Tianyi Cui
2745879132
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.
RFCs
One kind of design doc lives here. An RFC records a decision or proposal that shapes this codebase — the why and what we gave up, the parts code and docs can't carry. (Earlier this split into separate "ADR" and "RFC" trees; they were unified, since most ADRs were simply implemented RFCs.)
Layout and naming
Every RFC has two axes, both encoded in its path — {lifecycle}/{class}/yyyy-mm-dd-topic-title.md:
- Lifecycle (the top-level folder) is the RFC's status, and an RFC moves between folders as that status changes:
proposed/— proposals reviewed before implementation; not yet built (or only partly).implemented/— the decision shipped. The file records what was decided and what was rejected, and is kept current with what actually shipped: when the code later moves a file, renames a package, or changes a key/default, the RFC is updated in the same change to match (facts only — paths, names, structure — not the decision itself). See implemented/AGENTS.md.rejected/— the proposal was considered and declined. Kept for the record so the rejection isn't re-litigated.
- Class (the nested folder) is the kind of decision — see Classification below.
The date in the filename is when the topic was first proposed (per git history). Cross-references between RFCs use relative markdown links ([topic](../../implemented/architecture/2026-…-….md)) — never bare prose or numbers — so they are mechanically checkable and survive moves between folders.
Classification
Each RFC is filed under exactly one class — the kind of decision it records. The class is encoded in the path (the folder is the label, so a file's location declares its class) and the set is closed: scripts/rfc-index.ts owns the canonical set, scripts/verify-rfc-classification.ts rejects any folder outside it, and the index tables below are generated from the tree (pnpm run gen-rfc-index rewrites the marker-delimited regions from each RFC's path, H1 title, and filename date; the gate fails when they are stale). Adding a new class means amending that const and this section, not just dropping a new folder. See the classification RFC for why the taxonomy is path-encoded and gated, and the index-generation RFC for why the tables are generated while this prose stays curated.
| Class | What it covers |
|---|---|
feature |
A new user- or model-facing capability. |
bug-fix |
Corrects a defect or closes a gap a postmortem surfaced. |
simplification |
Removes code, behavior, or surface area without adding a capability. |
architecture |
A structural decision about the shipped source — how packages relate, what the runtime vocabulary is. |
process |
Tooling, policy, or workflow around the code — gates, the package manager, vendoring — not runtime behavior. |
testing |
Test infrastructure and strategy. |
The architecture / process line: architecture is about the source we ship; process is the surrounding tooling and workflow. (refactor is deliberately absent — it overlaps simplification, whose discriminator, "does observable behavior change?", already covers it.)
When to write one
Write an RFC when a decision is durable (it shapes the codebase beyond a single function or package), contested (there was a real alternative a reasonable engineer might have chosen), and surprising (a future reader would otherwise ask "why on earth is it done this way?"). A proposal for substantial future work starts in proposed/; a decision already made starts in implemented/. Pick the class folder that matches the decision (see Classification).
Do NOT write one for a mechanical or local choice (a variable name, a one-file refactor), for anything already enforced and explained by a gate or a convention in AGENTS.md, or for a still-provisional decision tagged TODO(...) in the code — record those as TODOs and promote to an RFC only once they settle. An RFC is never edited into a different decision: supersede it with a new one and cross-link. (Editing an implemented/ RFC to track where its already-made decision now lives — a moved file, a renamed package — is not a different decision and is required, not forbidden; see implemented/AGENTS.md.)
Proposed
Feature
| Title | First proposed |
|---|---|
| Agent Client Protocol (ACP) support — drive the coding agent from external editors | 2026-06-14 |
| Multiplex concurrent ACP sessions over one connection | 2026-06-14 |
| Optional Code Mode — model writes TypeScript against an SDK of all tools | 2026-06-15 |
| Pre-tool input rewrite — a consistent design | 2026-06-30 |
Simplification
Architecture
| Title | First proposed |
|---|---|
| Runtime schemas for the event vocabulary (Zod vs the merge-extensible-map pattern) | 2026-06-16 |
| Extract a generic long-running tool runtime | 2026-06-20 |
Process
| Title | First proposed |
|---|---|
| API extractor reports | 2026-06-11 |
| Architectural conformance — dependency rules and the adapter kit | 2026-06-11 |
| Supply chain checks and vendor drift verification | 2026-06-11 |
| Discover package inventories instead of maintaining static lists | 2026-06-20 |
Testing
| Title | First proposed |
|---|---|
| Deterministic tests, the replay invariant fixture, and race stress | 2026-06-11 |
| Mutation testing as the coverage counterweight | 2026-06-11 |
| Single-source the acp-agent replay config | 2026-07-04 |
Implemented
Feature
Simplification
| Title | First proposed |
|---|---|
| Drop the mutable session summary | 2026-06-19 |
| Fold trace-only session facts into load-bearing events | 2026-06-20 |
Drop the unconsumed llm/adapter-change event |
2026-06-20 |
| Drop unconsumed assembled LLM convenience surfaces | 2026-06-20 |
| Prune dead methods from the persistence seam | 2026-06-20 |
| Keep one public stop primitive | 2026-06-20 |
| Stop mirroring durable boundaries as agent events | 2026-06-20 |
Split the filesystem seam — provider text mutations plus the dsh-fs-policy plugin |
2026-06-26 |
| Stop mirroring the token stream as an agent event | 2026-07-02 |
Drop the image content block until a path can honor it |
2026-07-04 |
Architecture
Process
| Title | First proposed |
|---|---|
| Doc-sync enforcement | 2026-06-11 |
| Mechanical quality gates over prose guidelines | 2026-06-11 |
| tsdown for JS bundling instead of dumble | 2026-06-11 |
| Vendor Cordis as source, not npm dependencies | 2026-06-11 |
| pnpm as the package manager instead of Yarn 4 | 2026-06-16 |
| TSC-first build and one tsconfig | 2026-06-17 |
| Markdown cross-link validity linting | 2026-06-18 |
Core-data-structures catalog and the ts type-equiv drift gate |
2026-06-20 |
| Generated cordis events + services catalog | 2026-06-20 |
| Classify RFCs by kind via path-encoded subdirectories | 2026-06-20 |
| Bilingual documentation via paired sibling files and a pairing gate | 2026-07-02 |
| Generated tool-schema catalog (boot-and-harvest) | 2026-07-02 |
| Generate the RFC index tables | 2026-07-04 |
Testing
| Title | First proposed |
|---|---|
| Property-based testing for protocol-shaped code | 2026-06-11 |
| ACP snapshot tests — record-once / replay-deterministic | 2026-06-19 |
| Real-API e2e in CI against the external DeepSeek API | 2026-06-19 |
Use session.jsonl as the only snapshot session-log artifact |
2026-06-20 |
| Persist the seed boundary so fork-child replay routes correctly | 2026-06-22 |
| Record fork and mixed spawn+fork snapshot scenarios | 2026-06-22 |
| Per-session snapshot replay for nested agents | 2026-06-22 |
| Hook snapshot matrix — end-to-end goldens for both bridges | 2026-07-04 |
Rejected
Simplification
| Title | First proposed |
|---|---|
| Persist assembled assistant messages, not stream chunks | 2026-06-20 |
| Drop ACP session/load until resume has a product shape | 2026-06-20 |
Drop ACP terminal _meta rendering |
2026-06-20 |
| Drop bash full-output spill files | 2026-06-20 |
| Drop durable step boundary events | 2026-06-20 |
| Drop unused session lineage metadata | 2026-06-20 |
| Fold the persistence interface into dsh-session | 2026-06-20 |
| Collapse tool-owned UI presentation | 2026-06-20 |
| Retire mid-turn steering | 2026-06-20 |
| Return the ACP bridge to one live session per connection | 2026-06-20 |
| Truncate interrupted final turns on load | 2026-06-20 |
| Prune the unimplemented subagent seam vocabulary | 2026-07-04 |
Architecture
| Title | First proposed |
|---|---|
| Deep-readonly public surfaces | 2026-06-11 |
| Make the shared example base providerless | 2026-06-20 |