fix(compression): stop fallback summary triplicating the latest user ask

When LLM summarization fails, the deterministic fallback summary rendered
the latest user ask (active_task = "User asked: '<ask>'") verbatim under
THREE headings — Historical Task Snapshot, Historical In-Progress State,
and Historical Pending User Asks. Re-presenting an already-handled ask as
unresolved in-progress/pending work made the model re-answer it AND treat
the resurrected ask as the active turn, burying the genuinely-new
post-compaction user message (#49307: answer repetition + new-instruction
loss, P1).

Keep the latest ask once, under Task Snapshot, as historical context only.
The In-Progress and Pending-Asks sections now say 'Unknown / None
recoverable from deterministic fallback' (consistent with the Active
State / Key Decisions / Resolved Questions sections) and explicitly note
the ask is historical, not outstanding. The raw turn text still appears in
the verbatim 'Last Dropped Turns' transcript — that's the dropped-turn
record, not a re-labeled instruction.

Note: the separate role=assistant standalone-summary regurgitation
(#33256) is left as-is — that role choice is constrained by strict message
alternation (user collides with a user-ending head) and is already
mitigated by the summary end-marker; forcing the role would risk the
alternation invariant.

Co-authored-by: r266-tech <r2668940489@gmail.com>
Co-authored-by: kyssta-exe <kyssta-exe@users.noreply.github.com>

agent/context_compressor.py

@@ -1253,7 +1253,10 @@ Recovered from a deterministic fallback because the LLM context summarizer was u
 Unknown from deterministic fallback. Inspect current repository/session state if needed.
 
 {HISTORICAL_IN_PROGRESS_HEADING}
-{active_task}
+Unknown from deterministic fallback — the latest user ask is recorded once under
+"{HISTORICAL_TASK_HEADING}" above as historical context only. Do NOT treat it as an
+unfulfilled instruction to re-answer; verify current state and continue from the
+protected recent messages after this summary.
 
 ## Blocked
 {_bullets(blockers, limit=5)}
@@ -1265,7 +1268,9 @@ None recoverable from deterministic fallback.
 None recoverable from deterministic fallback.
 
 {HISTORICAL_PENDING_ASKS_HEADING}
-{active_task}
+None recoverable from deterministic fallback. (The latest user ask is preserved once
+under "{HISTORICAL_TASK_HEADING}" as historical context — it is NOT necessarily
+outstanding.)
 
 ## Relevant Files
 {_bullets(relevant_files, limit=12)}

tests/agent/test_context_compressor.py

@@ -170,6 +170,40 @@ class TestCompress:
         assert c._last_summary_fallback_used is True
         assert c._last_summary_dropped_count == 3
 
+    def test_fallback_summary_does_not_triplicate_latest_user_ask(self):
+        """Regression for #49307: the deterministic fallback summary used to
+        render the latest user ask verbatim under THREE headings (Task
+        Snapshot, In-Progress, Pending Asks). The model then re-answered it
+        and buried the genuinely-new post-compaction turn (answer repetition +
+        new-instruction loss). The latest ask must appear ONCE, as historical
+        context only — never re-presented as unfulfilled in-progress/pending
+        work.
+        """
+        with patch("agent.context_compressor.get_model_context_length", return_value=100000):
+            c = ContextCompressor(model="test/model", quiet_mode=True)
+
+        unique_ask = "PLEASE_COMPUTE_THE_ARITHMETIC_CHAIN_XYZ"
+        turns = [
+            {"role": "user", "content": unique_ask},
+            {"role": "assistant", "content": "working on it"},
+        ]
+        summary = c._build_static_fallback_summary(turns, reason="provider down")
+
+        # The triplication bug rendered the SAME ``active_task`` line —
+        # formatted as ``User asked: '<ask>'`` — verbatim under three
+        # headings (Task Snapshot, In-Progress, Pending Asks), making the
+        # model treat an already-handled ask as unresolved work and re-answer
+        # it. That exact formatted line must now appear at most ONCE (only as
+        # the historical Task Snapshot record). The raw ask text may still
+        # appear elsewhere (e.g. the "Last Dropped Turns" verbatim transcript),
+        # but never re-labeled as in-progress/pending work.
+        active_task_line = f"User asked: {unique_ask!r}"
+        count = summary.count(active_task_line)
+        assert count <= 1, (
+            f"active_task line should appear at most once (was triplicated in "
+            f"#49307), found {count}x:\n{summary}"
+        )
+
     def test_compression_increments_count(self, compressor):
         msgs = self._make_messages(10)
         # Default config (abort_on_summary_failure=False) — fallback path