Add comprehensive FlatBuffers documentation page

[oberstet]

Summary

Create a dedicated documentation page explaining autobahn-python's FlatBuffers features, bundled flatc compiler, and
integration with the WAMP ecosystem.

Background

autobahn-python now includes significant FlatBuffers functionality that is not well-documented:

1. Bundled flatc compiler in binary wheels (since v25.12.x)
2. Vendored FlatBuffers runtime for serialization
3. WAMP FlatBuffers schemas for efficient binary serialization
4. Cross-project version synchronization with zlmdb

Currently, FlatBuffers information is scattered across:

• FlatBuffers WAMP Schema Reference
• Python API Reference
  (autobahn.flatbuffers)

Proposed Documentation Content

1. Overview Section

• What is FlatBuffers and why autobahn-python uses it
• Benefits: zero-copy access, efficient serialization, cross-language compatibility
• Use cases: WAMP binary serialization, high-performance messaging

2. Bundled flatc Compiler

• Feature: Wheels include a pre-compiled flatc executable; source installs compile it from deps/flatbuffers
• Usage: After pip install autobahn, run flatc --version
• Platform support: Linux (x86_64, aarch64), macOS (arm64), Windows (x86_64)
• ISA requirements: Need GLIBC 2.28+ (e.g., Ubuntu 20.04+, Debian 11+, RHEL 8+)
  • Linux x86_64: manylinux_2_28 (GLIBC 2.28+)
  • Linux aarch64: manylinux_2_28 (GLIBC 2.28+)
• Benefits: No need to install system-wide flatc, version matches vendored runtime
• Source builds: Require cmake to compile flatc from deps/flatbuffers during install

3. Vendored FlatBuffers Runtime

• Version tracking: autobahn.flatbuffers.version() returns exact version tuple
• Location: autobahn/flatbuffers/ (vendored from google/flatbuffers)
• Includes reflection schema (reflection.fbs, reflection.bfbs)

4. WAMP FlatBuffers Schemas

• Schema files location: autobahn/wamp/flatbuffers/*.fbs
• Available schemas: wamp.fbs, session.fbs, auth.fbs, pubsub.fbs, rpc.fbs, roles.fbs, types.fbs
• Binary schemas (.bfbs) generated at wheel build time
• Link to existing schema reference
  documentation

5. Cross-Project Version Synchronization

• autobahn-python and zlmdb share the same FlatBuffers version
• Verification function: autobahn.check_zlmdb_flatbuffers_version_in_sync()
• Why this matters: cfxdb and Crossbar.io depend on both libraries
• Example usage:

  import autobahn
  version = autobahn.check_zlmdb_flatbuffers_version_in_sync()
  print(f"FlatBuffers version: {version}")  # e.g., (25, 9, 23, None, None)

6. Development & Build Information

• FlatBuffers source: deps/flatbuffers git submodule (tracks google/flatbuffers)
• Build process: hatch_build.py compiles flatc during both wheel and source builds
• Updating vendored FlatBuffers: just bump-flatbuffers
• Testing bundled flatc: just test-bundled-flatc

7. Troubleshooting

• "flatc not found after source install": Ensure cmake is installed before pip install
• Version mismatch with zlmdb: Update both packages to latest versions
• GLIBC errors on old Linux: Need GLIBC 2.28+ (e.g., Ubuntu 20.04+, Debian 11+, RHEL 8+)

Documentation Location

Suggested location: docs/wamp/flatbuffers.rst (or docs/flatbuffers.rst if scope extends beyond WAMP)

Should be linked from:

• Main documentation index
• WAMP serialization documentation
• Installation guide (mention bundled flatc)

Related

• [BUG] autobahn flatbuffers support requires nonexisting autobahn.flatbuffers #1817 - FlatBuffers vendoring verification
• Synchronize CI/CD, Flatbuffers vendoring and wamp-ai and wamp-cicd Submodules between autobahn-python and zlmdb #1821 - CI/CD and FlatBuffers sync with zlmdb
• Synchronize CI/CD, Flatbuffers vendoring and wamp-ai and wamp-cicd Submodules between autobahn-python and zlmdb #1822 - Synchronize CI/CD, FlatBuffers vendoring between autobahn-python and zlmdb
• Synchronize CI/CD, Flatbuffers vendoring and wamp-ai and wamp-cicd Submodules between autobahn-python and zlmdb zlmdb#100 - Sync autobahn-python and zlmdb

Checklist

• I have searched existing issues to avoid duplicates
• I have described the problem clearly
• I have provided use cases
• I have considered alternatives
• I have assessed impact and breaking changes