[rianjs]

Summary

• replace seven exported page structs and nine endpoint wire validations with generic Page[T] and pageResponse[T]
• preserve endpoint-specific item validation, playlist total/next consistency, and mixed-media playlist-item decoding
• centralize search query construction

LOC delta: +97/-228 (net -131)

Validation observations

• SearchTracks intentionally performs no per-item validation; album and artist search require nonblank item IDs
• current-user playlists require valid playlist IDs and nonnegative item-count metadata
• playlist items retain their separate wrapper decoding and track/episode/local/unavailable validation rules
• Page.Total is retained because playlist mutation flows consume it to detect provider drift during traversal

Verification

• go build ./...
• go vet ./...
• make test
• golangci-lint run

Closes #31

[rianjs]

TDD assessment

Insufficient.

The shared invalid-page logic is otherwise well pinned:

• TestCatalogSearchRejectsMalformedPages sends {} for album and artist search and expects ErrInvalidResponse, so the new value-typed missing-outer-envelope/zero-value path is covered. TestSearchTracksRejectsInconsistentPaging separately covers missing and null items; adding {} there would be harmless redundancy, not a requirement for a generic helper.
• Search, traversal, and playlist tests exercise missing items, offset mismatch, limit mismatch, negative total, and over-limit items through page(). Saved tests exercise the same shared path for missing items, offset/limit mismatch, and negative total but omit over-limit items; that duplication is not necessary because another caller pins the generic branch and saved tests prove those endpoints route through it.

The blocking gap is the successful playlist-item page mapping: ListPlaylistItems reconstructs PlaylistItemPage without Total, so the existing response with "total":27 returns page.Total == 0. That is observable and breaks callers that use totals for traversal/provider-drift checks, yet all unit tests pass.

Cheapest fix: in TestListPlaylistItemsUsesCurrentFixedPathAndDecodesMixedItems, add the exact assertion page.Total == 27 (equivalently fail when page.Total != 27) alongside the existing offset/HasNext assertions. That one assertion catches the current regression; no broad per-endpoint duplication of every shared validation branch is needed.