[Fix] Keep Fast tools available across task events

[daniel-lxs]

What changed

• Treat delegated-task platform events as inputs to the existing Fast conversation instead of as a reduced-capability mode.
• Keep Fast's ordinary orchestration actions available during those turns: launching a task, messaging or canceling an active task, calling an integration, and replying to the chat.
• Keep only genuinely contextual actions conditional: ignore_event for platform events, retry_task_start for eligible startup failures, and chat reactions for turns with an incoming message to react to.
• Make task launching and chat reply delivery required Fast dependencies so a supported entry point cannot silently omit them.
• Move the existing Slack Fast launcher into the shared Cloud Agents package and use it from both normal Slack turns and automatic task-event delivery.
• Preserve the single visible closeout and retry-aware delivery behavior for automatic events.

Why

Fast's action schema, prompt policy, runtime guard, and injected callbacks previously disagreed about whether an action was available. In particular, automatic delegated-task events rejected ordinary orchestration actions and did not receive the launcher used by normal Slack turns.

This change gives Fast one consistent operational model: the source of a turn changes its context and presentation, not its ordinary tools. Each action still applies its own argument, target, and permission validation.

Behavior

Action	Availability
launch_task, send_task_message, cancel_task, call_integration, send_chat_reply	Every supported Fast turn, subject to normal action validation
ignore_event	Platform-event turns only
retry_task_start	Eligible failed-start events only
send_chat_reaction_emoji	Turns with an incoming chat message to react to

Platform events remain trusted internal task updates rather than new human instructions. Fast may ignore routine events, use ordinary tools when the event and conversation justify them, and produces at most one visible closeout for an automatic event.

Validation

• Full Cloud Agents suite: 95 files, 767 tests passed
• Full SDK suite: 99 files, 995 tests passed
• Full API suite: 206 files, 1,780 tests passed
• pnpm lint
• pnpm check-types
• pnpm knip

[roomote-community]

No new code issues found. See task

• packages/cloud-agents/src/server/fast-agent/fast-agent-service.ts:779 Platform events permit launch_task, but their only production caller does not provide the required launcher, so every attempted launch fails as unavailable.

_{Reviewed d2bbdbd}