diff --git a/.envrc b/.envrc
new file mode 100644
index 00000000..2efe544e
--- /dev/null
+++ b/.envrc
@@ -0,0 +1,2 @@
+eval "$(devenv direnvrc)"
+use devenv
diff --git a/PLAN-calls.md b/PLAN-calls.md
new file mode 100644
index 00000000..d42fb949
--- /dev/null
+++ b/PLAN-calls.md
@@ -0,0 +1,81 @@
+  # Stabilize Existing VoIP Call Flow and Add Non-Fatal Diagnostics
+
+  ## Summary
+
+  Tighten the existing Matrix call flow in the current VoIP stack, focusing on real correctness issues already present in src/voip/CallManager.cpp and src/voip/WebRTCSession.cpp, and
+  add structured logging around non-fatal failures so future call bugs are diagnosable without crashing or silently retrying forever.
+
+  This plan targets:
+
+  - Core invite/answer/candidate/select-answer stability
+  - Inbound renegotiation support for m.call.negotiate
+  - Logging of non-critical exceptions and ignored/invalid call events
+  - No user-visible feature expansion beyond making current calls more reliable
+
+  ## Implementation Changes
+
+  - Fix the CallSelectAnswer rejection lookup bug in CallManager::handleEvent(const RoomEvent<CallSelectAnswer>&) by changing the std::find(begin, begin, ...) calls to search through
+    end(). This is a concrete logic bug that currently prevents expected branch behavior.
+  - Add strict call-id and state guards across inbound handlers in CallManager and log every early-return branch that currently drops events silently. Include at least:
+      - mismatched call_id
+      - wrong local webrtc::State
+      - duplicate answers/select-answer/reject
+      - self-echo cases
+      - candidates received before a call is initialized
+  - Implement WebRTCSession::acceptNegotiation(const std::string &) instead of the current unconditional false. Use the same parsing/validation style as acceptOffer:
+      - require an active session, not DISCONNECTED
+      - parse SDP as a remote offer
+      - validate required audio media and optional VP8 video media
+      - update remote video direction flags
+      - call set-remote-description
+      - create and send an answer through the existing answerCreated path
+      - keep wire format unchanged; do not add local renegotiation initiation in this pass
+  - Extend CallManager::handleEvent(const RoomEvent<CallNegotiate>&) so renegotiation only applies to the active call, logs dropped mismatches, and drains queued ICE candidates only
+    after renegotiation is accepted.
+  - Harden acceptICECandidates handling:
+      - log when candidates are ignored because the session is not ready
+      - keep buffering only in manager-side inbound invite/renegotiation waiting states
+      - avoid silent no-ops when candidates arrive for the wrong call or after teardown
+  - Improve failure handling around setup paths:
+      - log TURN retrieval failures in retrieveTurnServer() with the request error and retry interval
+      - log why createOffer, acceptOffer, acceptAnswer, and renegotiation fail, including current state and call id where available
+      - log pipeline creation failures with the missing device/element context instead of only generic “Problem setting up call”
+  - Add non-critical exception logging around call orchestration paths that touch cache/state but should not kill the process:
+      - syncEvent dispatch
+      - inbound call event handlers that query room info/members
+      - outbound invite setup that reads room/member data
+      - TURN response parsing/conversion
+        Catch std::exception and log with nhlog at warn or error depending on whether the call can continue; rethrow nothing for these paths. Add a final catch (...) only where needed
+        to prevent silent termination, with a clear “unknown exception” log line.
+  - Keep user notifications mostly unchanged. Prefer logs for diagnostics and only surface UI notifications for existing fatal outcomes such as setup failure, ICE failure, reject,
+    timeout, or answered elsewhere.
+
+  ## Public Interfaces / Behavior
+
+  - No QML property or signal changes.
+  - No Matrix event schema changes.
+  - Existing CallAnswer, CallCandidates, CallNegotiate, and CallSelectAnswer messages remain the transport surface.
+  - Behavioral change: inbound m.call.negotiate will now be handled instead of always failing.
+  - Behavioral change: previously silent dropped call events and recoverable exceptions will now emit logs with call id, party id, and local state.
+
+  ## Test Plan
+
+  - Add focused unit-style coverage where practical for pure call-manager logic, or otherwise add regression tests around isolated helper logic if the repo lacks VoIP integration
+    tests.
+  - Verify manually or with targeted harness coverage:
+      - outbound call reaches OFFERSENT, receives answer, transitions to CONNECTED
+      - inbound call invite buffers ICE before accept, then drains after accept
+      - duplicate CallAnswer and CallSelectAnswer are ignored with logs, not state corruption
+      - CallSelectAnswer rejection-party matching now works after the std::find fix
+      - incoming CallNegotiate on the active call produces a local answer instead of immediate failure
+      - CallNegotiate for a different call_id is ignored with a diagnostic log
+      - TURN retrieval failure logs retry details without crashing
+      - exceptions thrown from room/member lookup in call paths are logged and do not abort the process
+  - Run a build check after the changes. If the environment still lacks cmake, document that verification gap and at minimum run the strongest available static inspection.
+
+  ## Assumptions
+
+  - Use existing nhlog logging categories rather than raw printf; “prints” here means persistent diagnostic logging.
+  - Keep the existing user-facing notification policy unless a failure is already fatal to the active call.
+  - Renegotiation scope is inbound-only for now because the current codebase already receives m.call.negotiate but does not expose a local renegotiation initiator.
+  - No attempt will be made in this pass to redesign the entire call state machine or add automatic media-session recovery after teardown.
diff --git a/devenv.lock b/devenv.lock
new file mode 100644
index 00000000..4cdbba71
--- /dev/null
+++ b/devenv.lock
@@ -0,0 +1,65 @@
+{
+  "nodes": {
+    "devenv": {
+      "locked": {
+        "dir": "src/modules",
+        "lastModified": 1773179136,
+        "narHash": "sha256-aOxRGdpITEvasogdZXGqlSrr8pJQ+QGiRxpzmT3i/UQ=",
+        "owner": "cachix",
+        "repo": "devenv",
+        "rev": "169c048513ca064c02a4233ace0ecbdd935d4f80",
+        "type": "github"
+      },
+      "original": {
+        "dir": "src/modules",
+        "owner": "cachix",
+        "repo": "devenv",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "inputs": {
+        "nixpkgs-src": "nixpkgs-src"
+      },
+      "locked": {
+        "lastModified": 1772749504,
+        "narHash": "sha256-eqtQIz0alxkQPym+Zh/33gdDjkkch9o6eHnMPnXFXN0=",
+        "owner": "cachix",
+        "repo": "devenv-nixpkgs",
+        "rev": "08543693199362c1fddb8f52126030d0d374ba2e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "cachix",
+        "ref": "rolling",
+        "repo": "devenv-nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs-src": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1772173633,
+        "narHash": "sha256-MOH58F4AIbCkh6qlQcwMycyk5SWvsqnS/TCfnqDlpj4=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "c0f3d81a7ddbc2b1332be0d8481a672b4f6004d6",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "devenv": "devenv",
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}
\ No newline at end of file
diff --git a/devenv.nix b/devenv.nix
new file mode 100644
index 00000000..dfb4d0f9
--- /dev/null
+++ b/devenv.nix
@@ -0,0 +1,129 @@
+{ pkgs, lib, config, inputs, ... }:
+
+let
+  qtPackages = with pkgs.qt6Packages; [
+    qtbase
+    qtdeclarative
+    qtimageformats
+    qtkeychain
+    qtmultimedia
+    qtsvg
+    qttools
+    qtwayland
+    qt-jdenticon
+  ];
+
+  gstreamerPackages = [
+    pkgs.gst_all_1.gstreamer
+    pkgs.gst_all_1.gst-plugins-base
+    (pkgs.gst_all_1.gst-plugins-good.override { qt6Support = true; })
+    pkgs.gst_all_1.gst-plugins-bad
+  ];
+
+  cmakePackages = [
+    pkgs.cmark
+    pkgs.coeurl
+    pkgs.curl
+    pkgs.kdsingleapplication
+    pkgs.libevent
+    pkgs.libsecret
+    pkgs.lmdb
+    pkgs.lmdbxx
+    pkgs.mtxclient
+    pkgs.nlohmann_json
+    pkgs.olm
+    pkgs.re2
+    pkgs.spdlog
+  ] ++ qtPackages ++ gstreamerPackages ++ [ pkgs.libnice ];
+
+  runtimePackages = [
+    pkgs.pipewire
+  ];
+
+  qtPluginPath = lib.makeSearchPath "lib/qt-6/plugins" qtPackages;
+  qmlImportPath = lib.makeSearchPath "lib/qt-6/qml" qtPackages;
+  gstreamerPluginPath = lib.makeSearchPath "lib/gstreamer-1.0" gstreamerPackages;
+  runtimeLibraryPath = lib.makeLibraryPath runtimePackages;
+  cmakePrefixPath =
+    lib.concatStringsSep ":" (
+      (map (pkg: "${lib.getDev pkg}/lib/cmake") cmakePackages)
+      ++ (map (pkg: "${lib.getDev pkg}") cmakePackages)
+    );
+in
+{
+  packages = [
+    pkgs.asciidoc
+    pkgs.cmake
+    pkgs.direnv
+    pkgs.gcc
+    pkgs.git
+    pkgs.gnumake
+    pkgs.gdb
+    pkgs.ninja
+    pkgs.pkg-config
+    pkgs.pipewire
+    pkgs.qt6Packages.wrapQtAppsHook
+  ] ++ cmakePackages;
+
+  env = {
+    CMAKE_GENERATOR = "Ninja";
+    CMAKE_PREFIX_PATH = cmakePrefixPath;
+    GST_PLUGIN_SYSTEM_PATH_1_0 = gstreamerPluginPath;
+    LD_LIBRARY_PATH = runtimeLibraryPath;
+    NHEKO_BUILD_DIR = "build";
+    QT_PLUGIN_PATH = qtPluginPath;
+    QML2_IMPORT_PATH = qmlImportPath;
+  };
+
+  scripts."configure-nheko".exec = ''
+    cmake -S . -B "$NHEKO_BUILD_DIR" \
+      -G "$CMAKE_GENERATOR" \
+      -DCMAKE_BUILD_TYPE="''${CMAKE_BUILD_TYPE:-RelWithDebInfo}" \
+      -DCMAKE_EXPORT_COMPILE_COMMANDS=ON
+  '';
+
+  scripts."build-nheko".exec = ''
+    if [ ! -f "$NHEKO_BUILD_DIR/CMakeCache.txt" ]; then
+      configure-nheko
+    fi
+
+    cmake --build "$NHEKO_BUILD_DIR" --parallel "''${NIX_BUILD_CORES:-$(nproc)}"
+  '';
+
+  scripts."test-nheko".exec = ''
+    build-nheko
+    ctest --test-dir "$NHEKO_BUILD_DIR" --output-on-failure
+
+    binary="$(find "$NHEKO_BUILD_DIR" -maxdepth 4 -type f -name nheko -executable | head -n 1)"
+    if [ -z "$binary" ]; then
+      echo "Unable to locate the built nheko binary under $NHEKO_BUILD_DIR" >&2
+      exit 1
+    fi
+
+    QT_QPA_PLATFORM=offscreen "$binary" --help >/dev/null
+  '';
+
+  scripts."run-nheko".exec = ''
+    build-nheko
+
+    binary="$(find "$NHEKO_BUILD_DIR" -maxdepth 4 -type f -name nheko -executable | head -n 1)"
+    if [ -z "$binary" ]; then
+      echo "Unable to locate the built nheko binary under $NHEKO_BUILD_DIR" >&2
+      exit 1
+    fi
+
+    exec "$binary" "$@"
+  '';
+
+  enterShell = ''
+    echo "nheko devenv ready"
+    echo "  configure-nheko  Configure the CMake build tree"
+    echo "  build-nheko      Build the nheko binary"
+    echo "  test-nheko       Run ctest and a headless --help smoke test"
+    echo "  run-nheko        Launch the built client"
+  '';
+
+  enterTest = ''
+    test-nheko
+  '';
+}
diff --git a/devenv.yaml b/devenv.yaml
new file mode 100644
index 00000000..965f695f
--- /dev/null
+++ b/devenv.yaml
@@ -0,0 +1,12 @@
+# yaml-language-server: $schema=https://devenv.sh/devenv.schema.json
+inputs:
+  nixpkgs:
+    url: github:cachix/devenv-nixpkgs/rolling
+
+nixpkgs:
+  permittedInsecurePackages:
+    - "olm-3.2.16"
+
+# If you have more than one devenv you can merge them
+#imports:
+# - ./backend