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deepseek-harness/docs/rfc/implemented/architecture/2026-06-13-twin-llm-adapters.md
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Tianyi Cui e6fad266a6 docs(rfc): define and enforce a uniform RFC format; adopt it across the corpus
Define the in-file RFC contract in docs/rfc/README.md § The file format:
the header block (`# RFC: <title>` plus a dateless Status enum
cross-checked against the lifecycle folder), the per-lifecycle body
skeleton (a Problem opener everywhere; Proposal/Alternatives considered/
Acceptance criteria/Risks in proposed/; present-tense Decision/
Consequences with proposal-era headings banned in implemented/; the
frozen proposal shape in rejected/), and a mandatory Alternatives
considered section with a date-fenced grandfather comment for pre-format
RFCs whose alternatives are not reconstructible from the record.

Enforce it with a new doc-sync gate, scripts/verify-rfc-format.ts, and
normalize all 112 RFCs to it: ~15 Status-line spellings collapse to the
enum, 29 Context openers become Problem, the 39 legacy-format XXX debt
markers are resolved and banned from reappearing, proposal-era sections
in implemented RFCs are rewritten to shipped reality (including the
web/fs/subagent seam RFCs' migration plans and test checklists, closing
the doc-tiers deferred-work item on the web seam), every RFC gains an
Alternatives considered section or the grandfather comment, and the
bilingual pair is re-mirrored and re-recorded.

Move the generated index tables out of README.md into a fully generated
docs/rfc/INDEX.md — gen-rfc-index now writes the whole file, and
verify-rfc-classification checks its freshness and rejects index-shaped
rows in the curated README — which makes room for the format contract to
live in the README front door instead of a separate FORMAT.md.

The decision record, and the first RFC written in the new format, is
docs/rfc/implemented/process/2026-07-05-uniform-rfc-format.md.
2026-07-05 22:58:25 +08:00

2.8 KiB

RFC: Two LLM adapters as a design-verification twin

Status: implemented

Problem

dsh-llm owns a provider-neutral streaming vocabulary — the StreamChunk protocol (block-start, text-delta, reasoning-delta, tool-call-delta, block-end, usage, finish) and the content-block types (the content-block vocabulary). A vocabulary defined against a single adapter risks baking that adapter's quirks into the "neutral" contract: anything the one implementation happens to do becomes the de-facto spec, and the abstraction is unverified until a second provider arrives — by which point the leak is expensive to fix.

Decision

Ship two adapters against the one contract from the start, deliberately built on different internals:

  • dsh-llm-deepseek — hand-rolled fetch + SSE parsing against the DeepSeek API.
  • dsh-llm-pi-ai — the same endpoint through the @earendil-works/pi-ai library (its own event vocabulary).

The rule they enforce: anything the StreamChunk vocabulary cannot express for BOTH implementations is a core-vocabulary bug, caught immediately rather than at the next provider. The pair pinned down conventions now documented on StreamChunk in dsh-llm/src/types.ts: usage emitted before finish, nothing after finish, tool-call arguments as raw JSON strings end-to-end, and the two sanctioned error paths (throw from stream() or end with finish {kind:'error'|'aborted'}) that a consumer must handle on both sides — a divergence the library-backed adapter surfaced that a single hand-rolled adapter would have hidden.

Alternatives considered

  • A single adapter — less code and half the e2e cost, but leaves the "provider-neutral" claim unverified; the vocabulary would encode DeepSeek-via-fetch assumptions silently.
  • A mock second adapter — cheaper but doesn't exercise a real provider's wire quirks, so it proves little. The twin is real-on-real.

Consequences

Double the adapter maintenance and double the key-gated e2e surface (both adapters cover V4 Flash and Pro across representative thinking/effort modes). Bought: a continuously-verified neutrality guarantee for the most leak-prone abstraction in the codebase, and a worked second example for adapter authors. The two share the core Config shape (apiKey/baseURL/models) so a deployment swaps mostly one line, but the reasoning knob differs — dsh-llm-deepseek takes thinking/reasoningEffort, dsh-llm-pi-ai takes a single reasoning level — so a swap translates that field. If the maintenance cost ever outweighs the verification value (e.g. once conformance tests from architectural conformance cover the contract mechanically), retiring the twin to a single adapter + the conformance kit would be a new RFC superseding this one.