Tianyi Cui
e6fad266a6
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.
30 lines
4.0 KiB
Markdown
30 lines
4.0 KiB
Markdown
# RFC: Record fork and mixed spawn+fork snapshot scenarios
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Status: implemented
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## Problem
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The [seed-boundary RFC](2026-06-22-fork-child-replay-seed-boundary.md) made fork-child replay route correctly: `dsh-llm-replay` derives a child's script from the events at or after its persisted `seedLength` boundary, so a fork child's inherited parent prefix is not replayed as the child's own model calls. But it shipped with **no recorded fork scenario** — the slice was exercised only by `llm-replay`'s unit tests (a synthetic child fixture) and a persistence round-trip test. The full-transcript snapshot tier, the one net that boots the real `acp-agent` and replays an end-to-end nested transcript, had only spawn children (`subagent-spawn`, `subagent-multi`). A fork-routing regression that left the unit tests green would still have escaped the tier built to catch transcript regressions.
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The snapshot infrastructure to express a fork scenario was already in place — both in-process backends are wired into `cordis.yml` / `cordis.snapshot.yml` as two model-facing tools (`subagent` → spawn, `subagent_fork` → fork), the harness harvests every child log, and replay forwards per-child fixtures keyed by `seedLength`. What was missing was a *recorded scenario* that drives a fork child through it.
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## Decision
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Record two scenarios against the real API, both replayed keyless in the default gate:
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- **`subagent-fork`** — the parent completes a turn that establishes a fact, then delegates one subtask via `subagent_fork`. The fork child inherits the conversation (its log carries a non-zero `seedLength`), so it can answer from the parent's context. This is the focused regression: the child fixture's `seedLength` is the boundary the replay slice depends on, recorded from a real fork rather than hand-synthesized.
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- **`subagent-mixed`** — the parent completes a turn, then delegates once via `subagent` (a fresh spawn child, `seedLength` 0) and once via `subagent_fork` (a fork child, non-zero `seedLength`) in one transcript. This is the mixed spawn+fork scenario the seed-boundary and per-session-replay RFCs both named as a future addition: one transcript exercises both transports and both branches of the slice (`seedLength` 0 = no-op, `seedLength > 0` = trim the inherited prefix), with the two children ordered spawn-then-fork by `createdAt`.
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### Why a completed turn-1 is required
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The fork backend seeds the child with the parent's **balanced completed-turn prefix** ([`completedTurnPrefix`](../../../../packages/subagent/subagent-fork)). A parent that forks on its very first turn has no completed turn to inherit, so the seed is empty (≡ a fresh spawn, `seedLength` 0) — which would NOT exercise the slice. Both scenarios therefore use a two-prompt input: the first prompt completes a turn (establishing a codeword the child is later asked to recall), the second delegates the fork. The recalled codeword in the child's transcript is incidental to the model's behavior; the load-bearing artifact is the child fixture's recorded `seedLength`, which the replay slice consumes.
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## Consequences
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- The fork-routing slice is now guarded at the full-transcript tier, not just by unit tests. Removing the `slice(seedLength)` (replaying the whole child log) turns **both** new scenarios red — the fork child receives the parent's recorded chunks instead of its own — proving the guard bites (verified red→green when the scenarios landed).
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- `subagent-mixed` is the first snapshot scenario to drive two *different* subagent backends in one transcript, exercising the per-session replay keying across a spawn and a fork child simultaneously.
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- Out-of-process (ACP) subagent replay remains a different shape (each child is its own process with its own replay) and is still tracked as `TODO(acp-subagent-replay)` — these scenarios are in-process only.
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- Re-recording (`pnpm run test:snapshot:record`) regenerates all four fork/spawn fixtures from the live API; the two new scenarios self-skip without a key like every recorded scenario.
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<!-- rfc-format: alternatives-not-recorded (pre-format RFC) -->
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