ACP: mark the continuation nudge as harness-originated, emit it to clients, and allow disabling it #1128

Feature Description

In cmd acp (v1.88.5), when a turn's final text ends with "I'll …" or "Let me …", the continuation provider (createContinuationProvider / endsWithDanglingIntent) appends a user-role message:

You ended your turn right after saying you were about to do something, without doing it. Do it now — make the tool calls or produce the output you described; do not restate the plan. If the task is actually complete, state the final result instead.

For ACP hosts I'd like four changes:

1. Mark the nudge as coming from the harness, for example with system-reminder style wording, instead of a plain user turn. Right now the model can't tell it apart from the real user.
2. Emit it to the ACP client. Send a session/update for continuation_recovery (kind, attempt, maxAttempts) that includes the injected text. Today it has no session/update mapping, so the host can't show or explain it.
3. Make it possible to turn off. Add a config setting, env var, or session/new _meta field that disables intent recovery or lowers its attempt count. createContinuationProvider({}) is hardcoded today.
4. Recognise deferred-completion phrasing. Add "as soon as it lands", "when it finishes" and "once it completes" to the exclusion regex, so a turn that is deliberately waiting isn't treated as unfinished.

Use Case

ACP hosts that run sub-agents depend on the model ending its turn while background work runs. T3 Code works this way: an async delegate_task tool result tells the model "Completion wakes this thread, so end your turn. Do not wait on it or poll it."

What happened in a real session (Command Code over ACP, DeepSeek V4.1 Flash):

1. The model delegated a review to another agent (Opus 5.5) and correctly ended its turn with: "I'll report its verdict as soon as it lands."
2. Two seconds later Command Code injected the "Do it now" nudge as a user message.
3. The model's reasoning: "the user overrode: … Do it now." It polled the delegate four times, stopped waiting, and did the delegated work itself. That included destructive file changes the delegate had been asked to review first.
4. The host's UI showed no injected message, so from the user's side the model just turned impatient for no reason.

With the nudge marked as harness-originated, visible to the client, and possible to turn off, hosts could either show it or turn it off for sessions that intentionally wait.

Additional Context

• The code is in dist/cli.mjs: createContinuationProvider, endsWithDanglingIntent, and the dangling-intent and exclusion regexes. The counter allows 2 intent nudges per streak and resets only after a turn with tool calls.
• My T3 Code fork works around this on the host side by changing the delegate tool's wording so models end with a status line ("It is running.") instead of a promise. That only helps when the model follows the wording, which is why an upstream fix matters: https://github.com/timm-u/t3code
• Related: a Windows bug where editor-supplied stdio MCP servers fail silently when the command path has spaces (filed separately). In this same session it was the reason the model fell back to shell-based tool calls in the first place.

How important is this to you?

Important for my workflow