diff --git a/tests/common/empty.env b/tests/common/empty.env
new file mode 100644
index 00000000..99dbd0b0
--- /dev/null
+++ b/tests/common/empty.env
@@ -0,0 +1,24 @@
+# Intentionally empty config file for test-server startup.
+#
+# Used as `--config tests/common/empty.env` by the Playwright
+# webServer scripts (`tests/e2e/start-server*.sh`). Two properties
+# it gives us that a bare `cargo run` doesn't:
+#
+#   1. Loading an empty file overrides nothing, so every var
+#      Playwright places in the child process env (SERVER_PORT,
+#      STORAGE_PATH, RUST_LOG, OPAQUE_MODE, DPOP_MODE, whatever
+#      per-suite overrides land here) reaches the server intact.
+#
+#   2. Passing `--config <anything>` in main.rs takes the
+#      `Some(path)` branch and skips the fallback
+#      `dotenvy::dotenv()` probe of `$CWD/.env`. Without this a
+#      developer's local `.env` (typical:
+#      `OXICLOUD_METRICS_LISTEN=127.0.0.1:9090`) leaks into the
+#      test server via CWD auto-load and clashes with whatever
+#      the dev is already running.
+#
+# Hurl API tests use `tests/common/server.env` for --config
+# instead — they source it in shell first, so file-wins doesn't
+# matter there. Only Playwright needs the empty-file trick
+# because it applies per-suite env overrides that would otherwise
+# be clobbered by server.env's shared values.
diff --git a/tests/e2e/playwright.coverage.config.ts b/tests/e2e/playwright.coverage.config.ts
index 269b4d00..51ea26ab 100644
--- a/tests/e2e/playwright.coverage.config.ts
+++ b/tests/e2e/playwright.coverage.config.ts
@@ -94,6 +94,13 @@ export default defineConfig({
       // so they can sign proofs in-browser. Once landed, this
       // override goes and Playwright runs production-shape.
       OXICLOUD_DPOP_MODE: 'opportunistic',
+      // Explicitly clear OXICLOUD_METRICS_LISTEN so a developer's
+      // `.env` value (typical: `127.0.0.1:9090`) doesn't leak in via
+      // the parent-process env Playwright merges here — the test
+      // server would collide with the developer's own running
+      // instance on that port and main.rs would hard-fail. Empty
+      // string is the config-parser's "disabled" sentinel.
+      OXICLOUD_METRICS_LISTEN: '',
     },
   },
 });
diff --git a/tests/e2e/start-server-spa.sh b/tests/e2e/start-server-spa.sh
index 15a6b3a7..ba48af4b 100644
--- a/tests/e2e/start-server-spa.sh
+++ b/tests/e2e/start-server-spa.sh
@@ -36,5 +36,15 @@ mark "spawning test database…"
 bash "$REPO_ROOT/tests/common/spawn-db.sh"
 mark "database ready; starting server…"
 
-# Replace the shell with the server process so Playwright's PID tracking works.
-exec "$@"
+# Point `--config` at an INTENTIONALLY EMPTY file: blocks the
+# CWD `.env` fallback in main.rs (so developer envs don't leak
+# in) while overriding nothing (so every Playwright-set env var,
+# including per-suite DPOP/OPAQUE/plugin overrides, reaches the
+# server intact). See tests/common/empty.env and
+# tests/e2e/start-server.sh for the full rationale.
+CONFIG_PATH="$REPO_ROOT/tests/common/empty.env"
+if [[ "${1:-}" == "cargo" ]]; then
+  exec "$@" -- --config "$CONFIG_PATH"
+else
+  exec "$@" --config "$CONFIG_PATH"
+fi
diff --git a/tests/e2e/start-server.sh b/tests/e2e/start-server.sh
index 638db09d..19904ed4 100755
--- a/tests/e2e/start-server.sh
+++ b/tests/e2e/start-server.sh
@@ -36,5 +36,30 @@ mark "spawning test database…"
 bash "$REPO_ROOT/tests/common/spawn-db.sh"
 mark "database ready; starting server…"
 
-# Replace the shell with the server process so Playwright's PID tracking works.
-exec "$@"
+# Point `--config` at an INTENTIONALLY EMPTY file. Two reasons:
+#
+#   1. Blocks the fallback `dotenvy::dotenv()` probe of `$CWD/.env`
+#      in main.rs — otherwise a developer's local `.env`
+#      (typical: `OXICLOUD_METRICS_LISTEN=127.0.0.1:9090`) leaks
+#      into the test server via CWD auto-load and clashes with
+#      anything the dev is already running.
+#
+#   2. An empty file has nothing to override — so every var
+#      Playwright loaded into `webServer.env` from server.env AND
+#      every per-suite override on top (SERVER_PORT, STORAGE_PATH,
+#      RUST_LOG, OPAQUE_MODE, DPOP_MODE, …) reaches the server
+#      intact. We can't use `--config server.env` here because
+#      `dotenvy::from_filename_override` would clobber Playwright's
+#      per-suite overrides for the keys it shares with the file.
+#
+# See tests/common/empty.env for the header explaining this.
+CONFIG_PATH="$REPO_ROOT/tests/common/empty.env"
+
+# `cargo run` needs `--` to separate cargo's own flags from the
+# binary's — a direct-binary invocation takes them raw. First arg
+# tells us which we're in.
+if [[ "${1:-}" == "cargo" ]]; then
+  exec "$@" -- --config "$CONFIG_PATH"
+else
+  exec "$@" --config "$CONFIG_PATH"
+fi