diff --git a/install/install.sh b/install/install.sh
index 71853166..8ead80da 100644
--- a/install/install.sh
+++ b/install/install.sh
@@ -639,7 +639,7 @@ STRIPPED=$(echo "$STRIPPED" | sed -E 's/^[[:space:]]*[A-Za-z_][A-Za-z0-9_]*=[^[:
 FIRST=$(echo "$STRIPPED" | awk '{print $1}')
 
 case "$FIRST" in
-  grep|rg|egrep|fgrep|cat|head|tail|sed|awk|find) ;;
+  grep|rg|egrep|fgrep|cat|head|tail|find) ;;
   *) exit 0 ;;
 esac
 
@@ -677,7 +677,6 @@ case "$FIRST" in
   grep|rg|egrep|fgrep) echo "BLOCKED in indexed repo ($REPO_ROOT): use codedb_search \"<text>\" (codedb_word for an exact identifier, codedb_callers for call sites) instead of $FIRST — ranked + fewer tokens. Native $FIRST is allowed outside this repo or with CODEDB_NO_HOOKS=1." >&2; exit 2 ;;
   cat) echo "BLOCKED in indexed repo ($REPO_ROOT): use codedb_read path=<file> (codedb_outline first for a map) instead of cat. CODEDB_NO_HOOKS=1 to disable." >&2; exit 2 ;;
   head|tail) echo "BLOCKED in indexed repo ($REPO_ROOT): use codedb_read path=<file> line_start=.. line_end=.. instead of $FIRST. CODEDB_NO_HOOKS=1 to disable." >&2; exit 2 ;;
-  sed|awk) echo "BLOCKED in indexed repo ($REPO_ROOT): use codedb_edit (op=str_replace) instead of $FIRST for edits. CODEDB_NO_HOOKS=1 to disable." >&2; exit 2 ;;
   find) echo "BLOCKED in indexed repo ($REPO_ROOT): use codedb_find (fuzzy names) or codedb_glob (patterns) instead of find. CODEDB_NO_HOOKS=1 to disable." >&2; exit 2 ;;
 esac
 exit 0
@@ -808,22 +807,24 @@ main() {
   local dest="$INSTALL_DIR/codedb${ext}"
 
   printf "  ${D}│${N} %-12s " "codedb"
-  local tmp="/tmp/codedb.tmp.$$"
+  local tmp
+  tmp="$(mktemp "$INSTALL_DIR/.codedb-download.XXXXXX")"
+  trap 'rm -f "$tmp"' EXIT
   if curl -fsSL -A 'codedb-installer' "$url" -o "$tmp" 2>/dev/null; then
-    # Verify checksum when the release publishes a checksum manifest.
-    local checksum_text expected_hash checksum_notice="" actual_hash=""
+    # Keep any existing binary until the downloaded bytes are verified.
+    local checksum_text expected_hash actual_hash=""
     checksum_text="$(curl -fsSL -A 'codedb-installer' "$checksum_url" 2>/dev/null || true)"
-    expected_hash="$(printf '%s\n' "$checksum_text" | awk "/codedb-${platform}${ext}\$/ { print \$1 }")"
-    if [ -n "$expected_hash" ]; then
+    expected_hash="$(printf '%s\n' "$checksum_text" | awk -v asset="codedb-${platform}${ext}" '$2 == asset { count++; if (NF != 2) malformed=1; hash=$1 } END { if (count == 1 && !malformed) print hash }')"
+    if [[ "$expected_hash" =~ ^[0-9a-f]{64}$ ]]; then
       if command -v sha256sum >/dev/null 2>&1; then
         actual_hash="$(sha256sum "$tmp" | awk '{print $1}')"
       elif command -v shasum >/dev/null 2>&1; then
         actual_hash="$(shasum -a 256 "$tmp" | awk '{print $1}')"
       fi
       if [ -z "$actual_hash" ]; then
-        # No hashing tool on PATH. Never silently install an unverified
-        # binary — say so in the same place the skipped-manifest case does.
-        checksum_notice="  ${Y}warning:${N} checksum NOT verified — neither sha256sum nor shasum is on PATH\n"
+        printf "${R}failed${N}\n"
+        printf "\n  ${R}error: cannot verify download — install sha256sum or shasum first. Existing binary unchanged.${N}\n" >&2
+        exit 1
       elif [ "$actual_hash" != "$expected_hash" ]; then
         rm -f "$tmp"
         printf "${R}failed${N}\n"
@@ -833,10 +834,13 @@ main() {
         exit 1
       fi
     else
-      checksum_notice="  ${Y}warning:${N} checksum verification skipped (checksums.sha256 unavailable)\n"
+      printf "${R}failed${N}\n"
+      printf "\n  ${R}error: no unique valid checksum for this platform. Existing binary unchanged; retry when release checksums are available.${N}\n" >&2
+      exit 1
     fi
     xattr -c "$tmp" 2>/dev/null || true
     mv -f "$tmp" "$dest"
+    trap - EXIT
     chmod +x "$dest"
     printf "${G}✓${N}\n"
   else
@@ -848,24 +852,25 @@ main() {
 
   echo ""
   printf "  ${G}installed${N} ${D}→ $dest${N}\n"
-  if [ -n "$checksum_notice" ]; then
-    printf "$checksum_notice"
-  fi
   printf "  ${D}claude hook opt-out: CODEDB_NO_HOOKS=1 skips this run; CODEDB_PERSIST_NO_HOOKS=1 or touch ~/.codedb/no-hooks makes it permanent (rm ~/.codedb/no-hooks re-enables)${N}\n"
 
   # Register MCP server in coding tools
   echo ""
   printf "  ${W}registering integrations${N}\n"
   echo ""
-  register_claude "$dest"
-  register_codex "$dest"
-  register_codex_policy "$dest"
-  register_gemini "$dest"
-  register_cursor "$dest"
-  register_windsurf_devin "$dest"
-  register_detected_clients "$dest"
-  register_deepwiki
-  register_hooks
+  if [ -z "${CODEDB_NO_INTEGRATIONS:-}" ]; then
+    register_claude "$dest"
+    register_codex "$dest"
+    register_codex_policy "$dest"
+    register_gemini "$dest"
+    register_cursor "$dest"
+    register_windsurf_devin "$dest"
+    register_detected_clients "$dest"
+    register_deepwiki
+    register_hooks
+  else
+    printf "  ${D}skipped (CODEDB_NO_INTEGRATIONS)${N}\n"
+  fi
   print_hook_notes "$dest"
 
   # Check PATH
diff --git a/scripts/test_installer_safety.py b/scripts/test_installer_safety.py
new file mode 100644
index 00000000..ddfd4869
--- /dev/null
+++ b/scripts/test_installer_safety.py
@@ -0,0 +1,148 @@
+#!/usr/bin/env python3
+"""Installer failure paths must preserve the binary and avoid client config writes."""
+import hashlib
+import os
+import json
+from pathlib import Path
+import shutil
+import subprocess
+import sys
+import tempfile
+import tomllib
+
+
+def main():
+    installer = Path(__file__).resolve().parents[1] / 'install/install.sh'
+    payload = b'#!/bin/sh\nexit 0\n'
+    digest = hashlib.sha256(payload).hexdigest()
+    with tempfile.TemporaryDirectory(prefix='codedb-installer-') as directory:
+        root = Path(directory)
+        commands = root / 'commands'
+        commands.mkdir()
+        for command in ('mkdir', 'mktemp', 'awk', 'rm', 'mv', 'chmod'):
+            (commands / command).symlink_to(shutil.which(command))
+        (commands / 'uname').write_text('#!/bin/sh\ncase "$1" in -s) echo Darwin;; -m) echo arm64;; esac\n')
+        (commands / 'uname').chmod(0o755)
+        curl = commands / 'curl'
+        curl.write_text('#!' + sys.executable + '\n' + '''
+import os,sys
+from pathlib import Path
+args=sys.argv[1:];scenario=os.environ['INSTALLER_TEST_SCENARIO']
+digest=os.environ['INSTALLER_TEST_DIGEST']
+if any(a.endswith('checksums.sha256') for a in args):
+    if scenario=='unavailable':sys.exit(22)
+    if scenario=='missing':print(digest+'  other-platform');sys.exit(0)
+    if scenario=='malformed':print('not-a-hash  codedb-darwin-arm64');sys.exit(0)
+    if scenario=='trailing-field':print(digest+'  codedb-darwin-arm64 extra-field');sys.exit(0)
+    if scenario=='duplicate':print((digest+'  codedb-darwin-arm64\\n')*2);sys.exit(0)
+    print(('0'*64 if scenario=='mismatch' else digest)+'  codedb-darwin-arm64')
+else:
+    if scenario=='download-failed':sys.exit(22)
+    Path(args[args.index('-o')+1]).write_bytes(b'#!/bin/sh\\nexit 0\\n')
+''')
+        curl.chmod(0o755)
+        for scenario in ('unavailable', 'missing', 'malformed', 'trailing-field', 'duplicate', 'mismatch', 'no-hash-tool', 'download-failed', 'valid'):
+            target = root / (scenario + ' install with spaces')
+            target.mkdir()
+            binary = target / 'codedb'
+            binary.write_bytes(b'existing installation\n')
+            hash_tool = commands / 'shasum'
+            if hash_tool.exists():
+                hash_tool.unlink()
+            if scenario != 'no-hash-tool':
+                hash_tool.write_text('#!' + sys.executable + '\nimport hashlib,sys\nfrom pathlib import Path\nprint(hashlib.sha256(Path(sys.argv[-1]).read_bytes()).hexdigest()+"  binary")\n')
+                hash_tool.chmod(0o755)
+            fixture_home = root / (scenario + ' home')
+            fixture_home.mkdir()
+            claude_config = fixture_home / '.claude.json'
+            existing_config = json.dumps({'mcpServers': {'other': {'command': 'other-tool'}}})
+            if scenario in ('mismatch', 'trailing-field'):
+                claude_config.write_text(existing_config)
+            env = {k: v for k, v in os.environ.items() if not k.startswith('CODEDB_')}
+            env.update(HOME=str(fixture_home), PATH=str(commands), CODEDB_DIR=str(target),
+                       CODEDB_VERSION='0.2.5855', CODEDB_NO_INTEGRATIONS='1',
+                       INSTALLER_TEST_SCENARIO=scenario, INSTALLER_TEST_DIGEST=digest)
+            if scenario in ('mismatch', 'trailing-field'):
+                # A checksum failure must stop before normal client registration.
+                env.pop('CODEDB_NO_INTEGRATIONS')
+                env['CODEDB_INSTALL_DEEPWIKI'] = '0'
+                env['PATH'] += os.pathsep + os.environ['PATH']
+            done = subprocess.run(['/bin/bash', str(installer)], env=env, capture_output=True, text=True, timeout=20)
+            success = scenario == 'valid'
+            assert (done.returncode == 0) == success, (scenario, done.stdout, done.stderr)
+            assert binary.read_bytes() == (payload if success else b'existing installation\n'), scenario
+            assert not list(target.glob('.codedb-download.*')), scenario
+            assert 'unbound variable' not in done.stderr, done.stderr
+            if scenario in ('mismatch', 'trailing-field'):
+                assert claude_config.read_text() == existing_config, scenario
+            else:
+                assert not claude_config.exists(), scenario
+            assert not (fixture_home / '.codex').exists(), scenario
+            assert not (fixture_home / '.claude').exists(), scenario
+            print('PASS:', scenario)
+
+        # Drive the normal main() path inside a disposable HOME. This must
+        # reach detected-client registration and install the hook we exercise.
+        fixture_home = root / 'fixture-user'
+        fixture_home.mkdir()
+        project = root / 'project'
+        project.mkdir()
+        project = project.resolve()
+        registration = fixture_home / '.codedb/projects/test/project.txt'
+        registration.parent.mkdir(parents=True)
+        registration.write_text(str(project) + '\n')
+        claude_config = fixture_home / '.claude.json'
+        claude_config.write_text(json.dumps({'mcpServers': {'other': {'command': 'other-tool'}}}))
+        codex_config = fixture_home / '.codex/config.toml'
+        codex_config.parent.mkdir()
+        codex_config.write_text('[mcp_servers.other]\ncommand = "other-tool"\n')
+        qwen_config = fixture_home / '.qwen/settings.json'
+        qwen_config.parent.mkdir()
+        qwen_config.write_text(json.dumps({'mcpServers': {'other': {'command': 'other-tool'}}}))
+        normal_target = root / 'normal install with spaces'
+        normal_target.mkdir()
+        binary = normal_target / 'codedb'
+        binary.write_bytes(b'existing installation\n')
+        fake_codedb = commands / 'codedb'
+        fake_codedb.write_bytes(payload)
+        fake_codedb.chmod(0o755)
+        normal_env = {k: v for k, v in os.environ.items() if not k.startswith('CODEDB_')}
+        normal_env.update(HOME=str(fixture_home), PATH=str(commands) + os.pathsep + os.environ['PATH'],
+                          CODEDB_DIR=str(normal_target), CODEDB_VERSION='0.2.5855',
+                          CODEDB_INSTALL_DEEPWIKI='0', INSTALLER_TEST_SCENARIO='valid',
+                          INSTALLER_TEST_DIGEST=digest)
+        done = subprocess.run(['/bin/bash', str(installer)], env=normal_env,
+                              capture_output=True, text=True, timeout=20)
+        assert done.returncode == 0, (done.stdout, done.stderr)
+        assert binary.read_bytes() == payload
+        assert not list(normal_target.glob('.codedb-download.*'))
+        print('PASS: normal install through main')
+
+        configs = [
+            ('claude', json.loads(claude_config.read_text())['mcpServers']),
+            ('codex', tomllib.loads(codex_config.read_text())['mcp_servers']),
+            ('qwen detected client', json.loads(qwen_config.read_text())['mcpServers']),
+        ]
+        for name, config in configs:
+            assert config['other']['command'] == 'other-tool'
+            assert config['codedb']['command'] == str(binary)
+            assert config['codedb']['args'] == ['mcp']
+            print('PASS: normal', name, 'registration preserves other servers')
+
+        hook = fixture_home / '.claude/hooks/codedb-block-legacy.sh'
+        assert hook.is_file() and os.access(hook, os.X_OK)
+        settings = json.loads((fixture_home / '.claude/settings.json').read_text())
+        assert any('codedb-block-legacy.sh' in entry['hooks'][0]['command']
+                   for entry in settings['hooks']['PreToolUse'])
+        for command, expected in [('sed -i s/old/new/ code.py', 0), ('awk "{print}" code.py', 0),
+                                  ('rg handler .', 2), ('python3 edit.py', 0)]:
+            done = subprocess.run(['/bin/bash', str(hook)], cwd=project, env=normal_env,
+                                  input=json.dumps({'tool_input': {'command': command}}),
+                                  capture_output=True, text=True, timeout=10)
+            assert done.returncode == expected, (command, done.stderr)
+            assert 'codedb_edit' not in done.stderr
+            print('PASS: installed hook', command.split()[0])
+
+
+if __name__ == '__main__':
+    main()
diff --git a/website/app/install_script.sh b/website/app/install_script.sh
index 71853166..8ead80da 100644
--- a/website/app/install_script.sh
+++ b/website/app/install_script.sh
@@ -639,7 +639,7 @@ STRIPPED=$(echo "$STRIPPED" | sed -E 's/^[[:space:]]*[A-Za-z_][A-Za-z0-9_]*=[^[:
 FIRST=$(echo "$STRIPPED" | awk '{print $1}')
 
 case "$FIRST" in
-  grep|rg|egrep|fgrep|cat|head|tail|sed|awk|find) ;;
+  grep|rg|egrep|fgrep|cat|head|tail|find) ;;
   *) exit 0 ;;
 esac
 
@@ -677,7 +677,6 @@ case "$FIRST" in
   grep|rg|egrep|fgrep) echo "BLOCKED in indexed repo ($REPO_ROOT): use codedb_search \"<text>\" (codedb_word for an exact identifier, codedb_callers for call sites) instead of $FIRST — ranked + fewer tokens. Native $FIRST is allowed outside this repo or with CODEDB_NO_HOOKS=1." >&2; exit 2 ;;
   cat) echo "BLOCKED in indexed repo ($REPO_ROOT): use codedb_read path=<file> (codedb_outline first for a map) instead of cat. CODEDB_NO_HOOKS=1 to disable." >&2; exit 2 ;;
   head|tail) echo "BLOCKED in indexed repo ($REPO_ROOT): use codedb_read path=<file> line_start=.. line_end=.. instead of $FIRST. CODEDB_NO_HOOKS=1 to disable." >&2; exit 2 ;;
-  sed|awk) echo "BLOCKED in indexed repo ($REPO_ROOT): use codedb_edit (op=str_replace) instead of $FIRST for edits. CODEDB_NO_HOOKS=1 to disable." >&2; exit 2 ;;
   find) echo "BLOCKED in indexed repo ($REPO_ROOT): use codedb_find (fuzzy names) or codedb_glob (patterns) instead of find. CODEDB_NO_HOOKS=1 to disable." >&2; exit 2 ;;
 esac
 exit 0
@@ -808,22 +807,24 @@ main() {
   local dest="$INSTALL_DIR/codedb${ext}"
 
   printf "  ${D}│${N} %-12s " "codedb"
-  local tmp="/tmp/codedb.tmp.$$"
+  local tmp
+  tmp="$(mktemp "$INSTALL_DIR/.codedb-download.XXXXXX")"
+  trap 'rm -f "$tmp"' EXIT
   if curl -fsSL -A 'codedb-installer' "$url" -o "$tmp" 2>/dev/null; then
-    # Verify checksum when the release publishes a checksum manifest.
-    local checksum_text expected_hash checksum_notice="" actual_hash=""
+    # Keep any existing binary until the downloaded bytes are verified.
+    local checksum_text expected_hash actual_hash=""
     checksum_text="$(curl -fsSL -A 'codedb-installer' "$checksum_url" 2>/dev/null || true)"
-    expected_hash="$(printf '%s\n' "$checksum_text" | awk "/codedb-${platform}${ext}\$/ { print \$1 }")"
-    if [ -n "$expected_hash" ]; then
+    expected_hash="$(printf '%s\n' "$checksum_text" | awk -v asset="codedb-${platform}${ext}" '$2 == asset { count++; if (NF != 2) malformed=1; hash=$1 } END { if (count == 1 && !malformed) print hash }')"
+    if [[ "$expected_hash" =~ ^[0-9a-f]{64}$ ]]; then
       if command -v sha256sum >/dev/null 2>&1; then
         actual_hash="$(sha256sum "$tmp" | awk '{print $1}')"
       elif command -v shasum >/dev/null 2>&1; then
         actual_hash="$(shasum -a 256 "$tmp" | awk '{print $1}')"
       fi
       if [ -z "$actual_hash" ]; then
-        # No hashing tool on PATH. Never silently install an unverified
-        # binary — say so in the same place the skipped-manifest case does.
-        checksum_notice="  ${Y}warning:${N} checksum NOT verified — neither sha256sum nor shasum is on PATH\n"
+        printf "${R}failed${N}\n"
+        printf "\n  ${R}error: cannot verify download — install sha256sum or shasum first. Existing binary unchanged.${N}\n" >&2
+        exit 1
       elif [ "$actual_hash" != "$expected_hash" ]; then
         rm -f "$tmp"
         printf "${R}failed${N}\n"
@@ -833,10 +834,13 @@ main() {
         exit 1
       fi
     else
-      checksum_notice="  ${Y}warning:${N} checksum verification skipped (checksums.sha256 unavailable)\n"
+      printf "${R}failed${N}\n"
+      printf "\n  ${R}error: no unique valid checksum for this platform. Existing binary unchanged; retry when release checksums are available.${N}\n" >&2
+      exit 1
     fi
     xattr -c "$tmp" 2>/dev/null || true
     mv -f "$tmp" "$dest"
+    trap - EXIT
     chmod +x "$dest"
     printf "${G}✓${N}\n"
   else
@@ -848,24 +852,25 @@ main() {
 
   echo ""
   printf "  ${G}installed${N} ${D}→ $dest${N}\n"
-  if [ -n "$checksum_notice" ]; then
-    printf "$checksum_notice"
-  fi
   printf "  ${D}claude hook opt-out: CODEDB_NO_HOOKS=1 skips this run; CODEDB_PERSIST_NO_HOOKS=1 or touch ~/.codedb/no-hooks makes it permanent (rm ~/.codedb/no-hooks re-enables)${N}\n"
 
   # Register MCP server in coding tools
   echo ""
   printf "  ${W}registering integrations${N}\n"
   echo ""
-  register_claude "$dest"
-  register_codex "$dest"
-  register_codex_policy "$dest"
-  register_gemini "$dest"
-  register_cursor "$dest"
-  register_windsurf_devin "$dest"
-  register_detected_clients "$dest"
-  register_deepwiki
-  register_hooks
+  if [ -z "${CODEDB_NO_INTEGRATIONS:-}" ]; then
+    register_claude "$dest"
+    register_codex "$dest"
+    register_codex_policy "$dest"
+    register_gemini "$dest"
+    register_cursor "$dest"
+    register_windsurf_devin "$dest"
+    register_detected_clients "$dest"
+    register_deepwiki
+    register_hooks
+  else
+    printf "  ${D}skipped (CODEDB_NO_INTEGRATIONS)${N}\n"
+  fi
   print_hook_notes "$dest"
 
   # Check PATH
diff --git a/website/dist/install.sh b/website/dist/install.sh
index 71853166..8ead80da 100644
--- a/website/dist/install.sh
+++ b/website/dist/install.sh
@@ -639,7 +639,7 @@ STRIPPED=$(echo "$STRIPPED" | sed -E 's/^[[:space:]]*[A-Za-z_][A-Za-z0-9_]*=[^[:
 FIRST=$(echo "$STRIPPED" | awk '{print $1}')
 
 case "$FIRST" in
-  grep|rg|egrep|fgrep|cat|head|tail|sed|awk|find) ;;
+  grep|rg|egrep|fgrep|cat|head|tail|find) ;;
   *) exit 0 ;;
 esac
 
@@ -677,7 +677,6 @@ case "$FIRST" in
   grep|rg|egrep|fgrep) echo "BLOCKED in indexed repo ($REPO_ROOT): use codedb_search \"<text>\" (codedb_word for an exact identifier, codedb_callers for call sites) instead of $FIRST — ranked + fewer tokens. Native $FIRST is allowed outside this repo or with CODEDB_NO_HOOKS=1." >&2; exit 2 ;;
   cat) echo "BLOCKED in indexed repo ($REPO_ROOT): use codedb_read path=<file> (codedb_outline first for a map) instead of cat. CODEDB_NO_HOOKS=1 to disable." >&2; exit 2 ;;
   head|tail) echo "BLOCKED in indexed repo ($REPO_ROOT): use codedb_read path=<file> line_start=.. line_end=.. instead of $FIRST. CODEDB_NO_HOOKS=1 to disable." >&2; exit 2 ;;
-  sed|awk) echo "BLOCKED in indexed repo ($REPO_ROOT): use codedb_edit (op=str_replace) instead of $FIRST for edits. CODEDB_NO_HOOKS=1 to disable." >&2; exit 2 ;;
   find) echo "BLOCKED in indexed repo ($REPO_ROOT): use codedb_find (fuzzy names) or codedb_glob (patterns) instead of find. CODEDB_NO_HOOKS=1 to disable." >&2; exit 2 ;;
 esac
 exit 0
@@ -808,22 +807,24 @@ main() {
   local dest="$INSTALL_DIR/codedb${ext}"
 
   printf "  ${D}│${N} %-12s " "codedb"
-  local tmp="/tmp/codedb.tmp.$$"
+  local tmp
+  tmp="$(mktemp "$INSTALL_DIR/.codedb-download.XXXXXX")"
+  trap 'rm -f "$tmp"' EXIT
   if curl -fsSL -A 'codedb-installer' "$url" -o "$tmp" 2>/dev/null; then
-    # Verify checksum when the release publishes a checksum manifest.
-    local checksum_text expected_hash checksum_notice="" actual_hash=""
+    # Keep any existing binary until the downloaded bytes are verified.
+    local checksum_text expected_hash actual_hash=""
     checksum_text="$(curl -fsSL -A 'codedb-installer' "$checksum_url" 2>/dev/null || true)"
-    expected_hash="$(printf '%s\n' "$checksum_text" | awk "/codedb-${platform}${ext}\$/ { print \$1 }")"
-    if [ -n "$expected_hash" ]; then
+    expected_hash="$(printf '%s\n' "$checksum_text" | awk -v asset="codedb-${platform}${ext}" '$2 == asset { count++; if (NF != 2) malformed=1; hash=$1 } END { if (count == 1 && !malformed) print hash }')"
+    if [[ "$expected_hash" =~ ^[0-9a-f]{64}$ ]]; then
       if command -v sha256sum >/dev/null 2>&1; then
         actual_hash="$(sha256sum "$tmp" | awk '{print $1}')"
       elif command -v shasum >/dev/null 2>&1; then
         actual_hash="$(shasum -a 256 "$tmp" | awk '{print $1}')"
       fi
       if [ -z "$actual_hash" ]; then
-        # No hashing tool on PATH. Never silently install an unverified
-        # binary — say so in the same place the skipped-manifest case does.
-        checksum_notice="  ${Y}warning:${N} checksum NOT verified — neither sha256sum nor shasum is on PATH\n"
+        printf "${R}failed${N}\n"
+        printf "\n  ${R}error: cannot verify download — install sha256sum or shasum first. Existing binary unchanged.${N}\n" >&2
+        exit 1
       elif [ "$actual_hash" != "$expected_hash" ]; then
         rm -f "$tmp"
         printf "${R}failed${N}\n"
@@ -833,10 +834,13 @@ main() {
         exit 1
       fi
     else
-      checksum_notice="  ${Y}warning:${N} checksum verification skipped (checksums.sha256 unavailable)\n"
+      printf "${R}failed${N}\n"
+      printf "\n  ${R}error: no unique valid checksum for this platform. Existing binary unchanged; retry when release checksums are available.${N}\n" >&2
+      exit 1
     fi
     xattr -c "$tmp" 2>/dev/null || true
     mv -f "$tmp" "$dest"
+    trap - EXIT
     chmod +x "$dest"
     printf "${G}✓${N}\n"
   else
@@ -848,24 +852,25 @@ main() {
 
   echo ""
   printf "  ${G}installed${N} ${D}→ $dest${N}\n"
-  if [ -n "$checksum_notice" ]; then
-    printf "$checksum_notice"
-  fi
   printf "  ${D}claude hook opt-out: CODEDB_NO_HOOKS=1 skips this run; CODEDB_PERSIST_NO_HOOKS=1 or touch ~/.codedb/no-hooks makes it permanent (rm ~/.codedb/no-hooks re-enables)${N}\n"
 
   # Register MCP server in coding tools
   echo ""
   printf "  ${W}registering integrations${N}\n"
   echo ""
-  register_claude "$dest"
-  register_codex "$dest"
-  register_codex_policy "$dest"
-  register_gemini "$dest"
-  register_cursor "$dest"
-  register_windsurf_devin "$dest"
-  register_detected_clients "$dest"
-  register_deepwiki
-  register_hooks
+  if [ -z "${CODEDB_NO_INTEGRATIONS:-}" ]; then
+    register_claude "$dest"
+    register_codex "$dest"
+    register_codex_policy "$dest"
+    register_gemini "$dest"
+    register_cursor "$dest"
+    register_windsurf_devin "$dest"
+    register_detected_clients "$dest"
+    register_deepwiki
+    register_hooks
+  else
+    printf "  ${D}skipped (CODEDB_NO_INTEGRATIONS)${N}\n"
+  fi
   print_hook_notes "$dest"
 
   # Check PATH