diff --git a/.gitea/workflows/manifest-entry-existence-check.yml b/.gitea/workflows/manifest-entry-existence-check.yml
new file mode 100644
index 000000000..3af8cb947
--- /dev/null
+++ b/.gitea/workflows/manifest-entry-existence-check.yml
@@ -0,0 +1,52 @@
+name: manifest-entry-existence-check
+
+# PR-time defense against bad manifest.json entries (#2185).
+#
+# A manifest entry whose `repo` does not exist on Gitea only surfaces
+# as a failure in publish-workspace-server-image.yml *after* merge,
+# which fires the main-red watchdog. This workflow checks every
+# (plugin + workspace_template + org_template) entry at PR-review
+# time so broken entries are caught before they reach main.
+#
+# Design notes
+# ------------
+# - Uses the same AUTO_SYNC_TOKEN secret that publish-workspace-server-image.yml
+#   uses for cloning manifest deps. Some entries are platform-private, so an
+#   anonymous API check would 404 on valid entries; auth is required.
+# - Only checks repo existence, not ref resolvability (#2185 scope).
+# - Mirrors clone-manifest.sh retry behavior (3 attempts, backoff).
+# - Triggers only when manifest.json changes to keep CI load minimal.
+#
+# Related: #2183 (incident), #2184 (fix), #2185 (this gate).
+
+on:
+  pull_request:
+    branches: [main, staging]
+    paths:
+      - 'manifest.json'
+
+permissions:
+  contents: read
+
+jobs:
+  # bp-required: pending #2185 — new PR-time gate; branch-protection update tracked in the same issue.
+  check-entries:
+    name: Verify manifest entries exist on Gitea
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    steps:
+      - name: Check out PR head
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd  # v6.0.2
+
+      - name: Verify each manifest entry resolves on Gitea
+        env:
+          GITEA_HOST: git.moleculesai.app
+          GITEA_TOKEN: ${{ secrets.AUTO_SYNC_TOKEN }}
+        run: |
+          set -euo pipefail
+          bash scripts/manifest-entry-existence-check.sh
+
+      - name: Regression test manifest-entry-existence-check script
+        run: |
+          set -euo pipefail
+          bash scripts/test-manifest-entry-existence-check.sh
diff --git a/scripts/manifest-entry-existence-check.sh b/scripts/manifest-entry-existence-check.sh
new file mode 100755
index 000000000..e03f918be
--- /dev/null
+++ b/scripts/manifest-entry-existence-check.sh
@@ -0,0 +1,107 @@
+#!/usr/bin/env bash
+# manifest-entry-existence-check.sh — PR-time guard: verify every repo listed in
+# manifest.json actually exists on Gitea before merge.
+#
+# Mirrors clone-manifest.sh retry behavior (3 attempts, linear backoff) and
+# fails closed on any exhausted non-200 status (404, 500, 403, auth/network
+# failures, etc.) so bad manifest entries cannot slip through.
+#
+# Usage:
+#   GITEA_HOST=git.example.com GITEA_TOKEN=xxx ./manifest-entry-existence-check.sh [manifest.json]
+#
+# Exit:
+#   0  all repos exist / were reachable
+#   1  one or more entries could not be validated
+#   2  bad usage / missing inputs / required env not set
+
+set -euo pipefail
+
+MANIFEST="${1:-manifest.json}"
+GITEA_HOST="${GITEA_HOST:-}"
+GITEA_TOKEN="${GITEA_TOKEN:-${MOLECULE_GITEA_TOKEN:-}}"
+GITEA_API="${GITEA_API:-https://${GITEA_HOST}/api/v1/repos}"
+
+if [ ! -f "$MANIFEST" ]; then
+    echo "::error::manifest not found: $MANIFEST" >&2
+    exit 2
+fi
+
+if [ -z "$GITEA_HOST" ]; then
+    echo "::error::GITEA_HOST is not set" >&2
+    exit 2
+fi
+
+if [ -z "$GITEA_TOKEN" ]; then
+    echo "::error::GITEA_TOKEN (or MOLECULE_GITEA_TOKEN) is not set" >&2
+    exit 2
+fi
+
+# Strip JSON5-style // comments before parsing (same as clone-manifest.sh)
+_strip_comments() {
+    sed '/^[[:space:]]*\/\//d' "$MANIFEST"
+}
+
+MANIFEST_JSON="$(_strip_comments)"
+
+TOTAL=0
+MISSING=()
+
+_check_entry() {
+    local name="$1" repo="$2"
+    local last_http_code=""
+
+    for attempt in 1 2 3; do
+        local http_code
+        http_code=$(curl -sS -o /dev/null -w '%{http_code}' --max-time 10 \
+            -H "Authorization: token ${GITEA_TOKEN}" \
+            "${GITEA_API}/${repo}" 2>/dev/null || true)
+        last_http_code="$http_code"
+
+        if [ "$http_code" = "200" ]; then
+            echo "  OK: $name -> $repo"
+            return 0
+        elif [ "$http_code" = "404" ]; then
+            echo "::error::manifest entry '$name' points at $repo which does not exist on Gitea (404)"
+            MISSING+=("$name:$repo (404)")
+            return 0
+        else
+            echo "  attempt $attempt: '$name' -> $repo returned HTTP ${http_code:-(none)}, retrying"
+            sleep $((attempt * 2))
+        fi
+    done
+
+    # After exhausting retries, any non-200 status that wasn't already recorded
+    # as 404 is a validation failure (500, 403, auth/network gateway errors, etc.).
+    echo "::error::manifest entry '$name' -> $repo could not be validated after 3 attempts (last HTTP ${last_http_code:-(none)})"
+    MISSING+=("$name:$repo (last HTTP ${last_http_code:-(none)})")
+}
+
+# Categories to check — must match manifest.json schema
+_check_category() {
+    local category="$1"
+    local count
+    count=$(echo "$MANIFEST_JSON" | jq -r ".${category} | length")
+
+    local i=0
+    while [ "$i" -lt "$count" ]; do
+        local name repo
+        name=$(echo "$MANIFEST_JSON" | jq -r ".${category}[$i].name")
+        repo=$(echo "$MANIFEST_JSON" | jq -r ".${category}[$i].repo")
+        TOTAL=$((TOTAL + 1))
+        _check_entry "$name" "$repo"
+        i=$((i + 1))
+    done
+}
+
+_check_category "plugins"
+_check_category "workspace_templates"
+_check_category "org_templates"
+
+if [ "${#MISSING[@]}" -gt 0 ]; then
+    echo "::error::${#MISSING[@]} of ${TOTAL} manifest entries are broken:"
+    printf '  - %s\n' "${MISSING[@]}"
+    exit 1
+fi
+
+echo "::notice::All ${TOTAL} manifest entries resolve to existing Gitea repos."
+exit 0
diff --git a/scripts/test-manifest-entry-existence-check.sh b/scripts/test-manifest-entry-existence-check.sh
new file mode 100755
index 000000000..45e046d77
--- /dev/null
+++ b/scripts/test-manifest-entry-existence-check.sh
@@ -0,0 +1,214 @@
+#!/usr/bin/env bash
+# scripts/test-manifest-entry-existence-check.sh
+#
+# Regression tests for scripts/manifest-entry-existence-check.sh.
+# Verifies the retry loop fails closed on persistent non-200 statuses
+# (500, 403, network failures) and succeeds when retries eventually return 200.
+#
+# Run: bash scripts/test-manifest-entry-existence-check.sh
+# Expected: "All N tests passed" + exit 0.
+
+set -euo pipefail
+
+SCRIPT="$(cd "$(dirname "$0")" && pwd)/manifest-entry-existence-check.sh"
+TMP="$(mktemp -d)"
+trap 'rm -rf "$TMP"' EXIT
+
+PASS=0
+FAIL=0
+
+# ─────────────────────────────────────────────────────────────────────────────
+# Helpers
+# ─────────────────────────────────────────────────────────────────────────────
+
+run_script() {
+    # Args: <fixture-file> [extra-env...]
+    local fixture="$1"
+    shift
+    set +e
+    env \
+        GITEA_HOST="git.example.com" \
+        GITEA_TOKEN="test-token" \
+        PATH="$TMP:$PATH" \
+        "$@" \
+        bash "$SCRIPT" "$fixture" 2>&1
+    local rc=$?
+    set -e
+    echo "EXIT_CODE=$rc"
+}
+
+assert_match() {
+    local name="$1" got="$2" pattern="$3"
+    if printf '%s' "$got" | grep -qE "$pattern"; then
+        PASS=$((PASS + 1))
+        printf '  ✓ %s\n' "$name"
+    else
+        FAIL=$((FAIL + 1))
+        printf '  ✗ %s\n    want pattern: %s\n    got:\n%s\n' "$name" "$pattern" "$got"
+    fi
+}
+
+assert_not_match() {
+    local name="$1" got="$2" pattern="$3"
+    if printf '%s' "$got" | grep -qE "$pattern"; then
+        FAIL=$((FAIL + 1))
+        printf '  ✗ %s\n    bad pattern matched: %s\n    got:\n%s\n' "$name" "$pattern" "$got"
+    else
+        PASS=$((PASS + 1))
+        printf '  ✓ %s\n' "$name"
+    fi
+}
+
+# ─────────────────────────────────────────────────────────────────────────────
+# Mock curl
+# ─────────────────────────────────────────────────────────────────────────────
+
+# The mock curl reads MOCK_MODE to decide what status to return.
+# It accepts the same flags the script uses and echoes the status code.
+# jq is also mocked so tests run on hosts without jq installed.
+mkdir -p "$TMP"
+
+cat > "$TMP/jq" <<'EOF'
+#!/usr/bin/env python3
+import json, re, sys
+# The checker invokes jq as: jq -r ".<category> | length" or jq -r ".<category>[N].<field>".
+# The query is always the last argument; -r can be ignored for the mock.
+query = sys.argv[-1]
+obj = json.load(sys.stdin)
+
+# Support queries used by the script: .<category> | length  and  .<category>[N].<field>
+m = re.fullmatch(r'\.([A-Za-z_][A-Za-z0-9_]*)\s*\|\s*length', query)
+if m:
+    print(len(obj.get(m.group(1), [])))
+    sys.exit(0)
+
+m = re.fullmatch(r'\.([A-Za-z_][A-Za-z0-9_]*)\[(\d+)\]\.([A-Za-z_][A-Za-z0-9_]*)', query)
+if m:
+    cat = obj.get(m.group(1), [])
+    idx = int(m.group(2))
+    field = m.group(3)
+    if idx < len(cat):
+        print(cat[idx].get(field, ''))
+    else:
+        print('')
+    sys.exit(0)
+
+print(json.dumps(obj))
+EOF
+chmod +x "$TMP/jq"
+
+cat > "$TMP/curl" <<'EOF'
+#!/usr/bin/env bash
+# Mock curl for manifest-entry-existence-check tests.
+# Returns the status stored in MOCK_MODE for every URL.
+set -euo pipefail
+mode="${MOCK_MODE-200}"
+# Consume and ignore flags; the script always passes -sS -o /dev/null -w etc.
+while [ "$#" -gt 0 ]; do
+    case "$1" in
+        -s|-S|-o|--max-time) shift 2 ;;
+        -w|-H) shift 2 ;;
+        *) URL="$1"; shift ;;
+    esac
+done
+printf '%s\n' "$mode"
+EOF
+chmod +x "$TMP/curl"
+
+# ─────────────────────────────────────────────────────────────────────────────
+# Fixtures
+# ─────────────────────────────────────────────────────────────────────────────
+
+cat > "$TMP/all-good.json" <<'EOF'
+{
+  "plugins": [
+    {"name": "plugin-a", "repo": "molecule-ai/plugin-a"}
+  ],
+  "workspace_templates": [
+    {"name": "template-a", "repo": "molecule-ai/template-a"}
+  ],
+  "org_templates": []
+}
+EOF
+
+cat > "$TMP/mixed.json" <<'EOF'
+{
+  "plugins": [
+    {"name": "plugin-a", "repo": "molecule-ai/plugin-a"},
+    {"name": "plugin-b", "repo": "molecule-ai/plugin-b"}
+  ],
+  "workspace_templates": [],
+  "org_templates": []
+}
+EOF
+
+# ─────────────────────────────────────────────────────────────────────────────
+# Test cases
+# ─────────────────────────────────────────────────────────────────────────────
+
+echo "1. All entries return HTTP 200 — clean exit"
+got=$(MOCK_MODE=200 run_script "$TMP/all-good.json")
+assert_match "all-good-success-message" "$got" "All .* manifest entries resolve"
+assert_match "all-good-exit-zero" "$got" "EXIT_CODE=0"
+
+echo
+echo "2. Persistent HTTP 404 — fails loudly"
+got=$(MOCK_MODE=404 run_script "$TMP/all-good.json")
+assert_match "404-reports-entry" "$got" "does not exist on Gitea \(404\)"
+assert_match "404-exit-one" "$got" "EXIT_CODE=1"
+
+echo
+echo "3. Persistent HTTP 500 after retries — fails closed"
+got=$(MOCK_MODE=500 run_script "$TMP/all-good.json")
+assert_match "500-reports-last-code" "$got" "last HTTP 500"
+assert_match "500-exit-one" "$got" "EXIT_CODE=1"
+assert_match "500-attempts-three" "$got" "attempt 3"
+
+echo
+echo "4. Persistent HTTP 403 after retries — fails closed"
+got=$(MOCK_MODE=403 run_script "$TMP/all-good.json")
+assert_match "403-reports-last-code" "$got" "last HTTP 403"
+assert_match "403-exit-one" "$got" "EXIT_CODE=1"
+
+echo
+echo "5. Empty HTTP code (network/gateway failure) — fails closed"
+got=$(MOCK_MODE="" run_script "$TMP/all-good.json")
+assert_match "empty-code-reports-failure" "$got" "could not be validated after 3 attempts"
+assert_match "empty-code-exit-one" "$got" "EXIT_CODE=1"
+
+echo
+echo "6. Mixed entries with one 404 and one 200 — counts correctly"
+# Use a per-URL mock: plugin-a 200, plugin-b 404
+cat > "$TMP/curl" <<'EOF'
+#!/usr/bin/env bash
+set -euo pipefail
+while [ "$#" -gt 0 ]; do
+    case "$1" in
+        -s|-S|-o|--max-time) shift 2 ;;
+        -w|-H) shift 2 ;;
+        *) URL="$1"; shift ;;
+    esac
+done
+case "${URL:-}" in
+    *plugin-b*) printf '404\n' ;;
+    *)          printf '200\n' ;;
+esac
+EOF
+chmod +x "$TMP/curl"
+got=$(run_script "$TMP/mixed.json")
+assert_match "mixed-reports-404" "$got" "does not exist on Gitea \(404\)"
+assert_match "mixed-reports-count" "$got" "1 of 2 manifest entries are broken"
+assert_match "mixed-exit-one" "$got" "EXIT_CODE=1"
+assert_not_match "mixed-does-not-report-500" "$got" "last HTTP 500"
+
+# ─────────────────────────────────────────────────────────────────────────────
+# Summary
+# ─────────────────────────────────────────────────────────────────────────────
+
+echo
+echo "─────────────────────────────────────────────"
+echo "Tests:  $PASS passed, $FAIL failed"
+if [ "$FAIL" -gt 0 ]; then
+    exit 1
+fi
+echo "All tests passed."