workflow-fix: select_step9c_tests must include touched tests/*.py in subset

Overview / Motivation

Auto-filed by the workflow-fix-on-bug protocol from an orchestrator observation on task #851 (Step 9c test-verdict gate, 2026-07-02).

Goal

scripts/select_step9c_tests.py must include touched tests/*.py files from the branch diff in its printed pytest command.

Workflow gap

• Bug observed: on issue-851 (git diff main...HEAD touching tests/test_graded_judge.py + tests/test_eval_margin.py among 7 files), uv run python scripts/select_step9c_tests.py --base main printed only the 32-file workflow-invariant subset — the branch's OWN new test files were absent from the run list, and stderr carried NO untested touched file: WARN for them (or for the touched src/scripts files they cover).
• Why it is a workflow gap: the Step 9c gate's touched scope exists to verify the diff; omitting the diff's own test files means a branch whose new tests fail would PASS the gate unless the orchestrator manually appends them (as #851's orchestrator did). Silent under-selection of the very tests written for the change defeats the gate.
• Confidence (emitter): high (observed live; the printed command is in #851's epm:test-verdict marker).

Proposed change (candidate diff sketch — refine in planning)

+ In select_step9c_tests.py's subset computation:
+   touched = git diff --name-only <base>...HEAD
+   test_files = [f for f in touched if f.startswith("tests/") and f.endswith(".py")]
+   subset = workflow_invariant_subset | mapped_tests_for_touched_source_files | set(test_files)
+ Also: emit the documented `untested touched file: <path>` WARN for touched
+ source files with no mapped/co-named test, which did not fire on #851.
+ Add a regression test: a diff adding tests/test_foo.py must appear in the
+ printed command.

Scope / surfaces

• Primary target: scripts/select_step9c_tests.py
• Secondary: its pinning test (add one if none exists).

Constraints / invariants

• Workflow-surface only. scripts/workflow_lint.py passes; ruff on touched files passes.
• The printed command shape (single uv run pytest <files> -v --tb=short line) is consumed verbatim by the /issue Step 9c prose — keep it stable.

Provenance

• workflow_fix_target: scripts/select_step9c_tests.py
• fingerprint: e3013d01ea8c