feat(firmware): wire temporal_task.c + Kconfig + ruv_temporal component (Phase 6, #513)

Phase 6 of #513: C-side wiring for the on-device temporal head. Builds
cleanly with feature OFF (default); 8MB binary delta is +96 bytes vs
v0.6.4-esp32 — that's the no-op shim path. Feature ON depends on the
Rust component (Phase 5, currently blocked by upstream esp-rs nightly).

Files:

- main/temporal_task.{c,h} — owns the FreeRTOS task lifecycle. Per
  ADR-095 §3.3 the task has its own 16 KB stack pinned to Core 1 and
  is fed via a 32-deep FreeRTOS queue. With feature OFF the .c file
  collapses to three ESP_ERR_NOT_SUPPORTED stubs so callers don't
  need #ifdefs at every call site.
- main/temporal_task.h — defines rv_temporal_pkt_t (40 bytes,
  magic 0xC5110007 — next free in the existing 0xC5110001..0006
  family) and the task lifecycle API. Build-time _Static_assert
  pins the wire format.
- main/Kconfig.projbuild — new menu "On-device temporal head
  (ADR-095, #513)" with CONFIG_CSI_TEMPORAL_HEAD_ENABLED (default n)
  plus four runtime-tuneable knobs: TEMPORAL_INPUT_DIM (16),
  TEMPORAL_WINDOW_LEN (256), TEMPORAL_N_CLASSES (4), and
  TEMPORAL_CLASSIFY_PERIOD_MS (1000).
- main/CMakeLists.txt — adds temporal_task.c to SRCS unconditionally
  (the .c file feature-gates internally), and adds ruv_temporal to
  REQUIRES only when the feature is enabled so default builds don't
  pull in the Rust component.
- main/adaptive_controller.c — fast_loop_cb now extracts the 9
  feature floats from the pkt it just built and pushes them into
  temporal_task_push_frame after the existing stream_sender_send.
  Non-blocking; queue-full drops are coalesced and logged 1/sec.
- main/main.c — temporal_task_start() called right after
  adaptive_controller_init(). Wrapped in #ifdef so feature-off
  builds don't reference the (no-op-anyway) function.
- components/ruv_temporal/CMakeLists.txt — restructured. Top-level
  Kconfig guard registers an empty component when the feature is
  off (avoids running cargo without a working toolchain).
  add_custom_command moved AFTER idf_component_register so it
  doesn't fire in script mode (required by ESP-IDF v5.4).

Validation:
- Firmware builds clean with default config (feature OFF) on
  ESP-IDF v5.4 / esp32s3 target. Binary 1062 KiB / 2 MiB partition,
  48 % free.
- Static assertion catches wire-format drift (rv_temporal_pkt_t size).
- Host-side `cargo test -p wifi-densepose-temporal` still 5/5 from
  the earlier commit (no regression, this commit only touches
  firmware/).

Phase 7 (flash to COM8 + soak) deferred this iteration — board is
currently not enumerating on COM8; will pick up next iteration when
the ESP32 is reattached.

Co-Authored-By: claude-flow <ruv@ruv.net>

firmware/esp32-csi-node/components/ruv_temporal/CMakeLists.txt

@@ -1,16 +1,27 @@
 # ESP-IDF component manifest for the ruv_temporal Rust staticlib (ADR-095).
 #
 # Build flow:
-#   1. Run `cargo +esp build --release --target xtensa-esp32s3-none-elf` in
-#      this directory. Output: target/xtensa-esp32s3-none-elf/release/libruv_temporal.a
-#   2. Register the resulting static library and the public header dir
-#      with idf_component_register so it shows up on the firmware's
-#      include path and link line.
+#   - When CONFIG_CSI_TEMPORAL_HEAD_ENABLED is OFF (default): register an
+#     empty stub. main/temporal_task.c compiles the no-op shim path, no
+#     cargo, no Rust toolchain dependency. Default firmware build is
+#     unaffected.
+#   - When CONFIG_CSI_TEMPORAL_HEAD_ENABLED is ON: invoke
+#     `cargo +esp build --release --target xtensa-esp32s3-none-elf`,
+#     register the resulting libruv_temporal.a, and expose include/.
 #
-# Phase 4: scaffold only — registered but no kernel work runs yet.
-# Phase 5: cross-compile validated, binary delta measured.
-# Phase 6: enabled via CONFIG_CSI_TEMPORAL_HEAD_ENABLED Kconfig flag and
-#          fed from edge_processing.c.
+# add_custom_command is intentionally placed AFTER idf_component_register
+# because ESP-IDF runs every component's CMakeLists.txt twice — once in
+# script mode for dependency discovery (where add_custom_command is
+# forbidden), and once for the actual build.
+
+if(NOT CONFIG_CSI_TEMPORAL_HEAD_ENABLED)
+    # Feature disabled — register an empty component so the directory's
+    # mere existence doesn't break the build, but do NOT invoke cargo
+    # or pull include/ onto consumers' include paths (the C ABI header
+    # would advertise capabilities we cannot honour).
+    idf_component_register()
+    return()
+endif()
 
 set(RUV_TEMPORAL_DIR "${CMAKE_CURRENT_SOURCE_DIR}")
 set(RUV_TEMPORAL_TARGET "xtensa-esp32s3-none-elf")
@@ -18,9 +29,13 @@ set(RUV_TEMPORAL_PROFILE "release")
 set(RUV_TEMPORAL_LIB
     "${RUV_TEMPORAL_DIR}/target/${RUV_TEMPORAL_TARGET}/${RUV_TEMPORAL_PROFILE}/libruv_temporal.a")
 
-# Run the cargo build as a custom command. ESP-IDF's CMake runs at
-# configure time; we want the staticlib to exist before idf_component_register
-# runs so it can be added as INTERFACE_LINK_LIBRARIES.
+idf_component_register(
+    SRCS "shim.c"
+    INCLUDE_DIRS "include"
+    PRIV_REQUIRES "esp_common"
+)
+
+# Custom command + target run only at build time, not in script mode.
 add_custom_command(
     OUTPUT "${RUV_TEMPORAL_LIB}"
     WORKING_DIRECTORY "${RUV_TEMPORAL_DIR}"
@@ -30,12 +45,5 @@ add_custom_command(
 )
 add_custom_target(ruv_temporal_rust_build ALL DEPENDS "${RUV_TEMPORAL_LIB}")
 
-idf_component_register(
-    SRCS "shim.c"                # tiny C shim so idf_component_register has a SRCS
-    INCLUDE_DIRS "include"
-    PRIV_REQUIRES "esp_common"
-)
-
-# Wire the staticlib in.
 add_dependencies(${COMPONENT_LIB} ruv_temporal_rust_build)
 target_link_libraries(${COMPONENT_LIB} INTERFACE "${RUV_TEMPORAL_LIB}")