Driving wpd from an agent

# Driving wpd from an agent

For an agent consuming `wpd`. wpd finds and investigates; it does not grade, rank, or recommend. It
hands you typed, measurement-tagged numbers and a clean exit code; the judgment stays with you.

## The loop

1. **Record.** `wpd record <module> [flags]` writes a recording plus siblings. One `record` is one
   capture pass.
2. **Query.** Read the recording through the `query` verbs. **Never read the recording file directly**
   -- it can be many MB. Drill instead:

```
query spans <file>              # overview: one row per span, one shape across chrome/firefox/node
  -> query span <file> <kind:label>   # one span's full anatomy
       -> query get <file> <id>       # one raw event (stack + args); needs --deep or firefox
```

- Every verb takes `latest` in place of `<file>` (a cwd-keyed pointer, never resolved by mtime).
- Span identity is **kind + label**. A bare label that matches more than one kind is a collision;
  qualify it (`run`, `step:first increment`, `measure:hydrate`).
- `query spans --label X` with no match is a **filter**: it reports the empty result and exits 0.
  `query span X` with no match is a **lookup**: it exits 1. Pick the verb for the branch you want.
- Other verbs: `query cpu` (hot functions + rollup), `query frame <id>` (one function's callers and
  callees), `query blame --forced` (forced-layout read sites), `query events` (the raw log).