fix(bin): parse cleanly under macOS system bash 3.2

[ammar00sheikh]

Problem

On a stock macOS host the system shell is bash 3.2.57, and /usr/bin/env bash resolves to it when no newer bash is installed.
Running any ship scaffold (bin/fm-brief.sh <id> <repo>) failed:

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

Root cause (verified by bisection): bash 3.2's naive $(...) scanner tracks quote state through a heredoc body nested in a command substitution, so the apostrophe in the no-mistakes DOD wording ("firstmate's authority check", introduced in ec09871 / #945) inside DOD=$(cat <<EOF ... EOF) broke the parse of the entire rest of the script.
Every ship-task scaffold on a stock-bash mac failed; scout scaffolds escaped only because they exit 0 before the parser reaches the ship-mode case.
The issue #166 regression test did not catch this because its bash -n runs under the dev bash, whose scanner accepts the wording.

Fix

Structural, not a rewording: every VAR=$(cat <<EOF ... EOF) in bin/ now uses the IFS= read -r -d '' VAR <<EOF ... EOF || true idiom plus a single trailing-newline strip, so no heredoc lives inside $(...) and future copy edits adding apostrophes, backticks, or parens cannot re-break parsing.
The emitted brief text is byte-identical: the diff touches only assignment wrappers (zero body lines), and the idiom was empirically verified equivalent to $(cat <<EOF) under bash 3.2, including expansion and backtick handling.

Converted sites:

• bin/fm-brief.sh - the three ship-mode DOD heredocs and the unguarded Herdr section (the reproduced failure).
• bin/fm-fleet-snapshot.sh (4 sites) and bin/fm-bootstrap.sh (1 site) - the audit's remaining $(cat << instances; they parse today only because their apostrophes happen to balance, so they were converted rather than listed.

Regression coverage

tests/fm-brief.test.sh (extended in place because CI test lanes are explicit hand-maintained lists):

• bash -n now also runs under the system /bin/bash - the real 3.2 gate on macOS.
• A sweep syntax-checks every bin/*.sh and bin/backends/*.sh under /bin/bash, guarding the whole bug class.
• The per-mode scaffold test asserts non-empty output containing each delivery mode's definition-of-done marker.

Pipeline follow-ups on this branch: documentation of the heredoc rule, and the macOS CI lane now runs the fm-brief regression gate so the sweep executes under a real bash 3.2 in CI, not only on developer macs.

Verification (on the affected stock-bash mac)

• Reproduced first on the default branch: /bin/bash -n bin/fm-brief.sh exit 2 with the exact error above.
• After the fix: /bin/bash -n clean on all bin scripts; real scaffolds for no-mistakes, direct-PR, local-only, --scout, and --secondmate all generate correctly under bash 3.2.
• tests/fm-brief.test.sh green; bin/fm-test-run.sh --changed (~40 suites) exit 0; bin/fm-lint.sh green under pinned ShellCheck 0.11.0.
• Pre-existing, unrelated: tests/fm-bearings-snapshot.test.sh fails identically on the clean default branch on this host.

🤖 Generated with Claude Code

[kunchenguid]

Speaking as Kun's firstmate: closing this as stale. It has been waiting on a contributor update for 14+ days with no author push or comment. Reopen if you want to pick it back up.