patches: msys variant of the tebako spawn hook (fix the target_file shadowing)

[ronaldtse]

Summary

Fixes the reason the windows argv bridge (merged in #102) had no effect on the packed-mn acceptance: the spawn patch never reached msys builds at all.

Root cause (proven, not hypothesized)

PatchSelection#filter_platform (tools/lib/tfs/patch_selection.rb:135-138) implements the msys shadow rule: a base patch is dropped when an _msys-suffixed sibling targets the same file (by +++ b/ header). Lines 3.2/3.3/3.4 carry process_c_clock_guard_msys.patch (target: process.c), which shadows the base process_c_tebako_spawn.patch (target: process.c).

Local proof with the repo's own tooling:

3.3.12 msys pass2 set: 19 patches; the only process.c toucher is
process_c_clock_guard_msys — process_c_tebako_spawn: DROPPED
(linux-gnu keeps it, as expected)

So windows runtimes have never contained the spawn hook — not even the pre-#102 no-op stub. The packed-mn#251 windows acceptance on runtime 0.16.13 failed with the byte-identical jing error (Unable to access jarfile A:/__tfs__/...jing-20091111.jar) because there was nothing in the binary to rewrite the token.

Fix

Add process_c_tebako_spawn_msys.patch (byte-identical to the base — the POSIX half is #ifndef _WIN32 and compiles out; the win32 argv bridge compiles in) plus the manifest entry on the three affected lines (3.2, 3.3, 3.4). Lines 3.1 and 4.0 have no clock_guard_msys, so the base patch already lands there — verified, no change.

Validation

• Selection proof (this branch), all five lines, msys pass2 vs linux-gnu:
  • 3.1.7 / 4.0.6: msys carries base (unchanged — no shadow)
  • 3.2.11 / 3.3.12 / 3.4.10: msys now carries process_c_tebako_spawn_msys; POSIX unchanged
• tools/lint OK on 3.1.7 / 3.2.11 / 3.3.12 / 3.4.10 / 4.0.6 (lint checks each patch independently — necessary, not sufficient)
• Scenario composition proof (the gate that actually models the build): tools/apply <v> --platform msys --pass 2 succeeds for 3.2.11 / 3.3.12 / 3.4.10, and the composed msys process.c contains the bridge (tfs_spawn_prepare, tebako_path_is_embedded, tebako_fs_exec_materialize at the bridge sites), composing cleanly with clock_guard_msys.

Follow-ups

• Release chain after merge: tag v0.2.30 → factory 0.16.14 re-cut → packed-mn#251 re-pin → windows acceptance re-run.
• A lint gate asserting "no base patch is silently shadowed by an _msys sibling without an explicit decision" is queued as debt (the trap this PR fixes was silent by construction).