Install daedalus-decoder.pc for sibling consumers

Adds pkg-config plumbing so consumers (daedalus-v4l2 daemon for the
upcoming PR-Q3a shadow-mode wiring; the daedalus_decode_h264 CLI when
built outside this tree) can locate libdaedalus_decoder.a + the public
header via pkg_check_modules / pkg-config.

Mirrors daedalus-fourier's relocatable-prefix scheme: prefix is derived
from ${pcfiledir} so cmake --install --prefix /foo produces a .pc that
resolves to /foo at lookup time. Verified across two install prefixes.

daedalus-fourier is declared as a public Requires: because consumers
static-linking libdaedalus_decoder.a also need libdaedalus_core.a in
their link line to resolve the daedalus_ctx_* / daedalus_recipe_*
symbols this archive references.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CMakeLists.txt

@@ -162,14 +162,123 @@ add_executable(bench_flush_frame tests/bench_flush_frame.c)
 target_link_libraries(bench_flush_frame PRIVATE daedalus_decoder)
 target_compile_options(bench_flush_frame PRIVATE -O2)
 
+# ---- Tools (not gated by ctest; opt-in via DAEDALUS_BUILD_TOOLS) ----
+#
+# daedalus_decode_h264 — option A standalone test harness that
+# wraps libavcodec + daedalus-decoder and bit-exact-compares their
+# outputs on real H.264 streams.  Identity-passthrough mode in this
+# first iteration (predicted = AVFrame pixels, coeffs = 0, no
+# deblock edges); follow-up PRs use the per-MB inspection callback
+# (marfrit-packages patch 0016) to feed REAL per-MB state.
+#
+# Requires libavcodec + libavformat headers + libs.  Off by default
+# so the standard ctest build doesn't pull in FFmpeg as a hard dep.
+option(DAEDALUS_BUILD_TOOLS "Build daedalus-decoder CLI tools (requires libavcodec)" OFF)
+if(DAEDALUS_BUILD_TOOLS)
+    # Optional path to a private FFmpeg install carrying the per-MB
+    # inspection callback (marfrit-packages patch 0016).  When set,
+    # the CLI links against it instead of the system FFmpeg and the
+    # inspection-callback code path is compiled in.
+    set(DAEDALUS_FFMPEG_PREFIX "" CACHE PATH
+        "Path to a patched FFmpeg install (with 0016 mb-inspect-callback) for daedalus_decode_h264. Empty = use system pkg-config FFmpeg.")
+
+    if(DAEDALUS_FFMPEG_PREFIX)
+        message(STATUS "daedalus_decode_h264: patched FFmpeg at ${DAEDALUS_FFMPEG_PREFIX}")
+        set(FFMPEG_INCLUDE_DIRS ${DAEDALUS_FFMPEG_PREFIX}/include)
+        set(FFMPEG_LIBRARY_DIRS ${DAEDALUS_FFMPEG_PREFIX}/lib)
+        # Patched libavcodec is built static (no shared libs in the private prefix).
+        # System pull-ins are still needed for libav* dependencies.
+        set(FFMPEG_LIBRARIES
+            ${DAEDALUS_FFMPEG_PREFIX}/lib/libavformat.a
+            ${DAEDALUS_FFMPEG_PREFIX}/lib/libavcodec.a
+            ${DAEDALUS_FFMPEG_PREFIX}/lib/libavutil.a
+            ${DAEDALUS_FFMPEG_PREFIX}/lib/libswresample.a
+            m z pthread)
+        set(FFMPEG_CFLAGS_OTHER "-DDAEDALUS_HAVE_H264_MB_INSPECT_CB=1")
+
+        # PR-A3+ optional: also point at the patched FFmpeg SOURCE TREE
+        # so the CLI can include libavcodec/h264dec.h directly and
+        # dereference H264Context fields (the side-buffer mb_inspect_coeffs
+        # added in marfrit-packages patch 0017, the cur_pic.f for
+        # pre-deblock pixel access, etc.).  When set, the internal-header
+        # include codepath is compiled in.
+        set(DAEDALUS_FFMPEG_SRC "" CACHE PATH
+            "Path to patched FFmpeg source tree (= path to FFmpeg/ checkout where build was run; contains config.h + libavcodec/h264dec.h). Empty = h264dec.h includes are disabled.")
+        if(DAEDALUS_FFMPEG_SRC)
+            message(STATUS "daedalus_decode_h264: FFmpeg source at ${DAEDALUS_FFMPEG_SRC}")
+            # IMPORTANT: source tree FIRST in -I order — its
+            # libavutil/common.h does #include "intmath.h" with HAVE_AV_CONFIG_H,
+            # which resolves to libavutil/intmath.h (in the source tree
+            # only — that header isn't installed since it's arch-dispatched).
+            # The installed-prefix include path's libavutil/common.h is the
+            # same file textually but resolves "intmath.h" against the
+            # install dir where it doesn't exist.
+            set(FFMPEG_INCLUDE_DIRS ${DAEDALUS_FFMPEG_SRC})
+            set(FFMPEG_CFLAGS_OTHER
+                "${FFMPEG_CFLAGS_OTHER} -DDAEDALUS_HAVE_H264_MB_INSPECT_COEFFS=1 -DHAVE_AV_CONFIG_H")
+            # Convert space-separated string to list (CMake idiom for compile flags).
+            separate_arguments(FFMPEG_CFLAGS_OTHER UNIX_COMMAND "${FFMPEG_CFLAGS_OTHER}")
+        endif()
+    else()
+        pkg_check_modules(FFMPEG REQUIRED libavcodec libavformat libavutil)
+        message(STATUS "daedalus_decode_h264: system FFmpeg (no inspection callback)")
+    endif()
+
+    add_executable(daedalus_decode_h264 tools/daedalus_decode_h264.c)
+    target_link_libraries(daedalus_decode_h264
+        PRIVATE daedalus_decoder ${FFMPEG_LIBRARIES})
+    target_include_directories(daedalus_decode_h264
+        PRIVATE ${FFMPEG_INCLUDE_DIRS})
+    target_link_directories(daedalus_decode_h264
+        PRIVATE ${FFMPEG_LIBRARY_DIRS})
+    target_compile_options(daedalus_decode_h264
+        PRIVATE -O2 ${FFMPEG_CFLAGS_OTHER})
+endif()
+
 # ---- Install ------------------------------------------------------
 #
-# Library + public header.  Stage 2/3 will add a pkg-config file and
-# CMake config exports once the API stabilises; pre-0.1 the scaffold
-# install just gives the static archive a home.
+# Installs:
+#   - libdaedalus_decoder.a       → ${CMAKE_INSTALL_LIBDIR}
+#   - include/daedalus_decoder.h  → ${CMAKE_INSTALL_INCLUDEDIR}
+#   - daedalus-decoder.pc         → ${CMAKE_INSTALL_LIBDIR}/pkgconfig
+#
+# The .pc lets sibling consumers (daedalus-v4l2 daemon, the
+# daedalus_decode_h264 CLI when built externally) discover the static
+# archive + headers via pkg-config.  daedalus-fourier is declared as a
+# public `Requires:` because the consumer (which static-links
+# libdaedalus_decoder.a) also needs daedalus-fourier in its own link
+# line to resolve the daedalus_ctx_* / daedalus_recipe_* symbols this
+# archive references.
+#
+# Relocatable-prefix scheme mirrors daedalus-fourier's .pc generation:
+# `prefix` is derived from ${pcfiledir} so `cmake --install --prefix /foo`
+# produces a .pc that resolves prefix=/foo at lookup time, regardless of
+# what CMAKE_INSTALL_PREFIX was at configure time.
 
 include(GNUInstallDirs)
 install(TARGETS daedalus_decoder
     ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR})
 install(FILES include/daedalus_decoder.h
     DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})
+
+file(RELATIVE_PATH PKGCONFIG_PCDIR_TO_PREFIX
+    "${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_LIBDIR}/pkgconfig"
+    "${CMAKE_INSTALL_PREFIX}")
+
+set(PKGCONFIG_OUT ${CMAKE_CURRENT_BINARY_DIR}/daedalus-decoder.pc)
+file(WRITE ${PKGCONFIG_OUT}
+"prefix=\${pcfiledir}/${PKGCONFIG_PCDIR_TO_PREFIX}
+exec_prefix=\${prefix}
+libdir=\${prefix}/${CMAKE_INSTALL_LIBDIR}
+includedir=\${prefix}/${CMAKE_INSTALL_INCLUDEDIR}
+
+Name: daedalus-decoder
+Description: Frame-major H.264 decoder on V3D7 via daedalus-fourier primitives
+Version: ${PROJECT_VERSION}
+Libs: -L\${libdir} -ldaedalus_decoder
+Requires: daedalus-fourier
+Cflags: -I\${includedir}
+")
+install(FILES ${PKGCONFIG_OUT}
+    DESTINATION ${CMAKE_INSTALL_LIBDIR}/pkgconfig
+)