2026.10.1.1: member selection, build programs prepared once, a pack over several members, and output streams (#748, #749, #750)

.agents/docs/2026-10-01-member-selection-verify.sh

@@ -0,0 +1,156 @@
+#!/usr/bin/env bash
+# Sandbox verification of the release that implements
+# .agents/docs/2026-09-30-member-selection-and-build-program-cost-plan.md
+# (#748, #749, #750), run against the PUBLISHED release inside an xlings
+# sandbox:
+#
+#   B64=$(base64 -w0 .agents/docs/2026-10-01-member-selection-verify.sh)
+#   xlings subos new v1001 2>/dev/null || true
+#   xlings subos use v1001 --sandbox --cmd "echo $B64 | base64 -d > /tmp/v.sh && VER=<version> bash /tmp/v.sh"
+#
+# VER selects the release under test. Running it with VER=2026.9.30.2 is the
+# control: every section marked CHANGE must fail there, and every other
+# section must pass on both.
+#
+# Every probe directory is removed at the start of its section, because the
+# sandbox's $HOME persists between runs of the same subos. A section that does
+# not run is reported as SKIP and counted apart from a pass.
+set -u
+VER="${VER:?VER=<version under test>}"
+W="${W:-$HOME/v1001}"
+fails=0; passes=0; skips=0
+pass() { echo "PASS  $1"; passes=$((passes+1)); }
+fail() { echo "FAIL  $1"; [ -n "${2:-}" ] && [ -f "$2" ] && tail -20 "$2"; fails=$((fails+1)); }
+skip() { echo "SKIP  $1"; skips=$((skips+1)); }
+
+# 0. The release under test, from the published channel, with the CN mirror.
+if [ -n "${MCPP_OVERRIDE:-}" ]; then
+    MCPP="$MCPP_OVERRIDE"
+else
+    xlings config --mirror CN >/dev/null 2>&1 || true
+    xlings update >/dev/null 2>&1 || true
+    xlings install "mcpp@$VER" -y > /tmp/v1001-install.log 2>&1 || true
+    MCPP="$HOME/.xlings/data/xpkgs/xim-x-mcpp/$VER/bin/mcpp"
+fi
+if [ ! -x "$MCPP" ]; then
+    echo "FATAL: mcpp $VER is not installable from the index"; tail -20 /tmp/v1001-install.log; exit 2
+fi
+got=$("$MCPP" --version 2>&1 | head -1)
+case "$got" in *"$VER"*) pass "0 installed: $got";; *) fail "0 version: $got";; esac
+# The sandbox's home is empty, so the mirror is set inside it. A run on a host
+# with MCPP_OVERRIDE leaves the host's configuration as it is.
+[ -n "${MCPP_OVERRIDE:-}" ] || "$MCPP" self config --mirror CN >/dev/null 2>&1 || true
+mkdir -p "$W"
+
+lib_member() {   # <dir> <name> <value>: a library member with one module and one test
+    mkdir -p "$1/src" "$1/tests"
+    printf '[package]\nname = "%s"\nversion = "0.1.0"\n\n[targets.%s]\nkind = "lib"\n' "$2" "$2" > "$1/mcpp.toml"
+    printf 'export module %s;\nexport int %s_value() { return %s; }\n' "$2" "$2" "$3" > "$1/src/$2.cppm"
+    printf 'import %s;\nint main() { return %s_value() == %s ? 0 : 1; }\n' "$2" "$2" "$3" > "$1/tests/test_$2.cpp"
+}
+
+# 1. CHANGE (#750): a repeated -p selects every member it names.
+rm -rf "$W/s1"; mkdir -p "$W/s1"; cd "$W/s1"
+printf '[workspace]\nmembers = ["a", "b", "c"]\n' > mcpp.toml
+lib_member a a 1; lib_member b b 2; lib_member c c 3
+if "$MCPP" test -p a -p b > s1.log 2>&1 \
+   && grep -q 'test_a' s1.log && grep -q 'test_b' s1.log && ! grep -q 'test_c' s1.log; then
+    pass "1 CHANGE: mcpp test -p a -p b tests a and b, and not c"
+else fail "1 CHANGE: a repeated -p" s1.log; fi
+
+# 2. CHANGE: --exclude, and a member name that matches nothing.
+cd "$W/s1"
+if "$MCPP" test --workspace --exclude c > s2a.log 2>&1 \
+   && grep -q 'test_a' s2a.log && grep -q 'test_b' s2a.log && ! grep -q 'test_c' s2a.log; then
+    pass "2a CHANGE: --workspace --exclude c tests a and b"
+else fail "2a CHANGE: --exclude" s2a.log; fi
+if "$MCPP" build -p nosuch > s2b.log 2>&1; then fail "2b an unknown member was accepted" s2b.log
+elif grep -q 'nosuch' s2b.log; then pass "2b an unknown member is refused by name"
+else fail "2b the refusal does not name the member" s2b.log; fi
+
+# 3. CHANGE (R1, R2): run -q writes exactly the program's output, and a
+# failed build exits 101.
+rm -rf "$W/s3"; mkdir -p "$W/s3/src"; cd "$W/s3"
+printf '[package]\nname = "p3"\nversion = "0.1.0"\n\n[targets.p3]\nkind = "bin"\nmain = "src/main.cpp"\n' > mcpp.toml
+printf '#include <cstdio>\nint main() { std::puts("OUT"); std::fputs("ERR\\n", stderr); return 0; }\n' > src/main.cpp
+"$MCPP" run -q > s3.out 2> s3.err; rc=$?
+if [ "$rc" = 0 ] && [ "$(od -c s3.out | head -1)" = "$(printf 'OUT\n' | od -c | head -1)" ]; then
+    pass "3a CHANGE: run -q writes exactly the program's stdout"
+else fail "3a CHANGE: run -q stdout (rc=$rc)" s3.out; fi
+printf 'int main() { x }\n' > src/main.cpp
+"$MCPP" run -q > s3b.log 2>&1; rc=$?
+if [ "$rc" = 101 ]; then pass "3b CHANGE: a run whose build failed exits 101"
+else fail "3b CHANGE: exit status $rc for a failed build" s3b.log; fi
+
+# 4. CHANGE (R3): a build narrates on stderr.
+cd "$W/s1"
+out=$("$MCPP" build --workspace 2>/dev/null)
+if [ -z "$out" ] && "$MCPP" build --workspace 2>&1 >/dev/null | grep -q 'Finished'; then
+    pass "4 CHANGE: status lines are on stderr and stdout is empty"
+else fail "4 CHANGE: status stream"; echo "$out" | head -5; fi
+
+# 5. index packages build and run with the release.
+rm -rf "$W/s5"; mkdir -p "$W/s5/src"; cd "$W/s5"
+printf '[package]\nname = "eco"\nversion = "0.1.0"\n\n[dependencies]\n"compat.zlib" = "*"\n"mcpplibs.cmdline" = "*"\n\n[targets.eco]\nkind = "bin"\nmain = "src/main.cpp"\n' > mcpp.toml
+cat > src/main.cpp <<'EOF'
+#include <cstdio>
+#include <zlib.h>
+import mcpplibs.cmdline;
+int main() { std::printf("zlib %s\n", zlibVersion()); return 0; }
+EOF
+if "$MCPP" run > s5.log 2>&1 && grep -q '^zlib ' s5.log; then
+    pass "5 compat.zlib and mcpplibs.cmdline from the index build and run"
+else fail "5 index packages" s5.log; fi
+
+# 6. CHANGE (#748): four members' build programs import one host module of a
+# path dependency; the module is compiled once for the four, and the engine's
+# own module is kept in the global cache.
+rm -rf "$W/s6"; mkdir -p "$W/s6/rules/src"; cd "$W/s6"
+printf '[workspace]\nmembers = ["m1", "m2", "m3", "m4"]\n' > mcpp.toml
+printf '[package]\nname = "rule6"\nversion = "0.1.0"\n\n[targets.rule6]\nkind = "lib"\n' > rules/mcpp.toml
+printf 'export module v6.rules;\nimport mcpp;\nexport void apply(const char* d) { mcpp::define(d); }\n' > rules/src/rule6.cppm
+for m in m1 m2 m3 m4; do
+    mkdir -p $m/src
+    printf '[package]\nname = "%s"\nversion = "0.1.0"\n\n[build-dependencies]\nrule6 = { path = "../rules", host-module = true }\n\n[targets.%s]\nkind = "bin"\nmain = "src/main.cpp"\n' $m $m > $m/mcpp.toml
+    printf 'int main() { return 0; }\n' > $m/src/main.cpp
+    printf 'import mcpp;\nimport v6.rules;\nint main() { apply("V6_%s=1"); return 0; }\n' $m > $m/build.mcpp
+done
+if MCPP_VERBOSE=1 "$MCPP" build --workspace > s6.log 2>&1; then
+    compiles=$(grep -cE "host module 'v6\.rules' (precompile|compile):" s6.log || true)
+    ran=$(grep -cE "^ *build\.mcpp m[1-4] .* ran " s6.log || true)
+    if [ "$compiles" = 1 ] && [ "$ran" = 4 ]; then
+        pass "6 CHANGE: one host module compile for four build programs"
+    else fail "6 CHANGE: $compiles host module compiles for $ran programs" s6.log; fi
+else fail "6 the workspace of four build programs did not build" s6.log; fi
+
+# 7. CHANGE (#749): one pack of two program members that share a member with a
+# build program: one package per member, and the shared program runs once.
+rm -rf "$W/s7"; mkdir -p "$W/s7/core/src"; cd "$W/s7"
+printf '[workspace]\nmembers = ["core", "cli", "gui"]\n' > mcpp.toml
+printf '[package]\nname = "core"\nversion = "0.1.0"\n\n[targets.core]\nkind = "lib"\n' > core/mcpp.toml
+printf 'export module v7core;\nexport int core_answer() { return 42; }\n' > core/src/core.cppm
+cat > core/build.mcpp <<'EOF'
+import mcpp;
+#include <fstream>
+#include <string>
+int main() {
+    std::ofstream log(std::string(mcpp::out_dir()) + "/runs.log", std::ios::app);
+    log << "ran\n";
+    return 0;
+}
+EOF
+for m in cli gui; do
+    mkdir -p $m/src
+    printf '[package]\nname = "%s"\nversion = "0.1.0"\n\n[dependencies]\ncore = { path = "../core" }\n\n[targets.%s]\nkind = "bin"\nmain = "src/main.cpp"\n' $m $m > $m/mcpp.toml
+    printf '#include <cstdio>\nimport v7core;\nint main() { std::printf("%s %%d\\n", core_answer()); }\n' $m > $m/src/main.cpp
+done
+if "$MCPP" pack --workspace --format dir > s7.log 2>&1; then
+    packed=$(grep -cE '^ *Packed ' s7.log || true)
+    runs=$(find core -name runs.log -exec cat {} + 2>/dev/null | grep -c ran || true)
+    if [ "$packed" = 2 ] && [ "$runs" = 1 ]; then
+        pass "7 CHANGE: one pack of two members, and the shared build program ran once"
+    else fail "7 CHANGE: $packed packages, the shared program ran $runs times" s7.log; fi
+else fail "7 CHANGE: mcpp pack --workspace" s7.log; fi
+
+echo "---- $passes passed, $fails failed, $skips skipped"
+[ "$fails" = 0 ]

.agents/docs/README.md

@@ -18,7 +18,7 @@ superseded_by: 2026-09-07-....md  # when status is superseded
 ---
 ```
 
-320 records.
+321 records.
 
 ## By subject
 
@@ -30,6 +30,7 @@ Records that declare one. Everything else is listed by date below.
 
 ### design
 
+- [Member selection, build programs prepared once, a pack over several members, and the output streams of `mcpp run`: the plan for the release after 2026.9.30.2 (#748, #749, #750)](2026-09-30-member-selection-and-build-program-cost-plan.md) — landed
 - [The build's wall time, its progress count, a hang after the build, and #732 and #744: measurements and a remediation plan](2026-09-30-build-wall-time-progress-count-and-hang-plan.md) — landed
 - [Build output, revision 3: every package that does work is named, the live display is one line drawn in one write, and a repeated warning is stated once per file](2026-09-30-build-output-refinement-design.md) — landed
 - [The workspace as the unit of build: one graph per configuration, one scheduler, product directories, and a reusable graph module](2026-09-29-workspace-build-graph-design.md) — landed
@@ -111,6 +112,7 @@ Records that declare one. Everything else is listed by date below.
 
 ### 2026-09
 
+- [Member selection, build programs prepared once, a pack over several members, and the output streams of `mcpp run`: the plan for the release after 2026.9.30.2 (#748, #749, #750)](2026-09-30-member-selection-and-build-program-cost-plan.md) — landed
 - [The build's wall time, its progress count, a hang after the build, and #732 and #744: measurements and a remediation plan](2026-09-30-build-wall-time-progress-count-and-hang-plan.md) — landed
 - [Build output, revision 3: every package that does work is named, the live display is one line drawn in one write, and a repeated warning is stated once per file](2026-09-30-build-output-refinement-design.md) — landed
 - [The workspace as the unit of build: one graph per configuration, one scheduler, product directories, and a reusable graph module](2026-09-29-workspace-build-graph-design.md) — landed

.github/workflows/ci-windows.yml

@@ -394,7 +394,9 @@ jobs:
           # the global default in `toolchain list` / doctor output.
           TMP=$(mktemp -d); cd "$TMP"
 
-          out=$("$MCPP_SELF" toolchain default msvc); echo "$out"
+          # Both streams: `Detected` and `Default set to` are narration, on
+          # standard error since 2026.10.1.1.
+          out=$("$MCPP_SELF" toolchain default msvc 2>&1); echo "$out"
           grep -q "Detected"     <<<"$out"
           grep -q "msvc@system"  <<<"$out"
 

CHANGELOG.md

@@ -4,6 +4,98 @@
 > Each `## [<version>]` section is that release's notes. Entries are written in English
 > from 2026.9.28.3 on; earlier entries remain as written.
 
+## [2026.10.1.1] - 2026-10-01
+
+This release implements the plan for member selection, build programs prepared
+once, a pack over several members, and the output streams
+(`.agents/docs/2026-09-30-member-selection-and-build-program-cost-plan.md`),
+and resolves mcpp#748, mcpp#749 and mcpp#750. Two changes are observable by
+scripts: narration moves to standard error, and a `mcpp run` whose build failed
+exits 101 (both under **Changed**).
+
+### Changed
+
+- **Narration is written to standard error, and a command's result to
+  standard output.** The narration is what says what a command is doing: the
+  status lines that begin with a verb (`Resolving`, `Compiling`, `Finished`,
+  `Running`, `Packed`, `Downloading` and the others), the progress bars, the
+  status row of a terminal, and the blank line after `Running`. The result is
+  what the command was asked to produce: the program's output under `mcpp run`,
+  a document or a listing, and for `mcpp test` each verdict, the `test result`
+  line and the `workspace result` line. Releases up to 2026.9.30.2 wrote the
+  narration to standard output. A script that read a status line from standard
+  output changes: `mcpp build | tee log` becomes `mcpp build 2>&1 | tee log`. A
+  CI log, which captures both streams, is unaffected. The live status row is
+  drawn on standard error, whether or not standard output is a terminal
+  (e2e 864 to 866).
+- **A `mcpp run` whose planning or build failed exits 101**, as `cargo run`
+  does. It exited 1 or 2, which a program that returns 1 also does. The
+  program's own status still passes through, a refused start keeps 125 to 127,
+  and `build`, `test` and `pack` keep their statuses. A program or runner that
+  itself returns 101 reads as a failed build (e2e 863).
+- **`mcpp test` over several members plans once per configuration.** The
+  members of one configuration are one plan with each member's tests, so a
+  package they share is compiled once with the union of their features and its
+  build program runs once; then each member's tests run in `[workspace]
+  members` order with that member's runtime directories, continuing past a
+  member that fails. The JSON stream adds a `group_build` record before a
+  group's first test and a `build_group` field in each member's summary, whose
+  `build_ms` is the group's build time; each test record adds `build_ms`, the
+  build time of its own binary. `--workspace-timeout` bounds the runs and
+  `--build-timeout` the build (e2e 854 to 856).
+- **A workspace's build programs share what they import and compile at the
+  same time (mcpp#748).** The bundled `mcpp` module and each host module are
+  compiled once per key: the host compiler, the standard and every flag of the
+  compile, the imported BMIs and the interface's content. The engine's module
+  and the host modules of index packages are kept in the global cache, where
+  `mcpp cache gc` collects them; a host module of a path or git dependency or
+  of a workspace member is kept under the workspace's
+  `target/.build-mcpp/host-modules/`. The members' programs are compiled
+  together, up to the job count, and run in the order they always ran, so the
+  plan is the one a serial build writes. On a fixture of #748's shape the whole
+  build takes 0.33 to 0.48 s instead of 0.89 to 1.22 s (e2e 857 to 861).
+
+### Added
+
+- **A repeated `-p` selects every member it names (mcpp#750).** `build`,
+  `test`, `pack` and `mcpp emit build-database` read one selection: a set of
+  members in `[workspace] members` order, whatever the order of the `-p`
+  values. A value that names no member is refused before planning, and the
+  refusal lists the members. `mcpp run` executes one program and refuses a
+  second `-p`, naming both; `--workspace` together with `-p` is refused
+  (e2e 852, 853).
+- **`--exclude <member>`** removes members from a whole-workspace selection
+  (`--workspace`, or a virtual root without `-p`), on `build`, `test`, `pack`
+  and `mcpp emit build-database`. It is refused with `-p`, for a name that
+  matches no member, and when it leaves no member (e2e 853).
+- **`mcpp pack` over several members (mcpp#749).** `--workspace`, a repeated
+  `-p` and `--exclude` pack several members with one plan per configuration and
+  one build; each member is staged in a tree of its own, its build program sees
+  its own `pack_stage_dir()`, and a dispatched format runs one second pass per
+  configuration. A positional target, several `--target` values, an `--output`
+  that is a file, a member no provider of the requested format acts for, and
+  two members that would write one destination are refused before anything is
+  compiled. A member whose distribution step fails is reported by name and the
+  others are packed; the members are reported in `[workspace] members` order,
+  and `${mcpp.target_file:<name>}` names the target of the member an action is
+  for. `mcpp pack -p <member>` keeps its meaning. The JSON envelope adds
+  `data.stages` and a `member` field per artifact when several members are
+  packed (e2e 867 to 870).
+
+### Fixed
+
+- **A repeated `-p` no longer keeps only its last value (mcpp#750).**
+  `mcpp test -p a -p b` tested `b` alone and exited 0.
+- **Starting a child process is safe for concurrent callers.** A pipe created
+  by one thread could be inherited by a child another thread started, and the
+  first thread's reader then waited for end of file until the unrelated child
+  exited. Pipes are created close-on-exec on Linux; on macOS and Windows the
+  creation of a pipe, the start of the child and the parent's close of the
+  write end form one critical section. The registry of children for signal
+  forwarding is serialised and holds 256 entries.
+- **`mcpp run -q` writes exactly the program's standard output.** It began
+  with an empty line (e2e 862).
+
 ## [2026.9.30.2] - 2026-09-30
 
 This release answers five reports on 2026.9.30.1 while building xlings

docs/04-mcpp-toml.md

@@ -1391,6 +1391,13 @@ What is **not** cached: `path` and `git` dependencies, at any depth, and
 workspace members. Their sources can change without their `name@version`
 changing, so no key over that identity could notice the change.
 
+The modules a build program imports follow the same rule (2026.10.1.1+). The
+bundled `mcpp` module and the host modules of index packages are kept in the
+global cache, and a host module of a `path` or `git` dependency or of a workspace
+member is kept under `target/.build-mcpp/host-modules/`, never in the global
+cache. `--cache local` and `--cache off` keep all of them in the project. See
+[30 — Placement of compiled host modules](30-build-mcpp.md).
+
 Inspection and reclamation:
 
 ```