CARD: scaffold-e-fast-loop — Per-Cell Fast Verification Loop (TypeScript)

Band 1 — Identity & Recognition

02Classification: layer=E (verification) + H (weak-reader); mechanism=scaffold E.

03Intent: Guarantee every cell is independently type-checkable and testable in seconds (tsc --noEmit -p <cell> + vitest run <cell>), so an agent's edit→check→read-error→edit loop gets a first signal fast enough to steer — the substrate that makes every other scaffold's pass/fail usable.

04Also Known As: tight feedback loop; incremental check; project-reference isolation; per-project typecheck; watch mode; agent-computer interface.

05Applicability / Recognition: Apply when — a cell cannot be checked without type-checking/building the whole repo; the only verification is a multi-minute CI run; an agent must wait minutes for a signal. Detector seed: tsc --noEmit -p <cell> or vitest run <cell> fails to run in isolation, OR the cell has no project reference / vitest project → recognition fires (verification locality beats capability, R3-007).

Band 2 — Justification & Tradeoffs

06Motivation: A weak agent in a bounded loop gets one signal per multi-minute CI run — useless. With tsc --noEmit -p <cell> + vitest run <cell> returning in seconds (sub-second under the TS 7 / "Corsa" native compiler, ~10× faster checking), the same agent iterates ten times in the budget that previously bought zero feedback. The interpreter-budget result confirms: more local runs help agents that can use feedback; the loop is the amplifier.

07Structure & Participants: Cell isolation (a project reference / a vitest project) · Fast checker (tsc --noEmit -p + vitest) · Structured error (Class F) · Budget guard (first signal < ~60s).

08Collaborations: Runs Classes C/D/G checks and the type-level tests (guide §12); consumes Class B's compile checks; emits Class F diagnostics. The raid executor runs this per batch.

09Goals / Non-Goals: Goals: sub-minute first signal per cell; make the loop the standard agent workflow. Non-Goals: NOT replacing full CI (still runs at merge); does NOT create capability — scaffolds amplify, they do not create.

10Consequences: (+) every other scaffold becomes loop-usable; (+) iteration count rises within budget; the native Corsa compiler sharpens this further. (−) requires cells genuinely isolable (drives §3 cell design); barrel-file sprawl breaks project-reference isolation; (−) fast checks may miss what full CI catches — gate-mode checks backstop.

11Alternatives: whole-repo tsc/CI only (too slow for an agent loop); manual testing (not mechanical). Neither is a substitute.

12Risks & Assumptions: assumes cells are isolable; god-modules and giant barrels break this (anti-pattern). Sunset: none — the loop is foundational.

13Evidence & Transfer-strength: R3-007 (verification locality, theory), R2C interpreter-budget result (more runs amplify capable agents, benchmark), BLD-010 (30–60s practical threshold). Class: benchmark + theory. Tag: [E-strong].

Band 3 — Operation

trigger: WHEN a cell lacks a sub-minute isolated check, OR verification requires a full-repo typecheck/build THEN apply
mode: gate            # a structural precondition, verified at merge
routine:
  1. Make the cell an independently checkable unit (a project reference + a vitest project).
  2. Provide `tsc --noEmit -p <cell>` scope for it.
  3. Ensure `vitest run <cell>` runs in isolation, < ~60s.
  4. Wire the cell's Class C/D/G + type-level checks into that command.
  5. Confirm first-signal latency is within budget; if not, narrow the project or reduce test case counts.
checker: harness assertion `cell-fast-loop-present` (cell type-checks+tests in isolation under budget)
raid_role: layer=infrastructure; order=after:cell-boundaries; batch=cell
budget: active_rules=1; first_signal=<60s by definition