fix: round 8 of the release review of 6.3.0, for 6.3.1

Round 8 (0f400d3..29b4ac9, BLOCK: 1 BLOCKER, 12 MAJOR, 1 MINOR). Each fix
began with a test that failed on 29b4ac9 (13 tests, all red there); suite
2221 (2219/0/2).

- BLOCKER: a backticked check whose trailing comment holds a quote, $,
  backtick or backslash is refused, not dropped. The comment was never
  screened, while the executor hands the Verify span as written to red
  proof, the test lock and the done line inside --cmd "...", where a $(...)
  runs and a quote ends the argument. trekplan's text and the reviewer's
  NOT RUN table say so.
- A span that is only a comment is not-a-command, not a placeholder. The
  dropComment text says the allowlist still refuses a word with a # in it.
- The criteria runner, comparison-gate and end-state-gate use isMain: they
  did nothing and exited 0 under a symlinked path. The test now refuses any
  process.argv[1] comparison outside lib/util/is-main.mjs.
- Files: in a field with backticked paths, a plain word counts only before
  the entry's description (a dash, or a colon after the path); a name with
  no slash only first in its entry or after and/or/+/&. "mocks
  fs.readFileSync", "runs on Node.js 22.x" or "no change to package.json"
  no longer make a tests-only step look like it builds something.
  Lowercase makefile, rakefile and justfile are build files. Measured on the
  520 Files: fields in 48 plans of the marketplace and the test repo:
  3 fields read differently (two notes no longer read as files, one
  duplicate name dropped), tests-only changed in 0.
- The test lock compares --cmd without its trailing comment, and the test
  lock and the done line read a stop with stoppedBy, the one reading.
  red-proof drops its second reading, spawnError.
- release-check reads a relative --review in --repo or, when only that one
  exists, from the current directory as 6.3.0 did; two different files are
  exit 2, never guessed. The runbook says so.
- One trailing-json reader: a closing fence may be longer than three
  backticks, in the block reader and the verdict gate alike, and the review
  validator and the synthesis digest use it, so three backticks inside a
  JSON string no longer hide a BLOCKER from the remediation-step check.

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

agents/brief-conformance-reviewer.md

@@ -111,6 +111,7 @@ column names the reason the runner gave:
 | `placeholder` | the text is a template placeholder (`{exact command}`) |
 | `not-a-command` | the sentence opened by NAMING a flag or a path (`--verbose`, `tests/`) rather than by invoking something. Running it would have produced exit 2 or exit 126 — a number about the sentence, not about the code |
 | `outside the allowlist` | the command is not a known test-runner invocation, or it carries a shell operator. It was never run — say so; do not treat it as a broken criterion |
+| `a trailing comment with a quote, $, backtick or backslash` | the backticked command ends in a `#` comment that a shell would still read inside double quotes. It was never run — say so; do not treat it as a broken criterion |
 | `the program could not start` | the runner is not installed where the review ran. Nothing was measured — say so; do not treat it as a broken criterion |
 
 In every one of those cases, judge the criterion on delivered code alone and