docs(subagent): scope report acceptance to parent resolution, not delivery

The README claimed "acceptance is governed by registry presence" as a
universal statement, but `sendReport` translates a registered parent's
send rejection into the same PARENT_UNAVAILABLE code — registry presence
governs parent *resolution*, while acceptance additionally depends on the
parent's log still admitting appends. Soften both languages to the
precise contract and re-record the pair.

packages/subagent/tool-subagent-report/README.md

@@ -4,7 +4,7 @@ English | [中文](README.zh.md)
 
 The optional child-scoped `report` tool is a thin adapter over `ctx.subagents.reportFrom()`. It gives every continuable in-process child a return channel to the Agent that started it. The package registers a continuable-child setup contribution instead of a global tool, so `report` exists only inside those children. Roots, one-shot subagents, remote subagent providers, sibling scopes, and agentless tool execution never present or execute it. Installing this package grants only that child-scoped capability; the parent-to-child direction remains the independent [`@deepseek-ai/dsh-tool-subagent-control`](../tool-subagent-control/README.md), and continuable mode depends on neither package.
 
-A child may call `report` zero or many times in one turn. A successful call neither concludes the turn, settles the Activation, nor prevents later parent follow-ups, and finishing a turn never reports automatically. The tool accepts no recipient: `exec.agent` is the sender's exact live Agent and the authority credential, and the service derives the sole recipient from that child's durable `parentSession`. Success returns the stable `MessageId` of the parent-accepted message, not a read receipt, an inbox-occurrence id, a parent-log acknowledgement, a turn-completion receipt, or a persistence flush. A parent absent from the registry fails the call with `direct parent is not live; report was not delivered` — acceptance is governed by registry presence, so a parent already in host-owned disposal but still registered still accepts. The service performs no injection, parent cold resume, or offline mailbox write; the durable child transcript remains the recovery source, and a failed tool call does not prove non-delivery (a later `tools/post-execute` veto can fail a call whose report was already accepted).
+A child may call `report` zero or many times in one turn. A successful call neither concludes the turn, settles the Activation, nor prevents later parent follow-ups, and finishing a turn never reports automatically. The tool accepts no recipient: `exec.agent` is the sender's exact live Agent and the authority credential, and the service derives the sole recipient from that child's durable `parentSession`. Success returns the stable `MessageId` of the parent-accepted message, not a read receipt, an inbox-occurrence id, a parent-log acknowledgement, a turn-completion receipt, or a persistence flush. A parent absent from the registry fails the call with `direct parent is not live; report was not delivered` — registry presence governs parent resolution, and a registered parent already in host-owned disposal still accepts while its log admits appends. The service performs no injection, parent cold resume, or offline mailbox write; the durable child transcript remains the recovery source, and a failed tool call does not prove non-delivery (a later `tools/post-execute` veto can fail a call whose report was already accepted).
 
 `reportDelivery` selects parent scheduling for every accepted report. `quiet` (the default) uses `parent.inject()`, adding model-facing context without starting a parent model request: an idle parent's append completes before the call returns, while a report reaching an admitting or running parent stages for the next safe log position. `wakeup` uses `parent.followup()`, creating exactly one ordinary later parent turn and waking a parked parent driver; it never steers an open turn. This is deployment scheduling policy, so the model-facing schema cannot select or override it per call.