fix(server): preserve resumed subagent identity

A resumed native child can be announced under a fresh tool call while retaining its session-scoped task identity. Treat later tool-call identifiers as aliases so lifecycle, usage, and timeline events continue through the original descriptor instead of splitting into contradictory rows.

docs/agent-lifecycle.md

@@ -160,6 +160,7 @@ Claude Code announces subagent lifecycle on the SDK stream (`task_started` / `ta
 - **Not every announced task belongs in the track.** Task subagents announce as `local_agent` and workflows as `local_workflow`; a backgrounded shell announces as `local_bash` with the same `tool_use_id` shape, and ambient housekeeping sets `skip_transcript`. The Claude provider normalizes a workflow to a generic provider-subagent descriptor titled `Workflow`, using Claude's summary as its description and timeline opener. Shared storage, protocol, and UI do not distinguish it from another provider subagent.
 - **A task that was never declared gets no descriptor, by any route.** Filtered tasks still emit `task_notification`s carrying a `tool_use_id`, and still emit frames carrying `parent_tool_use_id`. Attributing either produces a descriptor with no identity and a defaulted `running` status — a nameless row that never finishes. Status, presentation updates, and sidechain frames all route through the declaration table.
 - **Task ids are session-scoped, not turn-scoped.** Cancelling a turn must not clear the routing table: a backgrounded child settles after the interrupt and needs its descriptor to still exist. Cancellation instead terminalizes the declared children that were running in the foreground, and a later `task_notification` is free to correct that guess. Backgrounded children are identified by `task_updated.patch.is_backgrounded`.
+- **A resumed task can be announced again with a new `tool_use_id`.** The first Task tool id remains the canonical descriptor and later ids are routing aliases for the same session-scoped task. The resumed prompt is added to that child timeline.
 - **Effort is only reachable through hooks.** It appears nowhere on the message stream at any depth, and the level Paseo requests is not necessarily the level that runs — a model that does not support it is silently downgraded. A hook firing inside a subagent reports the active post-downgrade level next to its `agent_id`, which is the same id `task_started` calls `task_id`.
 - **Backgrounded subagents emit no frames carrying `parent_tool_use_id` at all.** Everything keyed off that field sees nothing for one; they are visible only because the task protocol announces them.
 - **On replay, `<session>/subagents/` holds every descendant, not just this session's children.** `agent-<id>.meta.json` carries `spawnDepth`: `1` is a direct child, `2+` was spawned by another subagent and its `toolUseId` names a Task call made inside its parent's session, which nothing in this transcript can resolve. Replaying those adds rows the live stream never showed, each with no Task card and no recoverable outcome, so they render as running forever. One recorded session showed 10 subagents live and would have replayed 22.