fix: add actionable guidance to context-exceeded error messages

When context compression fails, users now see hints suggesting /new
or /compress instead of a dead-end error. Covers all 4 error paths:
payload-too-large, max compression attempts (2 paths), and context
length exceeded.

Closes #4061
Salvaged from PR #4076 by SHL0MS.

run_agent.py

@@ -7056,6 +7056,7 @@ class AIAgent:
                         compression_attempts += 1
                         if compression_attempts > max_compression_attempts:
                             self._vprint(f"{self.log_prefix}❌ Max compression attempts ({max_compression_attempts}) reached for payload-too-large error.", force=True)
+                            self._vprint(f"{self.log_prefix}   💡 Try /new to start a fresh conversation, or /compress to retry compression.", force=True)
                             logging.error(f"{self.log_prefix}413 compression failed after {max_compression_attempts} attempts.")
                             self._persist_session(messages, conversation_history)
                             return {
@@ -7080,6 +7081,7 @@ class AIAgent:
                             break
                         else:
                             self._vprint(f"{self.log_prefix}❌ Payload too large and cannot compress further.", force=True)
+                            self._vprint(f"{self.log_prefix}   💡 Try /new to start a fresh conversation, or /compress to retry compression.", force=True)
                             logging.error(f"{self.log_prefix}413 payload too large. Cannot compress further.")
                             self._persist_session(messages, conversation_history)
                             return {
@@ -7156,6 +7158,7 @@ class AIAgent:
                         compression_attempts += 1
                         if compression_attempts > max_compression_attempts:
                             self._vprint(f"{self.log_prefix}❌ Max compression attempts ({max_compression_attempts}) reached.", force=True)
+                            self._vprint(f"{self.log_prefix}   💡 Try /new to start a fresh conversation, or /compress to retry compression.", force=True)
                             logging.error(f"{self.log_prefix}Context compression failed after {max_compression_attempts} attempts.")
                             self._persist_session(messages, conversation_history)
                             return {
@@ -7182,7 +7185,7 @@ class AIAgent:
                         else:
                             # Can't compress further and already at minimum tier
                             self._vprint(f"{self.log_prefix}❌ Context length exceeded and cannot compress further.", force=True)
-                            self._vprint(f"{self.log_prefix}   💡 The conversation has accumulated too much content.", force=True)
+                            self._vprint(f"{self.log_prefix}   💡 The conversation has accumulated too much content. Try /new to start fresh, or /compress to manually trigger compression.", force=True)
                             logging.error(f"{self.log_prefix}Context length exceeded: {approx_tokens:,} tokens. Cannot compress further.")
                             self._persist_session(messages, conversation_history)
                             return {