Behaviours and polish

M4 was where the agents stopped being decoration and started reading the room.

Behaviours follow the route. The island gained a small FSM: wander on home, flee from the screen centre on a new custom 404, and align — calm, faint — behind a case study’s Architecture chapter (10daa09). The maths stayed pure functions over a seeded RNG, so align and flee arrived with their own unit tests rather than an eyeball check. Pressing d now draws the real velocity, steering-force, and wander-circle vectors in instrument amber (8ae1c92) — the curtain-pull the brief always wanted. One claim I had to scope honestly: the ~1s behaviour blend only holds for transitions inside one mounted island; cross-route changes are fresh per-page mounts, so the PRD wording was narrowed to match (918c769).

A review finding reversed an earlier call. In M2 I removed the focus ring on chapters because it flashed a box on every arrow press — the right instinct, the wrong mechanism. The M4 adversarial review showed the no-ring region was a real WCAG 2.4.7 (Focus Visible) failure, a Must rather than a preference. The fix kept the instinct and addressed the cause: chapter changes no longer steal focus at all, an aria-live region announces the change, and a subtle inset bar marks the region only when a keyboard user genuinely tabs onto it (cc9f16b, 276052f). Accessibility and taste were never in conflict; the first design had just confused them.

Performance as a feature. Per-project Open Graph cards now render at build from one branded template, beside a sitemap, canonical URLs, and a domain-tracking robots.txt (5f204b1). The receipt is the number: Lighthouse 100/100/100/100 on the home page, a case study, and a note, with 11.8 KB of JavaScript site-wide against a 50 KB budget.

The near-miss worth recording. One SEO commit shipped a TypeScript error that astro build waved through — it strips types — which only astro check caught, in CI (c80e59c). The gate worked; the local gate had not. It now chains check, build, and test behind a single exit code (e2b90d9), so verify-before-commit can no longer be fooled by a truncated log.