diff --git a/scripts/test.sh b/scripts/test.sh
index 0aafe6c20..43c140fee 100755
--- a/scripts/test.sh
+++ b/scripts/test.sh
@@ -346,6 +346,12 @@ CBM_TEST_BINARY="$WATCHDOG_BINARY" bash "$ROOT/tests/test_worker_error_response.
 echo "=== Step 5e: watcher_enabled kill-switch regression (#335) ==="
 CBM_TEST_BINARY="$WATCHDOG_BINARY" bash "$ROOT/tests/test_watcher_disabled.sh"
 
+# Step 5f: a supervised worker is scoped to the request the daemon admitted,
+# never to the CBM_ALLOWED_ROOT it inherited from the daemon starter's
+# environment. Reuses the prod binary built in Step 5.
+echo "=== Step 5f: worker request-scope regression ==="
+CBM_TEST_BINARY="$WATCHDOG_BINARY" bash "$ROOT/tests/test_worker_session_scope.sh"
+
 # Step 6: security-strings URL allow-list regression. The MSYS2 CLANG64 toolchain
 # bakes its package-tracker URL into the static Windows .exe; the binary string
 # audit must allow-list it (Windows-only — Linux smoke never saw it).
diff --git a/src/main.c b/src/main.c
index 8a575c44f..a836b7ac0 100644
--- a/src/main.c
+++ b/src/main.c
@@ -676,6 +676,36 @@ static bool cli_first_nonspace_is_brace(const char *s) {
 static char *main_local_cli_daemon_execute(const char *tool_name, const char *args_json,
                                            bool quiet_requested);
 
+/* A supervised worker runs in the DAEMON's environment, not the requesting
+ * client's. The daemon admitted this request under the client's session policy
+ * and re-executed us with the canonical repo_path in the args (both daemon
+ * spawn paths rewrite it), so the request itself is the worker's workspace
+ * scope: repository == session root == allowed root. Without this, a fresh
+ * server fell back to the process-wide CBM_ALLOWED_ROOT inherited from whoever
+ * started the daemon and refused every admitted session outside it. Returns
+ * NULL once scoped, otherwise the reason to fail closed: a worker never indexes
+ * under an ambient policy.
+ *
+ * A repository that cannot be canonicalized (it does not exist) can only have
+ * been admitted by a session with no declared boundary, because containment
+ * needs a real path. The worker mirrors that with an explicit unrestricted
+ * policy - still never the environment fallback - so the pipeline reports the
+ * missing repository as the tool error it always was, instead of the
+ * supervisor misreading a refused worker as a crash. */
+static const char *main_index_worker_scope_request(cbm_mcp_server_t *srv, const char *args_json) {
+    char *repo_path = cbm_mcp_get_string_arg(args_json, "repo_path");
+    if (!repo_path || !repo_path[0]) {
+        free(repo_path);
+        return "request names no repo_path";
+    }
+    char canonical[MAIN_PATH_CAP];
+    bool exists = cbm_canonical_path(repo_path, canonical, sizeof(canonical)) != 0;
+    const char *scope = exists ? canonical : repo_path;
+    bool scoped = cbm_mcp_server_set_session_context(srv, scope, exists ? scope : NULL);
+    free(repo_path);
+    return scoped ? NULL : "session context could not be installed";
+}
+
 static int run_cli(int argc, char **argv, cbm_project_lock_manager_t *project_locks,
                    main_local_maintenance_context_t *maintenance_context) {
     cbm_cli_output_flags_t output_flags;
@@ -817,11 +847,15 @@ static int run_cli(int argc, char **argv, cbm_project_lock_manager_t *project_lo
     };
     bool maintenance_binding_failed = false;
     bool maintenance_cancelled = false;
+    const char *worker_scope_refused = NULL;
     if (!index_worker) {
         result = main_local_cli_daemon_execute(tool_name, args_json, output_flags.quiet_requested);
     } else {
         srv = cbm_mcp_server_new(NULL);
         if (srv) {
+            worker_scope_refused = main_index_worker_scope_request(srv, args_json);
+        }
+        if (srv && !worker_scope_refused) {
             /* The in-process worker is a standalone instance: it may not
              * launch MCP-session background tasks. It receives project_locks
              * from its own process-level coordination setup and therefore
@@ -834,8 +868,8 @@ static int run_cli(int argc, char **argv, cbm_project_lock_manager_t *project_lo
                                                               main_local_cli_mutation_try_begin);
             }
         }
-        maintenance_binding_failed = srv && !maintenance_context;
-        if (srv && maintenance_context) {
+        maintenance_binding_failed = srv && !worker_scope_refused && !maintenance_context;
+        if (srv && !worker_scope_refused && maintenance_context) {
             main_local_maintenance_server_bind(maintenance_context, srv);
             result = cbm_mcp_handle_tool(srv, tool_name, args_json);
             /* Unbind under the same mutex used by cancellation before any
@@ -847,7 +881,10 @@ static int run_cli(int argc, char **argv, cbm_project_lock_manager_t *project_lo
         }
     }
     if (!result) {
-        if (maintenance_binding_failed) {
+        if (worker_scope_refused) {
+            (void)fprintf(stderr, "error: request workspace scope invalid: %s\n",
+                          worker_scope_refused);
+        } else if (maintenance_binding_failed) {
             (void)fprintf(stderr,
                           "error: local %s maintenance cancellation could not bind safely\n",
                           index_worker ? "worker" : "CLI");
diff --git a/tests/test_worker_session_scope.sh b/tests/test_worker_session_scope.sh
new file mode 100644
index 000000000..fed32e97e
--- /dev/null
+++ b/tests/test_worker_session_scope.sh
@@ -0,0 +1,107 @@
+#!/usr/bin/env bash
+# A supervised index worker (`cli --index-worker index_repository ...`) runs in
+# the DAEMON's environment, not the requesting client's. The daemon has already
+# admitted the request under the client's session policy and re-executes the
+# worker with the canonical repo_path in its args, so the worker must scope its
+# own workspace boundary to that request. Before the fix it built an unscoped
+# server, fell back to the process-wide CBM_ALLOWED_ROOT it inherited from the
+# daemon starter, and refused every admitted session outside that root with
+# "... is outside the allowed root". A missing repo_path must fail closed: a
+# worker never indexes under an ambient policy.
+set -euo pipefail
+
+ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+BINARY="${CBM_TEST_BINARY:-${ROOT}/build/c/codebase-memory-mcp}"
+if [[ ! -x "${BINARY}" && -x "${BINARY}.exe" ]]; then
+  BINARY="${BINARY}.exe"
+fi
+
+if [[ ! -x "${BINARY}" ]]; then
+  echo "missing binary: ${BINARY}" >&2
+  exit 2
+fi
+
+if command -v shasum >/dev/null 2>&1; then
+  BUILD_FINGERPRINT="$(shasum -a 256 "${BINARY}" | awk '{print $1}')"
+elif command -v sha256sum >/dev/null 2>&1; then
+  BUILD_FINGERPRINT="$(sha256sum "${BINARY}" | awk '{print $1}')"
+elif command -v openssl >/dev/null 2>&1; then
+  BUILD_FINGERPRINT="$(openssl dgst -sha256 "${BINARY}" | awk '{print $NF}')"
+else
+  echo "no SHA-256 command available for worker build binding" >&2
+  exit 2
+fi
+if [[ ! "${BUILD_FINGERPRINT}" =~ ^[0-9a-f]{64}$ ]]; then
+  echo "invalid worker build fingerprint: ${BUILD_FINGERPRINT}" >&2
+  exit 2
+fi
+
+# shellcheck source=../scripts/test-runtime.sh
+source "${ROOT}/scripts/test-runtime.sh"
+cbm_test_runtime_init
+tmpdir="${CBM_TEST_RUNTIME_ROOT}"
+cleanup() {
+  cbm_test_runtime_cleanup "${BINARY}"
+}
+trap cleanup EXIT
+
+# Product-facing path, the way the daemon hands it to the worker: canonical on
+# POSIX, mixed-style on a native Windows binary (test-runtime.sh's convention).
+product_path() {
+  case "$(uname -s)" in
+    MINGW*|MSYS*|CYGWIN*) cygpath -m "$1" ;;
+    *) (cd "$1" && pwd -P) ;;
+  esac
+}
+
+# Root A is what the daemon's starter allowed; the admitted session lives under
+# root B. The two share no prefix.
+mkdir -p "${tmpdir}/root-a" "${tmpdir}/root-b/tiny"
+printf 'int tiny_main(void) { return 0; }\n' >"${tmpdir}/root-b/tiny/tiny.c"
+root_a="$(product_path "${tmpdir}/root-a")"
+repo="$(product_path "${tmpdir}/root-b/tiny")"
+
+run_worker() {
+  local args="$1" response="$2" out="$3" err="$4"
+  CBM_ALLOWED_ROOT="${root_a}" \
+    "${BINARY}" cli --index-worker \
+    --index-worker-build "${BUILD_FINGERPRINT}" \
+    index_repository "${args}" \
+    --response-out "${response}" >"${out}" 2>"${err}"
+}
+
+response="${tmpdir}/scoped.response"
+if ! run_worker "{\"repo_path\":\"${repo}\",\"mode\":\"fast\"}" "${response}" \
+  "${tmpdir}/scoped.out" "${tmpdir}/scoped.err"; then
+  echo "worker exited nonzero for an admitted request" >&2
+  cat "${tmpdir}/scoped.err" >&2
+  exit 1
+fi
+if [[ ! -s "${response}" ]]; then
+  echo "worker delivered no response" >&2
+  exit 1
+fi
+if grep -q 'outside the allowed root' "${response}"; then
+  echo "worker re-decided the workspace boundary from the daemon environment" >&2
+  cat "${response}" >&2
+  exit 1
+fi
+if ! grep -q '"status":"indexed"' "${response}"; then
+  echo "worker did not index the admitted repository" >&2
+  cat "${response}" >&2
+  exit 1
+fi
+
+# Fail closed: no repo_path means no request scope, so no indexing at all.
+unscoped="${tmpdir}/unscoped.response"
+if run_worker '{"mode":"fast"}' "${unscoped}" "${tmpdir}/unscoped.out" "${tmpdir}/unscoped.err"; then
+  echo "worker ran without a request workspace scope" >&2
+  exit 1
+fi
+if [[ -s "${unscoped}" ]] || ! grep -q 'request workspace scope invalid' "${tmpdir}/unscoped.err"; then
+  echo "worker without repo_path did not fail closed on scope" >&2
+  cat "${tmpdir}/unscoped.err" >&2
+  exit 1
+fi
+
+echo "ok: index worker is scoped to the admitted request, not the daemon environment"