Build Log

Arc Slice — Recovering the Transcript Measurement Spike

July 18, 2026

An unplanned VS Code close lost the live session mid-build. The spike files survived on disk untouched by git — recovered them, verified all six review fixes actually landed (not just claimed), closed the one open gap, and got the work into version control for the first time.

ForgeKit OSArc SliceSession Recovery

22 → 27

regression tests, before and after closing the transcript_reference gap

6/6

prior review findings confirmed already fixed on disk, verified by running the suite, not by reading comments

files recovered and committed — spike had zero git history before this session

Timeline

Start

Untracked spikes/ folder found

git status showed forgekit-os/scripts/spikes/ untracked, file timestamps after the last commit — real WIP, not noise

+10m

Prior review pasted, checked against disk

Read all three spike files; code comments and test suite showed v4 already implemented 5 of 6 review fixes

+15m

Ran full test suite

22/22 passing — confirmed the fixes were real, not just claimed in comments

+30m

Closed the transcript_reference gap

Added resolvedStartUuid to the DAG walk, built the candidate transcript_reference shape, added 5 new tests — 27/27 passing

+40m

Committed and retro'd

First commit for this spike; gate evidence marker rewritten fresh per Monorepo Safety Gate

What shipped

Recovered forgekit-os/scripts/spikes/ (transcript-adapter.mjs, derive-arc-preview.mjs, run-arc-spike.mjs, 15 test fixtures) — a spike that measures a Claude Code JSONL transcript into structured, reproducible turn-level metrics

Verified (by running tests, not reading comments) that all 6 findings from a prior review were already fixed: inclusive range semantics, DAG-based mainline selection instead of chronology/linked-list, four independent range-quality dimensions replacing a misleading 'truncated' flag, end_boundary_status, and deterministic structured output + hash

Closed the one remaining gap: added resolvedStartUuid to transcript-adapter.mjs's mainline walk, and built the candidate transcript_reference output in derive-arc-preview.mjs — the minimal durable pointer (provider, provider_session_id, inclusive start/end entry_uuid, aggregate session_coverage) with all diagnostic/derived fields correctly excluded

Added 5 new regression tests for transcript_reference (null in unbounded mode, correct shape in bounded mode, explicit --start honored, diagnostic fields excluded, session_coverage reflects ForgeKit anchors) — 27/27 total passing

First commit for this spike — it existed only on local disk before this session

“This is done. The pasted review text was the critique that produced v4 — and v4, sitting on disk from the crashed session, already implements every one of the six fixes.”
— Claude, on verifying the recovered spike against the pasted review before acting on it