docs(tasks): condense background task prose

The background-task change repeated its lifecycle design across implemented RFCs, package READMEs, JSDoc, test commentary, and model-visible schemas. That repetition obscured the contracts that maintainers must preserve and added avoidable prompt tokens.

Rewrite the implemented RFCs around the current design, keep authorization, exact-owner cleanup, wait/abort ordering, producer quiescence, and teardown-failure guarantees at their owning surfaces, and remove peer surveys, review history, control-flow narration, and emphatic restatement.

Shorten the task and subagent schema wording, synchronize the bilingual tool cookbook, and regenerate the config, service, RFC, tool, and replay snapshot derivatives. Runtime behavior is unchanged; test edits update prose-only assertions and descriptions.

packages/subagent/tool-subagent/tests/tool-subagent.spec.ts

@@ -81,7 +81,7 @@ describe('dsh-tool-subagent', () => {
     expect(schema!.description).not.toContain('task_output')
   })
 
-  it('refuses a forced run_in_background at execution time when the instance disables it (review finding)', async () => {
+  it('refuses a forced run_in_background at execution time when the instance disables it', async () => {
     // Schema omission is advertising, not enforcement: the arg validator
     // allows undeclared keys, so the opt-out must also hold in execute().
     const ctx = await setup({ provider: 'mock', enableRunInBackground: false })
@@ -253,7 +253,7 @@ describe('dsh-tool-subagent', () => {
     // Backend reloads with a DIFFERENT conversation-history descriptor: the wording is re-derived
     // from the fresh provider, not served stale from the first mount.
     await ctx.plugin(mock, { name: 'mock', inheritsParentContext: true })
-    expect(ctx.tools.schemas().find(s => s.name === 'subagent')!.description).toContain('INHERITS this conversation')
+    expect(ctx.tools.schemas().find(s => s.name === 'subagent')!.description).toContain('inherits this conversation')
   })
 
   it('the tool PLUGIN fiber owns its lifecycle listeners: disposal unmounts, and a disposed fiber never zombie-mounts', async () => {
@@ -303,10 +303,10 @@ describe('dsh-tool-subagent', () => {
     expect(props['prompt']!.description).toContain('include everything it needs')
   })
 
-  it('derives fork-shaped wording from a seeded-conversation provider (the description stops lying)', async () => {
+  it('derives inherited-context wording from a seeded-conversation provider', async () => {
     const ctx = await setup({ provider: 'mock', toolName: 'subagent' }, { inheritsParentContext: true })
     const schema = ctx.tools.schemas().find(s => s.name === 'subagent')!
-    expect(schema.description).toContain('INHERITS this conversation')
+    expect(schema.description).toContain('inherits this conversation')
     expect(schema.description).not.toContain('does not see this conversation')
     const props = (schema.parameters as { properties: Record<string, { description: string }> }).properties
     expect(props['prompt']!.description).toContain('completed turns')
@@ -711,8 +711,7 @@ describe('dsh-tool-subagent background mode', () => {
   })
 
   it('forwards task_kill reasons through the run signal (and defaults one when absent)', async () => {
-    // A provider whose runs settle only on signal abort — the mock settles on a
-    // microtask, too fast to observe a LIVE kill through the real tools.
+    // Use a provider that remains live until its signal is aborted.
     const ctx = await backgroundSetup({ provider: 'mock', agentOptions: { model: 'child-model' } })
     const parent = ownerAgent(ctx, 'sess-parent')
     const cancels: (string | undefined)[] = []
@@ -736,9 +735,7 @@ describe('dsh-tool-subagent background mode', () => {
         }
       },
     })
-    // Direct apply (schema bypass): schemastery would default agentOptions to
-    // an (truthy) empty object — the raw config exercises the omitted branch
-    // on the background start request.
+    // Direct apply preserves omitted agentOptions instead of applying schema defaults.
     tool.apply(ctx, { provider: 'hanging', toolName: 'subagent_hang' })
 
     const startOne = await ctx.tools.execute({ callId: CallId('h1'), name: 'subagent_hang', arguments: { description: 'one', prompt: 'p', run_in_background: true }, agent: parent })
@@ -810,9 +807,7 @@ describe('dsh-tool-subagent background mode', () => {
 
 describe('background preflight failure (no orphaned child, by construction)', () => {
   it('never starts the child when tasks.start preflight throws', async () => {
-    // TaskService is loaded but NO control surface is attached: tasks.start
-    // preflights that fence BEFORE invoking the producer's run(), so the
-    // provider is never asked to spawn — there is no orphan to roll back.
+    // With no control surface, task preflight fails before the provider can spawn.
     const ctx = await setup({ provider: 'mock' })
     await ctx.plugin(AgentRegistry)
     await ctx.plugin(TaskService)