2026.10.5.1: mcpp run hands the terminal to the program, and the follow-ups of #766

[Sunrisepeak]

Summary

This pull request releases 2026.10.5.1. It gives the program that mcpp run starts the terminal, and it closes every follow-up of #761, #763 and #765 recorded in #766. The design record is .agents/docs/2026-10-05-run-terminal-handoff-and-766-follow-ups-design.md (revision 3, which lists where the implementation departs from the reviewed revision 2).

mcpp run and the terminal

run_exec starts every child in a process group of its own, so that a killed mcpp does not leave ninja running (#555). mcpp run used the same launcher for the user's program. On a terminal that group is a background group: the program's first read stopped it with SIGTTIN, and Ctrl-C reached mcpp, which killed the program instead of letting its handler run.

• POSIX: process::run_foreground replaces mcpp with the program (execve) once the build is done. The program reads the terminal, receives Ctrl-C, Ctrl-\ and Ctrl-Z, and runs with the process id the shell started, so nothing of mcpp outlives it. A refused exec keeps the existing classification (125-127).
• Windows: winproc::run_foreground starts the program without CREATE_NEW_PROCESS_GROUP in a kill-on-close job, and mcpp ignores Ctrl-C and Ctrl-Break while it waits.
• Closing notices are printed before the Running line.
• A death by signal reaches the caller as that signal, as in a direct run, instead of 128+n.

The follow-ups of #766

Item	Change
P0 key name	auto_export becomes windows_auto_export before its first release. SPEC-004 §5.3: a key that takes effect on one platform carries that platform's prefix.
P0 exports on PE	coff-def --exports-file narrows the discovered symbols. Source declarations still decide the export set, and exports beside them is a warning. windows_auto_export = false with exports is refused when an MSVC-ABI row is planned. --required makes an empty export surface an error when a program of the build links the DLL.
P1 placement	One predicate, links_objects_of, decides a member's or an artifact's objects and the packages whose shared dependencies it links. It covers statics placed in the owner's own image and excludes statics placed in another package's image.
P1/P2 glob inputs	The walk of sources globs moved to mcpp.modgraph.glob (walk_glob_tree), and the scanner and the fingerprint now share it (symlinks followed with the cycle guard, same exclusions). A pattern no walk can enter is reported. Absolute patterns match absolute paths. A pattern that leaves a registry or git dependency is refused.
P2 IR text	SPEC-009 §10.5 adds gate G7: E2E 881 must pass with a candidate LLVM release on MSVC-ABI rows.
P3	The coff-def tool runs concurrently. docs/04 covers an executable and its package's own shared library. SPEC-004's dangling references are fixed. run_all.sh bounds each test on hosts without GNU timeout (_timeout.py), which is the cause of the macOS 721 hang.

Closes #766.

Test plan

• E2E 883 (new) drives mcpp run through a pseudo-terminal. It covers line input on the fast and prepared paths, Ctrl-C reaching the program's handler (status 3), piped input, signal status parity with a direct run, and a terminated run leaving no process. It fails against a binary without the change (STATUS hung).
• E2E 880 has a placed-static variant that fails before the change with undefined reference to delta@t880_support().
• E2E 882 adds an absolute pattern, an unwatchable-pattern warning, and the refusal in a git dependency.
• E2E 881 adds cases I-L (narrowing, the warning beside declarations, the refusal, --required). It requires MSVC and runs on the Windows shards.
• Local Linux x86_64 / gcc 16.1 with a fresh 2026.10.5.1 binary: full mcpp test passes (146 test binaries, 0 failing); mcpp test -p mcpp.buildmcpp passes; E2E 00, 01, 113, 194, 612, 872, 880, 882 and 883 pass.
• check_docs_style, check_docs_structure, check_modules_wiring, check_narrow_conversions, check_version_pins, check_file_lengths, check_workflow_assertions and git diff --check pass.
• All CI checks pass.