feat(api): manifest formatter with token-budget truncation

app/core/deep_agent.py

@@ -60,6 +60,41 @@ def _language_instruction(context: dict[str, Any]) -> str:
         f"All your output text must be written in {lang}."
     )
 
+MANIFEST_TOKEN_BUDGET = 3000  # rough budget for <linked_folder> block
+
+
+def format_folder_manifest(manifest: dict | None) -> str:
+    """Format a folder manifest into the <linked_folder> block.
+
+    Truncates by mtime DESC if estimated tokens exceed MANIFEST_TOKEN_BUDGET.
+    Returns empty string if manifest is None or has no files.
+    """
+    if not manifest or not manifest.get("files"):
+        return ""
+    files = list(manifest["files"])
+    files.sort(key=lambda f: f.get("mtimeMs", 0), reverse=True)
+
+    header = (
+        f"<linked_folder>\npath: {manifest.get('folderPath', '?')}  "
+        f"({len(files)} files, scanned {manifest.get('lastScannedAt', '?')})\nfiles:\n"
+    )
+    footer_template = "… {} more files omitted, use read_project_folder_file to access by path\n</linked_folder>"
+
+    char_budget = MANIFEST_TOKEN_BUDGET * 4  # ~4 chars/token
+    body = ""
+    included = 0
+    for f in files:
+        line = f"- /{f['relPath']}  [{f.get('kind','text')}]  {f.get('summary','')}\n"
+        if len(header) + len(body) + len(line) + len(footer_template.format(0)) > char_budget:
+            break
+        body += line
+        included += 1
+    omitted = len(files) - included
+    if omitted > 0:
+        return header + body + footer_template.format(omitted)
+    return header + body + "</linked_folder>"
+
+
 def _datetime_context_injection(context: dict[str, Any]) -> str:
     """Build a comprehensive DATE CONTEXT block with pre-computed ms-epoch boundaries for common ranges."""
     fp = context.get("format_prefs")