fix(scripts): replace mapfile with bash 3.2-compatible read loop

[benoitf]

Summary

Replace mapfile -t with a while read loop in docker-build-image.sh and stage-prebuilt-binaries.sh to ensure compatibility with bash 3.2, the default shell on macOS.

mapfile (also known as readarray) was introduced in bash 4.0. macOS ships with bash 3.2 due to the GPLv3 licensing change in bash 4+, so any script using mapfile fails on a stock macOS developer machine:

line XX: mapfile: command not found

Related Issue

Changes

All three call sites follow the same mechanical replacement:

# Before (requires bash 4.0+)
mapfile -t arches < <(prebuilt_arches)

# After (works on bash 3.2+)
local arches=()
while IFS= read -r _a; do arches+=("$_a"); done < <(prebuilt_arches)

File	Location	Function
tasks/scripts/docker-build-image.sh	missing_prebuilt_paths()	Detects which prebuilt binaries are absent
tasks/scripts/docker-build-image.sh	ensure_prebuilt_binaries()	Stages prebuilt binaries before Docker build
tasks/scripts/stage-prebuilt-binaries.sh	top-level	Detects host architectures for cross-compilation

Testing

• mise run pre-commit passes
• Unit tests added/updated
• E2E tests added/updated (if applicable)

Manual Testing

• Run tasks/scripts/stage-prebuilt-binaries.sh on macOS (bash 3.2) and confirm it no longer errors on mapfile.
• Run mise run docker:build and verify prebuilt binary staging still works on both macOS and Linux.

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture docs updated (if applicable)

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[benoitf]

PR rebased

[maxamillion]

LGTM 👍