ci(buildv2): add build/QEMU/Linux jobs for Build system v2

Add the parallel set of CI jobs that exercise the cmakev2 path end-to-end
via the IDF_BUILD_V2 shim. All jobs are gated on the `buildv2` MR label
with `allow_failure: true` so unrelated MRs do not pay for the extra
build matrix.

- `.gitlab/ci/build.yml`: add the buildv2 child build pipeline that
  re-runs the full app build matrix with IDF_BUILD_V2=y, plus the
  Windows buildv2 build job. The generator script injects IDF_BUILD_V2
  and a PIPELINE_COMMIT_SHA suffix into each child job and broadens
  target_test job filters so v1 and buildv2 artifacts upload to distinct
  s3 cache paths and each child pipeline tests its own binary.
- `.gitlab/ci/host-test.yml`: add the QEMU (esp32, esp32c3) and Linux
  pytest buildv2 jobs.
- `.idf_build_apps.toml`: parameterize build_dir with BUILDV2_DIR_SUFFIX
  (set to _v2 only on the buildv2 pipeline).

tools/ci/dynamic_pipelines/scripts/patch_buildv2_child_pipeline.py

@@ -0,0 +1,76 @@
+# SPDX-FileCopyrightText: 2026 Espressif Systems (Shanghai) CO LTD
+# SPDX-License-Identifier: Apache-2.0
+"""Patch the generated Build system v2 build child pipeline in place.
+
+The buildv2 build child pipeline is generated by ``idf-ci gitlab build-child-pipeline``
+from the same manifest as the default pipeline. This script post-processes that
+generated YAML so the cmakev2 path is exercised end to end:
+
+1. Inject ``IDF_BUILD_V2`` into each child build job so cmake activates the
+   cmakev2 shim.
+
+2. Inject ``PIPELINE_COMMIT_SHA: ${PIPELINE_COMMIT_SHA}_buildv2`` into each child
+   build job. idf-ci reads ``PIPELINE_COMMIT_SHA`` when computing the s3
+   upload/download prefix (``project/<sha>/...``). Suffixing it for v2 jobs only
+   routes v2 binaries to a distinct s3 key namespace without renaming build_dir.
+
+3. Redefine ``generate_pytest_child_pipeline`` so its script also runs
+   ``patch_buildv2_target_test_pipeline.py`` against the emitted
+   ``target_test_child_pipeline.yml`` and injects the same
+   ``PIPELINE_COMMIT_SHA`` override into each target_test job. Without this, the
+   v2 target_test pipeline would still download from the default pipeline's s3
+   keys (race-determined, mostly cmakev1 binaries).
+"""
+
+import argparse
+
+import yaml
+
+PIPELINE_COMMIT_SHA_V2 = '${PIPELINE_COMMIT_SHA}_buildv2'
+
+
+def patch(path: str) -> None:
+    with open(path) as f:
+        d = yaml.safe_load(f)
+
+    injected = []
+    for k, v in d.items():
+        if isinstance(v, dict) and 'extends' in v:
+            v.setdefault('variables', {})['IDF_BUILD_V2'] = '1'
+            v['variables']['PIPELINE_COMMIT_SHA'] = PIPELINE_COMMIT_SHA_V2
+            injected.append(k)
+
+    # Redefine generate_pytest_child_pipeline (included from
+    # tools/ci/dynamic_pipelines/templates/test_child_pipeline.yml) so its script
+    # also rewrites target_test_child_pipeline.yml. GitLab CI merges values at the
+    # keyword level, so only `script` is overridden; `needs`, `artifacts`,
+    # `image`, etc. come from the included version.
+    d['generate_pytest_child_pipeline'] = {
+        'script': [
+            'python tools/ci/dynamic_pipelines/scripts/generate_target_test_child_pipeline.py',
+            'python tools/ci/dynamic_pipelines/scripts/patch_buildv2_target_test_pipeline.py '
+            'target_test_child_pipeline.yml',
+        ],
+    }
+
+    with open(path, 'w') as f:
+        yaml.safe_dump(d, f, sort_keys=False)
+
+    print('Injected IDF_BUILD_V2 + PIPELINE_COMMIT_SHA into build jobs:', injected)
+    print('Redefined generate_pytest_child_pipeline with post-processing step')
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser(description=__doc__, formatter_class=argparse.RawDescriptionHelpFormatter)
+    parser.add_argument(
+        'pipeline_yaml',
+        nargs='?',
+        default='buildv2_child_pipeline.yml',
+        help='Path to the generated buildv2 build child pipeline YAML to patch in place.',
+    )
+    args = parser.parse_args()
+    patch(args.pipeline_yaml)
+
+
+if __name__ == '__main__':
+    main()

tools/ci/dynamic_pipelines/scripts/patch_buildv2_target_test_pipeline.py

@@ -0,0 +1,56 @@
+# SPDX-FileCopyrightText: 2026 Espressif Systems (Shanghai) CO LTD
+# SPDX-License-Identifier: Apache-2.0
+"""Patch the generated Build system v2 target_test child pipeline in place.
+
+Inject ``PIPELINE_COMMIT_SHA: ${PIPELINE_COMMIT_SHA}_buildv2`` into every
+target_test job so idf-ci downloads the cmakev2 binaries from the distinct s3
+key namespace produced by the v2 build jobs, instead of racing with the default
+pipeline's binaries.
+
+Run from generate_pytest_child_pipeline (see patch_buildv2_child_pipeline.py),
+after generate_target_test_child_pipeline.py has emitted the YAML.
+"""
+
+import argparse
+
+import yaml
+
+PIPELINE_COMMIT_SHA_V2 = '${PIPELINE_COMMIT_SHA}_buildv2'
+
+# Target test jobs use extends: .dynamic_target_test_template, so their script:
+# comes from the template, not their own definition. These top-level keys are
+# pipeline configuration rather than jobs and must be skipped.
+SKIP_KEYS = {'include', 'workflow', 'default', 'variables', 'stages'}
+
+
+def patch(path: str) -> None:
+    with open(path) as f:
+        d = yaml.safe_load(f)
+
+    modified = 0
+    for k, v in d.items():
+        if k in SKIP_KEYS or not isinstance(v, dict):
+            continue
+        v.setdefault('variables', {})['PIPELINE_COMMIT_SHA'] = PIPELINE_COMMIT_SHA_V2
+        modified += 1
+
+    with open(path, 'w') as f:
+        yaml.safe_dump(d, f, sort_keys=False)
+
+    print(f'Injected PIPELINE_COMMIT_SHA override into {modified} target_test jobs')
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser(description=__doc__, formatter_class=argparse.RawDescriptionHelpFormatter)
+    parser.add_argument(
+        'pipeline_yaml',
+        nargs='?',
+        default='target_test_child_pipeline.yml',
+        help='Path to the generated target_test child pipeline YAML to patch in place.',
+    )
+    args = parser.parse_args()
+    patch(args.pipeline_yaml)
+
+
+if __name__ == '__main__':
+    main()