feat: derive the batch command union from the as-const registry (simplify #909) — Phase 1 step 7

[thymikee]

Phase 1 step 7 of the command-descriptor migration (ADR 0008)

Stacked on #911.

What

The command-descriptor registry became as const and started exporting type Command in #910. With literal name and literal batchable preserved per entry, the batch command-name union can now derive from the registry instead of being hand-authored.

This PR:

• Replaces the 43-member hand-authored StructuredBatchCommandName union (introduced in feat: build batch allowlist from descriptors, delete the hand list — Phase 1 step 4 #909, when the registry was not yet as const) with a derivation from the registry:

  export type StructuredBatchCommandName = Extract<
    (typeof commandDescriptors)[number],
    { batchable: true }
  >['name'];

• Deletes the now-tautological exhaustive Record<StructuredBatchCommandName, true> membership assertion in parity.test.ts — the type and the runtime value now derive from the same batchable: true entries, so the exhaustive cross-check is a tautology. tsc enforces the type; the kept invariant guards the runtime value (exported allowlist === derived fold, no dupes, all public, control-plane stays out).

Why it is strictly behaviorless

• Identical 43-member set. Confirmed the derived union is bidirectionally assignable to feat: build batch allowlist from descriptors, delete the hand list — Phase 1 step 4 #909's hand union and that both have exactly 43 members (type-level count check) — no member added or removed.
• Runtime allowlist unchanged. STRUCTURED_BATCH_COMMAND_NAMES still folds the registry via deriveStructuredBatchCommandNames; only the narrowing cast's source-of-truth comment changed.
• Public BatchCommandName structurally identical. The re-export through command-surface.ts resolves to the same union; a consumer switching on specific batch command names still typechecks (tsc green across the project, including the satisfies readonly DaemonCommandName[] guard in commands/batch/projection.ts).

Verification

• tsc -p tsconfig.json --noEmit — exit 0
• oxfmt --write + oxlint --deny-warnings on changed files — exit 0
• vitest run batch core/command-descriptor command-surface-metadata projection — all pass
• Layering Guard grep — empty

[github-actions]

Size Report

Metric	Base	Current	Diff
JS raw	1.4 MB	1.4 MB	0 B
JS gzip	445.5 kB	445.5 kB	0 B
npm tarball	584.7 kB	584.7 kB	0 B
npm unpacked	2.0 MB	2.0 MB	0 B

Startup median (7 runs, lower is better):

Scenario	Base	Current	Diff
CLI --version	27.3 ms	27.6 ms	+0.3 ms
CLI --help	48.6 ms	47.0 ms	-1.6 ms

Top changed chunks: no changes in the largest emitted chunks.

[github-actions]

PR Preview Action v1.8.1
Preview removed because the pull request was closed.
2026-06-27 19:24 UTC