reverse-proxy/tasks/fix/config-reload-static-drift.md

id, name, status, depends_on, scope, risk, impact, level, review_findings

id	name	status	depends_on	scope	risk	impact	level	review_findings
fix/config-reload-static-drift	Fix ConfigReloadHandle static config drift causing stale diff warnings	completed		narrow	medium	component	implementation	C4

Description

Fix the ConfigReloadHandle::reload() method which computes a diff of static config fields but never updates the stored StaticConfig. This means every reload compares against the original static config (from process start), not the last-reloaded one, causing repeated "static config fields changed" warnings for the same fields on every reload.

The architecture spec in config.md explicitly states: "The ConfigReloadHandle must track the last-known StaticConfig so that it can correctly detect changes on subsequent reloads. After each successful reload, the stored StaticConfig is updated with the new value."

Changes Required

src/config/dynamic_config.rs:

• Change ConfigReloadHandle.static_config from StaticConfig to ArcSwap<StaticConfig>
• Update ConfigReloadHandle::new() to wrap the static config in ArcSwap
• In reload(), after computing the diff, store the new static config: self.static_config.store(Arc::new(new_static))
• Add pub fn static_config(&self) -> Arc<StaticConfig> accessor if needed by other code
• Update diff_static_config to work with references (it already does — just need to use self.static_config.load() instead of &self.static_config)

Tests:

• Update ConfigReloadHandle tests to verify that a second reload only reports changes since the first reload, not changes since startup
• Verify that the static_config_diff_detects_changes test still works with ArcSwap<StaticConfig>

Implementation Note

The ArcSwap<StaticConfig> approach is already used for DynamicConfig in the same struct. The pattern is well-established in the codebase. ArcSwap provides lock-free reads (important since reloads are rare but reads could be concurrent), and Arc<StaticConfig> is cheap to clone for comparison purposes.

Acceptance Criteria

• ConfigReloadHandle.static_config is ArcSwap<StaticConfig> (not plain StaticConfig)
• After a successful reload, self.static_config is updated with the new value
• A second reload with no further static config changes reports an empty diff
• A second reload with different static config changes reports only the new changes
• Existing reload tests pass
• cargo clippy passes with no warnings

References

• docs/architecture/config.md — Static config changes during reload, ArcSwap pattern
• docs/reviews/002-implementation-review.md — C4 finding
• src/config/dynamic_config.rs — ConfigReloadHandle implementation

Notes

To be filled by implementation agent

Summary

To be filled on completion