7c400e9c02
Collapse docs/adr/ and docs/rfc/ into a single docs/rfc/ with proposed/, implemented/, and rejected/ subfolders. Every file is renamed to yyyy-mm-dd-topic-title.md, where the date is when the topic was first proposed (from git history). ADRs and RFCs that covered exactly the same topic are merged (property-based testing, session persistence); the umbrella RFC 005 stays split across its three implemented decisions, and RFC 006's deferred part-3 (API extractor reports) splits into its own proposed RFC. All cross-references become machine-checkable relative links instead of bare "ADR NNNN" / "RFC NNN" prose. Add a verify-md-links doc-sync gate (scripts/verify-md-links.ts) that checks every relative Markdown cross-link resolves, wired into doc-sync alongside verify-md-wrap. This makes the reorganization self-verifying: the same change that rewrote ~forty inter-doc links adds the check that proves none dangle. Document the cross-link convention in a new docs/AGENTS.md and record the gate as an implemented RFC. doc-sync, typecheck, lint, and the full test suite (667) all pass.
30 lines
3.1 KiB
Markdown
30 lines
3.1 KiB
Markdown
# RFC: Dev-mode invariants over compile-time deep-readonly
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Status: implemented (accepted 2026-06-13)
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<!-- XXX: legacy ADR/RFC body format, not yet normalized to a unified RFC template. -->
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## Context
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The session log is append-only by contract, but the types don't enforce it: `session.events` returns `readonly SessionEvent[]` whose *elements* are mutable, and `deriveMessages()` handed the logged `content` arrays/blocks out by reference. The loop then passes those derived messages into the `agent/request` waterfall and on to adapters, where mutating the request is sanctioned — so a request middleware could reach back and rewrite history, silently breaking replay equivalence and the derived-history guarantee. Separately, the event taxonomy (turn/step nesting, seq monotonicity, tool-call/result pairing, legal status transitions) was asserted only where individual tests happened to look.
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Two ways to defend the log: make immutability part of the type (`DeepReadonly<SessionEvent>` on the way out), or catch corruption at runtime in dev. The runtime-validation proposal took the runtime route; [the deep-readonly proposal](../rejected/2026-06-11-immutable-public-surfaces.md) took the type route.
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## Decision
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Reject the pervasive `DeepReadonly<T>` type flip. Instead:
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1. **Always-on:** `deriveMessages()` deep-clones the content it emits (one `structuredClone` per derived message). In-flight mutation of a request can no longer reach the log — this is the real fix, and it costs nothing meaningful next to a model call.
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2. **Dev-mode:** a new `dsh-invariants` plugin (pure listeners, off in production, on in tests and demos) asserts the event contract and `Object.freeze`s logged event data so any *other* code that mutates a logged event throws instead of corrupting silently. Seeded sessions are frozen and checked on `session/created` (the constructor copies the seed without emitting `session/event`).
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The invariants encode the *real* contract, not an idealized one: a `tool/call` may have no `tool/result` (a thrown `tools/execute` waterfall ends the step), and both `idle→disposed` and `running→disposed` are legal.
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`DeepReadonly` was rejected because it is compile-time only (a plugin casts straight through it), high type-noise across every log/message consumer and adapter, and would force readonly types through code where mutation is the sanctioned API. The clone draws the mutable/immutable boundary exactly at "logged vs in-flight" without any of that noise.
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## Consequences
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- History corruption is caught loudly in tests and demos, at zero production cost and zero type noise. The trade-off is that the guarantee is dynamic (a dev-mode tripwire) rather than static.
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- The invariants plugin doubles as executable documentation of the event taxonomy — the assertions are the contract.
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- `Session.events` keeps its `readonly SessionEvent[]` type; no consumer churn.
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- This folds in [the deep-readonly proposal](../rejected/2026-06-11-immutable-public-surfaces.md) — there is no separate deep-readonly record; this records the decision to *not* pursue that approach. `InvariantError` is a plain `Error` with a `code` for now; a later taxonomy change can promote it.
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