Merge remote-tracking branch 'Thecave3/e3-agent-framework' into integration_2026_w27

Implementation of the E3 Agent for dApps and E3AP (no service models) (#204)

These changes introduce an E3 Agent for dApps in the OAI codebase. dApps
are real-time microservices designed to operate within the O-RAN
ecosystem, enabling sub-10 ms Artificial Intelligence (AI) routines in
the Radio Access Network (RAN).

The E3 Agent enables spectrum sensing, frequency-domain signal logging,
and dynamic PRB (Physical Resource Block) policies through IPC/ZMQ
communication with dApps or xApps.

The dApps are designed for co-location with the CU/DU, where it can
interact directly with user-plane data to enable different network
management scenarios such as optimizing network slicing, scheduling, and
resource management.  A python library for the creation of the dApps is
available here [1].

Additional information about dApps:

- Paper on the dApp architecture [2]
- dApp framework presentation [3]
- Tutorial on dApp deployment on OAI [4]

As agreed in the original MR [5], this PR includes only the agent lifecycle,
configuration parsing, build plumbing, and the nr-softmodem init/destroy
hook.

It registers zero service models, so it builds and runs as an idle
agent. Concrete service models (e.g. spectrum sensing) and the PHY/MAC
hooks that drive them follow in later PRs.

Opt-in and dependencies

- Gated behind the E3_AGENT CMake option (OFF by default) / the
  --build-e3 build flag.  The default build is unaffected — e3ap is only
  compiled and linked into nr-softmodem when E3_AGENT=ON.

- When enabled, requires the external libe3 library [6] (vendor-neutral
  E3AP C++ lib), discovered via pkg_check_modules(CLIBE3 REQUIRED
  libe3). It is not vendored.

  Install libe3 (Debian/Ubuntu):

      git clone https://github.com/wineslab/libe3 && cd libe3
      ./build_libe3 -I      # installs deps: build-essential cmake pkg-config libzmq3-dev asn1c nlohmann-json3-dev libsctp-dev ...
      ./build_libe3 --install      # release build + installation

Build & test

Tested in RFsim: the gNB initializes the E3 agent, opens its setup
socket (/tmp/dapps/setup), registers zero service models, and runs
without crashing.  Configuration

The agent reads an optional E3Configuration section from the gNB config
file (parsed only when E3_AGENT=ON). If absent, it falls back to
built-in defaults (posix/ipc).

    E3Configuration : {
        link = "zmq";        # posix | zmq
        transport = "ipc";   # tcp | sctp | ipc
    };

The same parameters can be overridden on the command line (no
config-file edit required):

    sudo ./nr-softmodem -O <gnb.conf> ... --E3Configuration.link zmq --E3Configuration.transport ipc

Validated link/transport combinations: (zmq,ipc) (zmq,tcp) (posix,tcp)
(posix,sctp) (posix,ipc).

Notes

- I have added a new log component E3AP specific for the ops performed
  by the E3 Agent.
- This PR ships no gNB config file; the E3Configuration block / CLI
  override above is the documented way to enable the agent. Example
  configs follow in the next PRs.

[1] https://pypi.org/project/dapps/
[2] https://arxiv.org/pdf/2501.16502
[3] https://openrangym.com/o-ran-frameworks/dapps
[4] https://openrangym.com/tutorials/dapps-oai
[5] https://gitlab.eurecom.fr/oai/openairinterface5g/-/merge_requests/3361
[6] https://github.com/wineslab/libe3

Reviewed-by: Teodora Vladić <teodora.vladic@openairinterface.org>
Reviewed-by: Sagar Arora <sagar.arora@openairinterface.org>
Reviewed-by: Robert Schmidt <robert.schmidt@openairinterface.org>

cmake_targets/build_oai

@@ -43,6 +43,8 @@ Options:
    Sets build directory (will be <oai-root>/cmake_targets/<build-dir>/build)
 --build-e2
    Enable the the E2 Agent
+--build-e3
+   Enable the the E3 Agent
 -I | --install-external-packages
    Installs required packages such as LibXML, asn1.1 compiler, ...
    This option will require root password
@@ -143,6 +145,10 @@ function main() {
              CMAKE_CMD="$CMAKE_CMD -DE2_AGENT=ON"
              shift
              ;;
+       --build-e3 )
+             CMAKE_CMD="$CMAKE_CMD -DE3_AGENT=ON"
+             shift
+             ;;
        -I | --install-external-packages)
             INSTALL_EXTERNAL=1
             echo_info "Will install external packages"