fix(memory): prevent file upload events from persisting in long-term memory (#971)

* fix(memory): prevent file upload events from persisting in long-term memory

Uploaded files are session-scoped and unavailable in future sessions.
Previously, upload interactions were recorded in memory, causing the
agent to search for non-existent files in subsequent conversations.

Changes:
- memory_middleware: skip human messages containing <uploaded_files>
  and their paired AI responses from the memory queue
- updater: post-process generated memory to strip upload mentions
  before saving to file
- prompt: instruct the memory LLM to ignore file upload events

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix(memory): address Copilot review feedback on upload filtering

- memory_middleware: strip <uploaded_files> block from human messages
  instead of dropping the entire turn; only skip the turn (and paired
  AI response) when nothing remains after stripping
- updater: narrow the upload-scrubbing regex to explicit upload events
  (avoids false-positive removal of "User works with CSV files" etc.);
  also filter upload-event facts from the facts array
- prompt: move `import re` to module scope; skip upload-only human
  messages (empty after stripping) rather than appending "User: "

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix(memory): allow optional words between 'upload' and 'file' in scrub regex

The previous pattern required 'uploading file' with no intervening words,
so 'uploading a test file' was not matched and leaked into long-term memory.
Allow up to 3 modifier words between the verb and noun (e.g. 'uploading a
test file', 'uploaded the attachment').

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* test(memory): add unit tests for upload filtering in memory pipeline

Covers _filter_messages_for_memory and _strip_upload_mentions_from_memory
per Copilot review suggestion.  15 test cases verify:

- Upload-only turns (and paired AI responses) are excluded from memory queue
- User's real question is preserved when combined with an upload block
- Upload file paths are never present in filtered message content
- Intermediate tool messages are always excluded
- Multi-turn conversations: only the upload turn is dropped
- Multimodal (list-content) human messages are handled
- Upload-event sentences are removed from summaries and facts
- Legitimate file-related facts (CSV preferences, PDF exports) are preserved
- "uploading a test file" (words between verb and noun) is caught by regex

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
Co-authored-by: Willem Jiang <willem.jiang@gmail.com>

backend/src/agents/memory/updater.py

@@ -1,6 +1,7 @@
 """Memory updater for reading, writing, and updating memory data."""
 
 import json
+import re
 import uuid
 from datetime import datetime
 from pathlib import Path
@@ -135,6 +136,47 @@ def _load_memory_from_file(agent_name: str | None = None) -> dict[str, Any]:
         return _create_empty_memory()
 
 
+# Matches sentences that describe a file-upload *event* rather than general
+# file-related work.  Deliberately narrow to avoid removing legitimate facts
+# such as "User works with CSV files" or "prefers PDF export".
+_UPLOAD_SENTENCE_RE = re.compile(
+    r"[^.!?]*\b(?:"
+    r"upload(?:ed|ing)?(?:\s+\w+){0,3}\s+(?:file|files?|document|documents?|attachment|attachments?)"
+    r"|file\s+upload"
+    r"|/mnt/user-data/uploads/"
+    r"|<uploaded_files>"
+    r")[^.!?]*[.!?]?\s*",
+    re.IGNORECASE,
+)
+
+
+def _strip_upload_mentions_from_memory(memory_data: dict[str, Any]) -> dict[str, Any]:
+    """Remove sentences about file uploads from all memory summaries and facts.
+
+    Uploaded files are session-scoped; persisting upload events in long-term
+    memory causes the agent to search for non-existent files in future sessions.
+    """
+    # Scrub summaries in user/history sections
+    for section in ("user", "history"):
+        section_data = memory_data.get(section, {})
+        for _key, val in section_data.items():
+            if isinstance(val, dict) and "summary" in val:
+                cleaned = _UPLOAD_SENTENCE_RE.sub("", val["summary"]).strip()
+                cleaned = re.sub(r"  +", " ", cleaned)
+                val["summary"] = cleaned
+
+    # Also remove any facts that describe upload events
+    facts = memory_data.get("facts", [])
+    if facts:
+        memory_data["facts"] = [
+            f
+            for f in facts
+            if not _UPLOAD_SENTENCE_RE.search(f.get("content", ""))
+        ]
+
+    return memory_data
+
+
 def _save_memory_to_file(memory_data: dict[str, Any], agent_name: str | None = None) -> bool:
     """Save memory data to file and update cache.
 
@@ -244,6 +286,12 @@ class MemoryUpdater:
             # Apply updates
             updated_memory = self._apply_updates(current_memory, update_data, thread_id)
 
+            # Strip file-upload mentions from all summaries before saving.
+            # Uploaded files are session-scoped and won't exist in future sessions,
+            # so recording upload events in long-term memory causes the agent to
+            # try (and fail) to locate those files in subsequent conversations.
+            updated_memory = _strip_upload_mentions_from_memory(updated_memory)
+
             # Save
             return _save_memory_to_file(updated_memory, agent_name)