Dark target: aprender-core mutation_testing_tests MUT-05/06/07 read .github/workflows/ci.yml relative to cwd — fail under nextest/cargo test (cwd = crate dir); never run by any CI tier

[noahgift]

Measured 2026-09-11 15:47Z on the #3112 tree with cargo nextest run -p aprender-core --tests (15,547 tests, 3 failed):

FAIL aprender-core::mutation_testing_tests mut05_ci_mutation_workflow_exists   -> "MUT-05 FALSIFIED: No CI configuration found"
FAIL aprender-core::mutation_testing_tests mut06_mutation_artifacts_captured   -> read ci.yml: NotFound
FAIL aprender-core::mutation_testing_tests mut07_mutation_timeout_configured   -> read ci.yml: NotFound

crates/aprender-core/tests/includes/mut0.rs:155 does Path::new(".github/workflows/ci.yml") — cwd-relative. Both cargo test and nextest run a test binary with cwd = the package dir (crates/aprender-core), so the path never resolves. The target is DARK in CI: the quick tier runs a touched crate's lib + the tree-reader registry targets (the #3112 quick-tier log has zero mentions of mutation_testing_tests), and the full tier runs only the explicit --test list in ci.yml.

Same class as the two path assumptions the quick tier surfaced in falsification_model_oracle_tests today (#3112, commits 7f7e5bc and c51275b): tree-reading tests must anchor on CARGO_MANIFEST_DIR (crate) or walk up to the [workspace] manifest (repo), never on cwd.

Remedy: anchor the three MUT-0x paths on the workspace root (CARGO_MANIFEST_DIR/../.. or the [workspace] walk); then scripts/check_tree_reader_tests.sh --update should list mutation_testing_tests as a tree-reader target (it reads ci.yml) so the quick tier runs it. Verify with the same nextest command above: 15,547/15,547.

[noahgift]

Fixed on #3112's branch (PMAT-1102) as the sixth quick-tier round surfaced MUT-05 in CI: the three paths now anchor on the [workspace] manifest above CARGO_MANIFEST_DIR; cargo nextest run -p aprender-core --test mutation_testing_tests 16/16. Closes with #3112. — autonomous fleet loop