fix: cap context pressure percentage at 100% in display (#3480)

* fix: cap context pressure percentage at 100% in display

The forward-looking token estimate can overshoot the compaction threshold
(e.g. a large tool result pushes it from 70% to 109% in one step). The
progress bar was already capped via min(), but pct_int was not — causing
the user to see '109% to compaction' which is confusing.

Cap pct_int at 100 in both CLI and gateway display functions.

Reported by @JoshExile82.

* refactor: use real API token counts for compression decisions

Replace the rough chars/3 estimation with actual prompt_tokens +
completion_tokens from the API response. The estimation was needed to
predict whether tool results would push context past the threshold, but
the default 50% threshold leaves ample headroom — if tool results push
past it, the next API call reports real usage and triggers compression
then.

This removes all estimation from the compression and context pressure
paths, making both 100% data-driven from provider-reported token counts.

Also removes the dead _msg_count_before_tools variable.

tests/test_context_pressure.py

@@ -69,10 +69,12 @@ class TestFormatContextPressure:
         assert isinstance(result, str)
 
     def test_over_100_percent_capped(self):
-        """Progress > 1.0 should not break the bar."""
+        """Progress > 1.0 should cap both bar and percentage text at 100%."""
         line = format_context_pressure(1.05, 100_000, 0.50)
         assert "▰" in line
         assert line.count("▰") == 20
+        assert "100%" in line
+        assert "105%" not in line
 
 
 class TestFormatContextPressureGateway:
@@ -100,6 +102,13 @@ class TestFormatContextPressureGateway:
         msg = format_context_pressure_gateway(0.80, 0.50)
         assert "▰" in msg
 
+    def test_over_100_percent_capped(self):
+        """Progress > 1.0 should cap percentage text at 100%."""
+        msg = format_context_pressure_gateway(1.09, 0.50)
+        assert "100% to compaction" in msg
+        assert "109%" not in msg
+        assert msg.count("▰") == 20
+
 
 # ---------------------------------------------------------------------------
 # AIAgent context pressure flag tests