feat: add Python and Java regex engines

docs/GENERATED_CASES.md

@@ -25,10 +25,11 @@ The coverage report says `covered`, `partial`, `unsupported` or
 sampling strategy was requested. It does not mean every string in the regular
 language was enumerated.
 
-PCRE2 generation is unavailable in version 1. Its actual engine is complete for
-the advertised execution operations, but its current structural syntax
-provider is intentionally partial. Regex Tools does not feed PCRE2 syntax to
-the ECMAScript generator or relabel ECMAScript behavior.
+PCRE2, Python and Java generation is unavailable in version 1. Their actual
+engines are complete for the advertised execution operations, but their
+current structural syntax providers are intentionally partial. Regex Tools
+does not feed their syntax to the ECMAScript generator or relabel ECMAScript
+behaviour.
 
 ## Unsupported and partial constructs
 
@@ -75,7 +76,9 @@ removes the generation provenance.
 Candidate synthesis runs in a dedicated killable worker. The verifier then
 sends each exact candidate, pattern, flavour version, flags, engine options and
 scan mode through `EngineSupervisor`, which selects the registered real engine
-worker.
+worker. Version 1's eligibility gate accepts only the exact current ECMAScript
+snapshot; the generic supervisor boundary does not make partial-provider
+flavours eligible.
 
 - An intended positive is labelled `should-match` only after the engine returns
   at least one match.