fix(smoke): keep prose out of the single-quoted exec_test body

The agent-browser execution guard added on 2026-09-07 carried its explanation
INSIDE the single-quoted script body, and the explanation contained an
apostrophe ("the fleet\'s only recurring amd64 runtime proof"). Inside '...'
bash treats a backslash as literal, so \' does not escape the quote -- it CLOSES
the string. The body truncated at that point and the remaining lines were parsed
by the calling shell.

Consequences, both measured rather than inferred:
  - exec_test received 12 arguments instead of 2 (verified two-sided: the fixed
    tree yields argc=2, HEAD yields argc=12).
  - the leaked `v=$(agent-browser --version)` ran on the CI RUNNER instead of
    inside the image. The runner has no agent-browser, so smoke and
    smoke-studio both failed with "line 770: command not found" after
    build-base had already spent ~46 minutes. Every downstream job was skipped.
  - the truncated body still passed inside the container and printed its green
    tick first, so the log shows a PASS immediately followed by the failure --
    the tick was real, it just no longer covered the assertion.

The prose now sits above the exec_test call, where an apostrophe cannot
terminate anything, and a comment at that spot records why it must stay there.

Not a new failure class: shellcheck flagged it as SC2289 at severity error the
same day, so the lint job has been red since run 186 (2026-09-07 21:21) and was
not read. The gate did its job; nobody looked.

CHANGELOG.md

@@ -13,6 +13,29 @@ Pre-v1.0.0 tags followed the pi npm version (`v{pi_version}[letter]`).
 
 ## v1.8.14 — 2026-09-08
 
+> **First release attempt failed; fixed in this same entry.** The `smoke` and
+> `smoke-studio` jobs both failed at `scripts/smoke-test.sh:770` with
+> `agent-browser: command not found`, after `build-base` had already succeeded
+> (~46 min spent). Root cause was in the agent-browser execution guard added the
+> day before: the explanatory comment inside the **single-quoted** `exec_test`
+> body contained an apostrophe (`the fleet\'s`). Inside `'...'` bash treats a
+> backslash literally, so `\'` does not escape — it **closes the string**. The
+> body silently truncated (measured: `exec_test` received **12** arguments
+> instead of 2), and the remaining lines, including the `agent-browser --version`
+> assertion, were parsed by the **runner's** shell instead of executing inside
+> the image — and the runner has no agent-browser. The prose now lives above the
+> call, where an apostrophe is harmless.
+>
+> **The lint job had already caught this, and it went unread for 24 hours.**
+> `shellcheck` flagged it as `SC2289` at severity *error*, so the `actionlint`
+> job went red at run 186 on 2026-09-07 21:21 — the exact push that introduced
+> the guard — and stayed red for runs 187 and 188. `lint.yml` deliberately
+> excludes tag pushes (documented: the tagged tree was already linted on main,
+> and a tag-ref lint run would sort above the publish run), which is sound; the
+> broken assumption was different, namely that a tree whose lint FAILED would not
+> then be released. `docker-publish.yml` has no dependency on lint, so it built
+> for 50 minutes on a tree known to be defective.
+
 **A test that was quietly checking nothing, and a version number that was wrong.**
 Both found by delegating a read-only audit of this repo to a headless worker
 (`pi-toolkit` `bin/pi-task`) and then spot-checking its pointers from the