deepseek-harness/docs/rfc/implemented/simplification/2026-07-04-prune-producerless-vocabulary-variants.md

RFC: Prune producer-less vocabulary variants (block cache hints, the agent message source, the continuation turn trigger)

Status: implemented

Problem

The merge-extensible vocabulary maps are designed to grow by declaration merging, and the codebase already states the admission policy on TurnEndReasonMap (packages/core/session/src/types.ts): a variant like refusal is "deliberately omitted until" an adapter or loop first emits it. Three declared vocabulary items violated that policy — each had no producer and no consumer, and two had not even a test:

• CacheHint and its cache?: CacheHint block fields on TextBlock/ToolResultBlock (packages/llm/llm/src/types.ts; the image block carried a third such field, which left with it — see the drop-image RFC). Nothing constructed a block with cache: anywhere — src, tests, and doc pastes all came up empty — and neither adapter read .cache: DeepSeek prompt caching is automatic, so the adapters map prompt_cache_hit_tokens OUT of responses without ever sending a hint IN. This was Anthropic-style cache_control surface with no provider that could honor it.
• MessageSourceMap.agent ({ kind: 'agent'; agentId: string }, same file). Zero constructors, tests included. Its intended producer shipped without it: the subagent backends send the parent's prompt to the child with no source, so it logs as { kind: 'user' }, and the generic envelope renderer interpolates source.kind without ever routing on it.
• TurnTriggerMap.continuation (packages/core/session/src/types.ts). The loop structurally cannot emit it — continuation happens within a turn as further steps, never as a new turn — and it constructs only message and injection triggers. The only writer was one hand-built test fixture needing an arbitrary non-message trigger (packages/support/llm-replay/tests/llm-replay.spec.ts), which an injection trigger serves equally; the only production trigger reader, the ACP bridge, filters on kind === 'message'.

Decision

CacheHint, its cache? block fields, the agent message-source variant, and the continuation turn-trigger variant are deleted: the shipped vocabulary carries none of them. The llm-replay fixture uses an injection trigger (any non-message trigger serves its purpose). The type-equiv pastes in core.md and session.md match the pruned maps — both symbols keep their rows in scripts/type-equiv.manifest.json, since each map survives minus a member — and the content-block vocabulary RFC's consequences record cache hints as producer-gated rather than as having a home, per implemented/AGENTS.md.

Each variant returns the day it gains a real producer, exactly as the maps are designed to grow: a caching feature re-adds cache together with the adapter that transmits it; subagent attribution re-adds agent together with the backend that stamps it and a consumer that routes on it; an auto-continue feature that genuinely starts new turns re-adds continuation with the plugin that emits it.

Alternatives considered

Why not keep them?

The content-block vocabulary RFC listed "cache hints … have a home" as a design consequence, and reserved slots do advertise intent. But an empty slot is contract surface every implementation and consumer must consider (must my adapter honor cache? must my renderer route agent sources?), and the sibling map's own JSDoc already rejects reservation-without-emitter — refusal and max_turn_requests are named as variants to add when something first emits them, not declared in advance. Holding already-declared dead variants to the same standard makes the vocabulary mean something: if it is in the map, something produces it.

Verification

rg for CacheHint, the agent message-source spelling, and the continuation trigger spelling returns only RFC records (this one, and the drop-image RFC's account of the image block's own cache field); the llm-replay fixture asserts the same replay behavior with an injection trigger; the core-data-structures pastes and the type-equiv manifest are in sync.

Consequences

Nothing operational changed — nothing could construct these values. The mirror-event removals (the boundary-mirror RFC, the stream-chunk RFC) touch only transient agent/* events, never the durable vocabulary, so there is no collision. Elsewhere the admission policy already holds: rejected, prompt/blocked, and hook/invoked/hook/result each have live producers — this RFC extends the same bar to the three variants that lacked one. The image block's own cache? field belongs to the drop-image RFC, which removed it together with the block; this RFC covers the two fields on the block types that remain.