fix(bin): port upstream clean fixes — landed round-robin, handoff home parse, pr-merge set -u (#640 #686 #205)

[leo1oel]

First catch-up round after kunchenguid#555. Three low-risk upstream bug fixes to scripts the fork already runs.

kunchenguid#640 — balanced landed baseline (fm-bearings-snapshot.sh)

Default landed is now round-robin across deterministic home order (each home keeps its own newest-first order) instead of one global newest-first pass, so a home with the newest dates can't crowd every other home out of a tight overall cap. --all-landed still gives the full global newest-first set.

kunchenguid#686 — parse home after a parenthetical (fm-backlog-handoff.sh)

Resolve the (home: ...) field with a greedy prefix, so a parenthetical in the summary/scope prose before that field no longer makes the entry look like it "has no home".

kunchenguid#205 — set -u-safe array expansion (fm-pr-merge.sh)

Use ${arr[@]+"${arr[@]}"} for merge_args — an empty-array expansion under set -u fails on bash < 4.4 (stock macOS bash 3.2), which happens when the caller forwards an explicit merge method. The fork's fm-spawn already had this idiom; only fm-pr-merge needed it.

Tests

• bearings round-robin balance (two homes, tight cap → one per home, not both from the newest home)
• handoff parenthetical-home resolution

Local gate: shellcheck bin/*.sh tests/*.sh clean; all tests/*.test.sh pass (26 suites).

Next rounds (separate PRs): kunchenguid#637+kunchenguid#636 (guard/session-start, more involved), kunchenguid#556 (PR-check hardening), kunchenguid#687/kunchenguid#656 (features), kunchenguid#593 (durable decision holds), doc cherry-picks.

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Note

Low Risk
Localized script and jq projection changes with regression tests; no auth, data migration, or API surface changes.

Overview
Ports three upstream script fixes with matching behavior tests.

fm-bearings-snapshot.sh — Default bounded landed selection no longer sorts all homes globally by merge date. It keeps per-home newest-first caps, then round-robins across homes so a tight overall cap cannot be filled entirely by the main home. --all-landed is unchanged (full global newest-first).

fm-backlog-handoff.sh — secondmate_home parsing no longer requires no parentheses before (home: …); a greedy match finds the structured home field even when summary prose has earlier parentheticals.

fm-pr-merge.sh — Uses ${merge_args[@]+"${merge_args[@]}"} so an empty merge_args under set -u does not break on bash 3.2 when the caller passes an explicit merge method.

Tests cover round-robin landed balance and handoff after a parenthetical before (home: …).

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