ci: validate with mcpp 2026.9.29.3; latest_mcpp -> 2026.9.29.3

2026.9.29.3 (mcpp-community/mcpp#740) places the runtime files of a program a
member ships through artifacts beside it and no longer makes its link wait for
a plan-level runtime file.

Author: Sunrisepeak

.github/workflows/validate.yml

@@ -393,7 +393,11 @@ env:
   # module built, and a member's product directory holds every shared library
   # of its closure. 2026.9.29.1 is not used here: its sweep refused the 47
   # members that declare their own [indices].
-  MCPP_VERSION: "2026.9.29.2"
+  #
+  # 2026.9.29.3 (mcpp-community/mcpp#740): a program a member ships through
+  # `artifacts` waits for no plan-level runtime file, and its own runtime
+  # files are placed beside it in the member's product directory.
+  MCPP_VERSION: "2026.9.29.3"
 
 jobs:
   lint:

index.toml

@@ -126,13 +126,15 @@
 # registers mcpp.plugins 0.17.0, whose package floor it is. The release changes
 # no descriptor grammar; its `[package] mcpp` key is manifest vocabulary, which
 # an older engine reports as unsupported and ignores.
-# ── 2026-09-29: latest_mcpp -> 2026.9.29.2, min_mcpp unchanged ─────────────
+# ── 2026-09-29: latest_mcpp -> 2026.9.29.3, min_mcpp unchanged ─────────────
 #
-# Moved in the pull request that moves validate.yml's pin to 2026.9.29.2,
+# Moved in the pull request that moves validate.yml's pin to 2026.9.29.3,
 # which runs every member on every platform with it. 2026.9.29.1 is skipped:
 # it resolved a member's own relative [indices].path against the workspace
-# root. Neither release changes descriptor grammar.
+# root; 2026.9.29.2 is the version the full sweep ran with, and 2026.9.29.3
+# adds the runtime placement of programs shipped through `artifacts`. None of
+# the three changes descriptor grammar.
 [index]
 spec        = "1"
 min_mcpp    = "2026.9.18.3"
-latest_mcpp = "2026.9.29.2"
+latest_mcpp = "2026.9.29.3"