fix: honor config timeline diagnostics

docs/cli/gateway.md

@@ -112,7 +112,7 @@ Inline `--password` can be exposed in local process listings. Prefer `--password
 ### Startup profiling
 
 - Set `OPENCLAW_GATEWAY_STARTUP_TRACE=1` to log phase timings during Gateway startup, including per-phase `eventLoopMax` delay and plugin lookup-table timings for installed-index, manifest registry, startup planning, and owner-map work.
-- Set `OPENCLAW_DIAGNOSTICS=timeline` with `OPENCLAW_DIAGNOSTICS_TIMELINE_PATH=<path>` to write a best-effort JSONL startup diagnostics timeline for external QA harnesses. Add `OPENCLAW_DIAGNOSTICS_EVENT_LOOP=1` to include event-loop samples.
+- Set `OPENCLAW_DIAGNOSTICS=timeline` with `OPENCLAW_DIAGNOSTICS_TIMELINE_PATH=<path>` to write a best-effort JSONL startup diagnostics timeline for external QA harnesses. You can also enable the flag with `diagnostics.flags: ["timeline"]` in config; the path is still env-provided. Add `OPENCLAW_DIAGNOSTICS_EVENT_LOOP=1` to include event-loop samples.
 - Run `pnpm test:startup:gateway -- --runs 5 --warmup 1` to benchmark Gateway startup. The benchmark records first process output, `/healthz`, `/readyz`, startup trace timings, event-loop delay, and plugin lookup-table timing details.
 
 ## Query a running Gateway

docs/diagnostics/flags.md

@@ -61,6 +61,21 @@ OPENCLAW_DIAGNOSTICS_TIMELINE_PATH=/tmp/openclaw-timeline.jsonl \
 openclaw gateway run
 ```
 
+You can also enable it in config:
+
+```json
+{
+  "diagnostics": {
+    "flags": ["timeline"]
+  }
+}
+```
+
+The timeline file path still comes from
+`OPENCLAW_DIAGNOSTICS_TIMELINE_PATH`. When `timeline` is enabled only from
+config, the earliest config-loading spans are not emitted because OpenClaw has
+not read config yet; subsequent startup spans use the config flag.
+
 `OPENCLAW_DIAGNOSTICS=1`, `OPENCLAW_DIAGNOSTICS=all`, and
 `OPENCLAW_DIAGNOSTICS=*` also enable the timeline because they enable every
 diagnostics flag. Prefer `timeline` when you only want the JSONL timing