fix(brief): restore bash 3.2 parse of the no-mistakes definition-of-done

[ICGNU3]

Failure mode

bin/fm-brief.sh has not parsed under stock macOS bash since #945:

bin/fm-brief.sh: line 314: unexpected EOF while looking for matching `''
bin/fm-brief.sh: line 388: syntax error: unexpected end of file

Bash 3.2 mis-scans a bare apostrophe inside a heredoc nested in $( ), treating it as an unterminated single quote and failing the whole file. The apostrophe in firstmate's authority check (line 328, added by #945) is enough on its own.

Minimal reproduction:

$ cat repro.sh
X=$(cat <<EOF
firstmate's authority check
EOF
)
$ /bin/bash -n repro.sh          # bash 3.2.57, stock macOS
repro.sh: line 2: unexpected EOF while looking for matching `''

Quoting the delimiter (<<'EOF') does not help; the $( ) scan is what breaks.

Why CI is green: the runner is Linux with bash 5, where the file is valid. This is invisible from CI and only bites macOS users, where fm-brief.sh cannot execute at all, so brief scaffolding is dead.

ShellCheck also reports the file as clean, since it parses as modern bash. bash -n under 3.2 is the only signal.

This is a regression, not an unsupported platform. Every other script in bin/ parses under bash 3.2, and the repo uses no bash 4+ constructs (no declare -A, no ${var,,}, no mapfile/readarray).

Correction

Interpolate the apostrophe through $APOS so the scanner never encounters a bare quote. The heredoc is unquoted, so ${APOS} expands normally and the generated brief text is unchanged byte for byte — which matters, because tests/fm-ask-user-authority.test.sh pins that exact sentence.

I first tried simply rewording the possessive; that broke the contract test, which is the correct outcome. The brief text is a contract, so the mechanism is what changed instead.

Scope

One file. bin/fm-brief.sh, +9/-1, and the only behavioral line is the ${APOS} interpolation; the rest is the comment explaining the constraint.

bin/fm-teardown.sh is untouched, as is every other script. Confirmed against this branch:

• git diff --name-only origin/main lists bin/fm-brief.sh and nothing else
• tests/fm-teardown.test.sh: 32/32, identical to the origin/main baseline

Tests

On this branch (origin/main + this commit), macOS bash 3.2:

suite	before	after
fm-brief	fails to parse	15/15
fm-ask-user-authority	8 ok, 1 fail	9/9
fm-tangle-guard	5 ok, 1 fail	6/6
fm-secondmate-safety	0 ok, 1 fail	59/59
fm-teardown	32/32	32/32 (unchanged)

fm-secondmate-safety going from an immediate abort to 59 passing shows the reach: it depends on brief scaffolding and could not get past it.

shellcheck -e SC1091 bin/fm-brief.sh is clean, and /bin/bash -n bin/fm-brief.sh now exits 0.

[puneetv05]

Firstmate's own tooling can't start any worker right now — the step that writes a worker's instructions crashes on this Mac's built-in shell.
need this PR to be merged asap thanks