fix(build): enforce build-from-source for the lite backend (F15-1)

The lite-backend "signature verification" was attestation theater:
build-lite-backend-artifact.sh recorded a self-attested
signature_verification.verification_status="verified" with no cryptographic
check (the "verified" SHA was simply the artifact's own SHA), and CMake's
DRAGONX_LITE_BACKEND_REQUIRE_SIGNATURE gate trusted it — so a hand-edited
manifest could link an arbitrary prebuilt backend into ObsidianDragonLite.

Per the chosen remediation (build-from-source is the trust root):
- build-lite-backend-artifact.sh: reject --artifact/--no-build (prebuilt) and
  all --signature-* flags; the backend is always built from the vendored
  in-tree source (third_party/silentdragonxlite). Record built_from_source:true
  in the manifest provenance. Usage/header updated.
- CMakeLists.txt: remove the DRAGONX_LITE_BACKEND_REQUIRE_SIGNATURE option and
  its manifest signature-verification gate (kept the real required-symbol
  inventory check); update the config summary line.

Full-node CMake reconfigure + build pass; script bash -n clean and the removed
flags now hard-error. (The lite-backend link path needs cargo + backend and was
not runtime-tested in this environment.)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

CMakeLists.txt

@@ -53,7 +53,6 @@ set_property(CACHE DRAGONX_LITE_BACKEND_LINK_MODE PROPERTY STRINGS imported)
 set(DRAGONX_LITE_BACKEND_ABI "sdxl-c-v1" CACHE STRING "Expected lite backend C ABI version")
 set(DRAGONX_LITE_BACKEND_SYMBOLS_FILE "" CACHE FILEPATH "Path to generated lite backend exported-symbol inventory")
 set(DRAGONX_LITE_BACKEND_MANIFEST "" CACHE FILEPATH "Optional path to generated lite backend artifact manifest")
-option(DRAGONX_LITE_BACKEND_REQUIRE_SIGNATURE "Require verified signature metadata in the lite backend artifact manifest" OFF)
 set(DRAGONX_LITE_BACKEND_REQUIRED_SYMBOLS
     litelib_wallet_exists
     litelib_initialize_new
@@ -126,31 +125,12 @@ if(DRAGONX_ENABLE_LITE_BACKEND)
     if(DRAGONX_LITE_BACKEND_MANIFEST AND NOT EXISTS "${DRAGONX_LITE_BACKEND_MANIFEST}")
         message(FATAL_ERROR "DRAGONX_LITE_BACKEND_MANIFEST does not exist: ${DRAGONX_LITE_BACKEND_MANIFEST}")
     endif()
-    if(DRAGONX_LITE_BACKEND_REQUIRE_SIGNATURE)
-        if(NOT DRAGONX_LITE_BACKEND_MANIFEST)
-            message(FATAL_ERROR "DRAGONX_LITE_BACKEND_REQUIRE_SIGNATURE requires DRAGONX_LITE_BACKEND_MANIFEST")
-        endif()
-        file(READ "${DRAGONX_LITE_BACKEND_MANIFEST}" DRAGONX_LITE_BACKEND_MANIFEST_JSON)
-        string(JSON DRAGONX_LITE_SIGNATURE_STATUS ERROR_VARIABLE DRAGONX_LITE_SIGNATURE_STATUS_ERROR GET "${DRAGONX_LITE_BACKEND_MANIFEST_JSON}" signature_verification verification_status)
-        if(DRAGONX_LITE_SIGNATURE_STATUS_ERROR)
-            message(FATAL_ERROR "DRAGONX_LITE_BACKEND_MANIFEST is missing signature verification status")
-        endif()
-        if(NOT DRAGONX_LITE_SIGNATURE_STATUS STREQUAL "verified")
-            message(FATAL_ERROR "DRAGONX_LITE_BACKEND_REQUIRE_SIGNATURE requires verified signature metadata")
-        endif()
-        string(JSON DRAGONX_LITE_SIGNATURE_VERIFIED_SHA ERROR_VARIABLE DRAGONX_LITE_SIGNATURE_VERIFIED_SHA_ERROR GET "${DRAGONX_LITE_BACKEND_MANIFEST_JSON}" signature_verification verified_artifact_sha256)
-        string(JSON DRAGONX_LITE_ARTIFACT_SHA ERROR_VARIABLE DRAGONX_LITE_ARTIFACT_SHA_ERROR GET "${DRAGONX_LITE_BACKEND_MANIFEST_JSON}" artifact sha256)
-        if(DRAGONX_LITE_SIGNATURE_VERIFIED_SHA_ERROR OR DRAGONX_LITE_ARTIFACT_SHA_ERROR)
-            message(FATAL_ERROR "DRAGONX_LITE_BACKEND_MANIFEST is missing artifact/signature SHA-256 metadata")
-        endif()
-        if(NOT DRAGONX_LITE_SIGNATURE_VERIFIED_SHA STREQUAL DRAGONX_LITE_ARTIFACT_SHA)
-            message(FATAL_ERROR "DRAGONX_LITE_BACKEND_MANIFEST signature metadata does not verify the artifact SHA-256")
-        endif()
-        string(JSON DRAGONX_LITE_SIGNATURE_PERFORMED ERROR_VARIABLE DRAGONX_LITE_SIGNATURE_PERFORMED_ERROR GET "${DRAGONX_LITE_BACKEND_MANIFEST_JSON}" signature_verification verification_performed)
-        if(DRAGONX_LITE_SIGNATURE_PERFORMED_ERROR OR NOT DRAGONX_LITE_SIGNATURE_PERFORMED)
-            message(FATAL_ERROR "DRAGONX_LITE_BACKEND_REQUIRE_SIGNATURE requires verification_performed=true")
-        endif()
-    endif()
+    # Note (F15-1): the former signature-metadata gate was removed. It trusted a
+    # "verification_status: verified" field that scripts/build-lite-backend-artifact.sh
+    # self-attested with no cryptographic check (the "verified" SHA was just the artifact's
+    # own SHA). The trust root is now build-from-source: that script builds the backend from
+    # the vendored in-tree source and refuses prebuilt artifacts, so the library linked here
+    # is the one built from reviewed source. The required-symbol inventory check above stays.
 
     add_library(dragonx_lite_backend UNKNOWN IMPORTED)
     set_target_properties(dragonx_lite_backend PROPERTIES
@@ -1097,5 +1077,5 @@ message(STATUS "  Lite backend:   ${DRAGONX_LITE_BACKEND_READY}")
 message(STATUS "  Lite lib:       ${DRAGONX_LITE_BACKEND_LIBRARY}")
 message(STATUS "  Lite symbols:   ${DRAGONX_LITE_BACKEND_SYMBOLS_FILE}")
 message(STATUS "  Lite manifest:  ${DRAGONX_LITE_BACKEND_MANIFEST}")
-message(STATUS "  Lite signature: ${DRAGONX_LITE_BACKEND_REQUIRE_SIGNATURE}")
+message(STATUS "  Lite trust:     built-from-source (vendored third_party/silentdragonxlite)")
 message(STATUS "")