fix(execute): below 1.8 a plan that names no test file gets the files the helper wrote

Operator decision 41 (14.10); review finding 7b3b59ed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/HANDOVER-CONTRACTS.md

@@ -270,7 +270,7 @@ prose form (relaxed in S26 so the template's prose emission parses).
    - **K10 — `Regression:`** (optional step field): ONE backticked command the criteria runner's allowlist runs, with no pipe and no `&&` (first backticked span, as for `Verify:`). The executor runs it green before the step's checkpoint; a step without it runs nothing new. `Verify:` stays the step's own red-first test. One that can never run is `PLAN_STEP_REGRESSION_NOT_RUNNABLE` (an error; a warning under `--soft`).
    - **K11 — `On failure:`** opens with one of `revert`, `retry`, `skip`, `escalate` (case-insensitive; a leading `**`, `_`, backtick or `-` is ignored, other leading characters are not; `onFailureAction` in `lib/parsers/plan-schema.mjs`), the words `/trekexecute` reads; any other opening is the warning `PLAN_STEP_ON_FAILURE_UNKNOWN`. A missing `On failure:` is unchanged (the executor defaults to `escalate`).
    - **A step of only tests** (order 10, voyage-lekerepo trial 3, 2026-10-09): when every file in a step's `Files:` is a test (a file on its `Test first:` `File:` line, or a path `lib/util/test-path.mjs` reads as a test: under `tests/`, `test/`, `__tests__/`, `spec/`, `specs/`, or named `*.test.*`, `*.spec.*`, `*_test.*`, `*_spec.*`, `test_*.py`, but never a document such as `docs/specs/api.md`; `stepTestsOnly` in `lib/parsers/plan-schema.mjs`), the warning is `PLAN_STEP_TESTS_ONLY`: the behaviour its tests cover exists at its start point, so it can never be proven red. A step without `Files:` is not judged. At run time `red-proof.mjs --plan <plan.md> --step <N>` puts the same reading on a `not-red-at-base` as `tests_only`: the plan's `Files:` alone decides, and the step's diff is not read (operator 2026-10-11), and `/trekexecute` sends a `tests_only: true` step straight up to the plan.
-   - **The `Test first:` files** (operator decision 20, 2026-10-12): a step's test files are the backticked paths that stand right after `File:` on its `Test first:` `File:` line, separated only by commas or whitespace; a path in the description after them (`` covers `parse()` in `src/parser.mjs` ``) is no test file. This holds at every plan_version (`testFirstFiles` in `lib/parsers/plan-schema.mjs`; from 1.9 the line is read by the grammar of invariant 8). Below plan_version 1.9 the run also goes on past a note in brackets (`(new)`, `*(new)*`, `(existing …)`) and the words `and`, `plus` and `+`, to a further path only when it is clearly a test (as `lib/util/test-path.mjs` and the tests-only check read it); a path that is not ends the run (operator decision 28, 2026-10-13, and operator decision 31, 2026-10-14). `red-proof.mjs --plan <plan.md> --step <N>` reads them from the plan, and the documented call passes no `--tests` (operator decision 30, 2026-10-14): it prints the list it ran (`tests`); a given `--tests` that differs is `not-run` with reason `tests-mismatch` and the plan's list in `plan_tests`; a plan or step it cannot read is `not-run` with reason `plan-unreadable`.
+   - **The `Test first:` files** (operator decision 20, 2026-10-12): a step's test files are the backticked paths that stand right after `File:` on its `Test first:` `File:` line, separated only by commas or whitespace; a path in the description after them (`` covers `parse()` in `src/parser.mjs` ``) is no test file. This holds at every plan_version (`testFirstFiles` in `lib/parsers/plan-schema.mjs`; from 1.9 the line is read by the grammar of invariant 8). Below plan_version 1.9 the run also goes on past a note in brackets (`(new)`, `*(new)*`, `(existing …)`) and the words `and`, `plus` and `+`, to a further path only when it is clearly a test (as `lib/util/test-path.mjs` and the tests-only check read it); a path that is not ends the run (operator decision 28, 2026-10-13, and operator decision 31, 2026-10-14). `red-proof.mjs --plan <plan.md> --step <N>` reads them from the plan, and the documented call passes no `--tests` (operator decision 30, 2026-10-14): it prints the list it ran (`tests`); a given `--tests` that differs is `not-run` with reason `tests-mismatch` and the plan's list in `plan_tests`; a plan or step it cannot read is `not-run` with reason `plan-unreadable`; only when the plan names no test file (below plan_version 1.8 a `File:` line may name its test without backticks) does it answer `no test files given`, and then the helper runs it again with `--tests` naming the test files it wrote, and the executor with the files on the `tests:` line in the helper's report (operator decision 41, 2026-10-14).
 8. **plan_version 1.9 only** (1.8 and 1.7 plans are read as before, with one warning, `PLAN_STEP_PATH_UNTICKED`, for a path their reader found outside backticks; decision 16, operator 2026-10-11) — the file first on every line:
    - the entries of a step's `Files:` field are its first non-empty line and each list-item line (`-`, `*`, `+`, `1.`, `1)`); a line that is no list item continues the entry above it, when the entry so far ends with a comma, its text joins that entry with one space before the entry is read, so a list wrapped after a comma keeps its paths; otherwise it is description, never read, and so is every later wrapped line of that entry (operator decision 29, 2026-10-14); an entry with nothing on its own line (a `File:` line with nothing after it) takes its first wrapped line;
    - each entry opens with its backticked path(s), separated only by commas or whitespace; everything from the first other text on is description and is never read (`` `a.test.mjs` - covers `src/parse.mjs` `` names one file), so every path stands before any annotation (`` `src/a.mjs`, `src/b.mjs` (new) ``, never `` `src/a.mjs` (new), `src/b.mjs` ``);