fix(workflows): satisfy noUncheckedIndexedAccess in selection math

[flora131]

Summary

packages/workflows/builtin/selection-math.ts ships as raw TypeScript inside @bastani/atomic, so consumers typecheck it directly. Under noUncheckedIndexedAccess, the four indexed compound assignments in accumulate are number | undefined, and a consumer tsc --noEmit fails with four TS2532 errors at lines 130–133.

This adds the non-null assertions the rest of the file already uses, and locks the regression in the SDK type verifier.

Fixes #2543.

Changes

• packages/workflows/builtin/selection-math.ts — w[a]! += p; c[a]! += 1; w[b]! += 1 - p; c[b]! += 1;. No behavior change: a and b are candidate indices the caller sized w/c for, which test/unit/selection-math.test.ts asserts. The style matches mean_preference in the same file, which already used !.
• packages/coding-agent/scripts/verify-workflow-sdk-types.ts — new expect: "pass" variant auto-include-no-unchecked-indexed-access, with tsconfig extras { noUncheckedIndexedAccess: true, allowImportingTsExtensions: true }, reusing the existing auto-include-via-atomic-import consumer files. Importing @bastani/atomic pulls ambient → every builtin → tournament → selection-math, so the variant exercises the real consumer path.
• packages/workflows/CHANGELOG.md — one ### Fixed entry under ## [Unreleased]. No released section touched.

Diff is 3 files, +19 −4.

Verification

Check	Result
Smoke tsc on selection-math.ts (--strict --noUncheckedIndexedAccess --allowImportingTsExtensions --module NodeNext --moduleResolution NodeNext --skipLibCheck --ignoreConfig)	Before: (130,3) (131,3) (132,3) (133,3) error TS2532, exit 1. After: no output, exit 0
New verifier variant	Fails before the fix — and it is the only variant that fails, with the four TS2532 resolving inside node_modules/@bastani/atomic/dist/.../selection-math.ts(130–133), i.e. the consumer bug end-to-end. Passes after
bun run verify:workflow-types (from packages/coding-agent)	All 5 variants pass, exit 0
npm run test:unit -- test/unit/selection-math.test.ts	1 file, 9 tests passed
npm run check	biome + both typecheck passes + shrinkwrap check, exit 0

Two notes on how those commands had to be run

Both are properties of this checkout, not of the fix.

1. The smoke command needs --ignoreConfig. The repo pins typescript@7.0.2, which raises TS5112: tsconfig.json is present but will not be loaded if files are specified on commandline before any type checking. That error fires identically with and without the fix, so it cannot distinguish the two states. --ignoreConfig is TypeScript's own suggested remedy and leaves every other flag intact.
2. verify:workflow-types cannot run on a versionless base unaided. On a clean tree it fails at the first variant with No version matching "0.0.0" found for specifier "@bastani/atomic-natives" — the versionless-release-base design in AGENTS.md, pre-existing and unrelated to this issue. It was made runnable by temporarily stamping the published 0.9.14-alpha.5 with scripts/bump-version.ts, running the verifier, then restoring the 0.0.0 placeholder (confirmed: "version": "0.0.0", natives pin 0.0.0, empty git status).

Known limitation (not addressed here)

All three reviewers independently raised the same non-blocking point, classified beyond this issue's scope: the new variant is the only guard against this class of consumer-facing type break, but nothing runs it automatically. verify:workflow-types is referenced only by its own definition in packages/coding-agent/package.json — no CI job and no prek hook invokes it. Wiring it up (and giving it an escape hatch for versionless bases) is worth a follow-up issue.

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Greptile Summary

This change makes the raw workflow selection helper compatible with consumer projects that enable noUncheckedIndexedAccess, adds a matching SDK type-check fixture, and documents the fix. The potential consumer type-check failure was disproved by comparing the preceding revision and this revision under identical strict compiler settings: the earlier code produced four TS2532 indexed-accumulator errors, while the updated code completed successfully. The focused selection-math test suite also passed all 9 tests.

Confidence Score: 5/5

Safe to merge: the strict consumer compilation path now succeeds and focused selection-math behavior remains passing.

No remaining defects were evidenced. The affected type-checking path was exercised before and after the fix, reproducing the prior compiler failure and confirming that the updated implementation resolves it.

Files Needing Attention: No files need further attention; packages/workflows/builtin/selection-math.ts received direct strict-compilation and focused test coverage.

T-Rex Logs

What T-Rex did

• I ran an authored regression script that type-checked HEAD^ and the current packages/workflows/builtin/selection-math.ts with strict TypeScript and noUncheckedIndexedAccess; the predecessor exited with four TS2532 errors at the w and c indexed accumulator updates, while the updated source exited successfully, and then I ran the focused selection-math unit tests which all passed.
• I re-validated the type-path stability by comparing before and after results: the predecessor produced TS2532 errors, while the current selection-math.ts exits 0 under the same strict options, and the focused behavior coverage remained green.
• I prepared and attached artifacts documenting the regression script, TypeScript outcomes, and unit test results to support review.

_{Ran code and verified through T-Rex}

_{Reviews (1): Last reviewed commit: "fix(workflows): satisfy noUncheckedIndex..." | Re-trigger Greptile}