refactor: replace deprecated serde_yaml with serde_saphyr

[DavSanchez]

In preparation for the incoming kube-rs v4, we can start working to remove our dependency on serde_yaml!

Summary

This PR replaces the deprecated serde_yaml dependency with serde_saphyr across the entire workspace, while migrating abstract YAML DOM manipulations from serde_yaml::Value/Mapping/Number to serde_json::Value/Map/Number.

Motivation

The serde_yaml crate is officially deprecated and no longer maintained. serde_saphyr is the recommended modern replacement that provides YAML 1.2 serialization/deserialization via serde.

However, serde_saphyr intentionally does not provide Value/Mapping/Number types. All abstract YAML tree manipulations must be expressed through serde_json::Value/Map/Number instead.

Changes

Dependencies

• Removed serde_yaml from workspace Cargo.toml, agent-control/Cargo.toml, and test/e2e-runner/Cargo.toml
• Added serde-saphyr as the replacement for serde operations (from_str, to_string, from_reader, etc.)
• Relied on existing serde_json for abstract DOM types (Value, Map<String, Value>, Number)

Source Migration (~66 files)

Before (serde_yaml)	After (serde_saphyr / serde_json)
serde_yaml::Value	serde_json::Value
serde_yaml::Mapping	serde_json::Map<String, serde_json::Value>
serde_yaml::Number	serde_json::Number
serde_yaml::from_str	serde_saphyr::from_str
serde_yaml::to_string	serde_saphyr::to_string
serde_yaml::from_reader	serde_saphyr::from_reader
serde_yaml::to_value	serde_json::to_value
serde_yaml::from_value	serde_json::from_value

Behavioral Differences Handled

serde_saphyr has stricter defaults than serde_yaml. The following adjustments were made to preserve existing behavior:

1. Duplicate YAML keys: serde_saphyr errors by default on duplicate mapping keys, while serde_yaml silently accepted them. Production code paths (FileStore::get, YAMLConfig::try_from) now use serde_saphyr::from_str_with_options with DuplicateKeyPolicy::LastWins to match the previous behavior.

2. Null → String deserialization: serde_yaml deserialized name: (null value) into an empty String. serde_saphyr rejects this. The AgentTypeID deserialization was updated to use Option<String> fields with .unwrap_or_default() to handle this gracefully.

3. Error message formats: Several unit tests that asserted on exact serde_yaml error strings were updated to assert on the equivalent serde_saphyr error format.

4. Block scalar serialization: serde_saphyr::to_string emits multiline strings as quoted strings with \n escapes rather than YAML literal block scalars (|). One integration test's expected output was updated accordingly.

Error Enum Refactoring

Error variants were renamed to generic names not coupled to the old dependency:

• serde_yaml::Error variants → serde_json::Error and serde_saphyr::ser::Error variants with names like Serialization / Deserialization
• Affected files: agent_type/error.rs, k8s/error.rs, effective_agents_assembler.rs, config_migrate/migration/converter.rs, and others

Test Fixes

• 7 lib tests updated to match serde_saphyr error message formats
• 1 integration test (test_store_remote_no_mocks) updated expected YAML serialization format
• Turbofish syntax fixed in custom_agent_type.rs (Map<String, Value>::new → Map::<String, Value>::new)

Verification

• cargo check --workspace passes
• cargo test -p newrelic_agent_control --lib — 863 tests pass
• cargo test -p newrelic_agent_control --test integration_tests — 54 tests pass (76 ignored)
• cargo test --workspace --lib — all workspace lib tests pass
• cargo clippy -p newrelic_agent_control — clean (1 pre-existing warning fixed)
• No remaining serde_yaml references in source code or tests

Backward Compatibility

This change is intended to be behaviorally transparent to end users. All serialization/deserialization round-trips produce the same semantic results. The only user-visible difference is that YAML files with duplicate keys (which were previously silently accepted) are now also accepted via the LastWins policy.

Related

• serde_yaml deprecation notice: https://github.com/dtolnay/serde_yaml/issues/388
• serde-saphyr crate: https://crates.io/crates/serde-saphyr
• kube-rs crate switch: convert from serde-yaml to serde-saphyr kube-rs/kube#1975

[danielorihuela]

From my side we could merge it. Should we mention that on a Tech Talk just in case? I mean before merging.

[DavSanchez]

From my side we could merge it. Should we mention that on a Tech Talk just in case? I mean before merging.

Added item for next tech meeting

[sigilioso]

Maybe we should also remove it from the renovate rule:

newrelic-agent-control/.github/renovate-shared-base.json

Lines 94 to 99 in 0837997

	{
	"enabled": false,
	"matchPackageNames": [
	"/serde_yaml/"
	]
	},

[DavSanchez]

Maybe we should also remove it from the renovate rule:

newrelic-agent-control/.github/renovate-shared-base.json

Lines 94 to 99 in 0837997

	{
	"enabled": false,
	"matchPackageNames": [
	"/serde_yaml/"
	]
	},

Good catch! 54c8240

[sigilioso]

🚀