ci: migrate macOS validation to macos-15 runner

.github/workflows/tests.yml

@@ -21,7 +21,7 @@ jobs:
       fail-fast: false
       matrix:
         os:
-          - macos-14
+          - macos-15
           - ubuntu-24.04
     steps:
       - uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4

CHANGELOG.md

@@ -7,7 +7,10 @@ and versions are tracked in the repo-root `VERSION` file.
 
 ## [Unreleased]
 
-No unreleased changes yet.
+### Changed
+
+- Moved hosted macOS validation to the pinned macOS 15 runner while preserving
+  the logical macOS 14 compatibility and release-platform contract.
 
 ## [2.2.2] - 2026-10-08
 

docs/consumer-validation-status.md

@@ -28,7 +28,9 @@ release-contract patch with no intended public API or runtime behavior changes.
 The latest completed full runtime validation is the [v2.2.0 release validation
 run](https://github.com/basefoundry/base-bash-libs/actions/runs/37647096223), which
 passed the release gates, supported Bash compatibility jobs, macOS 14 and
-Ubuntu 24.04 validation, and the downstream Beacon smoke. The corresponding
+Ubuntu 24.04 validation, and the downstream Beacon smoke. This historical run
+used the macOS 14 hosted image; current validation uses the pinned macOS 15
+runner for the same macOS 14 compatibility contract. The corresponding
 [Base Bash Demo v0.1.0 release run](https://github.com/basefoundry/base-bash-libs-demo/actions/runs/37652182510)
 passed its macOS Homebrew Bash, Ubuntu, minimum-Bash, and standalone-artifact
 jobs against the immutable v2.2.0 vendor. The earlier [Framework Compatibility

docs/release-process.md

@@ -87,7 +87,8 @@ policy](https://github.com/basefoundry/base/blob/main/docs/ecosystem-policy.md).
    uses the `C` locale, and archive creation supports GNU tar and bsdtar only;
    other tar implementations fail closed rather than claiming reproducibility.
    Generate the repository component row for the ecosystem BOM from the same
-   immutable merged commit:
+   immutable merged commit. Keep the logical macOS 14 support-platform value in
+   the row; the active hosted validation for that platform runs on macOS 15:
 
    ```bash
    scripts/release-bom-row --version X.Y.Z --commit "$release_commit" \

docs/support-matrix.md

@@ -8,7 +8,7 @@ unreported pass.
 | Dimension | Supported contract | Evidence |
 | --- | --- | --- |
 | Bash | 4.2.53 minimum; representative 4.4.23 and 5.0.18/5.2.37; current 5.x | Pinned networkless Bash containers, current runner validation, `tests/compatibility-matrix.sh`, deterministic property, artifact, and concurrency contracts |
-| macOS | Pinned GitHub-hosted macOS 14 with Homebrew Bash; system Bash 3.2 is rejected with remediation | macOS validation and unsupported-system-Bash smoke |
+| macOS | macOS 14 is the supported floor; hosted validation runs on the pinned GitHub-hosted macOS 15 runner with Homebrew Bash because no macOS 14 hosted runner is available; system Bash 3.2 is rejected with remediation | macOS validation and unsupported-system-Bash smoke |
 | Linux/glibc | Pinned Ubuntu 24.04 runner and Bash 4.2.53/4.4.23/5.0.18/5.2.37 containers | Ubuntu validation and compatibility workflow |
 | Linux/musl | Alpine/musl syntax and option-contract probe when the runner provides Docker | `tests/compatibility-matrix.sh --container alpine` |
 | BSD userland | Best-effort portability checks; no release guarantee until a maintained CI runner is available | Explicitly reported as advisory |