refactor(targets): unify queue/connectivity handling and coverage (#2953)

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>
Co-authored-by: marshawcoco <marshawcoco@gmail.com>

crates/audit/AGENTS.md

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+# Audit Crate Instructions
+
+Applies to `crates/audit/`.
+
+`rustfs-audit` is the domain layer for audit event fan-out and observability.
+It composes shared plugin/runtime abstractions from `rustfs-targets` and keeps
+audit-specific dispatch semantics, state transitions, and metrics in this
+crate.
+
+## Domain Boundaries
+
+- Keep audit-specific behavior here:
+  - audit event shaping and fan-out pipeline
+  - audit system lifecycle/state transitions
+  - audit metrics and reporting
+- Keep shared plugin/runtime mechanics in `rustfs-targets`:
+  - no duplicated replay worker orchestration
+  - no duplicated runtime manager primitives
+  - no plugin install/control-plane modeling in this crate
+
+## Runtime Layering Rules
+
+- `pipeline.rs` hosts:
+  - `AuditPipeline` (dispatch and snapshot access)
+  - `AuditRuntimeFacade` (runtime mutation path)
+  - `AuditRuntimeView` (runtime read path)
+- `registry.rs` should remain the single owner of runtime target container and
+  plugin registry composition for audit.
+- `system.rs` should coordinate lifecycle by calling facade/view/registry
+  boundaries rather than embedding low-level runtime logic.
+
+## Change Style
+
+- Preserve audit delivery semantics and error handling behavior unless the task
+  explicitly changes them.
+- Prefer extending shared abstractions in `rustfs-targets` over patching
+  one-off audit-only runtime flows.
+- Keep logging and observability machine-meaningful; avoid noisy churn in hot
+  dispatch paths.
+
+## Testing
+
+- Keep unit tests close to changed modules.
+- Keep pipeline-layer regressions in `tests/pipeline_layer_test.rs`.
+- Add regression tests for:
+  - runtime facade activation/replace/stop/shutdown behavior
+  - runtime view target/snapshot access
+  - system reload and runtime commit/clear boundaries
+- Suggested validation:
+  - `cargo test -p rustfs-audit`
+  - Focused: `cargo test -p rustfs-audit --test pipeline_layer_test`
+  - Focused: `cargo test -p rustfs-audit pipeline`
+- Full gate before commit: `make pre-commit`