slice 3.5c: seed 15 built-in skills across the 6 stacks

Hand-authored skill catalog anchored to real 2026-07 versions:
  - Rust 1.97.1 (stable), edition 2024
  - React 19.2.7, Server Components + Actions
  - TailwindCSS 4.3.3 (CSS-first config, Oxide engine)
  - three.js r185 (WebGPURenderer stable, BatchedMesh matured)
  - React Native 0.86 / Expo SDK 54+ (New Architecture default)
  - cargo-nextest 0.9.140, gitleaks 8.20+, cargo-audit 0.21+
  - Postgres 17 (18 in beta, don't rely on)
  - CUDA Blackwell, Metal Apple7+, ROCm CDNA3

Ships 15 skills across the categories:
  foundation/  workspace-repo-commit-protocol
               small-focused-commits
               tdd-red-green-refactor
               code-review-checklist
               int-xx-marker-protocol
               decompose-int-items
  rust/        write-rust-current-edition
               rust-error-handling
               cargo-test-driven-development
               rust-async-tokio-idioms
  backend/     postgres-migrations-forward-only
               postgres-index-selection
               api-pagination-day-1
  frontend/    react-19-server-components
               tailwind-v4-idioms
               component-4-state-model
  mobile/      expo-managed-vs-bare
               rn-flashlist-perf
  gpu/         gpu-coalescing-and-occupancy
               roofline-model
  threejs/     threejs-perf-and-teardown
  security/    cargo-audit-workflow
               secret-scanning-gitleaks

skills_loader.rs walks skills/**/*.md, parses YAML frontmatter
(name, description, when_to_use, tags), upserts via
skills_catalog::upsert_builtin. Idempotent per boot — bumps version
+ appends skill_versions row ONLY when body changes. Deterministic
sha256-derived ids so builtins are stable across boots.

Dockerfile copies skills/ to /etc/clawmates/skills. Server boot
task spawns loader alongside team_template_loader.

Follow-ups (Slice 3.5c continuation, future PRs):
  - 20-30 more skills (duckdb, shadcn composition, a11y, WebGPU
    migration, metal frame capture, rocprof, deep gitea forge
    integration, semgrep rulepacks)
  - Bind skills to team template roles (add [role.skills] refs to
    templates/teams/*.toml + wire template_role_skills population
    in team_template_loader)

Co-Authored-By: Claude Opus 4.7 <[email protected]>

skills/backend/api-pagination-day-1.md

@@ -0,0 +1,66 @@
+---
+name: api-pagination-day-1
+description: Every list endpoint paginates from the first version. Cursor-based over offset. Bounded max_limit. Includes total when cheap.
+when_to_use: You're the api_designer role, or a coder adding any `GET /...` endpoint that returns a collection.
+tags: [backend, api]
+---
+
+# List endpoints paginate from day 1
+
+Unpaginated lists are a production incident waiting to happen. The one time the endpoint is called with a million-row table, the response body fills the load balancer's buffer, memory spikes, and everything downstream 503s.
+
+## The pattern
+
+```rust
+#[derive(Deserialize)]
+struct ListQuery {
+    #[serde(default = "default_limit")]
+    limit: u32,
+    /// Cursor from a prior page's `next_cursor`. Opaque to the client.
+    cursor: Option<String>,
+}
+fn default_limit() -> u32 { 50 }
+const MAX_LIMIT: u32 = 500;
+
+#[derive(Serialize)]
+struct Page<T> {
+    items: Vec<T>,
+    next_cursor: Option<String>,
+    /// Present only when it's cheap to compute (COUNT(*) over a small
+    /// filtered set). Never for a full-table count.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    total: Option<u64>,
+}
+```
+
+## Cursor over offset
+
+- **Offset (`LIMIT 50 OFFSET 500`)** — Postgres scans and discards the first 500 rows on every request. Cost grows with page number.
+- **Cursor (`WHERE id > $cursor ORDER BY id LIMIT 50`)** — O(log n) always. The cursor is the last row's sort key, base64'd (or JWT-signed if you want tamper-detection).
+
+For clawmates, the standard cursor shape is `base64(json({"id": "...", "ts": "..."}))` — includes id + the ORDER BY tiebreaker so pages are deterministic even under concurrent inserts.
+
+## Bounds
+
+- **`limit.clamp(1, MAX_LIMIT)`** — server-side clamp, not just server-side validation. Never trust the client to respect `max_limit`.
+- **Return `413 Payload Too Large`** when a caller sends `limit=100000` if you'd rather they notice than have their traffic silently clamped.
+
+## Sorting
+
+- Every paginated endpoint has ONE canonical sort order.
+- Cursor must include the sort key + a tie-breaker (usually `id`). Otherwise two rows with the same sort key can be missed or duplicated across pages.
+
+## Total counts
+
+- Cheap: `SELECT count(*) FROM t WHERE small_indexed_filter`. Include it.
+- Expensive: unfiltered COUNT on a large table. **Don't run it.** Return `total: null` and let the UI show "50 of many".
+
+## OpenAPI
+
+The response schema declares `items`, `next_cursor`, and `total?`. Never return a bare array — you can't add a cursor later without a breaking change.
+
+## Anti-patterns
+
+- **`GET /foo` returning `[...]`** with no pagination shape. Every list route pays for future-proofing on day 1.
+- **`page=N&per_page=M`** — offset-based. Ships until traffic bites you.
+- **Cursor that includes an unsigned index into a mutable list** — reorders + inserts corrupt it. Cursor must be a stable identifier.