fix(agent): detect copied context-compression artifacts

(cherry picked from commit 09757f3af1c1b3eec1ccde560089448ffa704c92)

agent/tool_dispatch_helpers.py

@@ -19,6 +19,7 @@ from typing import Any, Dict, List, Optional
 from agent.message_metadata import stamp_message_timestamp
 from agent.tool_result_classification import (
     FILE_MUTATING_TOOL_NAMES as _FILE_MUTATING_TOOLS,
+    tool_may_have_side_effect,
 )
 from tools.threat_patterns import scan_for_threats
 
@@ -67,6 +68,54 @@ _DESTRUCTIVE_PATTERNS = re.compile(
 # Output redirects that overwrite files (> but not >>)
 _REDIRECT_OVERWRITE = re.compile(r'[^>]>[^>]|^>[^>]')
 
+# Legacy compressor builds ended long string leaves with these ambiguous tails.
+# Keep the compatibility guard narrow: real historical rewrites had a 200-char head.
+_LEGACY_CONTEXT_PRUNED_ARG_TAILS = ("...[truncated]", "…[truncated]")
+
+
+def _context_pruned_argument_paths(tool_name: str, args: Any) -> list[str]:
+    """Paths whose values contain model-visible context-compression artifacts.
+
+    The compressor's current marker carries numeric omitted/total counts. Match
+    that rendered shape rather than the prefix alone so Hermes can still edit
+    source/docs that mention the compression marker constant or its template.
+    Unknown/plugin/MCP tools stay effect-capable by default; known read-only
+    tools may inspect or quote compressed history.
+    """
+    if not tool_may_have_side_effect(tool_name):
+        return []
+
+    # Late import keeps this helper from making the dispatch module own a second
+    # copy of the compressor sentinel (and avoids a heavy import at CLI startup).
+    from agent.context_compressor import _COMPRESSION_MARKER_PREFIX
+
+    marker_re = re.compile(
+        re.escape(_COMPRESSION_MARKER_PREFIX)
+        + r"\s+\d[\d,]* of \d[\d,]* chars omitted here by Hermes's context compressor\."
+    )
+    found: list[str] = []
+
+    def _walk(value: Any, path: str) -> None:
+        if isinstance(value, str):
+            stripped = value.rstrip()
+            if marker_re.search(value) or (
+                len(stripped) > 200 and stripped.endswith(_LEGACY_CONTEXT_PRUNED_ARG_TAILS)
+            ):
+                found.append(path)
+            return
+        if isinstance(value, dict):
+            for key, child in value.items():
+                key_text = str(key)
+                child_path = f"{path}.{key_text}" if key_text.isidentifier() else f"{path}[{key_text!r}]"
+                _walk(child, child_path)
+            return
+        if isinstance(value, (list, tuple)):
+            for index, child in enumerate(value):
+                _walk(child, f"{path}[{index}]")
+
+    _walk(args, "$")
+    return found
+
 
 def _is_destructive_command(cmd: str) -> bool:
     """Heuristic: does this terminal command look like it modifies/deletes files?"""
@@ -543,7 +592,8 @@ def _maybe_wrap_untrusted(name: str, content: Any) -> Any:
 
 __all__ = [
     "_NEVER_PARALLEL_TOOLS", "_PARALLEL_SAFE_TOOLS", "_PATH_SCOPED_TOOLS", "_PATH_SCOPED_READERS",
-    "_PATH_SCOPED_WRITERS", "_DESTRUCTIVE_PATTERNS", "_REDIRECT_OVERWRITE", "_is_destructive_command",
+    "_PATH_SCOPED_WRITERS", "_DESTRUCTIVE_PATTERNS", "_REDIRECT_OVERWRITE", "_context_pruned_argument_paths",
+    "_is_destructive_command",
     "_plan_tool_batch_segments", "_should_parallelize_tool_batch", "_canonical_path",
     "_extract_parallel_scope_path", "_extract_parallel_scope_paths", "_paths_overlap",
     "_is_multimodal_tool_result", "_multimodal_text_summary", "_append_subdir_hint_to_multimodal",