tegwick 0c1eb9ecba ADR-0004: ratify AM-4a and AM-4b (maintainer decision)

Discharges the open item T07 raised. Values unchanged at 250,000 and
350,000; what was missing was a reviewed decision behind them, since
they had been set by the implementer in the commit that measured them
and that also changed the feature gating being measured.

The ADR supplies the argument T07's test requires -- why the targets
bind on FUTURE work rather than merely passing present work:

  AM-4a leaves 3,750 lines of headroom (1.5%), about one small crate,
  so any new shipped-runtime dependency breaches it almost immediately.
  That is intended: the shipped runtime should be effectively frozen.

  AM-4b leaves 32,979 lines (10.4%), deliberately looser -- dev tooling
  should absorb one moderate dependency without a spec change, not two.

  Both are ceilings on a quantity that only grows by choice. Nothing
  drifts across them; only adding a dependency does.

Falsification condition stated: if a later pass raises AM-4a to
accommodate a dependency it wants, that is the failure the ceiling
exists to catch, and the answer is an ADR arguing for the dependency.

First ADR written under the correction/retarget test; sets the shape.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

2026-07-31 09:45:35 +02:00

4 KiB

Raw Blame History

ADR-0004: ratify AM-4a and AM-4b

status: accepted date: 2026-07-31 decided by: maintainer (Bernd Worsch), 2026-07-31 tier: S (structural S — ratifies an existing target, creates no capability; chaos d4=3) supersedes: nothing; discharges the open item raised by CB-WP-0003 T07 references: GameKernel.md §4, InnerLoop.md §Step 4 (correction vs retarget), history/260731-inner-loop-rule-audit.md

Why this ADR exists

CB-WP-0003 T07 added a mechanical test separating a correction (the instrument disproved the target; the implementation did not change) from a retarget (the same commit moved both the target and the code it measures). AM-4a/AM-4b failed that test: they were set at 250,000 and 350,000 in commit 4be6e02, by the implementer, after seeing the measured 246,250 — and that commit also changed the feature gating the metric measures.

The reasoning was recorded at the time and is defensible. The structure was not, and the audit flagged both targets as unratified: make dep-weight has been enforcing thresholds no reviewed decision stood behind.

Decision

AM-4a (≤ 250,000 lines, shipped runtime) and AM-4b (≤ 350,000 lines, dev toolchain) are ratified as written. No values change.

The old target, and why it was abandoned

AM-4 originally read ≤ 20 transitive crates, set against boardgame.io's 120 npm packages. Retired for two measured reasons:

Unreachable without undoing this spec's own contracts. K5 (seeded ChaCha) and K7 (SHA-256) cost 12 crates between them. The measured ladder showed nothing reached 20 except reimplementing one of those primitives — trading an audited cryptographic implementation for a scoreboard number.
Crate count does not compare across ecosystems. Rust splits crates far more finely than npm, so the original 33-vs-120 comparison flattered us while the ≤20 target punished us, for the same reason.

The measurement that motivated the change

At the time of the retarget, make dep-weight:

configuration	crates	third-party LOC
shipped-runtime (`--no-default-features`)	23	246,250
dev-toolchain (default features)	29	317,021
own source	—	3,443

Why these targets bind on future work rather than merely passing present work

This is the question T07 requires an ADR to answer, and it is the reason ratification is defensible rather than a rubber stamp.

AM-4a leaves 3,750 lines of headroom — 1.5%. That is roughly one small crate. Any dependency added to the shipped runtime breaches it almost immediately, which is the intended behaviour: the shipped runtime is meant to be effectively frozen, and the target enforces that a new runtime dependency is a decision someone must argue for, not a default.
AM-4b leaves 32,979 lines — 10.4%. Deliberately looser. The dev toolchain is where scenario YAML, benchmarking, and future tooling land, and it does not ship to a player. It should be able to absorb one moderate dependency without a spec change, and not two.
Both are ceilings on a quantity that only grows by choice. Nothing drifts a project across these thresholds; only adding a dependency does. A target that can only be breached deliberately is a target that binds.

What would falsify this ratification: if a future pass finds itself raising AM-4a to accommodate a dependency it wanted, that is the failure mode the ceiling exists to catch, and the answer is a new ADR arguing for the dependency — not a quiet retarget.

Consequences

The open item in history/260731-inner-loop-rule-audit.md is discharged.
make dep-weight continues to fail the build on breach, now backed by a reviewed decision.
AM-4c (own source per 100k third-party lines) remains reported, not targeted, and is unaffected.
Precedent: this is the first ADR written under the correction/retarget test. Future retargets follow this shape — old target, the measurement, and an argument about future binding rather than present passing.

4 KiB Raw Blame History