chore(template): clean-slate template snapshot from bb4a0c7

Curated, product-agnostic snapshot of the post-story-04 tree: demo
content deleted, auth-only reference feature, web-next shell, all gates
green. Product-specific docs, ADRs 027-029, PRDs/epics/archive, editor
library traces, and product naming are curated out; generic template
repairs (coverage provider devDeps, root test:coverage script, live
lint fixes, root-only release-please) are kept. See TEMPLATE.md for
provenance, curation list, and usage.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016j8z4VHjedXDTjEDNg7qHK

docs/library-decisions/2026-05-14-superjson.md

@@ -0,0 +1,88 @@
+---
+package: superjson
+version: "^2.2.1"
+tier: core
+decision: approved
+date: 2026-05-14
+deciders: [Danijel Martinek]
+adr: null
+lastRevalidated: null
+is-sub-processor: false
+processes-pii: false
+filter-results:
+  license: MIT
+  types: native
+  maintenance: active
+  boundary-fit: pass
+  shadow-check: pass
+  eu-residency: n/a
+  cve-scan: clean
+  named-consumer: pass
+  socketRisk: clean
+verification-commands:
+  - npm view superjson license
+  - npm view superjson version
+  - pnpm audit --audit-level=moderate
+accepted-cves: []
+---
+
+## Filter: license
+
+<!-- Result: MIT -->
+
+`npm view superjson license` returns `MIT`. MIT is on the allowlist.
+
+## Filter: types
+
+<!-- Result: native -->
+
+superjson is authored in TypeScript and ships its own `.d.ts` declaration files. No separate `@types/superjson` package is needed.
+
+## Filter: maintenance
+
+<!-- Result: active -->
+
+Actively maintained. Last release < 18 months. Used widely in the tRPC and Next.js ecosystem.
+
+## Filter: boundary-fit
+
+<!-- Result: pass -->
+
+superjson is the serialization transformer used by the tRPC layer (`@repo/core-shared`) to handle non-JSON-serializable types (Dates, Maps, Sets) over the wire. `core-testing` uses it for mock tRPC client setup. No boundary rules restrict superjson to a specific tier.
+
+## Filter: shadow-check
+
+<!-- Result: pass -->
+
+superjson is the sole tRPC-compatible serialization transformer in the workspace. No competing serializer (devalue, msgpackr, etc.) is present.
+
+## Filter: eu-residency
+
+<!-- Result: n/a -->
+
+superjson is a pure serialization library with no network communication, telemetry, or data transmission. EU residency does not apply.
+
+## Filter: cve-scan
+
+<!-- Result: clean -->
+
+`pnpm audit --audit-level=moderate` reports no advisories against `superjson` at the time of this trace.
+
+## Filter: named-consumer
+
+<!-- Result: pass -->
+
+`@repo/core-shared` uses superjson as the tRPC transformer. `@repo/core-testing` uses superjson for mock tRPC client configuration. Named, non-hypothetical consumers exist today.
+
+## Prompt: replaces
+
+superjson replaces the default JSON-only serialization in tRPC, which would fail silently when Date objects or other non-JSON types are passed through procedure calls.
+
+## Prompt: migration-cost-out
+
+Low. superjson is used as the `transformer` option in the tRPC router and client configuration — two call sites in `core-shared`. Replacing it requires swapping the transformer and ensuring the replacement handles the same non-JSON types. No feature package references superjson directly.
+
+## Prompt: alternatives-considered
+
+1. **devalue** — Supports more types but is less mature in the tRPC ecosystem; superjson is the de-facto tRPC transformer standard.
+2. **JSON-only (no transformer)** — Rejected because it silently loses type fidelity for Dates and breaks any use case that returns or receives a `Date` value.