers must verify the Stripe-Signature header).

Acceptance Criteria

Stage 1 — Path-globbed domain handbooks (this ticket's MVP)

• New handbook category handbooks/domain/<area>/*.md discovered by Rex on every review
• Each handbook supports a paths: frontmatter field (list of globs). Rex loads the handbook only when the PR diff matches at least one glob (e.g. paths: ['scripts/github-emu-migration/**'])
• When paths: is absent or empty, the handbook always loads (foundational domain rules)
• ENFORCEMENT: blocking marker honoured (same shape as architecture/general/language handbooks)
• Custom-handbooks layer: <private>/custom-handbooks/domain/<area>/ discovered alongside the public tree, both loaded when matched
• handbooks/README.md documents the new category with the frontmatter convention
• handbooks/domain/README.md explains path-mirroring + the paths: field + a worked example
• AgDR records the design decision (why path-glob + frontmatter over a config table)
• No regression on existing architecture / general / language discovery

Stage 2 — Codify-rule capture (follow-up ticket)

• /codify-rule skill takes a human comment + diff context and proposes a handbook entry
• Operator reviews + accepts/rejects via Y/N before the handbook is written
• Captured rule includes the source PR for traceability

Stage 3 — Auto-propose from PR stream (follow-up ticket)

• /enrich-domain <area> skill walks recent merged PRs that touched the area
• Proposes additions Rex would have benefited from (new error messages, conditional branches, AgDR references)
• Operator-approved per finding

Design Notes

No UI changes — this is a Rex agent-prompt change + handbooks/ tree extension + two follow-up skills.

The framework layer change is small: Rex's prompt (.claude/agents/code-reviewer.md § 8) gains a fourth discovery glob alongside architecture / general / language. Path-match logic lives in Rex's prompt (no new hook needed — the glob runs at review time, not at edit time).

Out of Scope

• External-doc auto-fetch at review time. Tempting for ingesting GitHub's EMU docs, but introduces a freshness-versus-reproducibility tension we don't want in CI-class agents. Stays out unless an operator explicitly asks.
• Per-team / per-project handbook overrides — handbooks remain framework-level (with the custom-handbooks layer for split-portfolio adopters). Already deferred per the existing handbooks design.
• Stage 2 + Stage 3 implementations — included in ACs as follow-up scope but implemented as separate tickets so this MVP can land first.

Effort Estimate

Stage 1 only: ~2 days. Stages 2 + 3 are separate tickets.

Glossary