diff --git a/.github/workflows/CI.yaml b/.github/workflows/CI.yaml
index 8f5143407..0d7328c83 100644
--- a/.github/workflows/CI.yaml
+++ b/.github/workflows/CI.yaml
@@ -304,6 +304,23 @@ jobs:
       - name: Ensure clean modgraph
         run: git diff --minimal --exit-code
 
+  validate-module-refs:
+    runs-on: ubuntu-latest
+    name: validate-module-refs
+    env:
+      BASE_BRANCH: ${{ github.base_ref || github.event.repository.default_branch || 'main' }}
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+          persist-credentials: false
+
+      - name: Fetch base branch
+        run: git fetch --no-tags origin "${BASE_BRANCH}:refs/remotes/origin/${BASE_BRANCH}"
+
+      - name: Validate intra-repo module pins are reachable from the default branch
+        run: ./script/validate-intra-module-refs.sh "origin/${BASE_BRANCH}"
+
   checks:
     runs-on: ubuntu-latest
     needs:
@@ -314,6 +331,7 @@ jobs:
       - tidy-and-generate
       - integration-tests
       - modgraph
+      - validate-module-refs
     if: always()
     steps:
       - name: All tests ok
diff --git a/Makefile b/Makefile
index 09b98e243..c2212e6c3 100644
--- a/Makefile
+++ b/Makefile
@@ -36,6 +36,10 @@ generate: protoc mockery gomods ## Execute all go:generate commands (including p
 update-common-capabilities: ## Update chain_capabilities/common in aptos/evm/solana. Usage: make update-common-capabilities REF=<branch-or-commit>
 	./script/update-common-capabilities.sh $(REF)
 
+.PHONY: validate-module-refs
+validate-module-refs: ## Verify intra-repo module pins are reachable from the default branch. Usage: make validate-module-refs [BASE_REF=origin/main]
+	./script/validate-intra-module-refs.sh $(BASE_REF)
+
 .PHONY: help
 help: ## Display this help screen.
 	@grep -h -E '^[a-zA-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) | awk 'BEGIN {FS = ":.*?## "}; {printf "\033[36m%-30s\033[0m %s\n", $$1, $$2}'
diff --git a/script/validate-intra-module-refs.sh b/script/validate-intra-module-refs.sh
new file mode 100755
index 000000000..19f61a90d
--- /dev/null
+++ b/script/validate-intra-module-refs.sh
@@ -0,0 +1,79 @@
+#!/usr/bin/env bash
+#
+# Validate that every intra-repo module pin resolves to a commit reachable
+# from the default branch.
+#
+# This repo is a multi-module monorepo: modules require sibling modules
+# (e.g. chain_capabilities/evm -> libs, -> chain_capabilities/common) by
+# pseudo-version (vX.Y.Z-<timestamp>-<12-hex-sha>). There are no `replace`
+# directives wiring these locally, so the pinned SHA must be reachable from
+# the default branch, or external consumers (and fresh builds here) break
+# with "unknown revision".
+#
+# This guards against pinning to a non-default-branch commit (a PR/feature
+# commit), which is ephemeral: once the branch is gone, the SHA is GC'd and
+# every consumer fails. See `make update-common-capabilities`, which should
+# only ever be pointed at a commit already on the default branch.
+#
+# Usage: validate-intra-module-refs.sh [base-ref]
+#   base-ref defaults to origin/main.
+set -euo pipefail
+
+BASE_REF="${1:-origin/main}"
+MODULE_PREFIX="github.com/smartcontractkit/capabilities"
+REPO_ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+cd "$REPO_ROOT"
+
+if ! git rev-parse --verify --quiet "$BASE_REF" >/dev/null; then
+  echo "error: base ref '$BASE_REF' not found. Fetch it first (git fetch origin main)." >&2
+  exit 2
+fi
+
+fail=0
+seen_file="$(mktemp)"
+trap 'rm -f "$seen_file"' EXIT
+
+# All go.mod files except vendored ones.
+while IFS= read -r gomod; do
+  # Lines that pin an intra-repo module to a pseudo-version. Matches both
+  # require lines and `=> module version` replace targets.
+  while IFS= read -r line; do
+    # module is the token starting with the repo prefix; version is the next token.
+    module="$(printf '%s\n' "$line" | grep -oE "${MODULE_PREFIX}[a-zA-Z0-9._/-]*" | head -1)"
+    version="$(printf '%s\n' "$line" | grep -oE "v[0-9][^[:space:]]*" | head -1)"
+    [ -z "$module" ] && continue
+    [ -z "$version" ] && continue
+
+    # Only pseudo-versions carry a -<14-digit-timestamp>-<12-hex> suffix.
+    sha="$(printf '%s\n' "$version" | grep -oE '\-[0-9]{14}-[0-9a-f]{12}$' | grep -oE '[0-9a-f]{12}$' || true)"
+    [ -z "$sha" ] && continue                 # tagged release, not a pseudo-version
+    [ "$sha" = "000000000000" ] && continue   # zero pseudo-version (replaced module)
+
+    key="${module}@${sha}"
+    grep -qxF "$key" "$seen_file" && continue
+    printf '%s\n' "$key" >> "$seen_file"
+
+    # Reachable from the default branch? Treat "not an ancestor" and
+    # "object missing/GC'd" alike as failures.
+    if git merge-base --is-ancestor "$sha" "$BASE_REF" 2>/dev/null; then
+      echo "ok   ${key}  (reachable from ${BASE_REF}, ${gomod#./})"
+    else
+      echo "FAIL ${key}  (NOT reachable from ${BASE_REF}; pinned in ${gomod#./})"
+      fail=1
+    fi
+  done < <(grep -E "${MODULE_PREFIX}[a-zA-Z0-9._/-]* v[0-9]" "$gomod" || true)
+done < <(find . -name go.mod -not -path '*/vendor/*' -type f | sort)
+
+if [ "$fail" -ne 0 ]; then
+  cat >&2 <<EOF
+
+One or more intra-repo module pins reference a commit that is not on
+${BASE_REF}. This usually means a sibling module was pinned to a
+PR/feature-branch commit instead of a merged one. Merge the dependency to
+the default branch first, then re-pin to a commit that lives there
+(see: make update-common-capabilities REF=<commit-on-default-branch>).
+EOF
+  exit 1
+fi
+
+echo "All intra-repo module pins are reachable from ${BASE_REF}."