CORE-15424 schemaregistry: default enable schema_registry_enable_qualified_subjects

[pgellert]

For the 26.2 release, enable schema-registry context support by default by flipping schema_registry_enable_qualified_subjects from false to true and promoting the property to user visibility. Qualified subject syntax (e.g. :.context:subject) is now parsed out-of-the-box rather than requiring an opt-in cluster config change.

It also cleans up the startup_config-based locking of the value of the schema_registry_enable_qualified_subjects property, since the ae61cc7 already provides the desired behaviour for needs_restart properties.

Fixes https://redpandadata.atlassian.net/browse/CORE-15424

Backports Required

• none - not a bug fix
• none - this is a backport
• none - issue does not exist in previous branches
• none - papercut/not impactful enough to backport
• v26.1.x
• v25.3.x
• v25.2.x

Release Notes

Features

• Schema Registry context support is now enabled by default. Subjects of the form :.context:subject are parsed into a separate context. See upgrade considerations before upgrading clusters that may have stored literal :.-prefixed subject names.

[Copilot]

Pull request overview

Enables Schema Registry context support by default by flipping schema_registry_enable_qualified_subjects to true and making it user-visible, so qualified subjects like :.context:subject are parsed without an opt-in cluster config change.

Changes:

• Change the default for schema_registry_enable_qualified_subjects to true and promote visibility to user.
• Remove config::startup_config usage/implementation for SR qualified-subject parsing and rely on needs_restart config semantics instead.
• Update Python and C++ tests/build targets to reflect the new default and the removal of the startup-captured flag.

Reviewed changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/rptest/tests/schema_registry_test.py	Updates the “flag off” test to explicitly disable the setting now that default is enabled.
tests/rptest/tests/metrics_reporter_test.py	Drops redundant extra_rp_conf enabling the setting (now default).
tests/rptest/tests/audit_log_test.py	Removes redundant cluster-config enabling (now default).
src/v/security/tests/authorizer_test.cc	Removes per-test local enabling of qualified parsing (now default).
src/v/pandaproxy/schema_registry/types.h	Removes enable_qualified_subjects startup-captured flag type.
src/v/pandaproxy/schema_registry/types.cc	Reads schema_registry_enable_qualified_subjects directly from shard_local_cfg() during parsing.
src/v/pandaproxy/schema_registry/test/store_fixture.cc	Removes per-fixture enable/reset of qualified parsing (now default).
src/v/pandaproxy/schema_registry/test/storage.cc	Removes fixture SetUp/TearDown that toggled the old startup flag.
src/v/pandaproxy/schema_registry/test/context_subject.cc	Updates tests to toggle the config property instead of the removed startup flag.
src/v/pandaproxy/schema_registry/test/consume_to_store.cc	Removes per-test enabling/reset of qualified parsing (now default).
src/v/pandaproxy/schema_registry/test/BUILD	Adds //src/v/config dep for tests that now manipulate config directly.
src/v/pandaproxy/schema_registry/requests/test/post_subject_versions.cc	Removes per-test enabling/reset of qualified parsing (now default).
src/v/pandaproxy/schema_registry/api.cc	Removes startup init/reset of the removed startup-captured flag; logs current config value.
src/v/pandaproxy/schema_registry/BUILD	Removes startup_config deps; adds //src/v/config where needed.
src/v/config/tests/startup_config_test.cc	Removes tests for startup_config (feature removed).
src/v/config/tests/BUILD	Removes the startup_config_test target.
src/v/config/startup_config.h	Removes the startup_config implementation.
src/v/config/configuration.cc	Flips default to true and sets visibility to user for the SR qualified-subject config.
src/v/config/BUILD	Removes the startup_config library target.

[nguyen-andrew]

👍