initial commit: docker test-build toolchain

Extracted from the .extras/ dir of the sbo-slackbuilds package repo, where it
grew from a throwaway helper into a standalone tool. Git history starts fresh;
the original 41-commit development log is preserved in HISTORY.md.

Contents: the test-build CLI (resolves a local SlackBuild's deps from a
configured SBo tree and builds it in a throwaway container, lints, caches deps),
the image-builder chain that produces the images it consumes, their pure-logic
self-checks, design specs/plans, an install.sh for ~/bin, and docs.

Licensed GPLv2-only.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/overrides.example b/overrides.example
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+# current-vs-stable dep overrides for test-build.
+# Copy to ~/.config/sbo-testbuild/overrides and edit. Applied only when
+# targeting -current (15.0 is the SBo baseline). One rule per line.
+#
+#   drop:   <prog>            dep is a 15.0-only SBo package whose payload the
+#                             -current base already ships; skipped at resolution
+#                             (not built, not flagged UNMET). e.g. rust-opt:
+#                             15.0 needs the SBo rust-opt, current has rust in base.
+#   rename: <old> -> <new>    dep was renamed on -current
+#   fetch:  <prog>            dep was removed from the -current tree; pull via sbopkg
+#
+# Start light: add rules only when a real package needs them.
+
+# drop:   rust-opt
+# rename: python3-foo -> foo
+# fetch:  somelib