docs(subagent): update package READMEs for the activation lifecycle

Rewrites the service API table, authority-versus-provenance contract, residency
routing, and deferred-work list; scopes the in-process driver README to one-shot
runs; and restates both model-facing tools' outputs, which no longer carry a
task id.

packages/subagent/tool-subagent/README.md

@@ -10,7 +10,7 @@ Each plugin instance binds one `provider` to one `toolName`; the model receives
 
 A foreground call passes the execution signal through startup and execution, awaits `run.result`, and always awaits `run.dispose()` before returning. Only `completed` returns the canonical `{ kind: 'foreground', runId, output: JsonValue[] }`, rendered as the same final text; abort, refusal, token limit, and other failures become errored tool results without partial output.
 
-With `run_in_background: true`, `backgroundMode` selects the route. `one-shot` registers a plain parent-owned Task and returns canonical `{ kind: 'background', taskId }`, rendered as `started background subagent task <id>`, even when the provider supports resume. `continuable` requires `provider.resume`, calls `ctx.subagents.startContinuable()`, and returns `{ kind: 'background', taskId, subagentId }`, rendered as `started subagent <childId> as task <taskId>`. The optional global `send_message` tool is not required to start continuable work. Either route uses a Task-owned signal, settles only after startup rollback or run disposal, and maps completed final text, abort → `killed`, and other failures → `failed`. Generic task tools own later status, collection, cancellation, and notices. See the [background subagent Agent Note](../../../.agents/notes/implemented/feature/2026-07-08-background-subagent-tasks.md), the [continuable background subagents Agent Note](../../../.agents/notes/implemented/feature/2026-07-21-continuable-background-subagents.md), and the [merged-service Agent Note](../../../.agents/notes/implemented/simplification/2026-07-26-merge-subagent-control-service.md).
+With `run_in_background: true`, `backgroundMode` selects the route. `one-shot` registers a plain parent-owned Task and returns canonical `{ kind: 'background', taskId }`, rendered as `started background subagent task <id>`, even when the provider supports continuable children; generic task tools own its later status, collection, cancellation, and notices. `continuable` requires a provider with the `prepareContinuable` capability, calls `ctx.subagents.startContinuable()`, and returns `{ kind: 'continuable', subagentId }`, rendered as `started subagent <childId>`. The continuable route resolves at inbox acceptance: the child owns its own turns from there, so this call neither waits for nor collects a result, and the child does not report back — its transcript by that id is the source of its output, and the optional global `send_message` tool sends it more work. Starting continuable work does not require `send_message` to be loaded. See the [background subagent Agent Note](../../../.agents/notes/implemented/feature/2026-07-08-background-subagent-tasks.md), the [continuable subagents Agent Note](../../../.agents/notes/implemented/feature/2026-07-28-continuable-subagent-conversations.md), and the [merged-service Agent Note](../../../.agents/notes/implemented/simplification/2026-07-26-merge-subagent-control-service.md).
 
 `toolFilter` changes the child's global tool layer but is not a parent-derived authority ceiling. See the [agent-scope security non-goal](../../../.agents/notes/implemented/architecture/2026-07-08-agent-scope-contexts.md#security-and-authority-are-non-goals).
 
@@ -21,7 +21,7 @@ With `run_in_background: true`, `backgroundMode` selects the route. `one-shot` r
 | `provider` (required) | Provider name (`spawn`, `fork`, `acp`, ...). |
 | `toolName` | Model-facing name, default `subagent`; distinct for every loaded instance. |
 | `enableRunInBackground` | Exposes background mode, default `true`; disabling also rejects forced background calls. |
-| `backgroundMode` | Background lifecycle policy, default `one-shot`. `continuable` requires provider resume support and returns a durable child id; it does not require the follow-up tool. |
+| `backgroundMode` | Background lifecycle policy, default `one-shot`. `continuable` requires the provider's `prepareContinuable` capability and returns a durable child id; it does not require the follow-up tool. |
 | `agentOptions` | Provider-specific child `provider`, `model`, and positive `maxTokens`; the in-process provider treats explicit values as overrides of inherited parent options. |
 | `persona` | Per-child persona; requires provider `persona` capability. |
 | `toolFilter` | Per-child global-tool restriction; requires `toolFilter` capability. |
@@ -37,7 +37,7 @@ Foreground and background calls are exclusive. Children may share the parent's w
 
 #### What the model sees
 
-The generated default [`subagent` schema](../../../docs/tool-catalog.md#deepseek-aidsh-tool-subagent) under this instance's configured name while its provider exists. Provider context inheritance changes the tool and prompt descriptions; enabled background mode adds `run_in_background`.
+The generated default [`subagent` schema](../../../docs/tool-catalog.md#deepseek-aidsh-tool-subagent) under this instance's configured name while its provider exists. Provider context inheritance changes the tool and prompt descriptions; enabled background mode adds `run_in_background`, and continuable mode describes starting a background subagent that keeps its conversation and returns its subagent id, while one-shot mode describes a background task id collected with `task_output` and stopped with `task_kill`.
 
 #### Token effect
 
@@ -61,15 +61,15 @@ The prompt and result remain in parent history until compaction; child working c
 
 Append-only; newly visible content follows the reusable request prefix and does not invalidate existing KV-cache entries.
 
-### Background task result
+### Background result
 
 #### What the model sees
 
-Start returns exactly `started subagent <childId> as task <taskId>` in configured continuable mode, or `started background subagent task <id>` in configured one-shot mode. The generic task surface provides later status, final output, cancellation responses, and notices; an independently loaded `send_message` tool delivers follow-ups to a continuable child.
+Start returns exactly `started subagent <childId>` in configured continuable mode, or `started background subagent task <id>` in configured one-shot mode. In one-shot mode the generic task surface provides later status, final output, cancellation responses, and notices. In continuable mode the child does not report back; an independently loaded `send_message` tool delivers follow-ups, and the child's transcript by its id is the source of its output.
 
 #### Token effect
 
-The acknowledgement is retained; final output enters parent history only when collected or injected.
+The acknowledgement is retained; a one-shot final output enters parent history only when collected or injected, while a continuable child's output never returns through this tool.
 
 #### KV Cache effect
 
@@ -77,6 +77,6 @@ Append-only; newly visible content follows the reusable request prefix and does
 
 ## Known Limitations and Deferred Work
 
-- **Background runs expose final output only** — intermediate child steps stay in the child session.
+- **Background runs expose no result through this tool** — a one-shot task's final output is collected through the generic task surface, and a continuable child's output stays in its own session, read by its subagent id.
 - **Duplicate names across waiting instances are detected late** (`TODO(subagent-dup-toolname)`) — preventing provider-registration rollback requires a registry of intended names.
 - **Child policy is fixed per instance** — another model, persona, tool filter, or depth cap requires another distinctly named tool.