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Record cover image picker decision
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Jeremy Herve
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(Jun 10, 2026, 9:20 AM +0200)
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docs/decisions/0016-cover-image-picker.md
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docs/decisions/0016-cover-image-picker.md
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# 0016. Per-article cover image picker
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**Status:** Accepted
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**Date:** 2026-06-10
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## Context
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Until now the Bluesky card thumb was auto-derived from the first usable content
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image (`firstImageBlobRef`, Decision 0014), and articles had no explicit cover.
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The standard `site.standard.document` lexicon already defines an optional
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`coverImage` blob field (`image/*`, ≤1MB) that was never populated (deferred in
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Decisions 0006 and 0014).
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## Decision
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Add a per-article cover image picker as a strip BELOW the block editor (outside
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the editor canvas). It reuses the existing `mediaUpload` + blob-registry path
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(no second isolated-block-editor instance) and writes the chosen blob to
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`site.standard.document.coverImage`.
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Thumb resolution becomes: explicit `coverImage` → `firstImageBlobRef(blocks)` →
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omit. The auto-pick is now the fallback, so nothing regresses for articles
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without an explicit cover.
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The 1MB cap (equal to `BSKY_THUMB_MAX_BYTES` and the lexicon `maxSize`) is
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surfaced in the picker UI as helper text and as the oversize rejection message.
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## Consequences
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- Covers persist on the document, survive edits (re-previewed via `getBlob`), and
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become available to future reading-page/OG/RSS surfaces (still unwired —
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separate follow-up; see the 2026-06-09 OG design which deferred this field).
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- This partially supersedes Decision 0014: the first-image pick is retained only
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as the fallback when no explicit cover is set.
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- Consuming `coverImage` on the reading page / OG tags remains out of scope.