Add http3 module: HTTP/3 in the Java HTTP Client (JEP 517), opt-in, discovery modes, fallback timings, proxy downgrade and a packet-loss comparison

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01KqJyCidz3ZgRyHABv2GVJh

README.md

@@ -68,6 +68,7 @@ These modules keep only sources, a `run.sh` and their transcripts (`output/`). T
 | [`patterns/`](patterns) | Pattern Matching in Java: switch, Record Patterns and Primitive Patterns (JDK 21 to 27) | type and record patterns, guards and dominance errors, sealed exhaustiveness (with JDK 27's new `missing patterns` lines), `MatchException` from a throwing accessor and from separate compilation, unnamed patterns, primitive patterns with `--enable-preview` and the preview class-file trap |
 | [`sealed/`](sealed) | Sealed Classes and Interfaces: Modelling Domains with Exhaustive switch | a `Payment` model, `permits` and the three subclass modifiers, the `default` trap, generic and recursive hierarchies, the visitor for comparison, run-time enforcement and modules |
 | [`lazy-constants/`](lazy-constants) | Lazy Constants in JDK 27 (JEP 531): Replacing Double-Checked Locking | `LazyConstant` against the holder idiom and double-checked locking, the 26 to 27 failure-semantics change, `List`/`Map`/`Set.ofLazy`, the preview-flag traps and a JMH read-path benchmark |
+| [`http3/`](http3) | HTTP/3 in the Java HTTP Client (JEP 517): Migrating from HttpClient 11 | Java 11 code unchanged on 25 and 26, the `HTTP_3` opt-in on client vs request, the three `H3_DISCOVERY` modes, fallback timings (including the 60 s `HTTP_3_URI_ONLY` failure), proxy downgrade, HTTP/1.1 vs 2 vs 3 under iptables packet loss, with a local Hypercorn + aioquic server |
 
 ## Captured output (`docs/output/`)