fix(agents): scope Java transformer P0 and seed full-review perf facts

Auto-instrumentations still require InstrumenterModule; product
transformers do not. The full-review fixture now states the J10/J12
preconditions the performance override already requires.

Author: robertomonteromiguel

.agents/dd-apm-sdk-review-overrides/reviewers/design.md

@@ -20,7 +20,9 @@ Read **docs/add_new_configurations.md** — it owns the registration steps; chec
 
 ## Extension points (instrumentations)
 
-An instrumentation must go through `InstrumenterModule` + the `Instrumenter` type-matching interfaces (`ForSingleType`, `ForKnownTypes`, `ForTypeHierarchy`, `ForBootstrap`) and be discovered via `@AutoService(InstrumenterModule.class)` — see ARCHITECTURE.md § "agent-tooling/" and **docs/add_new_instrumentation.md** / **docs/how_instrumentations_work.md**. A bespoke `ClassFileTransformer` or advice registered outside this mechanism bypasses Muzzle's build-time version-safety checks entirely — that's a P0 shape problem, not a nit, independent of whether the bespoke code works.
+An **auto-instrumentation** under `dd-java-agent/instrumentation/` must go through `InstrumenterModule` + the `Instrumenter` type-matching interfaces (`ForSingleType`, `ForKnownTypes`, `ForTypeHierarchy`, `ForBootstrap`) and be discovered via `@AutoService(InstrumenterModule.class)` — see ARCHITECTURE.md § "agent-tooling/" and **docs/add_new_instrumentation.md** / **docs/how_instrumentations_work.md**. A bespoke `ClassFileTransformer` or advice registered outside this mechanism for an auto-instrumentation bypasses Muzzle's build-time version-safety checks entirely — that's a P0 shape problem, not a nit, independent of whether the bespoke code works.
+
+This rule is scoped to auto-instrumentations. Product subsystems that already register purpose-built transformers outside `InstrumenterModule` (CI Visibility coverage, debugger, IAST, AppSec, telemetry) are not in scope — do not raise a P0 solely because those products use a standalone `ClassFileTransformer`.
 
 ## Lifecycle / bootstrap
 

.llm-validation/suites/dd-apm-sdk-review.yaml

@@ -57,6 +57,10 @@ cases:
       inspect — this diff is the entire change set; do not attempt any git commands, go
       straight to running the reviewers on the pasted content below.
 
+      `byResource` is a lookup-by-key cache: callers only `get(resourceName)`. Insertion
+      order is not part of the contract. `describe()` is invoked on the per-span write
+      path (hot).
+
       ```diff
       diff --git a/dd-trace-core/src/main/java/datadog/trace/core/SpanCache.java b/dd-trace-core/src/main/java/datadog/trace/core/SpanCache.java
       index 1111111..2222222 100644