test: adapt summary-continuity + rotation-flush fixtures to the lean default

Continuity tests pin tail_mode=legacy (they assert the raw LLM text
terminates the stored summary; lean's verbatim-user appendix follows it by
design and the contract under test is mode-independent). The #57491
rotation fixture grows 200→2000 chars/message: at ~2.5K total tokens the
old fixture fit entirely inside lean's 10K tail floor, so the no-growth
guard correctly refused the rotation the test exercises.

tests/agent/test_context_compressor_summary_continuity.py

@@ -21,6 +21,11 @@ def _compressor(protect_first_n: int = 1) -> ContextCompressor:
             protect_first_n=protect_first_n,
             protect_last_n=1,
             quiet_mode=True,
+            # Pinned: these tests assert the stored summary ENDS with the raw
+            # LLM text. Lean mode (the default since the tail-default flip)
+            # appends the verbatim-user-quote appendix after it by design;
+            # the continuity contract under test is mode-independent.
+            tail_mode="legacy",
         )
 
 

tests/run_agent/test_compression_persistence.py

@@ -299,11 +299,14 @@ class TestFlushAfterCompression:
             # The transcript must also be large enough that the provider-less
             # static fallback net-shrinks it (middle drops must outweigh the
             # fixed compaction marker overhead), or the no-growth commit guard
-            # correctly refuses the rotation this test exercises.
+            # correctly refuses the rotation this test exercises. Sized for
+            # the lean tail default: the 10K-token tail floor must leave a
+            # substantial compressible middle (~2K chars/message × 40 ≈ 20K
+            # estimated tokens total).
             messages = [
                 {
                     "role": "user" if i % 2 == 0 else "assistant",
-                    "content": f"message {i} " + "x" * 200,
+                    "content": f"message {i} " + "x" * 2000,
                     "_db_persisted": True,
                 }
                 for i in range(40)