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ImageBlock had no production producer and every consumer dropped it: the deepseek serializer skipped it, the pi-ai converter skipped it as unrepresentable, the ACP bridge neither advertises image prompt capability nor forwards image blocks, and compact-basic charged a flat 85-token estimate and rendered an [image] placeholder. A block constructed today would silently vanish from the wire — the vocabulary advertised a capability no path honors, the silent-data-loss shape the defensive patterns warn against. The only constructors were tests pinning the skip/estimate branches. Remove ImageBlock and its ContentBlockMap entry (its cache?: CacheHint field leaves with it; CacheHint itself and the other two cache? fields are out of scope). compact-basic loses its explicit image estimate and placeholder arms (the merge-extensible default arms absorb the case); the deepseek serializer, pi-ai converter, and ACP codec already handled image in their default arms, so only their image-naming comments change. The codec's inbound rejection of ACP-protocol image prompt content stays — that guards wire content a client can send regardless of our vocabulary. Tests that constructed harness image blocks to pin the removed branches are dropped (the 85-token estimate pin) or retargeted onto plugin-added block types / other non-text blocks, which the surviving default arms own. Docs, the type-equiv pastes, and the content-block vocabulary RFC's block list and multimodal-home consequence are updated in the same change; the RFC moves to implemented/ and the index is regenerated. A real multimodal feature reintroduces image via declaration merging together with the adapter mapping, ACP advertisement, and compaction pricing that honor it.
28 lines
4.2 KiB
Markdown
28 lines
4.2 KiB
Markdown
# RFC: Drop the `image` content block until a path can honor it
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Status: implemented (proposed and accepted 2026-07-04)
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## Problem
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`ImageBlock` (`packages/llm/llm/src/types.ts`) had no production producer, and every consumer on every path DROPPED it: the deepseek adapter's serializer skipped image blocks (a documented MVP limitation), the pi-ai converter skipped them as unrepresentable, the ACP codec neither advertises image prompt capability nor forwarded image blocks outbound and REJECTS image prompt content inbound, and the compaction estimator charged a flat token constant and rendered `[image]`. An `ImageBlock` constructed then would silently vanish from the wire — the vocabulary advertised a capability no path honored, which is the silent-data-loss shape AGENTS.md's defensive patterns warn against. The only constructors anywhere were tests pinning the skip/drop/estimate branches.
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## Decision
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Remove `ImageBlock`, its `ContentBlockMap` entry (and its `cache?: CacheHint` field with it), the explicit `image` estimate/placeholder arms in compact-basic, and the image-naming comments in the deepseek serializer's, pi-ai converter's, and ACP codec's default arms — those default arms absorb the case the way they absorb any unknown block type. Updated in the same change: the vocabulary line in [architecture.md](../../../architecture.md), the block list in `packages/llm/llm/README.md`, the deepseek README's image-skip row, the pi-ai README's images-not-representable row, the compact-basic README's image-estimation and `[image]`-placeholder rows, the pastes in [core.md](../../../core-data-structures/core.md) and [llm-streaming.md](../../../core-data-structures/llm-streaming.md), and the [content-block vocabulary RFC](../architecture/2026-06-11-content-block-vocabulary.md)'s block list and multimodal-home consequence per [implemented/AGENTS.md](../AGENTS.md); the tests that constructed image blocks to exercise the removed branches were dropped (the estimate pin) or retargeted onto the merge-extensible default arms (plugin-added block types). The ACP codec's inbound rejection of image PROMPT content is unaffected — that guard is about protocol content a client can send regardless of our vocabulary, and it stays.
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## Why not keep it?
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This was the most contested cut in the batch. Multimodal input (screenshots) is a plausible near-term coding-agent feature, and the [content-block vocabulary RFC](../architecture/2026-06-11-content-block-vocabulary.md) reserved the slot deliberately. Two responses. First, `ContentBlockMap` is merge-extensible by design: a real multimodal feature reintroduces `image` in core in the same coordinated change that maps it in the adapters, advertises and renders it in ACP, and prices it in compaction — the producer and its consumers arrive together, which is how the map is meant to grow. Second, the middle option — keep the type but make adapters throw UNSUPPORTED instead of silently dropping — converts this into exactly the shape the sibling request-knobs proposal (`2026-07-04-drop-inert-request-knobs`) argues against: surface whose only implementation is rejection. Absence (a compile error at the would-be producer) is strictly clearer than either silent loss or universal throw.
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The recorded fallback, had review landed on keeping the slot: keep `ImageBlock` but replace every silent skip with a loud rejection, and document that policy in the vocabulary — the silent drop was the one state with no defender. Review landed on removal; the fallback stands as the documented alternative should the slot ever return ahead of a full feature.
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## Acceptance criteria
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- No `ImageBlock` / harness `type: 'image'` block construction outside this RFC; the codec's inbound ACP-image rejection still passes its tests.
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- Adapter/codec/compaction switches handle the case through their unknown-block default arms (pinned by the plugin-added-block tests).
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- Doc pastes, the manifest, and the architecture vocabulary list updated; `pnpm run doc-sync` green.
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## Risks
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Re-adding a core vocabulary type later touches several packages at once — but that coordinated change is the shape a real multimodal feature needs anyway (adapter mapping, ACP advertisement, compaction pricing), and none of it existed to preserve.
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