v2026.10.31.3

A large workspace keeps its bytes once and builds each output once (mcpp#874;
design 2026-10-31, workspace space and reuse). Measured on mcppls (6 members,
61 test programs, clang): bin/ 4 914 MiB -> 1 217 MiB, the tests' links
75 s -> 32 s.

Added

• split_debuginfo under [profile.<name>] ("unpacked" | "off",
  docs/04 §2.9). "unpacked", the default of dev and debug, leaves the
  debug information of the units compiled in the build directory beside their
  objects (-gsplit-dwarf) on an ELF target with a loader, ok images included;
  each program holds a skeleton that names it, and a test no longer carries a
  copy of its closure's debug information. An index package's units keep it in
  the object, since their objects enter the build cache. It applies with
  trim_paths off. e2e 999.
• mcpp clean --report: the bytes of each configuration's objects, BMIs and
  products and of each .build-mcpp area.
• mcpp cache clean --tools and host tool entries in cache list, prune,
  gc and verify.
• Collection by last use after a build: at most once a day, the build
  cache's package, host tool and std entries unused for [cache] unused_days
  (config.toml; default 30, 0 keeps all) are removed. A use sets the time of
  the entry's record file, at most once in 12 hours (an entry's files never
  change, and noatime mounts keep no reads); a package hit no longer rewrites
  its entry.json. A build that replays its graph without planning marks the
  entries its configuration names in uses.list through the sweep after it.
• mcpp self config --cache-unused-days <N> --keep-days <N> writes the two
  retentions into config.toml; mcpp self config shows them (docs/25).
• A warning before a build when the file system it writes to has less than
  2 GiB free.
• The sweep after a build: after mcpp build or mcpp test succeeds, at
  most once a day, the build directories of the project that no configuration
  used for [build] keep_days days (config.toml; default 3, 0 keeps all) are
  removed, with the generated-source and build-program directories none uses.

Changed

• Debug information is compressed on ELF (-gz=zlib on the compile and the
  link; --compress-debug-sections=zlib on an ok image's ld.lld link): a test
  program of mcppls 96.0 -> 35.7 MiB, with no measurable cost in compile time.
  Only with a toolchain whose link reads them: an LLVM toolchain is asked by
  one real link of an empty unit through the ld.lld its driver runs
  (-print-prog-name=ld.lld) with --compress-debug-sections=zlib, a GCC by
  its driver (-gz=zlib -###), once, and the answer kept under the probe cache.
  Measured on windows-2022: the xim LLVM 23.1.3 ships no ld.lld, its driver
  runs the image's own LLVM from PATH, and that one has no zlib.
  Mach-O, PDB, MinGW, WebAssembly and freestanding targets are unchanged;
  -gz=none in a package's flags turns it off.
• A static library holds its own package's objects (docs/12): a member's
  lib<target>.a held the objects of its whole closure (mui: 11 433 archive
  members for 2 666 objects, 5.3 GB). Programs of the build link objects and are
  unaffected; a consumer outside mcpp links each dependency's archive.
• A configuration keeps one build directory over time (design 2026-10-31
  §8). A new fingerprint of a lineage (compiler family, target, standard
  library family, standard, configuration flags) takes over the directory the
  lineage used last, and ninja rebuilds the edges whose commands changed: an
  mcpp upgrade that leaves the flags as they were compiles no unit again, where
  it opened a full new directory and rebuilt everything (mcppls: 2.9 GB per
  configuration per upgrade). A predecessor of another compiler build is
  removed. e2e 1000.
• mcpp clean --stale also removes .build-mcpp/out/<hash> and
  .build-mcpp/host/<group> that no kept configuration names in its
  uses.list.

Fixed

• A host tool has one store key whatever the command and the member. Its
  dependency closure is read from the tool package's manifests, as its build
  resolves them; it was read from the graph the command had walked -- empty
  under mcpp test --workspace, complete under mcpp build, and holding the
  dev-dependencies of the member under test -- so the tool's path changed and
  every action that ran it ran again (69 of 99.6 compile-minutes repeated in
  mui's run). e2e 997.

• An action that leaves its output as it was rebuilds nothing below it
  (restat = 1 on action rules). e2e 998 G.

• A shared library staged as an equal copy is placed again by a link, and a
  build program beside its record is a link to its group's binary.

• The build programs' graph builds its own build programs beside its group
  (<group>.<depth>), not in a copy of the host workspace under its target/.

• mcpp clean --stale keeps a rooted workspace's own build. It removed the
  members' build directories from before the workspace was the unit of build,
  and a workspace that lists itself (members = ["."]) had its own
  configuration directory removed as one of them. e2e 1000 F.

• A path host tool's superseded entries are removed when its tree changes.

• e2e 998 covers these and the archive, the placement and the collection.

• An ok image whose graph declares a prepare action builds (SPEC-013
  §4.6, mcpp#702). Every link edge waits for the phony of each package with a
  prepare action, and the ordering guard checks that it does. Under a platform
  with seal steps the link writes beneath obj/platform/ and a platform_seal
  edge publishes the artifact's name; the guard took that edge for the link and
  refused every such build as an emitter defect (mcppls-clangd's clangd.okb,
  whose libraries a prepare action builds). The emitter and the guard now name
  the link edge's output by one function. e2e 996 builds and runs such an image
  and finds the link edge waiting for the action.