docs(specs): SPEC-009, the support and maintenance of toolchains

Add SPEC-009 (docs/specs/toolchain-maintenance.md), the toolchain
specification approved in review on 2026-10-02: support tiers, the single
line table, whole-line moves, provenance, what supporting a line means,
the compiler-defect register, host platform releases, mirrors, the order
and the gate (G1 to G6, 10 percent) for moving a default, machines that
already have a default, mcpp building with what it gives, and the
conformance checks C1 to C7. Each rule carries an implementation status
and, where the status is not "implemented", the current behaviour.

SPEC-006 section 7 becomes a reference to SPEC-009 section 10 (v0.6); the
order of moving a C-library binding is carried into SPEC-009 section 10.10.
The specification index and both documentation indexes list SPEC-009.

Author: speak-agent

docs/README.md

@@ -164,3 +164,4 @@ downstream tooling.
   - [SPEC-006 — Toolchain management: identity, origin, selection and the payload contract](specs/toolchain-management.md)
   - [SPEC-007 — Build plugins: configuration, construction and verification, and the runtime and planning obligations](specs/build-plugins.md)
   - [SPEC-008 — A library's interface: public modules, the published closure, and one interface in both forms](specs/library-interface.md)
+  - [SPEC-009 — The support and maintenance of toolchains: lines, defaults, provenance, moves and retirement](specs/toolchain-maintenance.md)

docs/specs/README.md

@@ -35,9 +35,10 @@
 | [SPEC-003](exit-codes.md) | 退出码契约(分类、语义、稳定性承诺) | 评审中 v1.0 | 2026-09-01 | mcpp >= 2026.9.1.1 |
 | [SPEC-004](manifest-semantics.md) | `mcpp.toml` 的平面划分、条件化形状、解析轴与命名规约 | 草案 v1.10 | 2026-09-28 | 条件化形状 mcpp >= 2026.8.29.1;目标轴 mcpp >= 2026.9.6.4;`linkage` 默认值 mcpp >= 2026.9.15.2;链接 flag 的词读法 mcpp >= 2026.9.26.2;条件化的 `dialect_cxxflags` 与 `-p` 的包身份 mcpp >= 2026.9.28.1;条件表按具体程度生效 mcpp >= 2026.9.28.2 |
 | [SPEC-005](build-database.md) | 构建数据库:`mcpp emit build-database` 的内容、取值规则与不写工程目录的保证 | 评审中 v1.6 | 2026-09-29 | mcpp >= 2026.9.15.1;v1.3 条款 mcpp >= 2026.9.26.2;v1.4 条款 mcpp >= 2026.9.27.1;v1.5 条款 mcpp >= 2026.9.28.1;v1.6 条款 mcpp >= 2026.9.29.5 |
-| [SPEC-006](toolchain-management.md) | 工具链管理:身份、来源、选择与载荷契约 | 草案 v0.4 | 2026-09-28 | 逐条标注;已实现条款 mcpp >= 2026.9.24.1;§3.7 mcpp >= 2026.9.28.1;§3.7.1 mcpp >= 2026.9.28.2 |
+| [SPEC-006](toolchain-management.md) | 工具链管理:身份、来源、选择与载荷契约 | 草案 v0.6 | 2026-10-02 | 逐条标注;已实现条款 mcpp >= 2026.9.24.1;§3.7 mcpp >= 2026.9.28.1;§3.7.1 mcpp >= 2026.9.28.2;§2.2.1 与 §3.3 的非缺省来源 mcpp >= 2026.10.1.3 |
 | [SPEC-007](build-plugins.md) | 构建插件:配置、施工与校验的分工,运行时与规划期的义务 | 草案 v0.6 | 2026-09-28 | 逐条标注;mcpp >= 2026.9.26.2;v0.3 条款 mcpp >= 2026.9.27.1;v0.4 条款 mcpp >= 2026.9.28.1;v0.5 条款 mcpp >= 2026.9.28.2;v0.6(§9)mcpp >= 2026.9.28.3 |
 | [SPEC-008](library-interface.md) | 库的接口:公开模块、发布闭包与两种形态的一致 | 草案 v0.1 | 2026-09-28 | 第一阶段(只警告)mcpp >= 2026.9.28.3 |
+| [SPEC-009](toolchain-maintenance.md) | 工具链的支持与维护:版本线、默认值、来源、移动与退役 | 草案 v0.1 | 2026-10-02 | 逐条标注;本版只有规范,多数条款未实现 |
 
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