diff --git a/CMakeLists.txt b/CMakeLists.txt
index e13e79f..0a95d3b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -236,6 +236,9 @@ add_executable(udpscope
   src/waveform.cpp
   src/event_store.cpp
   src/acquisition.cpp
+  src/source/source_config.cpp
+  src/source/data_source.cpp
+  src/source/registry.cpp
   src/plot_host.cpp
   src/export.cpp
   src/search.cpp
diff --git a/src/model.cpp b/src/model.cpp
index 79fe9f1..765459f 100644
--- a/src/model.cpp
+++ b/src/model.cpp
@@ -3,8 +3,6 @@
 
 #include "model.hpp"
 
-#include <udps_client.h>
-
 #include <algorithm>
 #include <chrono>
 #include <cmath>
@@ -646,7 +644,7 @@ bool ScopeModel::is_time_signal(const std::vector<SignalInfo>& signals,
   // signal: it has stamps but no cadence of its own, because it is not data.
   // Data channels can also be declared full-array (per-element stamps), and they
   // keep a declared rate -- treating them as time signals hid every real channel.
-  if (s.time_mode == UDPS_TIME_FULL_ARRAY && s.elements() > 1 && s.sampling_rate == 0.0) {
+  if (s.time_mode == kTimeFullArray && s.elements() > 1 && s.sampling_rate == 0.0) {
     return true;
   }
   return false;
diff --git a/src/model.hpp b/src/model.hpp
index 338caef..88e4def 100644
--- a/src/model.hpp
+++ b/src/model.hpp
@@ -24,6 +24,13 @@
 
 namespace udpscope {
 
+/// `SignalInfo::time_mode` values. They equal the wire protocol's `UDPS_TIME_*`
+/// (`udps_source.cpp` static_asserts it), but the model must not name a source's own header.
+constexpr std::uint8_t kTimePacket = 0;
+constexpr std::uint8_t kTimeFullArray = 1;
+constexpr std::uint8_t kTimeFirstSample = 2;
+constexpr std::uint8_t kTimeLastSample = 3;
+
 /// One streamed signal, as the CONFIG packet described it.
 struct SignalInfo {
   std::string name;
diff --git a/src/source/data_source.cpp b/src/source/data_source.cpp
new file mode 100644
index 0000000..d6eeae2
--- /dev/null
+++ b/src/source/data_source.cpp
@@ -0,0 +1,24 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: 2026 Martino Ferrari
+
+#include "source/data_source.hpp"
+
+#include <utility>
+
+namespace udpscope {
+
+void DataSource::post(Command cmd) {
+  std::lock_guard<std::mutex> lk(cmd_mu_);
+  cmds_.push_back(std::move(cmd));
+}
+
+void DataSource::drain_commands() {
+  std::deque<Command> local;
+  {
+    std::lock_guard<std::mutex> lk(cmd_mu_);
+    local.swap(cmds_);
+  }
+  for (auto& c : local) c();
+}
+
+}  // namespace udpscope
diff --git a/src/source/data_source.hpp b/src/source/data_source.hpp
new file mode 100644
index 0000000..b6feb58
--- /dev/null
+++ b/src/source/data_source.hpp
@@ -0,0 +1,78 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: 2026 Martino Ferrari
+
+#pragma once
+
+#include "source/frame.hpp"
+
+#include <cstddef>
+#include <cstdint>
+#include <deque>
+#include <functional>
+#include <mutex>
+#include <vector>
+
+namespace udpscope {
+
+/// Work for the producer thread. UI code posts these; `poll()` drains and runs them, so a
+/// source's state is only ever touched by the thread that owns it.
+using Command = std::function<void()>;
+
+/// The counters `StreamStats` shows, in source-neutral form. Producer thread only.
+struct SourceStats {
+  std::uint64_t packets = 0;
+  std::uint64_t frames = 0;
+  std::uint64_t gaps = 0;
+  std::uint64_t late = 0;
+  std::uint64_t resequenced = 0;
+  std::uint64_t stale = 0;
+  std::uint64_t overflows = 0;
+  std::uint64_t reconnects = 0;
+  bool connected = false;
+};
+
+enum class SourceEvent { Connected, Disconnected, Error };
+
+/// Where a source delivers, from inside `poll()`.
+class SourceSink {
+ public:
+  virtual ~SourceSink() = default;
+  /// The signal set (re)defined. `publish_mode` is the stream's own publish mode.
+  virtual void on_config(const std::vector<SignalInfo>& signals, std::uint8_t publish_mode) = 0;
+  virtual void on_data(const Frame& frame) = 0;
+  virtual void on_event(SourceEvent event, const char* message) = 0;
+};
+
+/// Receives each raw datagram of a UDP-based source: bytes, length, receive time.
+using DatagramTap = std::function<void(const std::uint8_t*, std::size_t, double)>;
+
+/// The per-connection object. `Acquisition` owns one and drives it from the producer thread.
+class DataSource {
+ public:
+  virtual ~DataSource() = default;
+
+  /// Allocates and connects. Throws `std::runtime_error` with a message fit for the user.
+  /// Does not deliver: CONFIG and `Connected` arrive from `poll()`.
+  virtual void open(SourceSink& sink) = 0;
+  /// Runs queued commands, then waits up to `timeout_ms` for work and delivers it.
+  virtual void poll(int timeout_ms) = 0;
+  virtual void close() = 0;
+  /// Producer thread only.
+  virtual SourceStats stats() const = 0;
+  virtual bool connected() const = 0;
+  /// Optional: UDP-based sources feed the raw-packet capture through this.
+  virtual void set_datagram_tap(DatagramTap) {}
+
+  /// Thread-safe. The command runs inside a later `poll()`.
+  void post(Command cmd);
+
+ protected:
+  /// For `poll()` implementations: runs and clears the queue.
+  void drain_commands();
+
+ private:
+  std::mutex cmd_mu_;
+  std::deque<Command> cmds_;
+};
+
+}  // namespace udpscope
diff --git a/src/source/frame.hpp b/src/source/frame.hpp
new file mode 100644
index 0000000..15ff9e1
--- /dev/null
+++ b/src/source/frame.hpp
@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: 2026 Martino Ferrari
+
+#pragma once
+
+#include "model.hpp"
+
+#include <cstdint>
+
+namespace udpscope {
+
+/// One signal's values in a frame. `values` points into the source's own buffer and is valid
+/// only while the `on_data` call that received the frame is running.
+struct SignalValues {
+  const double* values = nullptr;
+  std::uint32_t count = 0;
+};
+
+/// A data frame in source-neutral form; it mirrors `udps_frame_t`. A source with no packet
+/// counter supplies a running one and `lost = 0`: the hole, backfill and time-base logic only
+/// needs `counter`, `lost` and `late`.
+struct Frame {
+  std::uint32_t counter = 0;
+  std::uint32_t lost = 0;
+  bool late = false;
+  double recv_time = 0.0;
+  std::uint8_t publish_mode = 0;
+  std::uint32_t num_samples = 0;
+  std::uint32_t num_signals = 0;
+  const SignalInfo* signals = nullptr;
+  const SignalValues* values = nullptr;
+
+  /// Element `elem` of signal `sig` at sample `sample`. Mirrors `udps_frame_value`: a scalar
+  /// signal carried once per sample is indexed by `sample`, a vector/matrix signal by `elem`.
+  /// Out of range reads 0.0.
+  double value(std::uint32_t sig, std::uint32_t sample, std::uint32_t elem) const noexcept {
+    if (sig >= num_signals) return 0.0;
+    const SignalValues& v = values[sig];
+    const std::uint32_t idx =
+        (v.count == num_samples && signals[sig].elements() == 1u) ? sample : elem;
+    return idx < v.count ? v.values[idx] : 0.0;
+  }
+};
+
+}  // namespace udpscope
diff --git a/src/source/registry.cpp b/src/source/registry.cpp
new file mode 100644
index 0000000..3c3c88e
--- /dev/null
+++ b/src/source/registry.cpp
@@ -0,0 +1,70 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: 2026 Martino Ferrari
+
+#include "source/registry.hpp"
+
+#include <algorithm>
+#include <cstdlib>
+
+namespace udpscope {
+namespace {
+
+std::vector<std::unique_ptr<SourceKind>>& owned() {
+  static std::vector<std::unique_ptr<SourceKind>> v;
+  return v;
+}
+std::vector<SourceKind*>& raw() {
+  static std::vector<SourceKind*> v;
+  return v;
+}
+
+std::string sanitize(const std::string& s) {
+  std::string out = s;
+  for (char& c : out) {
+    const bool ok = (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z') || (c >= '0' && c <= '9') ||
+                    c == '.' || c == '_' || c == '-';
+    if (!ok) c = '_';
+  }
+  return out;
+}
+
+}  // namespace
+
+void register_kind(std::unique_ptr<SourceKind> kind) {
+  if (!kind || find_kind(kind->id())) return;
+  raw().push_back(kind.get());
+  owned().push_back(std::move(kind));
+}
+
+SourceKind* find_kind(const std::string& id) {
+  for (SourceKind* k : raw()) {
+    if (k->id() == id) return k;
+  }
+  return nullptr;
+}
+
+const std::vector<SourceKind*>& kinds() { return raw(); }
+
+void register_builtin_sources() {
+  static bool done = false;
+  if (done) return;
+  done = true;
+  // Task 2: register_kind(make_udps_kind());
+  // Task 6: register make_probe_kind() when UDPSCOPE_PROBE_SOURCE_KINDS is set
+}
+
+std::string session_host(const std::string& kind_id, const SourceConfig& cfg) {
+  if (kind_id == "udps") return cfg.get("server", "127.0.0.1");
+  SourceKind* k = find_kind(kind_id);
+  return sanitize(kind_id + "-" + (k ? k->identity(cfg) : std::string("unknown")));
+}
+
+std::uint16_t session_port(const std::string& kind_id, const SourceConfig& cfg) {
+  if (kind_id == "udps") {
+    const long p = cfg.get_int("port", 8000);
+    return static_cast<std::uint16_t>(p > 0 && p <= 65535 ? p : 8000);
+  }
+  return 1;
+}
+
+}  // namespace udpscope
diff --git a/src/source/registry.hpp b/src/source/registry.hpp
new file mode 100644
index 0000000..5293000
--- /dev/null
+++ b/src/source/registry.hpp
@@ -0,0 +1,34 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: 2026 Martino Ferrari
+
+#pragma once
+
+#include "source/source_kind.hpp"
+
+#include <cstdint>
+#include <memory>
+#include <string>
+#include <vector>
+
+namespace udpscope {
+
+/// Takes ownership. A second kind with the same id is ignored.
+void register_kind(std::unique_ptr<SourceKind> kind);
+SourceKind* find_kind(const std::string& id);
+/// In registration order (the chooser's dropdown order).
+const std::vector<SourceKind*>& kinds();
+/// Registers the built-in kinds; idempotent. No static-init self-registration, which a linker
+/// may drop. A later `dlopen` loader would only call `register_kind()`.
+void register_builtin_sources();
+
+/// The built-in kinds, each defined in its own file (`udps_kind.cpp`, `probe_source.cpp`).
+std::unique_ptr<SourceKind> make_udps_kind();
+std::unique_ptr<SourceKind> make_probe_kind();
+
+/// The (host, port) pair that names a source's session file. UDPS keeps its legacy
+/// `server`/`port`; any other kind is `"<kind>-<identity>"` (characters outside `[A-Za-z0-9._-]`
+/// become `_`) on port 1 -- not 0, which the session-file parser rejects and waveform mode uses.
+std::string session_host(const std::string& kind_id, const SourceConfig& cfg);
+std::uint16_t session_port(const std::string& kind_id, const SourceConfig& cfg);
+
+}  // namespace udpscope
diff --git a/src/source/source_config.cpp b/src/source/source_config.cpp
new file mode 100644
index 0000000..99f810f
--- /dev/null
+++ b/src/source/source_config.cpp
@@ -0,0 +1,75 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: 2026 Martino Ferrari
+
+#include "source/source_config.hpp"
+
+#include <algorithm>
+#include <cctype>
+#include <cstdlib>
+
+namespace udpscope {
+
+void SourceConfig::set(const std::string& key, const std::string& value) {
+  for (auto& kv : items_) {
+    if (kv.first == key) {
+      kv.second = value;
+      return;
+    }
+  }
+  items_.emplace_back(key, value);
+}
+
+bool SourceConfig::has(const std::string& key) const {
+  return std::any_of(items_.begin(), items_.end(),
+                     [&](const auto& kv) { return kv.first == key; });
+}
+
+std::string SourceConfig::get(const std::string& key, const std::string& def) const {
+  for (const auto& kv : items_) {
+    if (kv.first == key) return kv.second;
+  }
+  return def;
+}
+
+long SourceConfig::get_int(const std::string& key, long def) const {
+  if (!has(key)) return def;
+  const std::string v = get(key);
+  char* end = nullptr;
+  const long n = std::strtol(v.c_str(), &end, 10);
+  return (end == v.c_str() || *end != '\0') ? def : n;
+}
+
+double SourceConfig::get_double(const std::string& key, double def) const {
+  if (!has(key)) return def;
+  const std::string v = get(key);
+  char* end = nullptr;
+  const double d = std::strtod(v.c_str(), &end);
+  return (end == v.c_str() || *end != '\0') ? def : d;
+}
+
+bool SourceConfig::get_bool(const std::string& key, bool def) const {
+  if (!has(key)) return def;
+  std::string v = get(key);
+  std::transform(v.begin(), v.end(), v.begin(),
+                 [](unsigned char c) { return static_cast<char>(std::tolower(c)); });
+  if (v == "1" || v == "true" || v == "yes" || v == "on") return true;
+  if (v == "0" || v == "false" || v == "no" || v == "off") return false;
+  return def;
+}
+
+bool SourceConfig::valid_key(const std::string& key) {
+  return !key.empty() && std::all_of(key.begin(), key.end(), [](unsigned char c) {
+    return std::isalnum(c) || c == '_';
+  });
+}
+
+bool SourceConfig::parse_assignment(const std::string& kv) {
+  const auto eq = kv.find('=');
+  if (eq == std::string::npos) return false;
+  const std::string key = kv.substr(0, eq);
+  if (!valid_key(key)) return false;
+  set(key, kv.substr(eq + 1));
+  return true;
+}
+
+}  // namespace udpscope
diff --git a/src/source/source_config.hpp b/src/source/source_config.hpp
new file mode 100644
index 0000000..01fa0ec
--- /dev/null
+++ b/src/source/source_config.hpp
@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: 2026 Martino Ferrari
+
+#pragma once
+
+#include <string>
+#include <utility>
+#include <vector>
+
+namespace udpscope {
+
+/// A source's settings: an ordered string key/value map. It is the stored form (top-level
+/// `source_opt_<key>` entries of a session), the `--source-opt k=v` form, and what a config form
+/// reads and writes. Order is insertion order, so a stored session stays diff-friendly.
+class SourceConfig {
+ public:
+  using Items = std::vector<std::pair<std::string, std::string>>;
+
+  SourceConfig() = default;
+  explicit SourceConfig(Items items) : items_(std::move(items)) {}
+
+  /// Replaces the value in place if the key exists, else appends.
+  void set(const std::string& key, const std::string& value);
+  bool has(const std::string& key) const;
+  std::string get(const std::string& key, const std::string& def = {}) const;
+  long get_int(const std::string& key, long def) const;
+  double get_double(const std::string& key, double def) const;
+  /// 1/true/yes/on and 0/false/no/off (case-insensitive); anything else gives `def`.
+  bool get_bool(const std::string& key, bool def) const;
+
+  /// Parses `k=v`; false (and no change) if there is no `=` or the key is not `valid_key`.
+  bool parse_assignment(const std::string& kv);
+
+  const Items& items() const noexcept { return items_; }
+  bool empty() const noexcept { return items_.empty(); }
+
+  /// `[A-Za-z0-9_]+` -- the characters that survive as a TOML bare key suffix.
+  static bool valid_key(const std::string& key);
+
+ private:
+  Items items_;
+};
+
+}  // namespace udpscope
diff --git a/src/source/source_kind.hpp b/src/source/source_kind.hpp
new file mode 100644
index 0000000..fac37bc
--- /dev/null
+++ b/src/source/source_kind.hpp
@@ -0,0 +1,64 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: 2026 Martino Ferrari
+
+#pragma once
+
+#include "source/data_source.hpp"
+#include "source/source_config.hpp"
+
+#include <gtk/gtk.h>
+
+#include <functional>
+#include <memory>
+#include <string>
+#include <vector>
+
+namespace udpscope {
+
+/// A kind's configuration UI, as pieces the chooser places in its own group. The widgets are
+/// floating `AdwPreferencesRow`s; the closures capture them, so a form must not outlive its rows
+/// (the chooser drops the form when it removes the rows).
+struct ConfigForm {
+  std::vector<GtkWidget*> rows;
+  /// Shown under the group's title; empty for none.
+  std::string description;
+  /// The widget that takes focus when the form is shown; may be null.
+  GtkWidget* focus = nullptr;
+  /// Puts `cfg` into the widgets (absent keys leave the kind's defaults).
+  std::function<void(const SourceConfig&)> write;
+  /// The widgets as a `SourceConfig`.
+  std::function<SourceConfig()> read;
+  /// Whether the form is complete enough to connect.
+  std::function<bool()> valid;
+  /// Calls `fn` whenever any widget changes.
+  std::function<void(std::function<void()>)> on_change;
+};
+
+/// A capability panel (signal generator, digital I/O, ...) for the side area.
+struct SourcePanel {
+  std::string id;     ///< stack page name
+  std::string title;
+  std::string icon;   ///< icon name for the tab, may be empty
+  GtkWidget* widget = nullptr;
+};
+
+/// One plugin type: its identity, factory and UI.
+class SourceKind {
+ public:
+  virtual ~SourceKind() = default;
+  virtual std::string id() const = 0;            ///< short, `[a-z0-9]+`; the CLI and session name
+  virtual std::string display_name() const = 0;
+  /// A stable, human-readable name for one configured source (`host:port`, a serial number).
+  virtual std::string identity(const SourceConfig& cfg) const = 0;
+  virtual std::unique_ptr<DataSource> make(const SourceConfig& cfg) const = 0;
+  virtual ConfigForm make_config_form() const = 0;
+  /// Panels for a live source. The widgets must reach the source only through `post()`.
+  virtual std::vector<SourcePanel> make_panels(DataSource& source) const {
+    (void)source;
+    return {};
+  }
+  /// Whether the source reports raw datagrams (enables the packet-capture UI).
+  virtual bool has_datagrams() const { return false; }
+};
+
+}  // namespace udpscope