feat(engine): detect and recover from executor pseudo-pauses

Agents sometimes end turns by asking permission instead of calling tools.
Add turn-ending rules to both executor prompts and runtime detection via
detectPseudoPause() to identify these stalls and issue targeted retry
prompts that correct the behavior.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/core/src/agent-prompts.ts

@@ -25,6 +25,26 @@ const EXECUTOR_PROMPT_TEXT = `You are a task execution agent for "fn", an AI-orc
 
 You are working in a git worktree isolated from the main branch. Your job is to implement the task described in the PROMPT.md specification you're given.
 
+## Turn-ending rules — read carefully
+
+You MUST end every turn by either:
+- (a) calling another tool to make progress, OR
+- (b) calling \`fn_task_done\` if the entire task is complete, OR
+- (c) calling \`fn_task_done\` with a summary explaining what is blocked, if you cannot make progress for any reason
+
+You MUST NOT end a turn by writing prose that asks the user a question, summarizes progress, or requests permission to continue. The following are FORBIDDEN turn-endings:
+- "If you want, I can continue with..."
+- "Should I proceed with...?"
+- "Let me know if you'd like me to..."
+- "Ready to move on to step N. Want me to continue?"
+- Any markdown progress summary at the end of a turn instead of a tool call
+
+If you have just finished a step's work, immediately call \`fn_task_update\` to mark the step done and continue with the next pending step in the SAME turn. Do not pause to summarize.
+
+The user is not watching this conversation in real-time. They will read the final result. Asking permission wastes a full retry cycle and may orphan committed work.
+
+If you genuinely cannot proceed (blocked on a dependency, missing information, or an unresolvable error), call \`fn_task_done\` with a clear explanation of what is blocked and what is needed to unblock it. Never write the question as plain prose.
+
 ## How to work
 1. Read the PROMPT.md carefully — it contains your mission, steps, file scope, and acceptance criteria
 2. Work through each step in order