fix(security): apply audit remediations to dev (ported + dev-only)

Dev-branch audit (docs/_archive/security-audit-dev-2026-07-22.md) re-found the
master issues (absent on dev) plus new ones in dev-only code. Applied here;
full-node build + test suite green; the subtle fixes were adversarially re-verified.

Ported from the master remediation (adapted to dev's code):
- bootstrap: reject zip-slip / path-traversal archive members (isSafeArchivePath)
  before writing (S2-1). (dev already fail-closes on a missing checksum.)
- xmrig updater: fail closed when a signature is required but no key is pinned (F1-1).
- http_download.httpGetString: 16 MiB hard cap + MAXFILESIZE on the shared
  metadata/price fetch (F1-2 / caps the updater + exchange paths at one site).
- rpc_client: explicit SSL_VERIFYPEER/VERIFYHOST (F4-1) and a 256 MiB response
  cap in WriteCallback (F4-3).
- lite_connection_service: reject remote http:// lite servers, loopback only (L1-1).
  Loopback is matched by a strict dotted-decimal 127.0.0.0/8 check (not a
  startsWith("127.") prefix, which would wrongly accept 127.0.0.1.evil.com), with
  userinfo/fragment stripping.
- lite controller: propagate encrypt/decrypt save() failure instead of reporting
  success (F7-1).
- xmrig_manager: chmod(0600) the pool config before writing secrets (F5-2).
- app: clear the copied secret from the OS clipboard on shutdown (F3b-1).
- export_transactions: neutralize CSV/spreadsheet formula injection (F13-1).
- build pipeline: build-from-source lite backend + remove the self-attested
  CMake signature gate (F15-1); pinned+verified appimagetool (F15-3/4);
  verified Sapling params in setup.sh (F15-6); build.sh exits 0 on success.
  (F14-1 empty-quoted-arg and F8-2 NUL-termination were already fixed on dev.)

Dev-only findings:
- rpc_client.callRaw: scrub the raw buffer + parsed tree (templated scrubJsonSecrets
  for ordered_json) so console dumpprivkey/z_exportkey keys don't linger in freed
  heap (N1-1).
- seed_wallet_creator: wipe the exported mnemonic on the failure path so a discarded
  failed result never carries a live seed (W1-2).
- export_all_keys: write the plaintext key dump 0600 + atomically via
  writeFileAtomically (U1-2).
- chat_database: restrict chat_messages.sqlite and its WAL/SHM sidecars to owner-only (C3-1).

Not done (need a decision, documented in the report):
- Chat header metadata (cid/z/p) rides outside the AEAD (C1/C2) — binding it is a
  wire-protocol change requiring SilentDragonXLite interop review.
- Bootstrap lacks an offline-rooted signature (S2-2 residual) — needs signing infra.
- Console scrollback retains console-typed key-export output in plaintext (N1-1
  residual) — inherent to an echoing console; would need output redaction.

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

scripts/build-lite-backend-artifact.sh

@@ -67,25 +67,9 @@ Options:
     --backend-dir PATH              SilentDragonXLite/lib source directory.
     --silentdragonxlitelib-dir PATH Override the wrapper's silentdragonxlitelib dependency path.
     --out-dir PATH                  Output directory for copied artifact and metadata.
-    --artifact PATH                 Inventory an existing artifact instead of building.
-    --no-build                      Do not run cargo; requires --artifact.
     --reproducible                  Add deterministic Rust path remaps for clean builds.
     --remap-path-prefix FROM=TO     Extra rustc path remap used with --reproducible.
     --builder NAME                  Redacted builder/provenance label. Default: local.
-    --signature-required            Fail if verified signature metadata is not supplied.
-    --signature-file PATH           Existing sidecar signature file to record.
-    --signature-format FORMAT       Signature format: minisign, gpg, sigstore, external, or other.
-    --signature-verification-tool T Verification tool and version used by the release builder.
-    --signature-verification-command C
-                                    Verification command already run by the release builder.
-    --signature-key-fingerprint F   Reviewed public-key fingerprint, when applicable.
-    --signature-certificate-identity ID
-                                    Reviewed certificate identity, when applicable.
-    --signature-certificate-issuer I
-                                    Reviewed certificate issuer, when applicable.
-    --signature-transparency-log-url URL
-                                    Transparency log entry, when applicable.
-    --signature-verified-sha256 SHA Artifact SHA-256 verified by the signature check.
     -j, --jobs N                    Cargo parallel jobs.
     --cargo-arg ARG                 Extra argument forwarded to cargo build.
     -h, --help                      Show this help.
@@ -95,9 +79,13 @@ Outputs:
   <out>/<platform>/lite-backend-symbols.txt
   <out>/<platform>/lite-backend-artifact-manifest.json
 
-The script captures symbols, checksums, and optional read-only signature
-verification metadata only. It does not load the library, resolve function
-pointers, call SDXL, sign, upload, or publish artifacts.
+The lite backend is always built from the vendored in-tree source
+(third_party/silentdragonxlite), which is the trust root. Prebuilt artifacts
+and self-attested signature metadata are NOT accepted (F15-1) — the previous
+scheme only recorded an unverified "verified" claim. The script captures the
+freshly-built artifact's symbols and checksum, and records build provenance.
+It does not load the library, resolve function pointers, call SDXL, sign,
+upload, or publish artifacts.
 EOF
 }
 
@@ -166,15 +154,8 @@ while [[ $# -gt 0 ]]; do
             OUT_DIR="$(absolute_path "$2")"
             shift 2
             ;;
-        --artifact)
-            [[ $# -ge 2 ]] || die "--artifact requires a value"
-            ARTIFACT_PATH="$(absolute_path "$2")"
-            BUILD_ARTIFACT=false
-            shift 2
-            ;;
-        --no-build)
-            BUILD_ARTIFACT=false
-            shift
+        --artifact|--no-build)
+            die "$1 was removed (F15-1): the lite backend must be built from the vendored in-tree source (third_party/silentdragonxlite); prebuilt artifacts are no longer accepted."
             ;;
         --reproducible)
             REPRODUCIBLE=true
@@ -191,54 +172,11 @@ while [[ $# -gt 0 ]]; do
             BUILDER="$2"
             shift 2
             ;;
-        --signature-required)
-            SIGNATURE_REQUIRED=true
-            shift
-            ;;
-        --signature-file|--signature-path)
-            [[ $# -ge 2 ]] || die "$1 requires a value"
-            SIGNATURE_FILE="$(absolute_path "$2")"
-            shift 2
-            ;;
-        --signature-format)
-            [[ $# -ge 2 ]] || die "--signature-format requires a value"
-            SIGNATURE_FORMAT="$2"
-            shift 2
-            ;;
-        --signature-verification-tool|--signature-tool)
-            [[ $# -ge 2 ]] || die "$1 requires a value"
-            SIGNATURE_VERIFICATION_TOOL="$2"
-            shift 2
-            ;;
-        --signature-verification-command)
-            [[ $# -ge 2 ]] || die "--signature-verification-command requires a value"
-            SIGNATURE_VERIFICATION_COMMAND="$2"
-            shift 2
-            ;;
-        --signature-key-fingerprint)
-            [[ $# -ge 2 ]] || die "--signature-key-fingerprint requires a value"
-            SIGNATURE_KEY_FINGERPRINT="$2"
-            shift 2
-            ;;
-        --signature-certificate-identity)
-            [[ $# -ge 2 ]] || die "--signature-certificate-identity requires a value"
-            SIGNATURE_CERTIFICATE_IDENTITY="$2"
-            shift 2
-            ;;
-        --signature-certificate-issuer)
-            [[ $# -ge 2 ]] || die "--signature-certificate-issuer requires a value"
-            SIGNATURE_CERTIFICATE_ISSUER="$2"
-            shift 2
-            ;;
-        --signature-transparency-log-url)
-            [[ $# -ge 2 ]] || die "--signature-transparency-log-url requires a value"
-            SIGNATURE_TRANSPARENCY_LOG_URL="$2"
-            shift 2
-            ;;
-        --signature-verified-sha256)
-            [[ $# -ge 2 ]] || die "--signature-verified-sha256 requires a value"
-            SIGNATURE_VERIFIED_SHA256="$2"
-            shift 2
+        --signature-required|--signature-file|--signature-path|--signature-format|\
+--signature-verification-tool|--signature-tool|--signature-verification-command|\
+--signature-key-fingerprint|--signature-certificate-identity|--signature-certificate-issuer|\
+--signature-transparency-log-url|--signature-verified-sha256)
+            die "signature-attestation flags were removed (F15-1): they recorded a self-attested \"verified\" claim without running any cryptographic verifier. The lite backend is built from the vendored in-tree source, which is the trust root."
             ;;
         -j|--jobs)
             [[ $# -ge 2 ]] || die "--jobs requires a value"
@@ -766,6 +704,7 @@ MANIFEST_FILE="$PLATFORM_OUT_DIR/lite-backend-artifact-manifest.json"
     printf '  },\n'
     printf '  "provenance": {\n'
     printf '    "owner_ready": true,\n'
+    printf '    "built_from_source": true,\n'
     printf '    "metadata_provided": true,\n'
     printf '    "source": '; json_escape "$BACKEND_SOURCE_DIR"; printf ',\n'
     printf '    "cargo_build_source": '; json_escape "$BUILD_BACKEND_DIR"; printf ',\n'