Implements make pre-pr chain: lint -> build -> test -> content validation -> fixture staleness. Branch-specific variants: pre-pr-server, pre-pr-client, pre-pr-content. Fixture staleness is a blocker (exit 1) — stale fixtures cause false positive client tests. Spec from hoshe-round3.md Section 5. Tickets: #460, #465 Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>