feat(capture): add Phase 3 PipeWire capture stub and config string safety

Add a linkable CaptureFactory stub so the capture API can be consumed

without unresolved symbols. Change remaining config string_view fields to

std::string to prevent dangling references. Update handoff memory.

.agents/MEMORY.md

@@ -4,10 +4,16 @@ Last updated: initial scaffold.
 
 ## Project state
 
-- Phase 1 complete: Meson build, C++20 module headers, agent workflow, clock
-  utility, and a passing unit test.
-- Active phase is now Phase 2 (software H.264 encode/decode).
-- No implementation yet for capture/codec/network/render.
+- Phase 2 follow-up review items addressed: encoder rate control is now
+  bitrate-only (removed CRF), encoder/decoder cache their SwsContext, configs
+  own their strings, bitstream helper is internal to the encoder with a NAL
+  length guard, FFmpeg open errors are reported, and the round-trip test
+  verifies Annex-B prefix and keyframes.
+- `.clang-format` added at repo root and clang-format enforcement added to
+  `AGENTS.md` and `cpp-meson-build/SKILL.md`.
+- Phase 3 capture now has a linkable stub (`src/capture/pipewire_capture.cpp`)
+  so the API can be consumed without an unresolved symbol.
+- Remaining implementation: capture, transport, rendering, and CLI/pipeline glue.
 
 ## Decisions
 
@@ -16,6 +22,8 @@ Last updated: initial scaffold.
 - Build system: Meson.
 - Capture: PipeWire + xdg-desktop-portal.
 - Encode/Decode: FFmpeg (libavcodec, libavutil, libswscale).
+- H.264 encoder path: software `libx264`, low-latency settings, Annex-B output.
+- Decoder receives SPS/PPS through `DecoderConfig.extradata`.
 - Transport: RTP over UDP; signaling via WebSocket/JSON.
 - Discovery: mDNS/Avahi.
 - Rendering: SDL2 or SDL3 + OpenGL.

include/screencast/capture/capture.h

@@ -3,26 +3,31 @@
 #include <cstdint>
 #include <memory>
 #include <optional>
-#include <span>
-#include <string_view>
+#include <string>
 #include <variant>
 #include <vector>
 
 namespace sc {
 
+enum class PixelFormat {
+    Rgba,
+    Yuv420p,
+};
+
 // Opaque resource owned by the capture implementation.
 struct CapturedFrame {
     int width = 0;
     int height = 0;
     uint64_t timestamp_ns = 0; // capture clock, monotonic
+    PixelFormat pixel_format = PixelFormat::Rgba;
+    int stride = 0; // bytes per row for the first plane; 0 means packed
     std::vector<std::byte> pixels;
-    // TODO: pixel format, stride, FD handle for dmabuf
 };
 
 // Capture target: whole monitor, specific window, or a region.
 struct CaptureTargetWholeScreen {};
 struct CaptureTargetWindow {
-    std::string_view window_id;
+    std::string window_id;
 };
 struct CaptureTargetRegion {
     int x = 0;
@@ -31,13 +36,10 @@ struct CaptureTargetRegion {
     int height = 0;
 };
 
-using CaptureTarget = std::variant<
-    CaptureTargetWholeScreen,
-    CaptureTargetWindow,
-    CaptureTargetRegion>;
+using CaptureTarget = std::variant<CaptureTargetWholeScreen, CaptureTargetWindow, CaptureTargetRegion>;
 
 class CaptureSession {
-public:
+  public:
     virtual ~CaptureSession() = default;
 
     // Blocking call to acquire one frame. Returns std::nullopt on graceful stop.
@@ -49,7 +51,7 @@ public:
 
 // Factory for the PipeWire / xdg-desktop-portal capture backend.
 class CaptureFactory {
-public:
+  public:
     static std::unique_ptr<CaptureSession> create(CaptureTarget target);
 };
 

include/screencast/render/renderer.h

@@ -2,36 +2,34 @@
 
 #include "screencast/codec/decoder.h"
 
-#include <cstdint>
 #include <memory>
-#include <optional>
-#include <string_view>
+#include <string>
 
 namespace sc {
 
 struct RendererConfig {
-    std::string_view window_title = "screencast receiver";
+    std::string window_title = "screencast receiver";
     int initial_width = 1280;
     int initial_height = 720;
 };
 
 class Renderer {
   public:
-    virtual ~Renderer () = default;
+    virtual ~Renderer() = default;
 
     // Present one decoded frame. Returns false if the window was closed.
-    virtual bool present ( const DecodedFrame &frame ) = 0;
+    virtual bool present(const DecodedFrame& frame) = 0;
 
     // Pump events (window close, resize). Non-blocking.
-    virtual bool poll_events () = 0;
+    virtual bool poll_events() = 0;
 
     // Destroy the window and release GPU resources.
-    virtual void shutdown () = 0;
+    virtual void shutdown() = 0;
 };
 
 class RendererFactory {
   public:
-    static std::unique_ptr<Renderer> create ( const RendererConfig &config );
+    static std::unique_ptr<Renderer> create(const RendererConfig& config);
 };
 
-}  // namespace sc
+} // namespace sc

src/capture/meson.build

@@ -0,0 +1,11 @@
+# Phase 3 capture placeholder. libpipewire-0.3 will be added when the portal
+# implementation is wired in.
+
+sc_capture_sources = files('pipewire_capture.cpp')
+
+# Built even though nothing links it yet, so the stub stays compile-clean.
+static_library('sc_capture',
+    sc_capture_sources,
+    include_directories : sc_core_inc)
+
+# sc_capture_dep will be declared once the app/pipeline code links against it.

src/capture/pipewire_capture.cpp

@@ -0,0 +1,13 @@
+#include "screencast/capture/capture.h"
+
+#include <memory>
+
+namespace sc {
+
+std::unique_ptr<CaptureSession> CaptureFactory::create(CaptureTarget /*target*/) {
+    // Phase 3 placeholder. The PipeWire / xdg-desktop-portal capture backend
+    // will be implemented here once the codec round-trip is solidified.
+    return nullptr;
+}
+
+} // namespace sc

src/meson.build

@@ -1,6 +1,8 @@
 # Core public headers / include dependency.
 sc_core_inc = include_directories('../include')
 
+subdir('capture')
+
 # Phase 2 codec dependencies.
 dep_avcodec = dependency('libavcodec')
 dep_avutil = dependency('libavutil')