Ensure 'main' alias is always stored as 'agent:main:main' to prevent
duplicate entries. Also update loadSessionEntry to check both forms
when looking up entries.
Fixes duplicate main sessions in session store.
- Add `label` field to session entries and expose it in `sessions.list`
- Display label column in the web UI sessions table
- Support `label` parameter in `sessions_send` for lookup by label instead of sessionKey
- `sessions.patch`: Accept and store `label` field
- `sessions.list`: Return `label` in session entries
- `sessions_spawn`: Pass label through to registry and announce flow
- `sessions_send`: Accept optional `label` param, lookup session by label if sessionKey not provided
- `agent` method: Accept `label` and `spawnedBy` params (stored in session entry)
- Add `label` column to sessions table in web UI
- Changed session store writes to merge with existing entry (`{ ...existing, ...new }`)
to preserve fields like `label` that might be set separately
We attempted to implement label persistence "properly" by passing the label
through the `agent` call and storing it during session initialization. However,
the auto-reply flow has multiple write points that overwrite the session entry,
and making all of them merge-aware proved unreliable.
The working solution patches the label in the `finally` block of
`runSubagentAnnounceFlow`, after all other session writes complete.
This is a workaround but robust - the patch happens at the very end,
just before potential cleanup.
A future refactor could make session writes consistently merge-based,
which would allow the cleaner approach of setting label at spawn time.
```typescript
// Spawn with label
sessions_spawn({ task: "...", label: "my-worker" })
// Later, find by label
sessions_send({ label: "my-worker", message: "continue..." })
// Or use sessions_list to see labels
sessions_list() // includes label field in response
```
