fix: round 5 of the release review of 6.3.0, the structural fix

Round 5 (v6.2.0..d37e538, WARN: 11 MAJOR, 2 MINOR). The patching did not
converge (the same two places every round), so the operator chose a
structural fix on 2026-10-11. Each change behind a test that failed first.

- A check runs with no shell. criteria-runner's runCommand starts the runner
  with the very words the screen checked (spawnSync(words[0], words.slice(1)),
  without NODE_TEST_CONTEXT); Phase 7 criteria, Regression: (its exec copy is
  gone, MINOR 0e98d5c7), proof of red, the done line and the test lock all
  run through it. No quote, glob, tilde or variable can rewrite a checked
  word any more. The screen stays and says why: a word that means something
  else in a shell (quote, backslash, $, brace, leading ~) is refused; a glob
  reaches only node --test, which expands its own patterns (sh read
  `tests/.?/` as `tests/../`); no path climbs out with .. or starts at /;
  a word starting with @ is refused (pytest reads @file as more arguments).
- The K6 plan-file sweep has v6.2.0's own Files: reader again (516dffa):
  backticked paths, and plain words only in a field without them. The
  shared reader from round 3 planned directories a description named and
  dropped paths v6.2.0 planned. fieldPaths stays for the tests-only check,
  with a path test on spans (`parse()`, `p.parse()` are no paths), plain
  descriptions ignored when the field has backticked paths, dotfiles,
  backslash paths and glued spans read.
- Skill frontmatter reads a value as YAML does: trailing space is nothing,
  and a comment ends a plain value, a flow list or a block indicator
  (`model: opus # pinned`). A comment that cuts a plain description, or is
  the whole value, is still a hazard.
- release-check reads the diff with --no-renames: a test moved into an
  allowed place after the review shows as removed.
- The example plan's step 2 heading no longer says "must FAIL initially";
  steps 1-2 keep the tests-only warning (operator 2026-10-09, 73262b6).

Open: MINOR c1fef1ad (one shared isMain helper) is not in this round.
Measured: 0 of 463 Files: fields with backticked paths (520 fields in 182
plans across the marketplace repos) carry another path-like word.

Suite 2185 (2183/0/2).

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

lib/verification/red-proof.mjs

@@ -42,6 +42,7 @@
 // (criteria-runner.mjs `allowedCommand`), and it is screened through the
 // plugin's own PreToolUse denylist (`screenCommand`): a command spawned from
 // node never passes through the Bash tool, so the hook cannot fire by itself.
+// It runs with no shell (`runCommand`): the words checked are the words run.
 //
 // When the output is TAP (`--test-reporter=tap`, pytest-tap, ...), the counts
 // `# tests N` / `# fail N` are reported per run. They show WHAT the red was:
@@ -58,7 +59,7 @@ import { spawnSync } from 'node:child_process';
 import { tmpdir } from 'node:os';
 import { dirname, isAbsolute, join, resolve } from 'node:path';
 import { fileURLToPath } from 'node:url';
-import { allowedCommand, screenCommand } from './criteria-runner.mjs';
+import { allowedCommand, runCommand, screenCommand } from './criteria-runner.mjs';
 import { commandEnv } from '../util/command-env.mjs';
 import { sliceSteps, stepTestsOnly } from '../parsers/plan-schema.mjs';
 
@@ -90,8 +91,9 @@ export function repoRoot(dir) {
 // failing test (independent review, 2026-10-08).
 const LOAD_ERROR = /^\s*SyntaxError: |ERR_MODULE_NOT_FOUND|does not provide an export named|Cannot find module|ERR_REQUIRE_ESM|ModuleNotFoundError|ImportError: /m;
 
+// No shell: the words the screen checked are the words that run.
 function run(cmd, cwd, timeoutMs) {
-  const r = spawnSync('/bin/sh', ['-c', cmd], { cwd, env: commandEnv(), encoding: 'utf8', timeout: timeoutMs, maxBuffer: 64 * 1024 * 1024 });
+  const r = runCommand(cmd, { cwd, timeoutMs });
   const output = `${r.stdout ?? ''}${r.stderr ?? ''}`;
   return { exit: r.status, signal: r.signal ?? null, tap: tap(output), tail: output.slice(-TAIL), spawnError: r.error ? r.error.message : null, loadError: LOAD_ERROR.test(output) };
 }
@@ -118,12 +120,13 @@ function testsOnly(o) {
   return { tests_only: stepTestsOnly(step.body).testsOnly };
 }
 
-// A shell that could not find or execute the command (126/127), a signal (the
-// timeout), or a spawn error is not a test verdict at all.
+// A program that could not start (a spawn error: not installed), a signal (the
+// timeout), or 126/127 from a script that could not run its own command is not
+// a test verdict at all.
 function unrunnable(r) {
   if (r.spawnError) return `the command could not start: ${r.spawnError}`;
   if (r.exit === null) return `the command was killed (${r.signal ?? 'timeout'})`;
-  if (r.exit === 126 || r.exit === 127) return `the shell could not run the command (exit ${r.exit})`;
+  if (r.exit === 126 || r.exit === 127) return `the command could not be run (exit ${r.exit})`;
   return null;
 }