fix: context pressure warning fires at 85% of context_length, not threshold

The _emit_context_pressure warning was firing at 85% of threshold_tokens
(the configurable compaction threshold), not 85% of context_length.
This caused it to fire at 42.5% of actual context when threshold_percent=0.50,
confusing users who expected alignment with the poka-yoke WARNING signal.

Fix: compare against context_length (0.85 * context_length) instead of
threshold_tokens. The compaction_progress passed to _emit_context_pressure
still uses threshold_tokens for the display bar, but the trigger condition
now matches the poka-yoke signal.

Closes #538

run_agent.py

@@ -6005,9 +6005,9 @@ class AIAgent:
         # can't reduce enough (e.g. threshold is very low, or system prompt
         # alone exceeds the warning level), keep the flag set to prevent
         # spamming the user with repeated warnings every loop iteration.
-        if self.context_compressor.threshold_tokens > 0:
-            _post_progress = _compressed_est / self.context_compressor.threshold_tokens
-            if _post_progress < 0.85:
+        if self.context_compressor.context_length > 0:
+            _context_fill = _compressed_est / self.context_compressor.context_length
+            if _context_fill < 0.85:
                 self._context_pressure_warned = False
 
         # Clear the file-read dedup cache.  After compression the original
@@ -8991,14 +8991,15 @@ class AIAgent:
 
                     # ── Context pressure warnings (user-facing only) ──────────
                     # Notify the user (NOT the LLM) as context approaches the
-                    # compaction threshold.  Thresholds are relative to where
-                    # compaction fires, not the raw context window.
+                    # compaction threshold.  Fires at 85% of context_length so
+                    # it aligns with the poka-yoke WARNING signal (#538).
                     # Does not inject into messages — just prints to CLI output
                     # and fires status_callback for gateway platforms.
-                    if _compressor.threshold_tokens > 0:
-                        _compaction_progress = _real_tokens / _compressor.threshold_tokens
-                        if _compaction_progress >= 0.85 and not self._context_pressure_warned:
+                    if _compressor.context_length > 0:
+                        _context_fill = _real_tokens / _compressor.context_length
+                        if _context_fill >= 0.85 and not self._context_pressure_warned:
                             self._context_pressure_warned = True
+                            _compaction_progress = _real_tokens / _compressor.threshold_tokens if _compressor.threshold_tokens > 0 else 1.0
                             self._emit_context_pressure(_compaction_progress, _compressor)
 
                     if self.compression_enabled and _compressor.should_compress(_real_tokens):