diff --git a/Makefile b/Makefile
index 43d4f927d..fa772ea0f 100644
--- a/Makefile
+++ b/Makefile
@@ -25,7 +25,7 @@ help:
 	@echo "  go-vet               - Run go vet"
 	@echo "  go-tidy              - Run go mod tidy"
 	@echo "  lint-md-links        - Check markdown files for broken in-repo links and anchors"
-	@echo "  script-test          - Run shell script tests (post-triage, post-code, post-review, pre-fetch-prior-review, reconcile-repos, validate-output-schema)"
+	@echo "  script-test          - Run shell script tests (post-triage, post-code, post-fix, post-review, pre-fetch-prior-review, reconcile-repos, validate-output-schema)"
 	@echo "  test                 - Run all checks: lint-all, go-test, script-test"
 	@echo "  e2e-test             - Run admin e2e tests (requires E2E_GITHUB_SESSION_FILE or E2E_GITHUB_USERNAME + E2E_GITHUB_PASSWORD)"
 	@echo "  e2e-export-session   - Login to GitHub and export a Playwright session file"
@@ -110,6 +110,7 @@ script-test:
 	bash internal/scaffold/fullsend-repo/scripts/post-triage-test.sh
 	bash internal/scaffold/fullsend-repo/scripts/post-prioritize-test.sh
 	bash internal/scaffold/fullsend-repo/scripts/post-code-test.sh
+	bash internal/scaffold/fullsend-repo/scripts/post-fix-test.sh
 	bash internal/scaffold/fullsend-repo/scripts/post-review-test.sh
 	bash internal/scaffold/fullsend-repo/scripts/reconcile-repos-test.sh
 	bash internal/scaffold/fullsend-repo/scripts/validate-output-schema-test.sh
diff --git a/internal/scaffold/fullsend-repo/scripts/post-fix-test.sh b/internal/scaffold/fullsend-repo/scripts/post-fix-test.sh
new file mode 100644
index 000000000..643b8099d
--- /dev/null
+++ b/internal/scaffold/fullsend-repo/scripts/post-fix-test.sh
@@ -0,0 +1,95 @@
+#!/usr/bin/env bash
+# post-fix-test.sh — Test the companion script fallback resolution logic
+# from post-fix.sh.
+#
+# Verifies that process-fix-result.py is found via the BASH_SOURCE path
+# first, falling back to ${FULLSEND_DIR}/scripts/ when not co-located
+# (e.g., when post-fix.sh runs from the content-addressed cache).
+#
+# Run from the repo root:
+#   bash internal/scaffold/fullsend-repo/scripts/post-fix-test.sh
+
+set -euo pipefail
+
+FAILURES=0
+
+# ---------------------------------------------------------------------------
+# Test helper — reimplements the companion resolution logic from post-fix.sh
+# so we can test it without running the full post-script.
+# ---------------------------------------------------------------------------
+resolve_companion() {
+  local script_dir="$1"
+  local fullsend_dir="$2"
+
+  local process_script="${script_dir}/process-fix-result.py"
+  if [ ! -f "${process_script}" ]; then
+    script_dir="${fullsend_dir:-.}/scripts"
+    process_script="${script_dir}/process-fix-result.py"
+  fi
+
+  if [ -f "${process_script}" ]; then
+    echo "resolved:${process_script}"
+  else
+    echo "not-found"
+  fi
+}
+
+run_test() {
+  local test_name="$1"
+  local expected_prefix="$2"
+  local actual="$3"
+
+  if [[ "${actual}" != ${expected_prefix}* ]]; then
+    echo "FAIL: ${test_name}"
+    echo "  expected prefix: '${expected_prefix}'"
+    echo "  actual:          '${actual}'"
+    FAILURES=$((FAILURES + 1))
+    return
+  fi
+
+  echo "PASS: ${test_name}"
+}
+
+# ---------------------------------------------------------------------------
+# Setup: create temp directories simulating cache and workspace layouts.
+# ---------------------------------------------------------------------------
+TMPROOT="$(mktemp -d)"
+trap 'rm -rf "${TMPROOT}"' EXIT
+
+CACHE_DIR="${TMPROOT}/cache/sha256/abc123/content"
+WORKSPACE_DIR="${TMPROOT}/workspace"
+
+mkdir -p "${CACHE_DIR}"
+mkdir -p "${WORKSPACE_DIR}/scripts"
+
+# The companion file exists only in the workspace scripts directory.
+touch "${WORKSPACE_DIR}/scripts/process-fix-result.py"
+
+# --- Test cases ---
+
+# 1. Cache-resolved path (no companion) with FULLSEND_DIR fallback
+result="$(resolve_companion "${CACHE_DIR}" "${WORKSPACE_DIR}")"
+run_test "cache-path-falls-back-to-workspace" "resolved:${WORKSPACE_DIR}/scripts/process-fix-result.py" "${result}"
+
+# 2. Direct path when companion is co-located (workspace-resolved)
+result="$(resolve_companion "${WORKSPACE_DIR}/scripts" "${WORKSPACE_DIR}")"
+run_test "workspace-path-resolves-directly" "resolved:${WORKSPACE_DIR}/scripts/process-fix-result.py" "${result}"
+
+# 3. Neither path has companion — reports not-found
+EMPTY_DIR="${TMPROOT}/empty"
+mkdir -p "${EMPTY_DIR}/scripts"
+result="$(resolve_companion "${CACHE_DIR}" "${EMPTY_DIR}")"
+run_test "neither-path-reports-not-found" "not-found" "${result}"
+
+# 4. FULLSEND_DIR unset (defaults to ".") — uses ./scripts/ as fallback
+result="$(resolve_companion "${CACHE_DIR}" "")"
+run_test "empty-fullsend-dir-defaults-to-dot" "not-found" "${result}"
+
+# --- Summary ---
+
+echo ""
+if [ ${FAILURES} -gt 0 ]; then
+  echo "${FAILURES} test(s) failed"
+  exit 1
+fi
+echo "All tests passed"
diff --git a/internal/scaffold/fullsend-repo/scripts/post-fix.sh b/internal/scaffold/fullsend-repo/scripts/post-fix.sh
index e055fd30c..049ff3e8b 100644
--- a/internal/scaffold/fullsend-repo/scripts/post-fix.sh
+++ b/internal/scaffold/fullsend-repo/scripts/post-fix.sh
@@ -301,8 +301,14 @@ fi
 export GH_TOKEN="${PUSH_TOKEN}"
 
 # Locate process-fix-result.py relative to this script.
+# When running from the content-addressed cache, companion files are not
+# co-located — fall back to the workspace scripts directory (FULLSEND_DIR).
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 PROCESS_SCRIPT="${SCRIPT_DIR}/process-fix-result.py"
+if [ ! -f "${PROCESS_SCRIPT}" ]; then
+  SCRIPT_DIR="${FULLSEND_DIR:-.}/scripts"
+  PROCESS_SCRIPT="${SCRIPT_DIR}/process-fix-result.py"
+fi
 
 # Find fix-result.json in the output directory.
 # RUN_DIR is the original cwd (runDir = <outputBase>/<sandboxName>), saved